Another "no start post"

[byron911]

I definitely agree on the ECU swap with another car, I'd hate do damage another guys car. Unfortunately the only other local Porsches around here aren't 3.2s anyway.

The engine swap wiring does worry me, it's really quite a mess. The challenge is to redo as much as i can, but with the 1978 circuits and fuse/relay setup being different to the 1984 engine it's a challenge.....I've built and wired from scratch two Cobras (with a little help from an auto elec) so I'm up for it

[ischmitz]

Greg,

if the DME relay is turning on properly and you get the correct fuel pressure this is good. What's still bothersome is that introducing additional fuel into the intake makes the car run. Maybe re-try that and confirm just to be sure. If that is confirmed you it suggests you are not getting enough fuel. Given that fuel pressure is good either your injectors are bad (maybe one is short) or your DME has an issue with the fuel output signal or you have a wiring issue.

Check that you see +12V at each injector plug on one side (red/white wire) with the ignition in RUN. If not you have a wiring issue.

Then check that you can measure conductivity from the other side to pin 14 or pin 15 of the 35-pin DME connector. Pin 14 supplies injector 1-3 (grey/white) and pin 15 supplies injector 4-6 (grey/brown).

Try to disconnect one injector at a time and try to start. If one injector is short it'll take the entire 6 down as they are all wired in parallel to the same driver. The DME has internal protection against shorts and reduces the current to the injectors when it detects a short. As a result the injectors hardly open at all. If you can isolate a bad (short) injector the other 5 will be able to run the engine.

Next you need to verify that you get fuel pulses and that the injectors are indeed firing. You can order a set of NOID lights on eBay (~15$). Better yet you need access to an oscilloscope.

Let's go through the possibilities and logic. If the fuel driver is completely dead there wouldn't even be a stumble. But you found the engine "wants" to start but just doesn't quite get there. Either too much fuel (bad CHT) or not enough fuel (bad injector, bad fuel output, bad AFM). When introducing fuel to the air filter helps it'll point to "not enough fuel".

So testing for a bad injector is one avenue and then it's off to more advanced diagnostics. You can also try and measure the DC resistance of each injector. It should be 2.6 Ohm. If you find one closer to zero there you go.

BTW: sounds like you have a Steve Wong chip installed and your DME was once worked on by Joerge in Florida. You should tell a potential re-builder or repair shop to keep the chip in there if you desire. There is no reason (from a repair point of view) not to. They can do their tests with a stock chip and then swap the other one back in there. I do it all the time.

Good luck,
Ingo

[byron911]

Thanks (again) Ingo
I really appreciate you sticking with this...
I'll get back to you after I've completed your advice, I actually need to do some other non porsche work!
Very inconvenient
Greg

[byron911]

Thanks (again) Ingo
I really appreciate you sticking with this...
I'll get back to you after I've completed your advice, I actually need to do some other non porsche work!
Very inconvenient
Greg

[silverc4s]

Greg,
Is the car running now?