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HELP! Porsche 924s no spark

 
Old 05-25-2017, 12:41 PM
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Chris Berry
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Default HELP! Porsche 924s no spark

Hello,

I've recently bought a Porsche 924s as a project, everything looks clean underneath the bonnet and under the car however its been in storage for several years without being started (5ish I believe). The car was last on the road in 2001 but was still running when it went into the garage. Since getting the car home I've found that there is an intermittent issue with spark.

Here are the tests which have been carried out:

- Spark has been confirmed at the coil
- The RF and speed sensors are testing ok (both around 1M ohms) and there is definitely a visible pulse going to the ECU via the RF sensor and a current going to the ECU via the speed sensor.
-When the DME relay is jumpered there is still no spark but the fuel pump does run
- I took the ECU apart today and it appears to have been refurbished before and there is visible corrosion inside (which I feel is my problem), I brushed some of the corrosion away and the spark did re-appear for about 4 seconds then disappeared again.

The problem is that due to it being refurbished before the label with the part number on it has been removed and if I'm potentially going to replace it I need to make sure that the replacement is going to work.

My Porsche is a European 924s, I've included pictures of the ECU below.










Any help would greatly appreciated.

Thanks,
Chris

Last edited by Chris Berry; 05-25-2017 at 01:00 PM.
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Old 05-25-2017, 02:53 PM
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Van
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If you're getting spark at the coil, but not at the plugs, have you check the cap/rotor/wires yet?
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Old 05-25-2017, 03:17 PM
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Chris Berry
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Thanks for the reply.

I've tested all the cables and everything seems as it should be, from what I can tell is that the coil is fine the sensors are all ok and the wiring harness is all testing ok. There is a separate green wire going to the coil which I presume is what transmits the signal for the coil to spark via the ECU/DME? I'm going to clean up the ECU tonight and test it again tomorrow. If it's still failing then I'll check the flywheel etc.. before sending the ECU off to be tested.

If I have to replace it I'm going to need to verify the Porsche/Bosch part number some how. I may call Porsche tomorrow and see if they can help.
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Old 05-25-2017, 03:28 PM
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odonnell
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If you're getting spark at the coil your DME is doing its job, all it does for spark is pulse the green wire (a pulsed GROUND) in accordance with RPM, spark angle, and dwell time. Your problem is after the coil. Check the obvious stuff and also check your ground between the bellhousing and firewall (The plugs have to ground too).
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Old 05-25-2017, 04:12 PM
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Condensate under the distibutor cap might make the brass a little green so you might polish that up with Emory cloth or a match book.

Cranking speed needs to be >200 rpm. Can you charge the battery?

Is the rotor button tight?

I would throw ten bucks at some spark plugs and try to start it in the dark.

Ran great when it was parked implies the opposite))lol. I believe the Euro ECU should have some resistor jumpers in lieu of our USA spec O2 sensors. So you might cycle those plugs to be sure there is good contact.
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Old 06-06-2017, 08:33 AM
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Chris Berry
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Hi all,

Thanks for all the replies, I managed to obtain a different ECU to try. The car is now sparking fine but won't start, I've got fuel to the injectors but the plugs aren't wet meaning the car isn't injecting.

I couldn't identify my part number for the ECU meaning I've had to guess, I have a 1987 Porsche 924s and the ECU I purchased is 944 618 121 04. Is anyone able to tell me if it's definitely compatible with my car? If not perhaps it could still be the source of my problem.

I also have the option to swap it for part number 944 618 121 03. Is there any way to be 100% as you can see from the photos someone has removed the sticker from the front of my original ECU.

Also if not the ECU could there be another source for this particular problem?

Thanks,
Chris
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Old 06-07-2017, 09:55 AM
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Humor me and do a compression test... You might have a broken timing belt.
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Old 06-08-2017, 04:12 AM
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Chris Berry
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Everything seems fine. The ECU is sending a pulse to the injectors and fuel is getting there. I think they are perhaps just blocked with 10 year old petrol. The injectors may just need cleaning. I'll let you know the outcome.
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Old 06-09-2017, 04:40 PM
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If the timing belt is intact and the fuel pump is functioning then the injectors do need a rebuild and the gasoline in the tank needs to be changed along with the fuel filter and tank screen. Plus,check for electrical shorts in the wiring. Good luck!
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Old 06-09-2017, 08:00 PM
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Chris Berry
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Well.. after changing the injectors and the fuel she finally started. After coughing black smoke and getting rid of the old fuel the car ran ok but seems to be injecting more fuel than required. I'd been away on holiday when the new ECU was fitted and after checking the part number it's not the one I ordered (but does work (ish)) but there is my problem as it doesn't correspond with my current AFM on the car. Also the tachometer doesn't work at all (could be a separate issue or also due to the ECU being incompatible). I've spoken to the people who sent the ECU who have said they knowingly sent the the alternate part to test; they have a 1987 924s and will be able to test their ECUs on Monday and hopefully come up with a workable part. I'll let you know how it goes!
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Old 06-15-2017, 05:18 PM
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How'd you make out?

It would be great to see if we can help you.

The ECU that fits your car should be one of these Bosch #s:
0261200077
0261200058
0261200086
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