David McLean

This is my first post from sunny Durban South Africa

So car running fine until I pay in new stereo (unless this is a co-incidence?), and then it will not start
1. Tried new DME relay - no joy
2. Bridged 87, 87b and 30 terminals - car started and runs perfectly
3. Tried old and new DME - no start
4. Checked all the earths I could find - no joy
5. Looked for ACU - could no find one nor is option 533 listed on VIN sticker

So please help if you can. Should I be looking elsewhere? Have brand new battery, no rev counter bounce, and as I say, with the DME relay bridged, car runs perfectly. I am very suspicious regarding factory alarm. No key on rear 1/4 panel, does this mean no alarm?

Thanks

Van

Sounds like you don't have a factory alarm.

You're saying the car ran fine until you put in an aftermarket radio? Did you do the work or did someone else do the work?

When you "bridged the terminals", what terminals are you talking about - those numbers correspond to all relay inputs/outputs. Perhaps you mean the DME relay? If that's the case, I'd say while putting in the radio, someone cut a wire from the DME back to the DME relay (maybe the ground trigger?)

David McLean

Yes, I did mean the dme relay inputs/outputs. The radio is now out. There is a black wire and a gray wire clad in black sleeve. Does joining these make any sense. The black wire is an earth and the gray does not carry any power.

Thanks for your reply it is most informative

Van

There are lots of black wires in that car... That's not enough information to suggest anything.

The way the DME relay works - it's really 2 relays - turning the ignition key sends +12v to the first half of the relay, which turns on the DME. When the DME senses cranking and engine RPM, it uses a ground trigger to activate the second part of the relay to turn on the fuel pump.

Because you can start the car with a relay jumper - forcing power to the DME and fuel pump - it makes me think that one of the signals to the DME relay has been severed.

Do a google search on 944 wiring diagrams, and then watch this video on how to read them:

V2Rocket

Can you try another ignition switch?
You said the car runs with the fuel pump relay socket bridged. This connects the fuel pump (and I believe DME power) directly to battery rather than through the switch.

David McLean

From position 5 on the dme I have traced a gray wire clad in a black sheath. According to the wiring diagram this is to earth position 85b on the dme relay via a wire which is marked sw which I understand is black. It is this latter wire I now seek although it may not be black. The previous stereo acted as a connection between the dme and the dme relay as an earth conduit! With the new stereo installation, this circuit was broken hence the spare gray wire. It is dark here in SA so I will get to this in the morning. I think, however, that this will be the solution

Thanks all, I will report back

Van

"sw" = schwartz (black in german)

David McLean

okay, so how about this. Turns out that the fault had nothing to do with the dme/dme relay and they were connected and talking to each other. The fault is in the ignition switch and when shorted, the car starts immediately. Only problem is now a VERY rough idle and the car will not accept any accelerator without stalling. Indeed, the rough idle does also cause the car to stall. I did disconnect the DME - could this be the problem and how do I reset/remap the DME? Help please

odonnell

The DME relay doesn't interact with the ignition switch, with the exception being that +12v from the ignition switch triggers the first stage of the relay. Bridging 30/87/87b takes the ignition switch out of the equation and connects the battery hot (pin 30) directly to the DME/injectors/and fuel pump (87 and 87b).

David McLean

When I turned the ignition, the voltmeter went to zero and the dash lights went out although the engine did crank. I am bridging the ignition switch and the car starts well and quick every time. It just won't run with the idle hunting between zero and 950 until it stalls. It will not accept and accelerator whatsoever without stalling. I thought that perhaps the DME needed to remap itself since having been disconnected?
The same problems now exist with relay bridge of 30/87/87b

Van

Make sure the AFM (air flow meter) is plugged in, and/or make sure you have no vacuum leaks.

David McLean

Thanks Van, will get onto this in the morning. Not sure how to test for vacuum leaks. Will really appreciate any advice here. One thing that is baffling me is how did these conditions now suddenly accrue? Meaning they weren't here a week ago

David McLean

1985 944 42,000 miles FSH



944, 1988 928 S4 manual 30,000 miles with FSH and 997.1 Carrera manual

V2Rocket

jeez, that thing is a beauty!
Make sure the AFM and Throttle position switch are plugged in.

DME does not adapt/learn in the 944.

David McLean

Thanks V2Rocket, will get onto it and report back Friday