tc944

Need some help. Working on a 85.5 n/a 944. When it got dropped off, it would start, run rough, and not rev very well. I checked the fuel pressure per Clark’s and pressure is good. Then checked tps and it was bad. Also noticed there was a lot of raw fuel in the throttle body area. Put in a spare Tps I had and verified that it was working. Tried to start it and it cranked for 5 seconds, fired, died. Won’t stay running.
I swapped out the dme relay for the one in my car, no difference. I swapped out the dme from my car, no difference. I ohm’d the speed and ref. sensors and they seem fine.

What I am noticing is that the tach doesn’t bounce for the first few seconds. Then it starts to bounce and it fires. Then it dies.

Any suggestions, this one has me stumped?

Forgot to add that I reset the gap on the ref sensors too.

sweetskillsrk

Different situation, but after I did the head gasket, I accidentally bolted the intake down wrong and left a gap between it and the head. It did the exact same thing you're describing and I troubleshot for days and days and couldn't figure it out. I enlisted more knowledgeable help and he showed me what I did, man I was kicking myself. Anyway because it wasn't able to build up vaccum pressure, it would start, but it wouldn't run. It would act like it would, but then immediately die because the air fuel mixture was all out of wack without proper vaccum pressure. All that to say, check your vaccum lines. Not sure if that has anything to do with it, but worth a shot.

T&T Racing

Test the fuel injectors. Remove the fuel rail with the injectors attached from the intake manifold. Set each injector into a plastic cup of equal volume. Crank the engine for several seconds. Determine the volume of fuel collected in each cup.

If there is fuel in some cups and not others. Then switch the good and bad injectors to see if there is a difference. If no difference, then the fuel injectors are fouling. Send them to SouthBay Fuel Injectors, contact on website, for cleaning and testing.

1.f no fuel, check voltage at injector pins, remove each pin connector from injector. One pin should read battery voltage, 12v + and the other pin should read 10.6v if battery voltage is 12.5v, adjust that reading if battery voltage is less than 12.5v
If readings are not close to these, then issues with fuel injector harness.

2. If step 1 is Ok, then find the +12v supply to the fuel injectors, in my 83 it is the red/blue 2.5mm wire out of the large plug above the brake vacuum booster. Cut the wire, but leave sufficient space to reconnect it. Connect the end of the wire that feeds directly to the fuel injectors with a jumper to the positive side of the battery. Crank the engine and see if it starts, runs, and idles.

If the engine does not start or stalls, then reconnect the wire with a solderless connector, then solder the butt joint and have a heat shrink insulator installed.

3. If step 2 Ok, then need to wire a relay into fuel injector circuit by using the other end of the cut wire to the coil of a NO relay and connect the battery to one contact and th. 12 feed to the fuel injectors to the other. There are water-tight relays available on the intermet.

4. If step 2 makes no difference, then check grounds between the chassis and the bell housing. Clean the connector contact points. Try to start engine

5. If step 4 makes no difference, then maybe there is an issue with the reference/speed sensor harness.

This is the logical test sequence. Report back on your findings.

tc944

Thanks for the input guys. I will check both of your suggestions this week and report back. Luckily, I don’t have a time limit in this one so I can work at it at my leisure.

tc944

You were right on. When putting everything back together, one of the large vacuum lines under the j-boot came off. Re-attached and it started right up. So the original problem was the tps. Should have checked vacuum lines first when it wouldn’t run.

Thanks!

sweetskillsrk

Awesome, glad to hear it buddy!