Carpokes Porsche Forum

eccs19 wrote: Sat May 09, 2026 8:56 am Got the car. Line from tank to pump wasn’t flowing. It’s been replaced along with the fuel pump. (Bosch) fresh fuel is now getting to the fuel rail. New speed and reference sensor. (Gapped) injectors removed, cleaned and confirmed flowing. New orings and filters in the injectors. Car turns over and will fire for a second or two, but that’s it. My observations are that when cranking, no tach bounce, but when it fires up, tach runs. New relay. Also jumped relay tried as well. New jboot as old one was toast. Have also done a compression test and all around 175. I do not have a pressure gauge. But cracking the line, I get plenty of gas squirting out.

Tom wrote: Sat May 09, 2026 10:38 am

eccs19 wrote: Sat May 09, 2026 8:56 am Got the car. Line from tank to pump wasn’t flowing. It’s been replaced along with the fuel pump. (Bosch) fresh fuel is now getting to the fuel rail. New speed and reference sensor. (Gapped) injectors removed, cleaned and confirmed flowing. New orings and filters in the injectors. Car turns over and will fire for a second or two, but that’s it. My observations are that when cranking, no tach bounce, but when it fires up, tach runs. New relay. Also jumped relay tried as well. New jboot as old one was toast. Have also done a compression test and all around 175. I do not have a pressure gauge. But cracking the line, I get plenty of gas squirting out.

Those symptoms would make me first suspect a bad air-fuel ratio, with the most common causes being a big vacuum leak or a bad AFM signal.

Backing up a bit, you 'should' see tach bounce when cranking, but the fact that it fires then dies suggests you do have an ignition pulse. "Bounce" is a misleading term really -- it's often not more than a tiny twitch. You can eliminate all doubt by pulling the #1 spark plug wire and checking to see if it sparks against the intake manifold (you'll need to pull the metal part out so it sits a mm or two from the intake, or use a screwdriver to extend it). If you have spark, you can forget about the speed/ref sensors, DME relay, DME itself, coil, etc. I have to believe you have spark since it fires up and dies, but no harm checking if you see no movement at all on the tach when you crank.

Assuming you have spark, I'd check closely for big vacuum leaks -- on old abandoned cars, a big split under a hose wouldn't be a surprise. A smoke test would help if nothing is obvious. If no vacuum leaks, then I'd test the AFM. The little carbon traces wear out and send bad signals, and the harness wiring can crack and fray. We have an AFM test guide here. Yours is the 12 volt version I believe, but the same basic procedure applies. Be sure to test at the DME connector to start, without removing the AFM, as that tests both the harness and AFM itself.

If none of that is it, it's also possible your fuel pressure regulator is bad. Check the vacuum hose going to it for wet fuel or strong smell of gasoline. When they go really bad, they leak gas into that hose. Absent that, you'd need to check fuel pressure with a proper gauge.

Could be just about anything on a rescue car (e.g., bad temp sensor or wiring, fuel contamination, stuck AFM or idle stabilizer, rats nests or blockages somewhere, etc.) , but the things above are my odds-on favorites...

spacecad3t wrote: Sat May 09, 2026 9:13 am Flipped reference sensor plugs? Mis-gapped?
Big ass air leak somewhere?

Tom wrote: Sat May 09, 2026 12:07 pm A disconnected oil sender will cause the gauge to max out, but it has no effect on whether the car starts or not.

944 harness wires can be deceiving as the problems are very often under the rubber boots. Read all about it here.

I assume you have spark too for the same reason, but never hurts to check. I only mentioned it because you said you saw no tach bounce -- but I discount that somewhat since the car fires up and then dies. That's a classic bad air-fuel ratio symptom.

I'd check the AFM for sure, and maybe the DME temp sensor. We have a test for that as well in the 944 Handbook. Then vacuum leaks, and fuel quality and pressure.

Removing the air filter would not stop the car from starting.

eccs19 wrote: Sat May 09, 2026 2:35 pm

Tom wrote: Sat May 09, 2026 12:07 pm A disconnected oil sender will cause the gauge to max out, but it has no effect on whether the car starts or not.

944 harness wires can be deceiving as the problems are very often under the rubber boots. Read all about it here.

I assume you have spark too for the same reason, but never hurts to check. I only mentioned it because you said you saw no tach bounce -- but I discount that somewhat since the car fires up and then dies. That's a classic bad air-fuel ratio symptom.

I'd check the AFM for sure, and maybe the DME temp sensor. We have a test for that as well in the 944 Handbook. Then vacuum leaks, and fuel quality and pressure.

Removing the air filter would not stop the car from starting.

Actually figured out the issue. I was working on the car myself originally, so didn’t see what was going on. Had my son help me this afternoon and had him punch some starter fluid into it. Of course it started up and ran for a second or two but he noticed the J-boot collapse. Checked the barn door and it was stuck, so not much air was getting into the engine. Got it all cleaned up, put it back together and it now runs. Granted it runs badly. Crap coming out the tailpipe, runs rough, but I don’t have much fuel in it, so I suspect it’s just good fuel mixed with old ¯\_(ツ)_/¯ stuff that was left in the tank. I’ll add more fuel and hopefully that helps it out. But it’s a good step in the right direction now.

Tom wrote: Sat May 09, 2026 2:59 pm

eccs19 wrote: Sat May 09, 2026 2:35 pm

Tom wrote: Sat May 09, 2026 12:07 pm A disconnected oil sender will cause the gauge to max out, but it has no effect on whether the car starts or not.

944 harness wires can be deceiving as the problems are very often under the rubber boots. Read all about it here.

I assume you have spark too for the same reason, but never hurts to check. I only mentioned it because you said you saw no tach bounce -- but I discount that somewhat since the car fires up and then dies. That's a classic bad air-fuel ratio symptom.

I'd check the AFM for sure, and maybe the DME temp sensor. We have a test for that as well in the 944 Handbook. Then vacuum leaks, and fuel quality and pressure.

Removing the air filter would not stop the car from starting.

Actually figured out the issue. I was working on the car myself originally, so didn’t see what was going on. Had my son help me this afternoon and had him punch some starter fluid into it. Of course it started up and ran for a second or two but he noticed the J-boot collapse. Checked the barn door and it was stuck, so not much air was getting into the engine. Got it all cleaned up, put it back together and it now runs. Granted it runs badly. Crap coming out the tailpipe, runs rough, but I don’t have much fuel in it, so I suspect it’s just good fuel mixed with old ¯\_(ツ)_/¯ stuff that was left in the tank. I’ll add more fuel and hopefully that helps it out. But it’s a good step in the right direction now.

Wahoo -- I said 'stuck AFM' in one of my comments! What do I win? Of course, I list almost every possibility, but still. Glad you got it going. Onward and upward from here!!

Tom wrote: Sat May 09, 2026 2:59 pm

Wahoo -- I said 'stuck AFM' in one of my comments! What do I win?