944M3

After several months, I have my '87 951 put back together. (I summarized by rebuild on a separate post). With much anticipation, I fired her up. She stayed on and stumbled for about 15 seconds and died. After tinkering, I found that I could hold open the barn door in the AFM, which raises the RPMs and the engine runs great. After further research and troubleshooting, I found that if I disconnect the engine temp sensor (NTCII) the car starts right up and stays on, only issue is that the RPMs surge up and down, not drastically or violently but definitely noticeable. But it does remain on and runs. I see no smoke or anything out of the ordinary when running. I did further research into this and found similar threads around disconnecting the engine temp sensor. I tested the wiring with an multimeter following several of these threads. Keep in mind I'm a complete amateur at this stuff, but so far what I have found is that I don't get any continuity on pin #16 of the KLR plug when the DME is plugged in (the KLR is not plugged in). Also note, I did put in a new harness from LIndsey that included the temp sensor. My understand is that this could be a sign of a bad DME. I did open the DME and noticed signs of corrosion and possible water damage, so it is possible its bad.

Also, I did try to bypass the KLR by jumping pins 9 and 16 of the KLR plug. Do difference.

At this point, I'm hoping to find someone I can borrow a known good DME and KLR that's in the Washington DC metro area, DMV. I'm willing to leave a deposit and a case of your preferred beverage. Hopefully this saves me some time. I did previously replace the original DME that was bad before i started the rebuild, when I first purchased the car, so this would be the second bad DME. I think I would purchase a VEMS PnP if it does turn out to be a bad DME.

Also open to any other possible testing I can do.

Thanks in advance.

Juan

alex.rhodes

Juan, have you tried dorkiphus? There are several 944 guys on there that night have one.

944M3

Thanks for the suggestion Alex. Will give that a try.

944M3

Solved:

Big DUH!! Moment. As part of the rebuild, I installed an adjustable fuel pressure regulator from LR. I ASSumed that the default pressure was 3 bar (at its lowest setting). But after speaking with Dave at LR he walked me through adjusting it and bingo, the car started right up and idled perfectly. He also took some time to walk me through some other troubleshooting steps, which I really appreciated.

Basically, what we think was happening was that when I disconnected the engine temp sensor, the DME pumped more fuel, thus compensating for the very low fuel pressure that the regulator was set at, and thus keeping the engine at idle.

Hope someone else learns from this thread. Though it sucked, I did get to learn more about how the DME, AFR, temp sensor and afp regulator work.

Juan