85 fuel delivery problem?
Im not sure if I have a fuel problem or a electrical miss. My exhaust is a little loud so its hard to tell. Car idles fine and revs fine when sitting still with no load on engine. When I accelerate hard, or pull a hill, car surges and runs rough. I have tried fuel additives and only run 93 octane. When car is first started it runs fine for about a minute then it starts to miss. If I stop for a few minutes and restart, it will run fine for another minute and then miss again. It is not a constant miss. When I decelerate it will run fine for about 5or 10 seconds before it starts missing again. It feels like it is starving for fuel. This has went on for about 200 miles. Enough time to run any "bad gas" through. I have replaced the dist. cap, rotor, plugs, plug wires, and coil. Any suggestions?
maybe it is the fuel pump....does the service engine soon light come on???
as of 7/28/07 Corvetteless, soon to change!
In other vehicles had a plugging fuel filter do the same. In my Haynes manual is a test for measuring fuel flow consisting of measuring the amount pumped into a cup in a number of seconds. If you dont have access to a manual, I'll send it along. Also had failing fuel pumps do simular. And our 85's have a screen on the pump also that could plug. Which would be rare.
I recently experienced the same type surge you describe and it was the MAF sensor that needed replacing on the '85. It has run great ever since.
I just went through a huge amont of diagnostic to fix a problem on my 85.
Do you get a check engine light??? That is crucial before we go further. Also, do you hear the engine "PING" when this is happening...or any black smoke out of the pipes?
Check engine light does not come on. No smoke. Feels like engine is not getting enough fuel. Idles fine. Runs fine at low RPM. Engine revs fine in neutral. Just runs rough at higher RPMs or when accelerating hard.
I think you have a bad EGR valve. It will only open in gear, and if it has a leak in the diaphram, it may be sticking, etc.
My guess is this because you do not appear to have any spark knock/ping coming from the engine. If you were having a major fuel restriction you would hear ping under a load.
Get a GM manual and follow the diagnostic procedure for a failed EGR valve. Only replace with a genuine GM, as the aftermarket valves are junk.
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