Normal Fuel Pressure - ZR-1 Net Registry Forums

Dandy97 · 10-15-2007

Would fuel pressures of 42psi at idle and 52psi at idle with the vacuum line to the pressure regulator removed be in the normal range or a tad low?

Aurora40 · 10-15-2007

The FSM lists the acceptable ranges, I think that sounds in the ballpark without looking at it?

Dandy97 · 10-16-2007

FSM listed 48-55 psi but I realized after looking again last night that is for key on, car not running. At idle the FSM says 43 psi, so I guess I'm golden. I guess my problem lies elsewhere.

bradslt5 · 10-16-2007

what is your problem?

Dandy97 · 10-17-2007

Quote:

Originally Posted by bradslt5

what is your problem?

A long time ago I think I was in a few fights that started with that question.

I have been fighting (pun intended) with a very bad stumble when the car is cold for awhile. It idles fine but if I try to drive it before it goes closed loop it's like it's running on 3 cylinders up until about 2500 rpm's then it kicks in. If I start the car and let it idle for about 15 minutes and get up to operating temperature, it runs fine. It doesn't throw any codes when it runs bad.

I have run through the diagnostic charts in the FSM that relate to this problem and have not found anything wrong.

Two weekends ago I replaced all of the primary fuel injectors because I had three bad ones, one measured 9 ohms at the coil and the other two measured about 6.5 ohms. Needless to say they were not working very well. I also replaced the coils as long as I had the plenum off again. Also in the last 1000 miles the following has been replaced for one reason or another:
secondary fuel injectors
secondary vacuum pump
plugs (about 250 miles on them)
plug wires
pcv's and top & bottom hoses
iac
map sensor
fuel filter
replaced an unknown custom prom with a marc h. prom

None of replacements effected this primary problem, they all fixed other problems of course. The stumble problem when cold has been uneffected and has gotten continually worse over the last year.

I have pretty much run out of ideas. Whatever it is, I think it must be an electrical device because it starts working better when reaching operating temperature. One thing I have thought about is the ecm, maybe the fuel injector drivers are shot from driving bad fuel injectors. I am probably going to try swapping out the ecm this weekend and see what that does. So we shall see. I really want to get this solved as I originally purchased the car to be my daily driver in the summer.

bradslt5 · 10-17-2007

man thats go to drive you nuts. the only thing i can think of other than the ecm would be a vaccume leak or i wonder if the fuel tank recirculation could cause this. one easy way to ck for vaccume leaks is to attach a 2-3ft hose to the end of a propane torch and just turn it on a little if you get an area that has a leak the motor speed will increase. on last thought you might ck around the plenum gaskets and throttle body. they might have a leak cold and it seals once things expand. dont know if this helps just thought to throw out some ideas . good luck hope you figure it out soon

Dandy97 · 10-18-2007

Quote:

Originally Posted by bradslt5

man thats go to drive you nuts. the only thing i can think of other than the ecm would be a vaccume leak or i wonder if the fuel tank recirculation could cause this. one easy way to ck for vaccume leaks is to attach a 2-3ft hose to the end of a propane torch and just turn it on a little if you get an area that has a leak the motor speed will increase. on last thought you might ck around the plenum gaskets and throttle body. they might have a leak cold and it seals once things expand. dont know if this helps just thought to throw out some ideas . good luck hope you figure it out soon

I have a vacuum leak detector, there are no leaks that I can find. Also, if it was a vacuum leak why would it go away once the engine was up to operating temperature? Anyway, if I get time this weekend I am going to try swapping out the ECM.

WB9MCW · 10-18-2007

GOOD LUCK THIS WEEKEND WITH THE TESTS

tccrab · 10-18-2007

I'll bet dollars to donuts that it's your ECM.
I had the *EXACT* same problem.

Read about it here:
http://www.zr1netregistry.com/forum/...ead.php?t=2206

Good luck!

Dandy97 · 10-20-2007

Well I swapped out the ECM after my son's football game and we fired it up and went for a ride. It ran perfect from the moment I started it up. I'm pretty happy I finally got to the bottom of it. Makes me wonder what in the ECM was failing, I'm thinking the injector drivers.

Tomorrow I think I'll hook up the Tech 1, go for a drive and see how everything looks. I'm also going to send in the old ECM for a rebuild, that way I'll have a back-up.

Now that I got it running good I can put in my Fidanza aluminum flywheel!

10-15-2007	#1
Dandy97 Join Date: Jun 2005 Location: Tax Hell, Wisconsin Posts: 53	Normal Fuel Pressure Would fuel pressures of 42psi at idle and 52psi at idle with the vacuum line to the pressure regulator removed be in the normal range or a tad low? __________________ 1991 ZR-1 #526 White/Red 1997 A4 Coupe [url]http://www.dd-designgroup.com/studio409/studio409.htm[/url]

10-15-2007	#2
Aurora40 Join Date: May 2005 Location: Leesburg, VA Posts: 2,713	Re: Normal Fuel Pressure The FSM lists the acceptable ranges, I think that sounds in the ballpark without looking at it? __________________ Bob Saveland Former owner of #2517 [IMG]http://a.random-image.net/aurora40/vette.jpg[/img]

10-16-2007	#3
Dandy97 Join Date: Jun 2005 Location: Tax Hell, Wisconsin Posts: 53	Re: Normal Fuel Pressure FSM listed 48-55 psi but I realized after looking again last night that is for key on, car not running. At idle the FSM says 43 psi, so I guess I'm golden. I guess my problem lies elsewhere. __________________ 1991 ZR-1 #526 White/Red 1997 A4 Coupe [url]http://www.dd-designgroup.com/studio409/studio409.htm[/url]

10-16-2007	#4
bradslt5 Join Date: Oct 2007 Location: lone pine and mammoth lakes ca. Posts: 544	Re: Normal Fuel Pressure what is your problem?

10-17-2007	#6
bradslt5 Join Date: Oct 2007 Location: lone pine and mammoth lakes ca. Posts: 544	Re: Normal Fuel Pressure man thats go to drive you nuts. the only thing i can think of other than the ecm would be a vaccume leak or i wonder if the fuel tank recirculation could cause this. one easy way to ck for vaccume leaks is to attach a 2-3ft hose to the end of a propane torch and just turn it on a little if you get an area that has a leak the motor speed will increase. on last thought you might ck around the plenum gaskets and throttle body. they might have a leak cold and it seals once things expand. dont know if this helps just thought to throw out some ideas . good luck hope you figure it out soon

10-18-2007	#8
WB9MCW Join Date: Dec 2003 Location: McHenry, Il. Posts: 6,607	Re: Normal Fuel Pressure GOOD LUCK THIS WEEKEND WITH THE TESTS __________________ http://i119.photobucket.com/albums/o...9mcw/SIG-2.jpg http://i119.photobucket.com/albums/o128/wb9mcw/vcm.gif "The Budget should be balanced, the Treasury should be refilled, public debt should be reduced, the arrogance of officialdom should be tempered and controlled, and the assistance to foreign lands should be curtailed, lest Rome will become bankrupt. People must again learn to work instead of living on public assistance." - Cicero, 55 BC " We the people are the rightful masters of both Congress and the courts, not to overthrow the Constitution but to overthrow the men who pervert the Constitution." - Abraham Lincoln

10-18-2007	#9
tccrab Join Date: Oct 2004 Location: Folsom CA Posts: 1,654	Re: Normal Fuel Pressure I'll bet dollars to donuts that it's your ECM. I had the EXACT same problem. Read about it here: http://www.zr1netregistry.com/forum/...ead.php?t=2206 Good luck! __________________ TomC '90ZR1 #792 Honorary Pirate [B]If it ain't FUN, you're doing something terribly WRONG. [/B]

10-20-2007	#10
Dandy97 Join Date: Jun 2005 Location: Tax Hell, Wisconsin Posts: 53	Re: Normal Fuel Pressure Well I swapped out the ECM after my son's football game and we fired it up and went for a ride. It ran perfect from the moment I started it up. I'm pretty happy I finally got to the bottom of it. Makes me wonder what in the ECM was failing, I'm thinking the injector drivers. Tomorrow I think I'll hook up the Tech 1, go for a drive and see how everything looks. I'm also going to send in the old ECM for a rebuild, that way I'll have a back-up. Now that I got it running good I can put in my Fidanza aluminum flywheel! __________________ 1991 ZR-1 #526 White/Red 1997 A4 Coupe [url]http://www.dd-designgroup.com/studio409/studio409.htm[/url]