No Spark

[ant7]

Hi All,
Its been a while, anyway, as the title states, no spark on my 1985 3.2, changed the Flywheel sensors, changed the DME Relay, made sure the both relays inside the DME Relay are activating when their supposed to ie; ignition on, one relay pulls in, turn the key to start, the second relay also pulls in operating the fuel pump etc.
While checking for spark, as the ignition is switched on, I get one spark from the coil lead, and that's it, no spark when cranking etc.
Help!!!|

[Schulisco]

I suppose a defective ECU due to either cold soldering points and/or bad capacitors. Also a defective ignition coil may cause these symptoms.
To rule out a defective DME relay use a cable bridge instead:
https://dorkiphus.net/porsche/showpost.php?p=193387&postcount=3

[mysocal911]

Originally Posted by ant7

Hi All,
Its been a while, anyway, as the title states, no spark on my 1985 3.2, changed the Flywheel sensors, changed the DME Relay, made sure the both relays inside the DME Relay are activating when their supposed to ie; ignition on, one relay pulls in, turn the key to start, the second relay also pulls in operating the fuel pump etc.
While checking for spark, as the ignition is switched on, I get one spark from the coil lead, and that's it, no spark when cranking etc.
Help!!!|

Plugged into the wrong connectors. Switch them.

[ant7]

Tried that Dave,
The problem was there before changing them, that's why I figured that was the first place to start after the DME Relay. I suspect its an ECU issue, but just want to make sure I haven't missed anything else before condemning it, I have opened up the Motronics unit to check for anything obvious, nothing burnt, all diodes check out, guess I will need to look further into it, Anyway, all input welcome.

Originally Posted by mysocal911

Plugged into the wrong connectors. Switch them.

[mysocal911]

Originally Posted by ant7

Tried that Dave,
The problem was there before changing them, that's why I figured that was the first place to start after the DME Relay. I suspect its an ECU issue, but just want to make sure I haven't missed anything else before condemning it, I have opened up the Motronics unit to check for anything obvious, nothing burnt, all diodes check out, guess I will need to look further into it, Anyway, all input welcome.

Read here; 911 3.2 No-Start Troubleshooting

You may remember the guy that posted that, since you've been a long time Forum poster.

[ant7]

Hi Dave,
Yes, I remember reading that, I have voltage at the coil, and I do get one initial spark from the coil lead to ground when the ignition is first switched on, once the engine turns, no more spark, which is odd, I am going to test for voltage at the Injectors next.

Originally Posted by mysocal911

Read here; 911 3.2 No-Start Troubleshooting

You may remember the guy that posted that, since you've been a long time Forum poster.

[mysocal911]

Originally Posted by ant7

Hi Dave,
Yes, I remember reading that, I have voltage at the coil, and I do get one initial spark from the coil lead to ground when the ignition is first switched on, once the engine turns, no more spark, which is odd, I am going to test for voltage at the Injectors next.

Which indicates the control digital logic of the DME ECM is bad or the input signals, e.g. speed & ref sensors.
You need to check the AC voltage of the sensors. Hopefully, the reference sensor pin isn't missing/damaged.

[ant7]

Agree!
However; as stated in my first post, they are brand new fitted yesterday, but as you say; still need to check that they are putting out a voltage.

Originally Posted by mysocal911

Which indicates the control digital logic of the DME ECM is bad or the input signals, e.g. speed & ref sensors.
You need to check the AC voltage of the sensors. Hopefully, the reference sensor pin isn't missing/damaged.

[ant7]

Well, after removing the ECU [Motronics unit] and opening it up to check for bad connections, or any signs of burning, I found nothing, inside was very clean, removed bottom plate, and inspected the soldering on that side too, all looked fine.
Replaced the unit back in the car, turned the key, and the car fired right up, and ran fine, I switched it off after about 10 mins, turned the key again, and it re-started again with no issues.
Next day, turned the key, no start again, so at this point I am at a loss, any input very welcome as its now driving me a bit mad!
Ant.

[mysocal911]

Originally Posted by ant7

Well, after removing the ECU [Motronics unit] and opening it up to check for bad connections, or any signs of burning, I found nothing, inside was very clean, removed bottom plate, and inspected the soldering on that side too, all looked fine.
Replaced the unit back in the car, turned the key, and the car fired right up, and ran fine, I switched it off after about 10 mins, turned the key again, and it re-started again with no issues.
Next day, turned the key, no start again, so at this point I am at a loss, any input very welcome as its now driving me a bit mad!
Ant.

You typically can't find intermittencies by visual inspections!

[ant7]

I get that Dave,
And will have to remove it once again, and do some actual checks on component values, and look for broken wiring between the two board layers etc.
A...

Originally Posted by mysocal911

You typically can't find intermittencies by visual inspections!

[wazzz]

If you manage to make it start again, keep it running and try to wiggle things like the ECU, the ECU connector, the DME relay and its connector and associated loom. See if it dies when doing so. That may point you to something.

The no start situation may also be due to a bad ref sensor or related circuit and logic, as Dave already mentioned. Once the car is running a bad ref sensor signal, whether due to the sensor itself or its logic circuitry, may not be noticed. The speed sensor is able do deal without it, provided it is good. But for the car to start the ref sensor signal needs to be good at least for the duration of cranking, until the engine runs.

But you probably know all this.

[ant7]

Hi Wazzz
Yes, good call, I am going to try it again today, the Reference sensors are brand new fitted last week, it has started and ran fine since fitting those, I changed those initially when the car first refused to start.

Originally Posted by wazzz

If you manage to make it start again, keep it running and try to wiggle things like the ECU, the ECU connector, the DME relay and its connector and associated loom. See if it dies when doing so. That may point you to something.

The no start situation may also be due to a bad ref sensor or related circuit and logic, as Dave already mentioned. Once the car is running a bad ref sensor signal, whether due to the sensor itself or its logic circuitry, may not be noticed. The speed sensor is able do deal without it, provided it is good. But for the car to start the ref sensor signal needs to be good at least for the duration of cranking, until the engine runs.

But you probably know all this.

[mysocal911]

Originally Posted by ant7

I get that Dave,
And will have to remove it once again, and do some actual checks on component values, and look for broken wiring between the two board layers etc.
A...

You first need to determine whether you have a spark/injectors or both problems.
If it's both, then focus on the sensors. Since there're new, that's unlikely the problem.

Again, read the link in post #5. Have you checked for an injector signal, not just voltage?
If the injectors are pulsing, then it's the spark output of the DME ECM.

[ant7]

Originally Posted by mysocal911

You first need to determine whether you have a spark/injectors or both problems.
If it's both, then focus on the sensors. Since there're new, that's unlikely the problem.

Again, read the link in post #5. Have you checked for an injector signal, not just voltage?
If the injectors are pulsing, then it's the spark output of the DME ECM.

[mysocal911]

Email the company referenced in post #5. They'll tell you what has the highest probability of the cause of your problem.
I've used them numerous times for help.

[Steve W]

ant7, most likely the ECU is failing and needs repair. mysocal911 knows that and why he is pretending to be a different person directing you to post #5, who is himself under a different alias who was banned, to get your business, by asking you PM him instead of discussing solving your problem out in an open forum. Is that even allowed?

BTW, someone said (several times) that our host has a repair service for many things, especially the Motronic ECU. Just type 'Motronic repair' in the search box at the top of the forum page. Good luck.

[mysocal911]

Originally Posted by mysocal911

Email the company referenced in post #5. They'll tell you what has the highest probability of the cause of your problem.
I've used them numerous times for help.

Well ant7, I saved you an email and talked to them myself. Since they do the majority of their business with Porsche dealers and independents,
they always enjoy helping Porsche owners.

They said the highest probability of failure on the 911 3.2 DME ECM is the ignition driver circuitry being intermittent.
This agrees with your post 9;

Replaced the unit back in the car, turned the key, and the car fired right up, and ran fine

Here's an image displaying the problematic three connections which require re-soldering;



This mainly occurs on the later ECMs, where the circuit board was changed to fiberglass. Hopefully, re-soldering these pins will solve your problem.

[mysocal911]

Another view of the ignition driver area;

[ant7]

Hi All,
Well, took out the ECU again Yesterday, looked at the main solder joints that I know from what a few of you have stated are the first port of call, when you get the no spark issue.
Although they looked to be fine, I decided to re-do many of the joints, including the large transistor, and what I deem as its drivers too, I removed the old solder first, and re-soldered using original lead and tin solder I use for repairs and re-work on older Audio Equipment, as it is much more forgiving as far as flex and vibration than modern Non-leaded etc.
Anyway after completing the task, I decided to leave all the covers off [just encase] and plug the unit back in the car naked, and see if it would now start, sure enough, it started right up, and ran fine as it always has, so let it run for a while, switched off, re-started it a few times, no issues. I then removed the ECU and re-fitted all the case work, and tried it again, sure enough it started fine again.
I am going to wait until tomorrow now and see if it will start from cold before I re-fit it permanently to the floor, but for now I am quietly confident, lets see, I will update you all soon.
Thanks to everyone who contributed so far.
Ant.