Ignition tests with an ignition analyzer

Purpose of this article

The purpose of this blog article is threefold:

  • For my visitors to see what I'm doing, and hopefully learn something new
  • For me to get everything properly documented
  • To share my experiences and results of actions taken with the companies that currently are supporting me with my ignition issues

Background

Sun 800 Motor tester, via Wikimedia Commons

Sun 800 Motor tester, via Wikimedia Commons, NJR ZA, CC BY-SA 3.0

This is a blog entry about how I tried to nail down why my engine doesn't run perfectly, especially on idle. Long read but hopefully you can learn something from my mistakes and/or can point out other solutions or experiences.

One of the larger, older analysis equipment from Bosch or Sun has been on my wish list for a long time. The latter being referred to in Mercedes workshop manuals from the 50s and 60s. They have an amazing functionality to analyze not only ignition but also to perform complete analysis of the exhaust gases. Furthermore, they can isolate the influence of individual cylinders on the analysis. If you also have a dyno/rolling road in the garage, we will talk about car pornography in the higher school. In addition to the fact that these analyzers are difficult to get hold of and are often quite expensive, they require both space and expertise.

They have also come of age and thus the components in them are starting to age. Today, getting them serviced to ensure they function as they should is not trivial. With a bit of persuasion, Bosch may still do it. I would think you are largely at the mercy of old and/or knowledgeable electronics enthusiasts with a large inventory of old spare parts.

Bosch engine tester EFAW 214

Bosch engine tester EFAW 214, see also Bosch Historic workshop equipment

While searching for the correct Air Fuel Ratio (AFR) for the Pontons I saw that the workshop manuals, as well as the Technical Data Manual (see Introduction article under Restoration) referred values from the Sun analyzer. In search for “translation” of these values to more common and modern AFR I contacted the company that today has the Sun brand, Snap-on Inc in US, their message was “Almost everything from that vintage has left the building”. Older user manuals can however be found on Ebay. So now I do have my own copies of manuals for some of the analyzers from both Bosch and Sun. But not the tester itself.

Due to continued poor engine performance and unknown cause, I wanted an oscilloscope to be able to, again, analyze the ignition. Bosch in Stockholm has done analysis of the different ignition components and there's a guy in Stockholm with a dyno and Bosch equipment which I've used but I want to do it when I have time, adjust things and re-test and to understand it myself. At this time I’m fairly certain the engine is mechanically sound, albeit not perfect, and the fuel supply and PAATI 32 carburetor are in order. So, a simple digital oscilloscope, GTC505M Engine Ignition Analyzer, from the Canadian company General Technologies Inc. was purchased in May 2023. A similar product under the name Busching 100682 is available in Europe but Amazon had a very good deal on the GTC.

GTC505 Engine Ignition Analyzer, © General Technologies Corp

GTC505 Engine Ignition Analyzer, © General Technologies Corp

This type of analyzer of course has its limitations compared to a full-size Bosch or Sun, e.g.:

  • only test one cylinder at a time,
  • only test the ignition, not the exhaust gases,
  • the screen is small,
  • you cannot make any printouts or save the results for deeper analysis in a PC or for historization purposes

But, it’s comparably cheap, easy to store and handle and you can bring it with you on trips. 

Two things can also be noted:

  • if you make measurements on the cable between the ignition coil and the distributor it of course gives the wrong rpm
  • in general the rpm reported by the GTC 505 are ~50rpm lower and more erratic than the rpm values given by my Würth Digital Multimeter 50/20. What that depends on I don't know so until I know, I take the Würth rpm as the truth

At the time of writing this article I suspect the electronics are being disturbed by interference (which I may correct or confirm later in the article but forget to correct here, so beware!). The accompanying documentation, and what I so far have found in FAQs, gives little help in interpreting the results. GTC's support has however been very quick and helpful. In line with this, I'm also unsure how its results, whose primary target group is likely to be newer cars, should be "translated" into an analysis relevant to a car from the fifties with its older, underlying technology and completely different tolerances than in later cars. I think it's easy, especially without a very good basic understanding and experience of engine, fuel and ignition technology, to overinterpret the results, to see errors that don't exist, or at least are within reasonable thresholds.

The GTC 505 comes with a flex-arm and two sensors, one for coil-on-plug and one for me, the spark plug wire sensor. I separately bought GTC014 Clip-On Spark Plug Sensor with 2m Cable. It's included in the GTC 505m set but I couldn't find set.

GTC014 Clip-On Spark Plug Sensor with 2m Cable, © General Technologies Corp

GTC014 clip-on spark plug sensor with 2m cable. © General Technologies Corp

I'm not going to go through all functionality etc, if you're interested the manual can be downloaded from their site, but it can be worthwhile to show the icons for the different combinations of measurement modes and views for your interpretation of the pictures and videos below:

  • Measuring/displaying spark burn (firing) time. (c) General Technologies Corp
  • Measuring/displaying dwell angle or ramp time (automatically selected depending on the connected sensor). (c) General Technologies Corp
  • Measuring/displaying RPM (tachometer). (c) General Technologies Corp
  • Measuring/displaying spark plug voltages. (c) General Technologies Corp

The different measuring modes of the GTC 505, click on thumbnails to get a short description. © General Technologies Corp 

  • Chart (i.e. trend line) view. (c) General Technologies Corp
  • Comparison view. (c) General Technologies Corp
  • Analog gauge and digital readouts. (c) General Technologies Corp
  • Waveform (i.e. oscilloscope) view, several types can be shown. (c) General Technologies Corp

The different views of the GTC 505's measurements, click on thumbnails to get a short description. © General Technologies Corp 

Pre-requisites

Ignition

Basic information about the Mercedes-Benz 219 you can find in the article “So, what is a Mercedes-Benz 219?”. Basic information about its ignition can be found under “Electrical equipment at engine (15, 30)”, especially in the PDF “BOSCH Service-Liste für Mercedes-Benz Personenkraftwagen 219, Baujahr 1956 - 1959” further down in the article. Deviating from the standard parts are:

  • Voltage regulator – DVR4N-12-22 Electronic regulator from Electrodynamic solutions, tested ok together with the generator by Bosch Högdalen. See article "Voltage regulator woes"
  • Generator – Bosch LJ/GG 240/12/2400 AR8 (also stamped "Max 360W Max 30A"), tested OK by Bosch Högdalen
  • Ignition coil – Red Bosch 0 221 119 031 with accompanying 1.8Ω pre/ballast-resistor. Primary circuit resistance ~1,4Ω and secondary circuit resistance 13,2kΩ. I am not 100% sure this is the coil to use with an electronic ignition module but Powerspark says it's ok. 
  • Capacitor – Disconnected due to electronic ignition
  • Contact set – K16 electronic ignition kit from PowerSpark
  • Ignition cables – Pertronix 7mm black Flame-Thrower carbon core
  • Spark plug boots – Initially New Old Stock Bosch 0 356 150 004 with 1,5kΩ suppression, during the tests these were replaced with crimped Pertronix boots without suppression
  • Spark plugs – NGK BP6HS (4511) with no interference suppression

  • Bosch 0 356 150 004 NOS (New Old Stock) spark plug boot
  • Bosch 0 356 150 004 NOS (New Old Stock) spark plug boot, spark plug end
  • Bosch 0 356 150 004 NOS (New Old Stock) spark plug boot, screw-in end

This is the Bosch Bosch 0 356 150 004 New Old Stock screw-in type 1500Ω spark plug boot which was initially used 

The original distributor has been gone through and tested ok by Bosch Högdalen, all adjustments in it were correct, vacuum adjustment and weights worked as they should and there was no play.

Resistance in ignition cables, measured with a Würth Digital Multimeter 50/20:

  • Ignition cable coil to distributor – 679Ω
  • Cylinder 1 – 662Ω, during tests replaced with new cable giving 776Ω (all cables to cylinders measured from bottom of distributor cap to spark plug boot)
  • Cylinder 2 – 698Ω, during tests replaced with new cable giving 742Ω
  • Cylinder 3 – 951Ω
  • Cylinder 4 – 1016Ω
  • Cylinder 5 – 1292Ω
  • Cylinder 6 – 1262Ω

Between the base plate of the distributor and ground I have 0.0Ω

  • Pertronix 7mm stock look carbon core spark plug cable (c) Pertronix
  • Pertronix 90 degrees spark plug boot for crimping (c) Pertronix
  • Pertronix straight terminal for crimping (c) Pertronix

The Pertronix Flamethrower carbon core ignition cables and one of their spark plug boot types. (c) Pertronix 

The ignition advance was checked and within specification (target values within brackets)

  • 800rpm w/o vacuum – 14° (10-19°)
  • 1500rpm w/o vacuum – 24° (23-30°)
  • 3000rpm w/o vacuum – 29° (28-34°)
  • 4500rpm w/o vacuum – x° (34-41°), the most important value to check but it was not measured due to a recent cylinder head work. I want to re-torque the cylinder head screws one or two more times before I check the advance on that rpm. On the other hand I've never been close to this rpm during the ignition tests either
  • 4500rpm with vacuum – x° (52-63°), note as above.

All spark plugs have a similar color, and the color is fully ok as far as I can judge.

Incoming voltage to ignition coil as of tests 6 June -23:

  • 12,1V before ballast resistor at idle
  • 13,2V before ballast resistor at 3000rpm, don't want to go higher due to recent cylinder head work
  • 11,2V after ballast resistor at idle
  • 10,4V after the ballast resistor at 3000rpm

The ignition coil is a few degrees warmer than surrounding equipment. After a 30 min drive the coil was 48-49C and the Bosch signal horn, 5-10cm away, was 45-46C. 

The engine itself

When the engine was rebuilt, we discussed going up one size in pistons due to some cylinder wear. However, the mechanic advised me to keep what I had as this is a vintage car whose future mileage would never come close to exceeding the tolerances. I have had compression and blow-by tests done and they show, according to the mechanics, no unexpected deviations. Possibly, the pressure loss on cylinder 3 was a bit high during the blow-by test. It can also be said that the engine is still not fully run in after the renovation, which according to them takes at least 20,000km. After that, all values ought to have settled and evened out, also according to them. At that time the engine only had run 4000km after the restoration...

  • 1st compression test on Mercedes-Benz M180  II/180.921
  • 2nd compression test on Mercedes-Benz M180  II/180.921, note too high values and that cyl 2 is re-checked

My engine is the older 7.6 version. The second compression test shows too high compression due to an error with the paper... Also cylinder 2 was re-checked 

I have no oil consumption to speak off, no oil in the coolant or vice versa.

The valves have been checked and they are all perfectly adjusted to tight 0,12mm on the intake valves and tight 0,20mm on the exhaust valves, i.e. how it should be.

The ATE T50 brake booster is restored and checked according to ATE's instructions, i.e. should be airtight. The connection between the brake booster and the manifold is checked and should be air/vacuum tight. I the car has been standing for a while and push the brake pedal, I can hear a "psshhhh" from it, i.e. as it should be, i.e. should be air/vacuum tight.

Exhaust manifold temperatures

With a Infrared Laser Thermometer from Würth I measured the temperature of the exhaust manifold, directly after driving with the engine idling and got some "interesting" results... The temperature ought to be higher the further back of the engine you go, i.e. the closer you get to cylinder 6.

  • Cylinder 1 – ~130C
  • Cylinder 2-3 – ~150C
  • Cylinder 4-5 – ~90C
  • Cylinder 6 – ~85C

Two things should be noted:

  1. I've just recently bought this thermometer, so I don't have older values, and I don't know what other Pontons with the M180 engine measure.  
  2. A few weeks before the ignition tests I had the Helicoil thread inserts on cylinder 5-6 replaced. Unfortunately, the shop used BGS solid bushing thread inserts with a collar instead of with Time-Serts similar inserts, but which ones are recessed in the cylinder head. The collar of the BGS inserts make the spark plug come a little less than 1mm higher up. According to the shop and other people I've spoken with this shouldn't matter. It can also be noted that the spark plugs on these cylinders look good, and similar to all the other cylinders. And the ignition analyzer hasn't revealed any deviations on these two cylinders. 

Carburetor

I have previously tried to get my original Solex PAATI 32 work. It didn't work even though I took it down several times, checked it and replaced all sealings and diaphragms. Bought a very good used and restored one. Both carburetors had their throttle shaft re-sealed. I took also the new one apart, checked it and replaced all sealings and diaphragms and the engine definitely runs better and the AFR values improved, got much more predictable and stable than with the old one. Except on idle where I still have issues getting the engine to run well, especially if I want to achieve good, and within specification, AFR and CO values. Fuel consumption ok, 1,0-1,2l/10km.

To rule out a leaking choke mechanism, which I don't think I have, it has been temporarily disabled/plugged upon recommendation.

I am pretty certain the carburetor is good, as good as a Solex PAATI 32 can be. They are famous for being problematic, but I don't want to replace it with a 220S carburetor setup. Yet...

The carburetor is currently equipped with:

  • standard 130 main jet
  • standard 47,5 idle jet
  • slightly dryer 180 emulsion jets

The Air Fuel Ratio is measured with Innovate Motorsports LM-2 and the CO with a calibrated Bosch ETT 008.05.

  • Bosch ETT 008.05 CO-analyzer
  • Bosch ETT 008.05 CO-analyzer, exhaust pipe hose

The Bosch ETT 008.05 CO-analyzer 

Test results 

13 May -23

Based on the somewhat erratic, first results the GTC delivered the day before (not documented, only "play-around"), and some preparatory reading on the ignition system and my Powerspark that I had done before delivery of the unit, I changed the red connection for the Powerspark ignition module from the plus pole on the ignition coil, i.e. after the pre/ballast resistor, to the incoming connection before the pre/ballast resistor. Looking at a few GTC 505 videos and reading I thought I had enough proof that having the electronic ignition module connected after the pre/ballast resistor often led to problems with the module. Powerspark's installation instruction doesn't mention this, and according to Powerspark support it shouldn't matter. There is a blog entry saying, "Some customers report that bypassing the ballast resistor by disconnecting the ballast feed wire (from the starter solenoid or built into the loom) and providing a direct 12V feed from the starter solenoid/relay or fuse box to the ignition coil has proved to be a success and has given good results". Pertronix is, however, clear on this in their instructions. 

  • How Powerspark recommends to connect the module to plus
  • How Pertronix recommends to connect the module to plus (c) pertronix

The first picture shows how Powerspark instructs you to connect their module to a system with pre/ballast resistor. The second picture how Pertronix requires you to connect it (c) Pertronix 

A pre/ballast resistor increases the resistance when the flow of current through it increases & decreases resistance when current flow decreases. As I've understood it, this results in voltages to the coil that fluctuate under 12V, sometimes down to 7V. The ignition module is supposed to be able to handle it, but... For me it gave slightly better engine behavior and a more even read-outs on the GTC 505. It can also be noted that I'm not 100% sure this is the coil to use with an electronic ignition module, but Powerspark says it's ok and so I've kept it.

With this done I wanted to see if I had any issues with my distributor cap and/or rotor. Four tests were carried out:

  1. The current Bosch distributor cap 1 235 522 109 and Bosch rotor 1 234 332 070 with 5524Ω resistance
  2. The current Bosch distributor cap 1 235 522 109 and a new "new old stock" Bosch rotor 1 234 332 070, this one with 4824Ω resistance
  3. The current Bosch distributor cap 1 235 522 109 and Bosch rotor ZVT53Z9 with 0Ω, i.e. without resistance
  4. A new "new old stock" Bosch distributor cap 1 235 522 109 and the new "new old stock" Bosch rotor 1 234 332 070 with 4824Ω resistance

Bosch distributor cap 1 235 522 109 and Bosch rotor 1 234 332 070

Bosch distributor cap 1 235 522 109 and Bosch rotor 1 234 332 070

Test 3 gave very bad results and test 2 probably the best, except on cylinder 2. Test 4, everything with brand new stuff, maaayyybeeee gave slightly more vibrations than test 1 and test 2 but I nevertheless decided to stick to this setup.

The question is what test 3 actually says. It failed on cylinder 1 - 3, i.e. one of the carburetor's venturi tubes. The other tube feeds cylinder 4 - 6 and they are not bad in these tests.... Is there something wrong with the carburetor and the air-fuel mixture from one of its venturi tubes?! Or in the engine itself in these cylinders?! 

  • Test 1, Voltage chart, ignition coil, GTC 505 and flex-arm with spark plug wire sensor, 13/5 -23
  • Test 1, Voltage chart, cylinder 1, GTC 505 and flex-arm with spark plug wire sensor, 13/5 -23
  • Test 1, Voltage chart, cylinder 2, GTC 505 and flex-arm with spark plug wire sensor, 13/5 -23
  • Test 1, Voltage chart, cylinder 3, GTC 505 and flex-arm with spark plug wire sensor, 13/5 -23
  • Test 1, Voltage chart, cylinder 4, GTC 505 and flex-arm with spark plug wire sensor, 13/5 -23
  • Test 1, Voltage chart, cylinder 5, GTC 505 and flex-arm with spark plug wire sensor, 13/5 -23
  • Test 1, Voltage chart, cylinder 6, GTC 505 and flex-arm with spark plug wire sensor, 13/5 -23

Test setup 1 

  • Test 2, Voltage chart, ignition coil, GTC 505 and flex-arm with spark plug wire sensor, 13/5 -23
  • Test 2, Voltage chart, cylinder 1, GTC 505 and flex-arm with spark plug wire sensor, 13/5 -23
  • Test 2, Voltage chart, cylinder 2, GTC 505 and flex-arm with spark plug wire sensor, 13/5 -23
  • Test 2, Voltage chart, cylinder 3, GTC 505 and flex-arm with spark plug wire sensor, 13/5 -23
  • Test 2, Voltage chart, cylinder 4, GTC 505 and flex-arm with spark plug wire sensor, 13/5 -23
  • Test 2, Voltage chart, cylinder 5, GTC 505 and flex-arm with spark plug wire sensor, 13/5 -23
  • Test 2, Voltage chart, cylinder 6, GTC 505 and flex-arm with spark plug wire sensor, 13/5 -23

Test setup 2 

  • Test 3, Voltage chart, ignition coil, GTC 505 and flex-arm with spark plug wire sensor, 13/5 -23
  • Test 3, Voltage chart, cylinder 1, GTC 505 and flex-arm with spark plug wire sensor, 13/5 -23
  • Test 3, Voltage chart, cylinder 2, GTC 505 and flex-arm with spark plug wire sensor, 13/5 -23
  • Test 3, Voltage chart, cylinder 3, GTC 505 and flex-arm with spark plug wire sensor, 13/5 -23
  • Test 3, Voltage chart, cylinder 4, GTC 505 and flex-arm with spark plug wire sensor, 13/5 -23
  • Test 3, Voltage chart, cylinder 5, GTC 505 and flex-arm with spark plug wire sensor, 13/5 -23
  • Test 3, Voltage chart, cylinder 6, GTC 505 and flex-arm with spark plug wire sensor, 13/5 -23

Test setup 3 

  • Test 4, Voltage chart, ignition coil, GTC 505 and flex-arm with spark plug wire sensor, 13/5 -23
  • Test 4, Voltage chart, cylinder 1, GTC 505 and flex-arm with spark plug wire sensor, 13/5 -23
  • Test 4, Voltage chart, cylinder 2, GTC 505 and flex-arm with spark plug wire sensor, 13/5 -23
  • Test 4, Voltage chart, cylinder 3, GTC 505 and flex-arm with spark plug wire sensor, 13/5 -23
  • Test 4, Voltage chart, cylinder 4, GTC 505 and flex-arm with spark plug wire sensor, 13/5 -23
  • Test 4, Voltage chart, cylinder 5, GTC 505 and flex-arm with spark plug wire sensor, 13/5 -23
  • Test 4, Voltage chart, cylinder 6, GTC 505 and flex-arm with spark plug wire sensor, 13/5 -23

Test setup 4 

14 May -23

Next step was to replace ignition cables for cylinder 1 and 2. On top of that I replaced the New Old Stock Bosch 0 356 150 004 spark plug boots with 1,5kΩ suppression, with crimped Pertronix boots without suppression (see "Ignition" above). The test showed that the vibrations were still there, and now there were drop-outs on both cylinders 1 and 2. Replacing the spark plug on cylinder 2 didn't make any major improvement. The spark plug for cylinder 2 looks too lean, but a quick test adjustments on its venturi tube's idle screw didn't bring any improvement.

I've made similar quick adjustment on other occasions during these tests with no visible improvement (maybe too quick). And the idle screws' position is supposed to be equal for both venturi tubes so I'll let it be for the time being. Later on I will try to richer idle jets and re-adjust. It can however be noted that I've earlier tested with up to 55 idle jets compared to the current standard 47,5 without difference in vibration but which has given my worse idle behavior. I've also gotten a far too rich AFR at low speeds (be aware of that the idle circuit is in play up to around 2000rpm depending on load, i.e. the vacuum in the venturi tube).

Note that the instrument shows that we now reach 8-9kV compared to earlier 6-7kV

  • Voltage chart, ignition coil, GTC 505 and flex-arm with spark plug wire sensor, 14/5 -23
  • Voltage chart, cylinder 1, GTC 505 and flex-arm with spark plug wire sensor, 14/5 -23
  • Voltage chart, cylinder 2, GTC 505 and flex-arm with spark plug wire sensor, 14/5 -23
  • Voltage chart, cylinder 3, GTC 505 and flex-arm with spark plug wire sensor, 14/5 -23
  • Voltage chart, cylinder 4, GTC 505 and flex-arm with spark plug wire sensor, 14/5 -23
  • Voltage chart, cylinder 5, GTC 505 and flex-arm with spark plug wire sensor, 14/5 -23
  • Voltage chart, cylinder 6, GTC 505 and flex-arm with spark plug wire sensor, 14/5 -23

Voltage 

  • Burn time chart, cylinder 1, GTC 505 and flex-arm with spark plug wire sensor 14/5 -23
  • Comparative burn time chart, all cylinders, GTC 505 and flex-arm with spark plug wire sensor 14/5 -23

Burn time 

Spark plug for cylinder 2 during the tests during 14 May -23

Spark plug for cylinder 2 during the tests 14 May -23. Maybe a bit too lean?!

15 May -23

Talked to Powerspark's support about my issues with cylinder 1 and 2. To see if there was an issue with the electronic ignition's magnet, which sits on the distributor shaft, they asked me to rotate the ring somewhat, so that a different part of the magnet would trigger the ignition module for these two cylinders. It didn't, I still got drop-outs. 

During these tests I also introduced running on higher rpm than idle and also to abruptly increase and decrease gas. This not only gave drop-outs (see first video below) but also the GTC 505's screen to turn blank with high rpm measured, requiring a reboot. My ears cannot hear any drop-outs during these tests and while cruising or accelerating in real life I don't feel them or hear them. So, are the drop-outs caused by issues with the engine, that I don't experience myself, or interference from the ignition system that the GTC 505 cannot handle? 

Youtube video of ignition voltage, measured with the standard flex-arm and its spark plug wire sensor, for cable from coil to distributor and for cylinder 3 and 4 while revving, 15 May -23

Youtube video of ignition voltage, measured with the standard flex-arm and its spark plug wire sensor, for cable from coil to distributor and for cylinder 3 and 4 while revving, 15 May -23

During the day I received the GTC014 clip-on spark plug sensor with its 2m cable so that I could test the ignition while driving. Connected it to cylinder 4, close to the spark plug,  and drove off. Awful results, see videos below. A lot of drop-outs, spikes and odd rpm's as far as I can see.

You may notice that I now not only show ignition voltage but also other features of the GTC 505; burn time, dwell and one of the secondary wave forms it can show. The dwell I actually don't know how to interpret in this case. First, it's set by the Powerspark, secondly it differs quite a lot from what the Würth instrument shows at idle if I remember correctly.

The odd squeak you here from time to time in the videos is the rubber mat that rubbs against the clutch pedal. In reality you almost don't hear it....

Youtube video of burn time, measured with the GTC014, for cylinder 4 while driving, 15 May -23

Youtube video of burn time, measured with the GTC014 connected close to spark plug, for cylinder 4 while driving

Youtube video of dwell, measured with the GTC014, for cylinder 4 while driving, 15 May -23

Youtube video of dwell, measured with the GTC014 connected close to spark plug, for cylinder 4 while driving

Youtube video of ignition voltage, measured with the GTC014, for cylinder 4 while driving, 15 May -23

Youtube video of ignition voltage, measured with the GTC014connected close to spark plug, for cylinder 4 while driving

Youtube video of secondary waveform, measured with the GTC014, for cylinder 4 while driving, 15 May -23

Youtube video of secondary waveform, measured with the GTC014connected close to spark plug, for cylinder 4 while driving

Upset, I started to google electronic ignitions and re-read the material from Powerspark and Pertronix. In the latter's documentation they point out that the distance between the ignition module and the magnet ring on the distributor shaft must be between 0,254 - 1,524mm. Powerspark's support said that they didn't have a distance specified but that it should be as small as possible, without touching each other. The distance was ~0,85mm, which ought to be ok, but I managed to close the gap down to ~0,5mm on the top of the magnet ring and ~0,6mm at its bottom. 

Powersparks ignition module and its magnet ring

Powersparks ignition module and its magnet ring

18 May -23

On the 16 May I did new tests with the GTC014 sensor connected to the ignition cables close to the spark plugs. I assumed this ought to be a better test, closer to "reality" but which I normally didn't do with the standard flex-arm and its sensor. With that I normally measured the cable around the distributor cap where it was easier to reach them and ensure good contact. The results of these tests were so disappointing that I didn't even take photos or videos. I understood absolutely nothing and went home and thought...

Spark plug for cylinder 1. In my opinion it looks decentSpark plug for cylinder 3 In my opinion it looks decent

Spark plugs for cylinder 1 and 3. In my opinion they look decent

21 May -23

For these tests I decided to skip the GTC014 sensor and only use the flex-arm and its spark plug wire sensor, still close to the spark plug boot, to see if that gave any improvements. The first test achieved better values, but I still had drop-outs on cylinder 1 and 2, and also 3 and 4. Was the GTC 505 still affected by interference? I made a second test where I measured with the sensor close to the distributor cap. Voila! The readings came out fine, except on cylinder 2...

Now is the question, are those drop-outs on cylinder 2 caused by interference, and in such a case what is causing this interference on only this cylinder, or is something wrong with the cylinder and its combustion? And when I had problems with other cylinders in earlier tests, they affected cylinder 1 mostly, sometimes cylinder 3 and very few times cylinder 4. Never 5 or 6. Why? (a bit unsure of what conclusions can be drawn about this as I'm not entirely sure if I measured at the distributor cap or at the spark plugs then...)

Below you can see the photos from the second test, i.e. where I measure on the ignition cable, close to the distributor cap. Measurements are over 20sec except for the cable from the ignition coil which is 40sec. Note that rpm on the ignition coil is six times the idle rpm of "obvious" reasons.

  • GTC 505 and flex-arm with spark plug wire sensor, burn time, on cable from ignition coil to distributor cap
  • GTC 505 and flex-arm with spark plug wire sensor, dwell, on cable from ignition coil to distributor cap
  • GTC 505 and flex-arm with spark plug wire sensor, rpm, on cable from ignition coil to distributor cap
  • GTC 505 and flex-arm with spark plug wire sensor, voltage, on cable from ignition coil to distributor cap

Different measurement modes on cable from ignition coil to distributor cap 

  • GTC 505 and flex-arm with spark plug wire sensor, burn time, cylinder 1
  • GTC 505 and flex-arm with spark plug wire sensor, dwell, cylinder 1
  • GTC 505 and flex-arm with spark plug wire sensor, rpm, cylinder 1
  • GTC 505 and flex-arm with spark plug wire sensor, spark plug voltage, cylinder 1

Different measurement modes on cylinder 1 

  • GTC 505 and flex-arm with spark plug wire sensor, burn time, cylinder 2
  • GTC 505 and flex-arm with spark plug wire sensor, dwell, cylinder 2
  • GTC 505 and flex-arm with spark plug wire sensor, rpm, cylinder 2
  • GTC 505 and flex-arm with spark plug wire sensor, spark plug voltage, cylinder 2

Different measurement modes on cylinder 2 

  • GTC 505 and flex-arm with spark plug wire sensor, burn time, cylinder 3
  • GTC 505 and flex-arm with spark plug wire sensor, dwell, cylinder 3
  • GTC 505 and flex-arm with spark plug wire sensor, rpm, cylinder 3
  • GTC 505 and flex-arm with spark plug wire sensor, spark plug voltage, cylinder 3

Different measurement modes on cylinder 3 

  • GTC 505 and flex-arm with spark plug wire sensor, burn time, cylinder 4
  • GTC 505 and flex-arm with spark plug wire sensor, dwell, cylinder 4
  • GTC 505 and flex-arm with spark plug wire sensor, rpm, cylinder 4
  • GTC 505 and flex-arm with spark plug wire sensor, spark plug voltage, cylinder 4

Different measurement modes on cylinder 4 

  • GTC 505 and flex-arm with spark plug wire sensor, burn time, cylinder 5
  • GTC 505 and flex-arm with spark plug wire sensor, dwell, cylinder 5
  • GTC 505 and flex-arm with spark plug wire sensor, rpm, cylinder 5
  • GTC 505 and flex-arm with spark plug wire sensor, spark plug voltage, cylinder 5

Different measurement modes on cylinder 5 

  • GTC 505 and flex-arm with spark plug wire sensor, burn time, cylinder 6
  • GTC 505 and flex-arm with spark plug wire sensor, dwell, cylinder 6
  • GTC 505 and flex-arm with spark plug wire sensor, rpm, cylinder 6
  • GTC 505 and flex-arm with spark plug wire sensor, spark plug voltage, cylinder 6

Different measurement modes on cylinder 6 

  • GTC 505 and flex-arm with spark plug wire sensor, burn time in cable from igntion coil to distributor cap
  • GTC 505 and flex-arm with spark plug wire sensor, burn time, cylinder 1
  • GTC 505 and flex-arm with spark plug wire sensor, burn time, cylinder 2
  • GTC 505 and flex-arm with spark plug wire sensor, burn time, cylinder 3
  • GTC 505 and flex-arm with spark plug wire sensor, burn time, cylinder 4
  • GTC 505 and flex-arm with spark plug wire sensor, burn time, cylinder 5
  • GTC 505 and flex-arm with spark plug wire sensor, burn time, cylinder 6

Measurement modes "Burn time" on cable from ignition coil and for all cylinders 

  • GTC 505 and flex-arm with spark plug wire sensor, dwell in cable from igntion coil to distributor cap
  • GTC 505 and flex-arm with spark plug wire sensor, dwell, cylinder 1
  • GTC 505 and flex-arm with spark plug wire sensor, dwell, cylinder 2
  • GTC 505 and flex-arm with spark plug wire sensor, dwell, cylinder 3
  • GTC 505 and flex-arm with spark plug wire sensor, dwell, cylinder 4
  • GTC 505 and flex-arm with spark plug wire sensor, dwell, cylinder 5
  • GTC 505 and flex-arm with spark plug wire sensor, dwell, cylinder 6

Measurement modes "Dwell" on cable from ignition coil and for all cylinders 

  • GTC 505 and flex-arm with spark plug wire sensor, rpm in cable from igntion coil to distributor cap
  • GTC 505 and flex-arm with spark plug wire sensor, rpm, cylinder 1
  • GTC 505 and flex-arm with spark plug wire sensor, rpm, cylinder 2
  • GTC 505 and flex-arm with spark plug wire sensor, rpm, cylinder 3
  • GTC 505 and flex-arm with spark plug wire sensor, rpm, cylinder 4
  • GTC 505 and flex-arm with spark plug wire sensor, rpm, cylinder 5
  • GTC 505 and flex-arm with spark plug wire sensor, rpm, cylinder 6

Measurement modes "Rpm" on cable from ignition coil and for all cylinders 

  • GTC 505 and flex-arm with spark plug wire sensor, voltage in cable from igntion coil to distributor cap
  • GTC 505 and flex-arm with spark plug wire sensor, spark plug voltage, cylinder 1
  • GTC 505 and flex-arm with spark plug wire sensor, spark plug voltage, cylinder 2
  • GTC 505 and flex-arm with spark plug wire sensor, spark plug voltage, cylinder 3
  • GTC 505 and flex-arm with spark plug wire sensor, spark plug voltage, cylinder 4
  • GTC 505 and flex-arm with spark plug wire sensor, spark plug voltage, cylinder 5
  • GTC 505 and flex-arm with spark plug wire sensor, spark plug voltage, cylinder 6

Measurement modes "Spark plug voltage" on cable from ignition coil and for all cylinders 

  • GTC 505 and flex-arm with spark plug wire sensor, burn time while revving, cylinder 4
  • GTC 505 and flex-arm with spark plug wire sensor, dwell while revving, cylinder 4
  • GTC 505 and flex-arm with spark plug wire sensor, rpm while revving, cylinder 4
  • GTC 505 and flex-arm with spark plug wire sensor, spark plug voltage while revving, cylinder 4

Different measurement modes while revving, on cylinder 4, unsure if measured at spark plug or distributor cap. I doesn't really matter since I got drop-outs at both places, less at the latter though 

  • GTC 505 and flex-arm with spark plug wire sensor, burn time while revving, cable ignition coil to distributor cap
  • GTC 505 and flex-arm with spark plug wire sensor, dwell while revving, cable ignition coil to distributor cap
  • GTC 505 and flex-arm with spark plug wire sensor, rpm while revving, cable ignition coil to distributor cap
  • GTC 505 and flex-arm with spark plug wire sensor, spark plug voltage while revving, cable ignition coil to distributor cap

Different measurement modes while revving, on cable from ignition coil to distributor cap. Unfortunately I didn't capture when revving up... 

And finally we have videos of different waveforms on the ignition coil and all the cylinders. They are measured with the flex-arm and the spark plug wire sensor, close to the distributor cap. I forgot to measure Detailed spark burn waveform. Note that rpm on the ignition coil is six times the idle rpm of "obvious" reasons. Note also that the idle sounds very nice on the videos, a bit better in reality I'm afraid and there are also vibrations.

Youtube video of the Primary current ramp waveform. I don't know if this waveform is valid for my car or if it is only applicable to modern coil-on-plug cars. Measured with the GTC 505

Youtube video of the Primary current ramp waveform. I don't know if this waveform is valid for my car or if it is only applicable to modern coil-on-plug cars.

Youtube video of Detailed secondary waveform with very odd rpm for cylinder 4 and 5. Bad connection between sensor and ignition cable? Measured with the GTC 505

Youtube video of Detailed secondary waveform with very odd rpm for cylinder 4 and 5. I didn't see it while recording and I have no idea what happened there. You hear nothing odd in the sound from the engine... Probably it was just a bad connection between sensor and ignition cable, maybe the unit was disturbed by interference.

Youtube video of the overall secondary waveform, measured with the GTC 505

Youtube video of the Overall secondary waveform

Thoughts so far

Except on idle, the engine ran pretty good before the tests above. That was achieved after a lot of other, previous fixes and adjustments to the engine itself, ignition system and the fuel system. But it didn't run as it should, being a straight 6-cylinder engine. The idle went slightly up and down, engine was vibrating and the AFR and CO values were impossible to get right. A decent mix of these values and an idle of around 750-800 rpm always landed at an AFR of 13,8-14,0. This is normally too lean for a good idle. As I've understood different papers and forums, and above all the Mercedes workshop manuals, you should strive for an AFR of 12,5-12,8 But then the CO has gone through the roof, or the rpm is way off. I also had some misfires/dropouts that could be felt at the exhaust pipe. But acceleration and cruising on country-side roads or highways, i.e. not running on the idle jets but the emulsion jets, was a dream. No power losses or hiccups/misfires and the spark plugs had a similar and an even color (well, I'm not a professional mechanic, maybe such a one would have another opinion, but at least there are no obvious deviations in color or between the plugs). But from time to time, especially during/after long drives, the AFR values changed inexplicably and often also gave a worsened idle and vibrating low-speed behavior.

After the adjustments I've made to the ignition during the tests so far, the car runs better. The misfires/dropouts that could be felt at the exhaust pipe at idle seem to be gone and no misses/dropouts can be heard. But, the vibrations and problematic AFR and CO values are still there and the GTC 505 says I have drop-outs, which seem to match the uneven idle. Note, that I haven't made any really long countryside/highways drives during these tests, so I don't know if those inexplicable issues with the AFR, bad idle and low-speed issues after long drives are still there.

My Mercedes-Benz 219 Ponton on a dyno, rolling road

My Mercedes-Benz 219 Ponton on a dyno, rolling road

Based on everything I've done with the engine and its equipment so far, partly described under the chapter Pre-requisites above, I'm fairly certain that the culprit is to be found in the ignition, but at the time of writing I'm definitely not sure. Or is there still something with the Solex PAATI 32 carburetor or the engine itself? Or am over-sensible as usual... Right now I don't know, so I go for what I can measure with the GTC 505 until the evidence/indications point in another direction. On the other hand I'm not 100% sure what it's telling me so it's difficult for me to understand what causes the drop-outs I see in the GTC 505's charts. How do I understand what the combination of tests and charts say:

  • Ignition failure? If so, can I see in what part?
  • Interference from the ignition, disturbing the instrument? Why, my Würth and AFR meters don't have problems. 
  • Too rich or too lean fuel mixture?
  • Other failures with engine/combustion?

And what are normal read-outs given the type of car, age and ignition system etc? What ignition voltage, burn time, dwell, waveforms etc should I expect? And what can be done if they are out of line?

A comment on one possible cause, the carburetor

After going through the results, and after writing the above, I realize that the 3rd test of 13/5 showed big problems on cylinders 1 - 3. Those are fed from one of the carburetor's venturi tubes. The other venturi tube feeds cylinder 4 - 6 and they are not bad in this test.... The tests during other days have shown issues with cylinder 2, sometimes cylinder 1. Never for 4 - 6. This can point towards that there is something wrong with the carburetor and the air-fuel mixture from one of its venturi tubes... But why would only the rotor that was used in the 3rd test have issues firing cylinders 1 - 3, while the other rotors only seem to have problems with cylinder 2 and not 1 or 3!? 

I do, however, not see how the carburetor can be bad. That the restoration of the original PAATI 32 didn't come out well I can understand. It was worn, e.g. the holes in the carburetor body for the idle screws looked worn out and I'm not sure the restoration of the throttle shaft came out well. During the restorations (!) and tests with the two carburetors (haven't had time to document all that on the site yet), the original one and the "new" one, I've learnt a lot about its function and construction as well as the importance of having really level surfaces and to look for air and fuel leaks in the oddest places. All jets, needles gaskets and diaphragms are new, all channels etc are clean. The "new" carburetor also reacts in a more stringent and predictable way in terms of fuel consumption, AFR and engine behavior when I adjust/change something. So, I would say that I feel comfortable with it. But I don't know...

Mercedes shipped 26.000 220a's and 28.000 219's with this carburetor. I must assume it worked [fairly] well during that time, 1954 -59, otherwise it would surely have been replaced. I know that a lot of 220a and 219 owners are complaining about it and replacing it with the two 220S carburetors or Fintail carburetors. No one has been able to tell me exactly what the issue with it is. 

6 June -23

Based on my too lean AFR at idle (given that the LM-2 connected at the tail pipe shows the right value) and that the spark plug color can be interpreted as too dry, I again tried to "force" the 47,5 idle jets to give me a richer AFR, i.e around 12,5-13,0 instead of +14,0. Maybe the improved ignition system setup would be able to achieve something new.

Again it failed. The Solex PAATI 32 doesn't like to have its idle adjustment screws turned out more than approximately 1,75 turns. To reach this rich mixture, 2 turns are necessary. Then the engine runs badly/uneven and when the car stands in an uphill slope, the engine stalls. My interpretation is that the gasoline flows backwards, "uncontrolled", from the from the float bowl, past the screws, into the venturi tubes.

I once more tried the richer 50 idle jets to achieve the 12,5-13,0 AFR. And again it resulted in a very bad engine behaviour on idle as well as on country side roads at 70-90km/h. At idle the GTC 505 showed massive drop-outs on cylinder #2 and a lot on #1. Obviously, my car doesn’t like this AFR at all or the information I’ve gotten is wrong./p>

To be honest I can’t say that the spark plugs after this try looked as they’ve been running richer. The spark plug foot for cylinder 2 may be slightly sootier than cylinder 3’s as shown in the pictures below.

  • Picture of spark plugs for cylinder 2 and 3 after running on rich idle AFR, approx 13
  • Picture of spark plugs for cylinder 2 and 3 after running on rich idle AFR, approx 13

Picture of spark plugs for cylinder 2 and 3 after running on rich idle AFR, ~13. Nota bene after a 10km trip and the last km on slow speed on suburban streets.

Back to 47,5 idle jets and another round of adjustments. By raising the idle rpm from ~750 to slightly above 800 (i.e. in the upper part of the workshop manual’s spectrum, 700-800rpm) I was able to achieve an AFR of around 13,0 and CO of 3,5 with very stable values. The idle screws are turned out 1,75 turns. There’s a tendency to stall in an uphill slope so I will try to screw them in a bit later. The idle is good (not perfect), exhaust gases come out in an even stream at the tail pipe, and I get decent behavior and AFR on low speeds as well. Cylinder 2 still has drop-outs, but not many, and also cylinder 1 showed one or two...

I also tested the incoming voltage to the ignition coil:

  • 12,1V before ballast resistor at idle
  • 13,2V before ballast resistor at 3000rpm, didn't want to go higher due to recent cylinder head work and the cylinder head screws need to be re-torqued one or two more times before I dare to go for higher rpm
  • 11,2V after ballast resistor at idle
  • 10,4V after the ballast resistor at 3000rpm