take the DME relay out and replace it with a 3x wire bypass as described on Clarkes Garage site in workshop manual.
http://www.clarks-garage.com/

The 3x wire bypass will supply 12v+ to the ECU the injectors , fuel pump, ignition amplifier etc and 5v to the sensors
(The fuel pump should now run continuously even with the ignition off.)

The car should now start.

I suspect you may have a problem with the engine temperature sensor (or possibly the AFM) or maybe the cold start system

The key grounds are MPl,fuel pump ground in rear hatch under carpet below hatch lock MPll & MPlll ground the DME relay and the ECU and are under the dashboard next to the fuse/relay box (all brown wires)

 

Fwiw, the shop just said there's no spark. Is that still a symptom of a bad DME relay? He's going to replace the relay Monday and then troubleshoot from there if still no start.

I had brought the car there just to do the shift cups and E brake. Its not a Porsche shop. It's just a local / convenient (VW/general) indy. I'm kinda stuck now since the car doesn't start. If I knew I was going to potentially need troubleshooting, I would have bought it to a 924/944 Porsche Indy. A good one is a town away (Protosport) but 25% more expensive per hour.

 

The DME relay is actually a double relay with independant operation.

The spark is controlled by the ECU .(Engine Control Unit ) The ECU pulses the ignition amplifier which amplifies the pulse for the coil which provides your spark .

I suggest you get someone who is familiar with the BoschMotronic fuel injection system to test your car or the local indy will simply replace everything until the car starts....expensive! Its a very complex engine management system way beyond the local indy knowledge I should have thought.


1. Remove the DME relay.
2. Check you have 12v+ constant supply to terminal 30 on the base of the DME relay socket with the ignition off (if not check for faulty ignition switch)
3. fit the 3x wire bypass into the DME relay socket in place of the DME relay. Terminals 30, 87 & 87b as per Clarkes.

4 If pump doesn't run continuously check pump fuse.
5. Try start the car. You should now have a spark, fuel pump and fuel delivery via the injectors.

Note the engine must turn over or crank at a minimum of 225rpm or the ECU will not pulse the injectors or the ignition system so make sure that the battery is fully charged or use a battery booster or jump leads

 

1. So jumping the DME relay is a better indicator than trying the new relay I gave them?

2. Is the ECM is the same thing as the DME (computer). The silver metal box.

3. Seems I can get a "new" DME with a 5 year warranty from DME doctors. However I thought tach bounce was a indicator that my DME was ok. I do have tach bounce.

4. Based on your help here, I think I should have it towed to Protosport. They will likely have spare parts to help troubleshoot with there.

 

Since the car is at the shop, I can't do the checking myself as your suggesting. When I tried to share my online findings earlier today, the shop owner seemed irritated and dismissed anything from the web. Ironic, as on the right fourms, the classic car mechanical info from the web is excellent.

I'm arranging moving the car first thing Monday.

 

scores of 944s have been discarded before owners were able to solve their electrical issues. talked to a guy who worked in the service department (Concourse Motors, Wisconsin) tell me the root cause of complete electrical failure was alarm systems shorting, effectively shutting down other parts of the electrical system. he mentioned that he used to pick up dead 944s and flip them. sounds plausible. is it true ? maybe, but if somebody knows—they ain't talkin'.

 

It's probably your reference sensors. They are usually the cause. Check/clean the connections and check the wiring underneath the rubber boot to make sure your wires aren't frayed.

 

Main grounds on your 924S.

 

If your tach bounces, the reference sensors are working.

If your tach bounces but the car has no spark, it's definitely possible that the DME is broken. A 944 specialist should have an extra DME on hand that they can try swapping in to see if that fixes the problem.

I would definitely say that going to a shop that knows these cars well is worth the premium - they may be 25% more per hour, but they can also often solve the problem in 75% of the time.

 

Thanks. Thats the exact (ground) chart I was hoping for. Sam one I have for the 928.

 

I agree. I only brought it to the INDY because it was going to be a simple shift cup job. Already called Protosport and left a msg. They are closed weekends. I'll have it towed Monday. I have a feeling it's DME too.

 

Yes I would take it to protosport ...... however why don't you do as I suggest and fit the 3xwire bypass in place of the DME relay and attach a good battery with some jump leads , chances are that the car will start up and run

 

I would have to tow to my house to work on it. Then Tow again if it doesn't start and run. I work full time and don't really have any time to mess with it in daylight - except weekends. I'd have to park it in the street - as there is no room on my property for a non runner. I don't mind paying someone to sort through it. Of course I don't want to get mired into a replace everything situation either. I also suspect the DME computer is the issue and Protosport will likely have spares to swap and verify.

 

sorry I understand your predicament its difficult to know what to do in this situation.

What i do not understand is that despite admitting knowing absolutely nothing about the car or the Bosch fuel injection and engine management system nor you or the indy having done any tests whatsoever... you ignore an experts advice and make the random decision that it must be the ECU at fault !..................What are you going to do when you fork out $100's for a replacement ECU and it still doesn't start ?


I'm afraid I cannot be of any further assistance to you .

I strongly suggest that you do a search on the forum for 'not starting' and read some of the thousands of previous threads about this common but highly complex subject and perhaps you might gain a little insight into the problem.

 

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