coothethird

Hello.

1985 corvette manual transmission

Starts right up then dies after a few seconds.

Fuel pressure is 38-39 with regulator vac line unhooked. Stays up through starting, so it seems the relay is staying on and there is no oil pressure sensor issue.

Fuel pressure holds well. It will hold pressure for at least 30min.

Block/pinch return line and the pressure builds to over 70psi. The car will actually start and run like this. I tested it out of curiosity.

The fans come on with the switch. When I attempt to jump A to B on the aldl the CEL does not blink, thus I cannot pull the codes.

If I apply a very slight amount of throttle right after it starts, I can get a high idle.

Any ideas? The car starting and running with the return line pinched made me think fuel regulator, but 38+ psi should be enough to run ( I would think). Lengthening the running time by opening the throttle body makes me think IAC. The fans coming on with the switch makes me think it is stuck in limp mode. I don't what to think about the CEL not blinking when A and B are connected.

Not sure where to go next. Could throw parts at it. Lol. But would rather hear from experienced owners.

Thanks,
Tom

Cruisinfanatic

unplug the MAF and see if it runs better

antfarmer2

Fuel filter?

coothethird

Thanks, I tried unplugging the MAF, no change.

I ordered a new fuel filter just to make sure, but have not received it yet. I put an extension on the return line and the flow seems to be plenty and the pressure seems reasonable. I don't think it's the filter, but will replace anyway.

Thanks again.

antfarmer2

While you're waiting take your coil and ignition module in for testing do not forget the thermal grease. and pull the vacumm line off the fpr and look and smell for fuel.

coothethird

When I pulled the vac line off the FPR to test pressure, I couldn't see any fuel residue. I'll pull the ignition coil and module, but the car will run with the return line pinched. It doesn't seem like an ignition problem, but I'll give it a shot.

antfarmer2

But does not cost anything to test might even test the water temp sensor for the puter too. Strange things can happen.

coothethird

Agreed, will add water temp sensor to the testing list.

VikingTrad3r

Very interesting about it running at 70psi (with return line clamped).

Would that have the effect of adding more fuel? Injector pulses stay the same but a bit more fuel getting in due to higher pressures?

if so, sounds like it's running lean, and when you enrichen the mixture (by inducing huger pressure it will run.

I'd be looking for either a huge vac leak, or clogged injectors/clogged fuel filter.

Your pressure may be just fine, but flow rate massively reduced due to the clog.

coothethird

Yes, seems fuel related to me as well. Will replace the fuel filter this afternoon (just came in) and see if it helps. That should be everything in the system sans regulator.

antfarmer2

If the tank is full best to pull the line off it or at least keep your mouth shut.

coothethird

Haha. Yes. I will break out the hemostats and try to reduce the flow of man cologne.

antfarmer2

Roach clips might not do it.

coothethird

Changed the filter. Still the same symptoms. Roach clips worked very well.

antfarmer2

More tests.

coothethird

What would keep the ecm to fail at giving codes? When I try to jump A to B on the aldl and it doesn't make the CEL blink at all.

VikingTrad3r

U r not getting code 12? No blinks at all? Ecm failure or is your all upside down? That happens a lot.

Battery unconnected or dead.

Fuse on idiot panel toast? Wiring to idiot panel compromised?

coothethird

No blinks at all. Just a solid lit CEL. Pretty sure it is the correct A and B. If it's upside down then you can't jumper anything because one space is empty, ie it has no pin/wire connected to it. I will check all the fuses again.

The cooling fans on when the switch is turned on. The ecm could be fired, or, like you say, wiring issues.

coothethird

Checked tps voltage, it was way low. I tested the tps and the resistance was within what others have found to be good. I adjusted it to as close to .54 volts (closed) as I could. It would only go to 2.0 volts wot. I think there must be resistance in the connection.

I also did the reset procedure on the iac actuator.

It now starts and idles fine. It has a nasty bog off idle, probably due to the tps not getting close to the 5v input.

antfarmer2

Good job sounds like you're sneeking up on it.