djmjr77

Hello all, I just got a 944 a few weeks back and have been going through it to get it running.
The only way I can start it is to three wire jump the DME relay port.
It came with an F9tech relay, which seems to fail Clark's Garage test, not sure if that relay can be tested the same way since it's solid state.
Bought two URO branded DME relays which pass the tests, but no fuel pump when starting.
I tested the ground and ignition power pins in the fuse block and those check out fine..
Found some really bad grounds which I fixed and thought would solve the problem but it didn't.

What else can I do to figure out why the relay won't function properly?

Thanks!!!!

Droops83

You should check if terminal 86 of the DME relay is getting +12V while the starter is cranking (this provides voltage to the positive side of the coil portion of the DME side of the relay) and that 85B (ground side of the coil of the fuel pump portion of the DME relay) is getting a ground signal from pin 20 of the DME control unit while the engine is cranking. The ground signal from the DME is a safety feature to ensure that the fuel pump is activated only if the engine is running or being cranked by the starter.

djmjr77

I had previously tested 86 and 85 but not 85b.
I am getting power on 86 when in run and cranking.
I am not getting ground on 85b though.
What does that mean, and what should i check to resolve that problem?
Thanks for you help!

Droops83

The ground from 85B is provided by the DME control unit. There is a connection (pin 5) at the T21 connector at the left side of the firewall, so you should check for the ground signal both there and at the DME while cranking.

djmjr77

Thanks so much for your help!
I'm not to familiar with this car yet so just learning, background is GM..
I do not seem to have ground on pin5 while cranking. I dis a continuity check between a bare spot kn the frame and the pin on bith sides, male / female, and no continuity. Was that the right way to check it?
how would I test ground at the DME?

djmjr77

I verified continuity between T21 pin 5 and the DME pin 20, so there is no breaks in that wire..
I checked and have grounds at all of the locations in the DME plug/connector.
i get about 900 OHMs testing speed and ref sensor at DME plug. Which is in spec.. no working oscilloscope to do further testing but tach bounce "means it may be good"
I get tach bounce when cranking
I verified the resistance of the DME coolant sensor and if seemed accurate for my current temperature.
Just no DME ground activation on pin 5 which is keeping the DME relay from working.
I read somewhere else, that the DME not sending the ground signal to pin 5 could mean its putting the car in limp mode, which is why it won't rev up when running on the three wire DME relay bypass. (Is this limp mode even a thing).
what else would cause the DME to think its not ok for the car to get fuel?
Please help what I should check next, feel like it's soo close!!

djmjr77

It also looks like the DME is not sending the 5 volts to the AFM. Wires are good, but no voltage with the key on.
Starting to look like a bad DME..
Any thoughts?

djmjr77

Any takers

944 timbo

Can you post a picture of your relay, top and bottom please.

djmjr77

I have a few different DME relays, they test fine. The DME computer is not sending the ground activation signal to trigger the secondary relay coil, which powers the fuel pump.

Chapman951

Could try soldering the DME.

djmjr77

I did reflow the ignition transistor (the three pins that some others had problems with) but that didn't help.
I traced DME pin 9 (responsible for the 5volts to the AFM) on the circuit board and found a diode that was allowing voltage in both directions. According to the DME schematic and board printing it is diode D202 and is a 1N4148 diode. I could easily replace it (and a couple others that are allowing reverse voltage) but am not confident that its not something on the circuit making them "look bad" and would test fine if removed from the circuit. I PMd f9tech since he would def know due to his expertise on reverse engineering these DMEs but doubt he will reply, probably a very busy person and that's ok if he doesn't.
would be great if someone else could verify this diodes function if they had an opened DME laying around..

djmjr77

Sooo.. to put a pin in this for now..

The DME was sent to FTech9 and tested on one of his turbos, and it worked fine.
I went ahead and got the Sprt DME with OBD anyways just so I can put the computer situation to bed once and for all, and I can get cool live data from the DME.
Ultimately the major running issues were caused by the cheap chinesium injectors installed by one of the PO's.
I put a good used set that were tested and cleaned by Joe at FTech9 and started right up running better than I had seen it yet.
I'm still chasing a connection issue which is being narrowed down to the DME relay socket in the fuse box..
was actually able to drive the car last weekend!
such a great car cannot wait till it's running tip top!

Thanks for everyones input and help on this!