74ZZ430

Help, I been trying for weeks to solve my fuel pressure problem, and its not the gauge. I have a 355 with a Edelbrock 110 gph pump using a bottom outlet plate. I've changed the pump, switched to fuel injection hose and metal lines, removed the fuel filter and replaced the tank strainer. For the first hour or so of driving the fuel pressure is fine, no matter how hard I drive, about eight pounds, but after the car gets good and hot the pressure starts dropping on hard acceleration the pressure will drop below three. Not only does the gauge show this but I wired my nitrous safety switch to a light inside the car that goes off any time the pressure goes below five pounds. It started going off once the car gets hot. The amount of fuel in the tank has no effect. I prefer not to go to electric but have run out off ideas.

Matt Gruber

return line hooked up?

74ZZ430

I had a fuel bypass hooked up on the the car that would keep the pressure down to six lbs. I temporally disconnected it but it made no difference.

Matt Gruber

with nitrous i can see your concern.
perhaps no2 guys will chime in.
without no2 it wouldn't worry me, as long as it stays strong WOT.
keep the return flowing as it keeps the gas cool

jpatrick636

I had a boiling problem with mine. I had to shield the line to the carb and install an isolation plate under the carb. Just a thaught.

bozzman3

How do you know your pressure is low?Does the car have any symptoms of low fuel psi?In line gauge are famous for poor readings.If the car shows no performance problems I would bet that the fuel pressure gauge and cut out switch are getting vapor locked giving poor readings.

duntovlives

you might check to see that the tank is venting properly. otherwise, it will create a vacuum in the tank. could make it hard for the pump to do its job.

KB9GKC

SmokedTires

Do you have a Holley type carb? Do you have a heat shield under it to prevent the gas from boiling out of the bowls when shut off and flooding your engine? Just a thought

74ZZ430

Thanks for all the suggestions. It's not a venting issue I still have the vapor canister hooked up and I drilled a 1/8" vent in the gas cap. I don't think it could be vapor lock because it will do this while your cruising at 65 MPH for miles and get on it. I don't have room for the factory thick carb gasket because of the nitrous plate and and a stock hood. I've ordered another fuel pump, I'll post whether that cures the problem.

cardo0

JFYI, a recirc back to tank using the old return line but through a 0.040" orifice keeps my supply line with fresh fuel.: : I was able to tee into the Qjet fuel bowl and my fuel recirc all the way from the carb.

Good luck,
cardo0

Wib69

Did you ever resolve this issue? II have the same trouble, 7-8 psi upon start up & when hot it drops to ~3psi. I have the return hooked up.

Neptune75

i think that the small lead of hose you have running from the steel line by the tank to the tank is colapsing when the fuel gets warm. i know this sounds crazy but it is a problem i noticed that u said u changed the line to high pressure fuel injection hose did you change the one by the tank.... ? i had this problem about a year ago... i sumped my tank and ran a 10 an s.s line from the tank to the mechanical holley h.p series mechanical pump that flows 170 gpm at a regulated 7 psi eliminating the use of all electric pumps for carberated engines. will support 800 hp on a holley 1050 at W.O.T.. jsut my 2 cents hope this is helpfull.. Neptune

MotorHead

I don't like it when people ask a question, get all kinds of advice and never report back the results, let alone thank the person or persons that came up with the answer for them. Have the common courtesy to report back your findings.

It really shouldn't matter too much for me because I just like to help with my own personal experiences but I hardly ever hear anything back good or bad.

As far as the fuel pressure gauge goes, throw it in the garbage most if not all read false ( low ) when warmed up

mrvette

Off hand, I think I know the answer from my past experineces.....the pump has to be located in the REAR, pushing all fuel forward through main line and any returns hooked up as needed/desired, allowing for various carbs.....Qjets like lo pressure from electric pumps, most other carbs can take the 8 lbs easy ...like the AFB/Edelbrock designs.....I know nothing of any Holley/related carb.....

Neptune75

normally i agree with wha motor head says... but i think the gauge is not at fault. its said through boyles law that temprature and pressure are inversly proportional... un related. if your useing a bourdon tube style gauge like most of us are from 0 to 15psig they are pretty acurate for what they are... oh motor head did u ever find that welder your looking for...?

...Roger...

Check the fuel pump pushrod for straightness.
If someone has ever used the bolt hole in the front of the block to hold the rod they could have bent the rod.