Motronic 3.2 debugging idle

[mysocal911]

Originally Posted by FrankM_

OK, back to the original problem ;-)

First we ran the car with another (known good) DME - no issues, clean idle, good injector waveforms, nice acceleration.

With the problem DME, idle was indeed rough but the ICV was regulating as Ingo said in a relatively small band around 800 rpm. However, the idle quickly got 'out of control' sweeping to 2000 rpm, dropping to 500 rpm and always eventually stalling. (Way too wide for the ICV to control anything)

Checked and known working : Idle switch, ICV, stable Vcc on the board (both 13.7 Vbat and 5.05V on the 5V level), O2 disconnected, Vref stable on the ADC, all inputs stable on the ADC, ref & speed pulses stable and correct on the uP.

When looking at the injection pulse (pin 1 uP) and the resulting 'peak & hold' output with the whole injector chain connected (I couldn't replicate that at home) the problem became clear : the injection pulse jumps up and then shortens, then jumps up again.

Given the signal from the fuel output of the processor, your problem is not in the injectors' drive circuitry.

Originally Posted by FrankM_

With 3 injectors connected now I can replicate the problem on the bench .

The uP pulse comes through correctly on the R421, although through ADV12 on this board (older board than the schematic). However T405 has been replaced by a 2N3019.

Another thing I noticed, even with 3 injectors running, I do not see the positive peak on the scope at closing (first pic below) as I do on my good running car (last pic below).

This is because you only have three injector connected, i.e. not enough output current.

Originally Posted by FrankM_

Any help in this area is greatly appreciated !

Probably gonna check my stash of electronics and see if I can find a BC639C to make
it closer to the original again.


Kind regards and thanks for helping me along this quest...

Frank

Arbitrary parts replacement, not good troubleshooting!

[ischmitz]

Frank,

after watching the videos it appears you assume the variation in injector duration (pin 1 uP) is root cause of your issue. Have you tried the known good DME on the simulator? Also, do both DME have the same software (chip)? This behavior might actually just be due to how your simulator drives the DME. If not it would be the A/D converter producing erratic values for load or CHT or all inputs.

BTW, the spike at the end is when the injectors turn off and their magnetic field breaks down. The active snubber T403, T404, T405 absorbs most of that energy when T404 turns on.

[FrankM_]

Ingo and others,

Thx for the feedback.

I will try my good DME on the sim, but the behaviour on the car was the same, only worse since the rpm input was not stable.
So I doubt it is a sim issue.

And indeed, it could be that the ADC is producing unstable output. I didn’t think of that.
I can only ‘see’ its inputs and as said, they are clean and stable (also both VRef’s). I cannot observe or decode the output.

Given that someone has changed at least one transistor in the injector driver (I cannot see those under the cooling fin - is there a good way to get that off, seems rivetted). And some points in that circuit have been resoldered, I immediately suspected that subsystem.

Now, even with 3 injectors there should be some ‘recoil’ ? Now there is nothing, less than 1 V !
If not those transistors, is the large diode maybe damaged ? (OF622)

Frank


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[FrankM_]

Originally Posted by mysocal911

Given the signal from the fuel output of the processor, your problem is not in the injectors' drive circuitry.



This is because you only have three injector connected, i.e. not enough output current.



Arbitrary parts replacement, not good troubleshooting!

I agree but this is puzzling me !


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[ischmitz]

Originally Posted by FrankM_

Ingo and others,

Thx for the feedback.

I will try my good DME on the sim, but the behaviour on the car was the same, only worse since the rpm input was not stable.
So I doubt it is a sim issue.

I only say that because my simulator's RPM signal is not very frequency-stable and I sometimes see similar funny patterns where the injector duration follows that. I would check for that just to be sure.

Originally Posted by FrankM_

And indeed, it could be that the ADC is producing unstable output. I didn’t think of that.
I can only ‘see’ its inputs and as said, they are clean and stable (also both VRef’s). I cannot observe or decode the output.

I have a reference DME with all chips socketed and the quickest way to test is to de-solder the IC in question and test it in my reference DME. Doesn't take more than a couple of minutes per IC and gives definitive answers. Decoding the A/D converter isn't straight forward.

Originally Posted by FrankM_

Given that someone has changed at least one transistor in the injector driver (I cannot see those under the cooling fin - is there a good way to get that off, seems rivetted). And some points in that circuit have been resoldered, I immediately suspected that subsystem.

The BC639 is a pretty generic small-signal version and I highly doubt it's the reason you're having issues with the DME. And the riveted transistors are most likely stock because else you'd see someone messed with the rivets.[/QUOTE]

Originally Posted by FrankM_

Now, even with 3 injectors there should be some ‘recoil’ ? Now there is nothing, less than 1 V !
If not those transistors, is the large diode maybe damaged ? (OF622)

Your previous messages stated you see a large spike in the car but not very much on the bench. If that is the case I don't see the diode as the issue unless it is short. You can easily measure that.

The spike at the end of the injector duration depends on what injectors you're using on the bench. In the end if the load is different the generated PWM pattern from the 0127 will be different and the amount of stored energy in the injectors is different. So unless you're having the exact same conditions on the injector output I wouldn't worry about this. I just use a big inductive load similar to injectors on my simulator so I get PWM patterns and reactive end spikes.

[FrankM_]

Nice setup if you have a tester-dme like that. Indeed that helps.

To be clear : the large spike on my good car is 6 injectors AND the good dme.

The ‘no spike’ is observed with 3 identical injectors (I’ll try 6 tomorrow) to my good car and the bad DME. Same was observed (no photo) on the car with 6 injectors.

I put a copy of my 1985 original eprom in the bad dme to make sure it is the same as there was an unknow chip in there.

I’ll have to read up on how this ADC works / is controlled by the cpu (OE, ALE ?) and check all the paths to the cpu.
Same for the latch and eprom paths.


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[ischmitz]

If you have access to a 2-channel o-scope you can verify the output of 0127 on pin 5 to see how the snubber turns on at the end of the injector cycle. Even with a 1-channel you should be able to check that signal from pin 5 through T405 and R413 and verify that T404 turns on.

[mysocal911]

Originally Posted by FrankM_

Ingo and others,

Thx for the feedback.

I will try my good DME on the sim, but the behaviour on the car was the same, only worse since the rpm input was not stable.
So I doubt it is a sim issue.

And indeed, it could be that the ADC is producing unstable output. I didn’t think of that.
I can only ‘see’ its inputs and as said, they are clean and stable (also both VRef’s). I cannot observe or decode the output.

Given that someone has changed at least one transistor in the injector driver (I cannot see those under the cooling fin - is there a good way to get that off, seems rivetted). And some points in that circuit have been resoldered, I immediately suspected that subsystem.

Now, even with 3 injectors there should be some ‘recoil’ ? Now there is nothing, less than 1 V !
If not those transistors, is the large diode maybe damaged ? (OF622)

Frank


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Keep changing those parts, surely you'll eventually find the bad one, right? Lucky for you that surface mount parts weren't used in the '80s when the Bosch DME ECU was designed.
Good luck, and have fun!

[FrankM_]

I am not changing any parts yet as you & Ingo pointed out there could be other reasons for the disturbance.

I will first compare again to my good dme on the sim (same conditions).
Then figure out a way to ‘see’ if the adc is generating a good output to the cpu. I assumed the digital board was indestructible ;-)

I will also hook up the full six injectors ( first check if my bench power supply can take that load).

When it eventually comes to it, no prob on redoing some components in the injector driver. I can order most of those for around 20 eur all together.
Even the adc is only a 6,5 eur part.

But as you stated, I’d better do some deeper analysis first.


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[wazzz]

Frank, you seen my answer to your PM last night? (Thank you again for the schematics.)

As I told you, I think the missing 50V pulse is intentional in the know good DME. Check this page with typical waveforms. Though different technologies, they show that the closing "high voltage" pulse is there to accelerate the closing of injectors. In the schematics, it appears that this function is provided by the ZY47 (D401) zener diode. This is a 47V diode. May be this diode should be checked?

[FrankM_]

OK,

so with the hints from yesterday, work continued.

I should have checked everything again when attaching the chain of injectors yesterday ! I was having a bad case of noise in my AFM feedback from the simulator to the Motronic. That was probably causing the jumping effect.
I seem not to be able to get rid of the noise, so I wired up my spare AFM and it is much more stable, on the 'good' and the 'bad' Motronic box.




Only significant difference is (same conditions, same inputs, same injectors) :
- good box : at closing a large positive peak is seen (as can be expected)
- bad box : no positive peak

@Ingo : I got my old analog scope back from the attic, here is a trace of pin 1 (drive of the main darlinton) vs pin 5 ('snubber') output of the Bosch 0127 IC. It seems that the snubber circuit is turned on much at the same time than the main transistor or am I reading this wrong ?

https://youtu.be/uYn7Jre2OiI

More investigation to do,

Frank

[FrankM_]

Sorry, wrong pic posted for the 'bad' ECU, this is the one with the same conditions.

[ischmitz]

Frank,

I noticed the funny pattern in the hold section of the injector duration in your “bad” DME. This doesn’t look right. It’s almost as if the current feedback is oscillating.

Look at your good DME where this pattern isn’t present. I have seen marginal 0127 before. They do work but have sustained some kind of degradation or damage. That’d be my guess.




I wasn’t able to see much on your analog scope video but if I have time I’ll record and post some scope traces later today.

[FrankM_]

Originally Posted by ischmitz

Frank,

I noticed the funny pattern in the hold section of the injector duration in your “bad” DME. This doesn’t look right. It’s almost as if the current feedback is oscillating.

Look at your good DME where this pattern isn’t present. I have seen marginal 0127 before. They do work but have sustained some kind of degradation or damage. That’d be my guess.

Sharp eye !

I have checked T406 : seems to be working, it opens during the whole cycle.
- bottom channel = T402 injection signal
- top = Collector - emitter voltage T406


Then after R413 i get this and don't understand how this is supposed to work :
- bottom = same T402 main injection
- top = base T403 (PNP)


More or less the same signal then at the T404


Frank

[FrankM_]

@Ingo : the bottom irregularities are due to the timebase on the el-cheapo scope (35 EUR). On the analog scope they line up quite nicely at the bottom.

As I didn't understand the previous waveforms, there had to be something wrong in the snubber circuit and I believe I found it finally. The diode over the T404 transistor appeared not to be doing it's job. So I desoldered it and
(a) it was the wrong type in there (possibly due to my schematics being of a later version that this board) and
(b) passing current happily in both directions ?!

Replaced by one that I had (1N4007 instead of a 1N4002) and I can now see a correct waveform.



The board is happily running now with 6 injectors. Heat after 30 min of running is 44°C or 113F on the heatsink, so well under control.



Too late to put it into the car and test it, that will be for tomorrow.

[ischmitz]

Originally Posted by FrankM_

(b) passing current happily in both directions ?!

That's a funny way of saying the diode was shorted and prevented the output to ever rise beyond the +12V level - just like your scope trace showed.

Ingo

[FrankM_]

Originally Posted by ischmitz

That's a funny way of saying the diode was shorted and prevented the output to ever rise beyond the +12V level - just like your scope trace showed.

Ingo

Indeed !

Spcial thanks to Ingo for all the help and asking the right questions. I runs super smooth in the car now ! It seems even better/smoother than my 'good ECU'.

And incidentally, once this was fixed, the heavy noise in the power supply and ADC of the arduino in the simulator are gone. it did add some caps to better control it though. But 2 projects finished at once : the bad ECU repaired and a good simulator for the future.

And I learned a new area of my Porsche that I didn't really know before.


Thanks again,

Frank