Interesting fuel pressure
 

Hey guys, just wanted to share some info and ask some opinions:

My car normally runs at 59 PSI fuel pressure (fuel pressure gauge indication) dyno of 202 whp

everything seems fine

yesterday ,while driving the car home, I noticed that under different loads in 4th gear (1/4 tank left) the fuel pressure seems to drop.

at small throttle, the pressure would still be 59

but if I go half throttle, it would be at about 58 ish
and at full throttle, it drops to 57 ish


fuel pump dying?

Uhh.. can't answer that. It's ONLY in 4th gear? I'm confused now...

well, I've only tried it in 4th gear, I'm pretty sure it happens in all gears

If your fuel level was low it could have been having trouble picking up fuel..

maybe, has it ever been replaced ? and whats ur miles again ?

its fine.

doesn't seem like much fluctuation; probably has to do with the level of fuel.

i have....10295 miles on my car, its never been replaced

the car still seems to run fine though, so I'm not worrying too much on it, just want to anticipate any problems since I'm getting all my stuff ready for the big mod-fest

details on 'mod-fest'? Inquiring minds want to know...

just all the stuff that has been sitting in my place for the past 3 months all together which never made it into the car, just need to put them all in sometime this month :) oh and a new paint job

It seems normal I wouldn't be too worried.

thanks guys, I was starting to think I have to shell out some mod-money to fix her :(

btw, she's proved to be resilient and more enduring than I can ever imagined, what with all the nitrous and everything :D

are you still on the 55 shot? any more dyno plans? :lol2:

we have a two speed pump that is switched by various commands. start up for instance is one. were you in a load situation with rpms over 5K and tps at more than 50%?
we are finding a 5-7% difference in readings over a fairly short period of time.
low fuel will not affect pressure until the pump can't pick any up and then the car will shut off/stumble.
I advise that no one ever let the tank go under 1/2 full.
It usually is not really a problem unless you go fi or you track your car.
we have a problematic fuel delivery system--still remains to be seen if it is filter, or the pump causing problems.
olddragger

yes OD, its what you said, and the tps was over 50% as I stated before, it happens at any given rpm above 4k for me

it doesn't do anything to the power delivery

just a slight variation in fuel pressure


I plan to up to a 100 shot once i get the EMU to work properly and go from there, but i gotta buy some stuff of CRH first

maybee just a clogged fuel filter....

a 2 psi drop at full throttle should not worry you..

beers :beer:

The tank can be run nearly dry and the pump won't loose its scavenging.
I know there have been a couple of people with a pickup problem at low fuel levels, but that is an anomaly.
A properly installed, healthy pump doesn't care what the fuel level is as long as the pickup is submerged.
I suppose if you stayed at a continuous lateral load long enough to generate sufficient centrifugal force to move all the fuel to the right saddle tank, you could starve the pump, but that would mean nearly a full g in a left turn and less than a gallon in the tank. Even then it is unlikely.

A few PSI drop under load is normal - the pump works against a restriction - low injector duty cycle.
When you romp on it, the pressure drops because the restriction drops.
This is a returnless system, so the pressure regulation is built into the pump vane clearance.

Yep probably nothing to worry about at this point. But if you are doing a 100 shot you are wise to keep an eye on it. I have never heard off anyone having fuel pickup issues while running in a straight line.
olddragger

wtf? and i thought he was seeing something like 4-5 psi like its a carburetor car...

and with driveability issues... i thought this was gonna make me scratch my head.

I have to disagree on this one....I have done a lot of track time with turn loads above 1G Lateral...and there is definitely a pickup and scavenging problem. I wish I had had the FP logging capability when I was still running th stock pump......Below 1/8 tank the system can't keep up at high fuel demand

oh sweet jeebus, not this thread subject again ....

conclusion: there is a reason why car manufacturer's don't put fuel pressure gauges in cars :)