Fuel pressure erratic at all rpm-Help!

YELLOW89' · 06-04-2001, 04:32 PM

My fuel pressure on my guage bounces from what it's set at down anywhere from 1-7 psi lower and then back again. It does not seem to be rpm dependant. Does it at idle most but even at wot it has some bounce. The fuel pressure guage actually is noisy it bounces so much!

300 hp NA car
1/2" intank pickup to big fuel filter to 255 lph INLINE pump to -8 to rail and then back with -6.

I had to set the pressure to 45 vac off otherwise it would hesitate at half to full throttle starting at 2000rpm. Help! It does pull good to 5500rpm but on the highway you can feel it hesitate slightly every few seconds.

I think the problem would be solved if I switced to a 255 INTANK pump and put the filter AFTER that. I was told the pump may not be holding pressure because of the -8 line.

This isn't normal right? What's the problem?

jimberg · 06-04-2001, 04:48 PM

Fuel pressure varies with engine vacuum. It should be lowest at idle or when decelerating and highest at WOT.

------------------
351W 89 Mustang GT Convertible

YELLOW89' · 06-04-2001, 07:08 PM

I think you misunderstood me-that's not the problem. My fuel pressure is about 45 at 0 vacuum and about 36 at idle.

The bouncing I'm refering to is VERY quick. For instance, if the car is just sitting at idle, the psi will jump from 36 to 33 like 5 times per second! The needle goes so fast you can't really see what pressure you are exactly at. Again, this happens at all rpms and all speeds wether on the gas or not.

06-04-2001, 04:32 PM	#1
YELLOW89' Registered Member Join Date: May 1999 Location: Ypsilanti, MI, USA Posts: 180	Fuel pressure erratic at all rpm-Help! My fuel pressure on my guage bounces from what it's set at down anywhere from 1-7 psi lower and then back again. It does not seem to be rpm dependant. Does it at idle most but even at wot it has some bounce. The fuel pressure guage actually is noisy it bounces so much! 300 hp NA car 1/2" intank pickup to big fuel filter to 255 lph INLINE pump to -8 to rail and then back with -6. I had to set the pressure to 45 vac off otherwise it would hesitate at half to full throttle starting at 2000rpm. Help! It does pull good to 5500rpm but on the highway you can feel it hesitate slightly every few seconds. I think the problem would be solved if I switced to a 255 INTANK pump and put the filter AFTER that. I was told the pump may not be holding pressure because of the -8 line. This isn't normal right? What's the problem?

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06-04-2001, 04:48 PM	#2
jimberg Registered Member Join Date: Oct 1998 Location: Rogers, MN Posts: 2,089	Fuel pressure varies with engine vacuum. It should be lowest at idle or when decelerating and highest at WOT. ------------------ 351W 89 Mustang GT Convertible

06-04-2001, 07:08 PM	#3
YELLOW89' Registered Member Join Date: May 1999 Location: Ypsilanti, MI, USA Posts: 180	I think you misunderstood me-that's not the problem. My fuel pressure is about 45 at 0 vacuum and about 36 at idle. The bouncing I'm refering to is VERY quick. For instance, if the car is just sitting at idle, the psi will jump from 36 to 33 like 5 times per second! The needle goes so fast you can't really see what pressure you are exactly at. Again, this happens at all rpms and all speeds wether on the gas or not.