Fuel pressure...Got issues. - ZR-1 Net Registry Forums

Paul Workman · 06-15-2009

Last fall, I baselined my Z before doing any mods. At that time I had them run an Air Fuel chart as well, and it showed initial AF was around 12.8 up to about 3500 where it began ramping up to about 5000 (from memory) where it leveled off at 14.0

So, with a top end porting done, before I ran it on the dyno again, I wanted to check out the leaning phenomenon. Sure enough, when I monitored FP at WOT, it went from 44#(?) at idle, would initially jump to 50# as I got into the accelerator, and like the AF graph predicted, the pressure began to fall off until it reached 40# where it seemed to remain steady from ~5000 to red line.

If the drop off was linear, I would say "obstruction", but the leveling off suggests (to me) some intervention is going on; regulator? fuel pump fluctuations? what?

So, the consensus of the meeting with the FBI yesterday seemed logical to me: changing the filter (easy) and work my way thru the pumps and finally the regulator. I'll letcha know what I find.

One thing I don't know is what is normal for FP over rpm at WOT? Should it remain rock steady, or is there some normal fluctuation, and if so how much and what would be considered acceptable? Any more thoughts?

P.

A26B · 06-15-2009

Try pinching off the vacuum line to the fuel pressure regulator. It should go to max capable mechanical (fuel pump) pressure with no vacuum to the regulator.

jonszr1 · 06-15-2009

i ck with corey on your issue and he said the following, you should have 50-55 lbs of pressure at WOT. if its less you may have a filter problem or your pumps might be getting weak, most likely the secondary pump from his experience .also ck the rubber fuel lines at the tank for cracking and sealing. hope this helps

Paul Workman · 06-16-2009

The trick is to keep one eye on the road, one eye on the fuel pressure gauge, and one eye on the tach...That's one too many eyes!

I decided to push ahead; try to resolve my FP issue AND bolt on the headers this w/e. Wish me luck!

P.

XfireZ51 · 06-16-2009

Should stay steady into the 50's at WOT.

06-16-2009

Change the filter. Most people forget there is one even there. Pressure should come right up. If it was a serious issue, you would be setting a fuel lean monitor code as well.

06-15-2009	#1
Paul Workman Join Date: Nov 2007 Location: Squires (near Ava MO in the Mark Twain N'tl Forest) - Missouri Posts: 6,466	Fuel pressure...Got issues. Last fall, I baselined my Z before doing any mods. At that time I had them run an Air Fuel chart as well, and it showed initial AF was around 12.8 up to about 3500 where it began ramping up to about 5000 (from memory) where it leveled off at 14.0 So, with a top end porting done, before I ran it on the dyno again, I wanted to check out the leaning phenomenon. Sure enough, when I monitored FP at WOT, it went from 44#(?) at idle, would initially jump to 50# as I got into the accelerator, and like the AF graph predicted, the pressure began to fall off until it reached 40# where it seemed to remain steady from ~5000 to red line. If the drop off was linear, I would say "obstruction", but the leveling off suggests (to me) some intervention is going on; regulator? fuel pump fluctuations? what? So, the consensus of the meeting with the FBI yesterday seemed logical to me: changing the filter (easy) and work my way thru the pumps and finally the regulator. I'll letcha know what I find. One thing I don't know is what is normal for FP over rpm at WOT? Should it remain rock steady, or is there some normal fluctuation, and if so how much and what would be considered acceptable? Any more thoughts? P.

06-15-2009	#2
A26B Join Date: Dec 2003 Location: Arcadia, OK Posts: 3,392	Re: Fuel pressure...Got issues. Try pinching off the vacuum line to the fuel pressure regulator. It should go to max capable mechanical (fuel pump) pressure with no vacuum to the regulator. __________________ Jerry Downey JERRYS LT5 GASKETS & PARTS http://www.jerrysgaskets.com 1994 *ZR-1*, Black/Black, Lingenfelter Aerobody, 416cu in, 3.91 gears, coil-over susp, Brembo brakes, etc. 2016 Black-Red, 3LT-Z51 Auto 8-speed.

06-15-2009	#3
jonszr1 Join Date: Sep 2006 Location: lone pine and mammoth lakes Posts: 1,406	Re: Fuel pressure...Got issues. i ck with corey on your issue and he said the following, you should have 50-55 lbs of pressure at WOT. if its less you may have a filter problem or your pumps might be getting weak, most likely the secondary pump from his experience .also ck the rubber fuel lines at the tank for cracking and sealing. hope this helps

06-16-2009	#4
Paul Workman Join Date: Nov 2007 Location: Squires (near Ava MO in the Mark Twain N'tl Forest) - Missouri Posts: 6,466	Re: Fuel pressure...Got issues. The trick is to keep one eye on the road, one eye on the fuel pressure gauge, and one eye on the tach...That's one too many eyes! I decided to push ahead; try to resolve my FP issue AND bolt on the headers this w/e. Wish me luck! P.

06-16-2009	#5
XfireZ51 Join Date: May 2007 Location: Chicagoland, IL Posts: 9,683	Re: Fuel pressure...Got issues. Should stay steady into the 50's at WOT.

06-16-2009	#6
Jeffvette Guest Posts: n/a	Re: Fuel pressure...Got issues. Change the filter. Most people forget there is one even there. Pressure should come right up. If it was a serious issue, you would be setting a fuel lean monitor code as well.