Forums/Z31P/z31-repairs-forums engine-mechanical/low fuel pressure after blown head gasket
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clostoyo: (2009-12-27 23:54:17)
my 86 na2t was just repaired by my mechanic, it had a blown head gasket . Now the fuel psi is below 20 even after warm up. I replaced the fpr for a good one and still same problem.The car bogs down real bad when it goes into boost. New walbro fuel pump was installed before head gasket blew. What can this be? Thanks
perna00: (2009-12-28 02:27:11)
If you know the fpr is good and should regulate at a higher pressure; it is either a leak or the fuel pump itself. If you know there is not a leak and the pump is working, some times you can have a problem where the pump is leaking the pressure partially back into the tank instead of the lines and you will only have partial pressure. A clog somewhere (fuel filter, line kink) could also cause it.
clostoyo: (2009-12-28 10:01:44)
Okay thanks, Ill look into that today.
perna00: (2009-12-28 12:20:12)
One other thing I thought about; the fuel pumps do not have a constant voltage from the eccs. On the z, the voltage will vary depending on running conditions. Try hooking up a constant power lead to the pump and see if it fixes your problems. Might just be a wire, relay, or connection problem as well.
clostoyo: (2009-12-28 17:32:52)
Thanks, I'll keep you guys posted. I'm going to work on it today when I get home. I also noticed that my temperature stays very low, no where near half way.
clostoyo: (2009-12-29 00:07:26)
Would putting a Turbo head gasket set on a non turbo motor cause this low fuel pressure problem? I think that car stuff sent me the turbo gasket set and the mechanic put it on my na2t car, will causethis problem?
perna00: (2009-12-29 00:42:24)
nope, fuel only goes through the lines and injectors. Nothing to do with engine gaskets or internals.
clostoyo: (2009-12-29 00:54:40)
Okay, I did notice that the pressure goes up when I pull out the vacuum hose from the top of the FPR but only up to 21 psi. I'm going to change the fuel filter tomorrow and see if that works, if not ill try wiring the pump directly, thanks for the help.
Matt89: (2009-12-29 13:40:42)
My bet is on a fuel pump problem.
clostoyo: (2009-12-29 22:22:29)
okay, I'm frustrated, changed the fpr, the fuel pump back to stock, fuel filter, and still no pressure, i also changed the pressure gauge and nothing. It climbs to 20 psi when I take out the vacuum hose from the FPR, what's going on?
perna00: (2009-12-29 23:14:07)
Well, the only components controlling pressure are the pump, fpr, filter, and lines. If you tried two pumps and two fpr, odds are you either have a kinked line not allowing the pressure to build or you have debris in the lines/filter from changing the pump/fpr. If you totally kink the rubber line after the gauge, see if the pressure builds up. It should quickly increase. If the pressure does not increase, you have a problem with the pump not building pressure. If it increases, you either don't have enough freeflowing space in your lines/filter to allow it travel through them fast enough to build up pressure or a bad seal on the pump.
Careless: (2009-12-30 01:48:46)
check the pressure at the fuel filter inlet. see if it even gets up passed 20 to begin with. Then check the pressure on the return.
clostoyo: (2009-12-30 03:45:54)
I'll check those tomorrow, thanks for the suggestions
clostoyo: (2009-12-31 00:23:26)
Kinked both lines and pressure built up pretty fast. I think that my mechanic kinked the fuel rail, so ill take off the plenum and see, another gasket to buy ugggggh! Thanks for all the help guys,
michaelp: (2009-12-31 00:39:25)
Kinked rail shouldnt affect pressure negatively…Also, use the metal plenum gaskets, I reuse those things religiously LOL
StreetFighter: (2009-12-31 00:49:13)
You know… the low fuel pressure might have caused the head gasket to fail. Low fuel pressure=lean=detonation=blown head gasket.
clostoyo: (2009-12-31 01:22:26)
What's crazy is that the pressure Was fine before the head gasket problem.
Careless: (2009-12-31 04:13:02)
that's not crazy. you have to remove virtually every part on the engine to get to the headgaskets, thus you're putting back old parts. once you touch old parts, they tend to break.
did you check the LINE pressure? your fuel pump should EASILY pressurize the rail to 45psi and beyond with the pump dead-headed to the gauge via the line BEFORE the fuel filter with no return.
clostoyo: (2009-12-31 17:32:48)
I'll check the line pressure and see wht i get. I have to get this car running before th 6th of January as my wife starts school then and shes goin to take my daily driver. I'll let you guys know, thanks
clostoyo: (2010-01-01 19:19:53)
Ok, i ran the pump with the fround to the body and the power to the battery and still got low pressure, like barely 10 psi. I plugged the line before the fuel filter and the pressure went up to 40 something very quickly. Im am pluzzled to what this is , ive changed the fuel pump back to the oem one that i know that works, FPR from a car that runs fine, Fuel filter to one that is not clogged i dont know what else to do. How much fuel dos it take in order for the tank to build pressure? IM currently about 1/2 tank. Any other suggestions? I dont know what to do ,thanks.
perna00: (2010-01-03 01:01:02)
Where is your pressure gauge located? Any chance you might have any lines crossed?
clostoyo: (2010-01-03 03:15:05)
I finally got the pressure to go up. It was the gauge that was getting a bad reading cause a piece of the silicone tape was blocking it. But now I have to figure out why my car bogs down when it goes into boost. At times it backfires and turns off on me wright after it attempts to go into boost.
Careless: (2010-01-04 00:20:21)
too much fuel? change afm?