Papamurphdog

This is EXACTY true. Happened to 3 of my four boots. No one seems to listen to this advice. It is the FIRST thing to check on a 20 year old car. Dang, four people told him the same thing and he still didn't listen. Sheeezzee.

Chris White

my guess would be you will have to post it 100 times ...

kghaas

I have open all four of the injector rubber boots. The wires are all good. It is not the problem on my car. My problem is not related to the injector harness, and it is now totaly dissconected at the DME connector. My problem is that the DME sends out a 6V signal on both pin 14 and 15.

I need someone to point me in the direction of why the DME sends out a signal at 6V when it should be at 12V. Is there some input signal which is off? Is there something in the DME?

I realy need to understand how the 14 and 15 are triggered...

Rich Sandor

Have you cracked open the DME box? I've seen DME's where the soldering inside has melted due to excessive heat.. the relay board itself blackened from the heat making it very obvious.

Also check all the battery cables and grounds. My 968 died on me once because the DME wasn't getting a full 12 volts because one of the battery vampire lines at the positive terminal was slightly loose.

theedge

If there is voltage present on pins 14 and 15 with the fuel injector pins removed, then something is wrong inside the DME.

The DME (well, any fuel injection really) triggers injectors by grounding them. Injectors are supplied with a constant 12 volts on one of their pins when the car is running or starting or whatever, then to trigger them the other pin is given a path to ground. That completes the circuit, and the inj fires. The path to ground is basically a big transistor.

If the injectors are unplugged and the wires are 100% good/wiring harness is unplugged, then there will never be voltage on pins 14 and 15.

It sounds like you have an internal short of some sort inside the DME.

kghaas

Thanks all for giving good tips. I will start by going throug all wiring(again) and take a good look inside the DME to see if I can spot something. Do findt it a bit curious that both DME's are broken but then again I have nothing to loose.
If I cant sort this within a week or two, I will either sell the car in parts or take it back to standard. Never had to give up on a car before......

blown 944

Should have 12v on both pins with key on.

there has to be a drain somewhere on the return path of the harness or in the DME.

You may try to un plug the pin(s) out of the DME plug for the ground side of the injectors. This would eliminate the DME as the short if it stays 6v. If it then shows 12v then the DME would be my guess

theedge

You should never get 12 volts on both fuel injector connector pins with the injectors unplugged. Or on pins 14/15, with the injectors all unplugged.

mikeyoman

Just measured my injector volts, no engine cranking.
Igniton OFF - open circuit Ohms to earth on one pin (call it a) & 120 Ohms to earth on the other (b)
Ignition ON - 10.3v on one pin (a) & 12v on the other pin (b)

6v on pin 14/15 suggests an earth/supply issue with the DME ?

The DME is not just a simple switch and you may well have volts present when the transistor is OFF as they often use pull-up voltages in circuits. Haven't had time to review the DME circuit yet.
circuit schematics available here http://www.the944.com

regards
Mike

blown 944

Brian,
I'm certainly not one to argue .... but that is exactly the way it it is.

I just went and tested it to make sure my memory was not failing me. The DME is sending a constant 12 through the injector and fires it when it grounds through the DME.

Maybe someone else will pull an injector plug and turn the key on and verify. I have tested this on both of my cars (it seems this conversation ha been had before). I'm pretty confident that anyone with a running car will see 12v on both sides of the injector harness plug pins with the key on.

eniac

After Lindsey's post, I went out and checked mine with one injector unplugged, key on, measured +12v on each side on the plug.

mikeyoman

You'll need to unplug them all to get a true reading as they are all tied together at pins 14/15, and the 12v supply from the other injectors will affect the measurment on the DVM (when not cranking/running)

kghaas

Thanks all for geting involved.
I have now tested with a Noid Light, and it looks like it is working as it should. The Noid is flashing on each of the injector plugs som I guess It is all ok. It still doesn't fire so I have to look elsewhere....
Also measured the fuel pressure and it is at 3 bar when cranking.(I have a 3bar FPR) som I guess it is ok... Tested with my old original 2.5FPR and it was also 3bar and then suddenly went to 10 bar! So I guess that one is bad.

I will close this thread and go back to the original no start thread so I can keep track of all the different things I try....
Original thread:
https://rennlist.com/forums/944-turb...lp-please.html