fuel pressure problem

[todd383]

On my friends challenger, 383, mildly built, the problem here is the fuel pressure drops after about 25 minuters of driving, it has a complete new fuel system,from tank to carb, and upgraded to 3/8 line, it has a holley mech. pump, 120gph, and edelbrock regulater, when u first start it, it has 6 1/2 lbs. of press. then it slowly drops too 3lbs, this is not normal i hope any body know what the problem might be , before i start changing parts

[GoodysGotaCuda]

New fuel filter? What about tank sock, or any junk in the tank? Check for any remotely kinked rubber lines, because they get sucked on while running and can make that kink worse. Also tighten up all the clamps.

[matt63]

Maybe check the fuel pump grounding???

[GoodysGotaCuda]

On my friends challenger, 383, mildly built, the problem here is the fuel pressure drops after about 25 minuters of driving, it has a complete new fuel system,from tank to carb, and upgraded to 3/8 line, it has a holley mech. pump, 120gph, and edelbrock regulater, when u first start it, it has 6 1/2 lbs. of press. then it slowly drops too 3lbs, this is not normal i hope any body know what the problem might be , before i start changing parts

Maybe check the fuel pump grounding???

Mech pump 

[Moparal]

Is the fuel tank vented good?  Will it do it with the gas cap off? Is the bowl vent open on the carb?

[MEK-Dangerfield]

I think all is well here. 

I have a hi-volume mechanical fuel pump on my car. Without a regulator I would see 9-10 at start-up, then it would drop to around 7 after driving it around for a while. I put a regulator on it to keep it at a steady 6 now. It is about 8 at start-up now, but drops to 6. I would suggest turning your regulator up a tad, that way it won't drop below 5-6 pounds.


  Mike

[Chryco Psycho]

as AL said if the tank is not vented well it could be locking up with vacuum

[GoodysGotaCuda]

as AL said if the tank is not vented well it could be locking up with vacuum

True, you need the pressure differential to make that work 

[matt63]

Maybe check the fuel pump grounding???

oops -forget that one.  I do like return lines on high flow pumps.

[todd383]

Everything is new, from tank to sending unit, high flow fuel filter, etc, etc, I have the same setup on my car and has no problems, but it does drop a little,  Thetank is vented, like i said, everything is NEW!!!!!!!!! when the car is cold, the pressure is 7lbs. and u can adjust it when the car is cold or running for a little bit, but when it is warmed up, after driving it for a little bit, it drops to 3 lbs. and when u try to adjust it, it does nothing , the rubber lines i checked, no collapsing.And it does have a new carb, and we did  switch carbs for the hell of it and still the same.    AGAIN

[MEK-Dangerfield]

You can drive with it 3 PSI, but that's scary low. I can't understand why adjusting the regulator does nothing, unless the problem is the fuel pump or further back. Do you have a new pushrod for the fuel pump installed in the block??  It could be a bad regulator too. If it were a plugged or kinked line, or no air getting into the tank, the pressure would eventually go to zero. I'm stumped. 


  Mike

[todd383]

Well,  i just got of the phone with my friend, what were gonna do is change the pump first, see what happens, and if that is not the problem , then change the regulater,and see what happens.

[Jacksboys]

Good luck on finding the problem   

[Chryco Psycho]

check the fuel pump pushrod while the pump is off , both ends should be equal lenght

[moparniac]

I had a brand new fuel pressure regulator that did nothing as well when adjusting it... I replaced the regulator and that solved the problem...