Fuel pressure mystery???

B

belsie

Active Member
Joined
May 16, 2011
MYSTERY???? Help........................

My fuel pressure died off to where it would not pull into boost and was hard starting, after sitting overnight and was running fine the night before! With key on & gauge on the pressure was slow to climb to 45 range then fell to zero. Turn key off wait a min. then re-do and same up to 40s then fall to 0. Since I have a trap door in the trunk I was able to clamp the return line at the tank then repeated key on & off. ( Pump & relay all working thru-out this )
With return clamped pressure shot up to 65 then leveled to 45 and held. Ran this test twice more with clamp on and all good. Removed clamp on return line and re-ran the key on & off twice more and all seems as it should and pressure is holding at 45. MYSTERY ????

Plenty of fuel, E-85 if that matters, billet reg. app 2 yrs old, Red A. pump & tank app 4 yrs old , sending unit & rear hoses 1 yr. old New 80 lb injectors & Wix filter 1 month ago................ Any thoughts or suggestions as this is the second time this has occurred and it has me baffled...................
 
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Pull the pump and see if that hose on the pump is blown out. I had that happen once, only could build 30 psi fuel pressure as it would just spray all back into the tank..
 
TurboTnZ06 said:
Pull the pump and see if that hose on the pump is blown out. I had that happen once, only could build 30 psi fuel pressure as it would just spray all back into the tank..
Click to expand...


I've had that hose fail before also but his system will hold pressure with the return line pinched so that should rule out the line being split. I'm thinking a bad check valve in the pump or possibly an intermittent regulator issue.
 
if you clamped return and pressure held your regulator isnt sealing 100%
 
I'm having the same issue. So the return comes out of the bottom of the regulator. Makes sense to me.
 
Clamping the return takes the reg out of the loop. [Pump is dead headed at the reg.]
If the pump has a relief, it should be set at some psi considerably higher than op psi. If you can't get it to go to some higher psi, then the relief in the pump is dumping back.
 
Yep, your deadhead pressure shouldn't have dropped. And the numbers should have been much higher.
 
In addition to the possible bad or stuck regulator I brought up the check valve in the pump because with the return clamped shut the extra pressure may have helped seat the check valve again or pushed out debrise. I agree that the deadhead pressure should have been higher but maybe the return is not completely clamped shut. If you remove the clamp and it loses all pressure with the key off then it's the regulator.
 
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Thanks everybody.............the mystery is the fact that when it faults the pressure goes up then drops to 0 until return is clamped then at first clamp press. shoots up high then settles & holds (Refer to my 1st thread for details)
After removing clamp all works fine?? Car starts & runs fine re-tested 10 times and all seems good.

My question is "where's the smoking gun?" ..note all components are newer and this is the second time for this problem..............I have no problem replacing any item once pinpointed but the mystery remains.......

Thanks again for the responses
 
When you clamped the return, that should have spiked the pressure way up to whatever the max it could provide. The first thing after the pump is a little piece of hose, that could have deteriorated or is loose and spraying right back into the tank before it ever leaves the tank. That or the line if blocked, or the pump is just going bad.
 
I just checked mine again with the return line clamped it spikes to 100 psi and then drops to about 10 and eventually 0 I'm guessing the injectors ? Any input thanks
 
Mike T said:
In addition to the possible bad or stuck regulator I brought up the check valve in the pump because with the return clamped shut the extra pressure may have helped seat the check valve again or pushed out debrise. I agree that the deadhead pressure should have been higher but maybe the return is not completely clamped shut. If you remove the clamp and it loses all pressure with the key off then it's the regulator.
Click to expand...

Unless its a Accufab regulator, they will drop like a rock when keyed off.
 
I just purchased a new fuel pump trying to decide to install it or return it and order new fuel injectors
 
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