Starting Issue on 305 TBI driving me insane and is getting progressivly worse. This used to happen every once in a while when I got it 2 years ago, now it happens every time I got to start it:

When I turn the key, the car will crank and fire only to die half a second later. It will do this about 4 times before it finally starts and goes into idle. I can also rev the engine right after it fires to keep it going and get into idle. Seems to run normal after that until lately. If I turn the AC on when warmed up, it will stall sometimes unless I rev it a bit before turning on the compressor.

I have thrown the parts cannon at it:

2 New IACs

New TPS

New EGR

Rebuilt TBI

New Fuel Pressure Spring

New acdelco injectors

New ICM

Spark plug are a year old as are the cap and rotor

New Fuel Filter

New CTS

New Fuel pump relay



No engine codes and WINALDL is reading that it is running slightly rich, blms are usually under 128. Vaccum test shows 21 in-Hg. The kpa readings form map seem normal, the temp reading from the CTS seem correct. TPS .57v. Only thing I have not checked is timing.



The pump primes when I turn the key and I also tested the fuel pressure, priming goes to 9psi and running at 10 psi. If I give it a rev, it is steady on 10psi. Seems to be low but still in spec or GM's 9-13psi. Does this feel like an ignition issue or fuel issue? Any ideas what to test next?

 

Agreed that the fuel pressure is a bit lower than a comfort-level measurement. I fought a couple of TBIs with pressure on the low end and they were temperamental, fussy, and quirky in some of the operating modes. One was a Fiero manual, and when I modded the TBI pod to regulate pressure up nearer the 13 PSI end, several troublesome issues improved.

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I agree. The fuel spec is dumb, they 'like" the very top end of the spec and suffer when they're below that. That spec represents a whopping 44% range in "acceptable" fuel pressure!? Give us a break. That would be like expecting a TPI engine run run 'fine" at 24 PSI. Would it? No.

Get the fuel pressure up to 13 or 14 pounds, then see how it runs.

 

Thanks guys, looks like it's fuel pump time... Now I have to muster up the courage to drop the rear.

 

Dropping the rear is not hard.


Buy a fuel pump for a MPFI application...not a TBI replacement pump.

 

It may not need a fuel pump. The FPR in the "rebuilt" TBI unit may or may not be set where you need it. The replaced spring may also not be sufficient.

If you restrict the return line and test the dead-head pressure of the pump, you can find out. It will require a few adapters and fittings, but is all top-side work and probably easier than dropping the fuel tank.

 

Vader is right. Do what he said, first.

 

What kind of pressure am I looking for on a dead head test? 15psi+?

Thanks again guys.

 

15 PSI would confirm that the pump CAN go higher than the 9-10 pounds you're seeing now....and that adjusting the regulator is all that is needed. Currently.

The TBI pumps are typically pretty crappy...I'll be surprised if you see any more than the 9-10 pounds you're already seeing now, since the pressure SHOULD always be, whatever the reg is set at, on those. Since you see a peak of 10 lbs, it should be 10 lbs all time; idle, WOT, 500 RPM, 5000 RPM....10 lbs. -Or whatever it's actually set to. So to me, since you mentioned 9 lbs but gets up to 10 lbs....I think the pump is suspect, but a test is in order, for sure.

 

The prior assumption could very well be correct, but an extra bit of time checking it out from the top could save a lot of frustration if changing the pump does nothing for improving pressure.

Yes, a pump without a return line could hit 20 PSI, but don't run it that way for more than a few seconds. I don't believe the later years had the pulsation damper in the tank like the '84-ish models had, so there should be no risk of bursting that.

Also, I've had a couple surprises "fixing" fuel pumps that wouldn't consistently make pressure. The one in the photo came out of the tank exactly as you see it, and sometimes would make the correct pressure. The car had been in an accident and I think the kinetics of the impact did the "inertial disconnection" shown.