A few problems that won't go away.

hoffmandj

Registered User
My problem's started when my stock fuel pump died. I checked my fuel pressure after replacing my pump and I'm getting around 32lbs of fuel pressure at idle, and it rises to 40lbs when you raise the rpm. I'm not sure if it is supposed to do that or not. Doesn't the pump run at the rated speed all the time the engine runs? Anyway I have a miss at idle and under moderate amounts of boost. Now before anyone says it I've already planned on changing my plugs and wires. I've had the induction apart and yes I've used rtv to reseal the tubes. I don't believe my engine is vacum leak free. I read the post about testing the induction system with an air compressor and some air regulators. That sounds like a error free way to test it. So If anyone could tell me what else could be causing my problems.
 
hoffmandj said:
My problem's started when my stock fuel pump died. I checked my fuel pressure after replacing my pump and I'm getting around 32lbs of fuel pressure at idle, and it rises to 40lbs when you raise the rpm. I'm not sure if it is supposed to do that or not. Doesn't the pump run at the rated speed all the time the engine runs?

Yes it is supose to increase the fuel pressure with increased boost. There is a small line going from the intake manifold plenium to the to the fuel pressure regulator.

Unfortunatly I don't know off hand what the pressure is supose to be. But I'm sure someone will shout out soon.

Originally posted by hoffmandj Anyway I have a miss at idle and under moderate amounts of boost. Now before anyone says it I've already planned on changing my plugs and wires. I've had the induction apart and yes I've used rtv to reseal the tubes. I don't believe my engine is vacum leak free. I read the post about testing the induction system with an air compressor and some air regulators. That sounds like a error free way to test it. So If anyone could tell me what else could be causing my problems.

Sounds to me your on the right track, If it is a random or ocasional miss.

don't forget to replace your fuel filter if you haven't already, I'm bad about ignoring it for a year or two.
 
Thanks

I know theres a vacum line attached to the fpr, and its a diaphram like vlv that close's of fuel to the rail when the pressure in the rail equals out, so I guess I knew the answer to that and just didn't think about it. I guess I'll just try and get everything sealed up and go from there. Any other inputs from you guys would be a help.
 
With vacuum/boost refrence line removed from the regulator the pressure should be between 38-40 psi at idle. As Rich said the pressure is supposed to increase pound for pound with boost. With the hose attached it will lower the fuel pressure about 5 or 6 psi depending on how much vacuum you engine is pulling. A quick stab of the throttle that shows 10 pounds of boost should result in 50 pounds of fuel pressure.

If the miss is more apparent or gets worse under heavy throttle (max boost) it's generally the plugs or wires. If it only misses at idle and part throttle, but seems to run okay under boost it's most likely a vacuum/boost leak. Vacuum leaks usually cause rough idle, hesitations and frequent stalling but they don't cause a miss unless they are pretty big.

David
 
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