sablebrown944

Hello everyone, i’ve got a 1984 Porsche 944 I just bought and it’s only currently running on two cylinders, so a few days ago i verified spark on the two not firing (3&4) and today I just swapped the fuel injectors ‘good ones’ to the ‘bad ones’, and i’m still not getting cylinders 3 and 4 to fire, 1 and 2 are firing on the swapped injectors though.

So from this point, it could be the electrical connections (injector harness) or possibly bad DME, correct?

And if so, does anyone have any suggestions on how to go about verifying which is bad?

The previous owner did put a brand new DME in, so i’m fairly sure it isn’t that. But just to be sure i’m curious if there’s a way to test that and the harness or if anyone else has any input as to why 3&4 are not firing,

Thanks in advance

931guru

Since you are having an issue with cylinders 3 and 4, most likely cause is a broken wire between the injectors and the DME. Check for continuity between pin #14 on the DME and the injector connectors.

sablebrown944

I checked for continuity on pin #14 you mentioned and the end fuel injector harness plugging into the fuel injectors and they all came out good, so i tested the DME relay on the pin that controls cylinders 3&4 and that actually came out bad so i thought i found the issue, so i bought a new one, and it’s the f9tech one i’ve heard good stuff about so i plug it in and still the same problem is happening, I also i just tested the new dme relay to be sure the new one was okay and it’s good.

So not too sure where to go from here, cylinders 3 and 4 still don’t wanna fire. I suppose I retest everything, perhaps a mistake on my end was made i don’t know, if anyone has any suggestions it would be very appreciated

Zirconocene

How are your grounds? The injectors fire when the DME grounds the power to the injectors but what I don't know is if the DME is using different ground paths for the different sets of injectors. That seems unlikely but stranger things have happened.

For the test you did on the DME relay, maybe you could clarify. Did you test for continuity between the socket for the relay and the DME pin? Because if that was bad, it has nothing to do with the relay itself (not this it's a bad thing to move to the F9 part, that will save you some heartache down the road). What I'm wondering is if you have a fault in the wiring to the DME relay socket. However, the signals run through there for all the injectors, so it seems unlikely that something would affect only 2 of the injectors.

How about this: can you check for power to the injectors, and not just continuity to the DME? The injectors should always be getting power and you can test the plugs for 12V.

Cheers

sablebrown944

Thanks for all the information man, i’ll get back to you tomorrow it’s a bit late here and I can’t work in my garage so not much light unfortunately. but I was just testing the ignition coil and I used this video ( ) on how to do it, I was getting 12 volts to both terminals, but then i took the wires off to check for resistance. I am not getting any resistance when checking the two terminals together it’s reading open loop or 00.0, so I mean this part is bad I believe, but my question is could that cause two cylinders to not fire and two to fire? I mean perhaps, but just strange it’s the two particular ones when i swapped the fuel injectors.

Again, thanks for all the information, I’ll get on it tomorrow

walfreyydo

Do a compression test on those cylinders just to be sure.

Have you confirmed the injectors aren't firing? Are you getting raw fuel on the spark plug for the cylinders in question? You can also try the cup method of removing the rail and having the injectors fire into cups.