FPR - quick question

slo95 · 04-03-2001, 04:43 PM

from previous posts, I am having some trouble...I think the FPR is bad.

AT KOEO, I have 40psi
AT IDLE, I have 30psi
reving it up, i get around 40psi
when I pinched the return, it shot up to 70+ psi. quickly.

Is this thing bad? for a daily driver, is stock replacement fine, or go with an adjustable?

jimberg · 04-03-2001, 07:00 PM

Pressure goes down when engine vacuum increases, so yes, it should drop when the engine is at idle.

Think of it this way, you have the cylinder trying to pull fuel into it and you have the fuel rails try to push fuel into the cylinders. The injector is the opening between the two. You want to maintain a constant relative pressure between the two since the injector is rated to let through a certain amount of fuel at a certain fuel pressure (39 psi). Since the cylinder is pulling hardest at idle, say at 10 psi, the fuel rail pressure needs to drop to 30 psi to maintain a constant relative pressure of 40 psi.

Vacuum drops at WOT to nearly 0 so you need to push the fuel at 40psi. The pressure you set the FPR to maintain with the vacuum line disconnected is the pressure that the engine will try to maintain all throughout the RPM range.

By the way, you should probably drop your fuel pressure to 38 psi.

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

slo95 · 04-03-2001, 08:53 PM

thanks, but I am now confused, not too difficult a task, mind you...
I am trouble shooting some serious annoyances, and thought the FPR was to blame. it is stock, so no adjustments, right? Chiltons says to pinch the return, and if the psi jumps rapidly, replace the unit. Well, $50 bucks into it, and no difference. Time to start tossing $$ at the potential problems.

jimberg · 04-03-2001, 09:27 PM

I read the other thread and I think your problem is that the EGR is stuck slightly open probably because of carbon deposits. It is possible for it to fail without getting codes. It's been 6 years which is about the time that mine went on me. The EGR is supposed to stay closed at WOT and idle which are the places you are having troubles.

I think your FPR is fine and am not sure about the Chilton's pinch test. It doesn't make sense to me. Of course the pressure will shoot up if you pinch the return line. That's basically what the FPR does.

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

slo95 · 04-03-2001, 09:50 PM

thanks again for the help. I am at wit's end with this thing! the EGR was my first choice, with all the symptoms I am getting...but no codes. torque converter slippage, poor mpg - this, wow. 40 miles today on a half tank. no kidding., what else, erratic idle, surges, all that. I will get one tomorrow. whats another hundo, right?
As for the Chilton's test, yeah, that was a nice little 50 dollar mis-print! oh well.

jimberg · 04-04-2001, 08:22 AM

It shouldn't be that much, but who knows? Call around. My brother just got one for his Metro and it was $125. I think they are about $70 for the Mustang.

You may want to try to clean the one you have. I think you said you did that in the other thread so I'm not sure if it's cleanable at this point. If you only did a basic cleaning, though, you may want to really focus on cleaning it to save the money. Concentrate on the valve opening. Find the best product you can for disolving carbon. You may even want it to soak, just doon't soak the diaphragm.

Just to see for sure, you may want to bolt a plate over the holes where the EGR goes. You'll probably have to fabricate it, but it shouldn't be that big of a deal. If performance improves, you know that you can just get a new EGR and fix it. If it doesn't, you can eliminate the EGR as a problem.

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

slo95 · 04-04-2001, 12:15 PM

I sure appreciate the help. I just got another EGR gasket and plan on cleaning the one I have. The first cleaning, yes, it was light, because I didn't want to damage the diaphram. So I will also try blocking off the EGR with a plate.

LX XLR8R · 04-04-2001, 02:16 PM

do you still have all the emmisons one ur car??the reason i ask is cuz i havent had a egr valve on my car for 2 years..nor a AIB..i made plates to cover the holes

------------------
1987 black notch(ex 4 banger)
DSS 306 w/ main support...Elderbrock 6028 heads..gt-40 intake..24# injectors...70 mm tb..77 pro-m...accel 300+..mac full legnth..tremec w/ pro5oh...full MAC exhaust,off road h-pipe,long tubes, catback...ron davis radiator..subframes, control arms...CFDF II..o yea holley FPR sucks..dont buy one..
AIM=onesillynotch

slo95 · 04-04-2001, 04:00 PM

yes, still have EGR and IAC valve.

jimberg · 04-04-2001, 07:01 PM

You definitely don't want to give up your IAB valve. It actually gives you a little more air flow at WOT.

[This message has been edited by jimberg (edited 04-04-2001).]

slo95 · 04-04-2001, 07:55 PM

no, won't do that...actually just completely cleaned out the EGR valve, it was filthy. Sorry to say the few hours worth of work made no difference, although it idles a lot better, but still the nasty ping. at least I still have the hundred bucks - for something else! I also got a hi dollar fuel system cleaner, installed thru vacuum and everything, no difference.

04-03-2001, 04:43 PM	#1
slo95 Registered Member Join Date: Dec 2000 Posts: 168	FPR - quick question from previous posts, I am having some trouble...I think the FPR is bad. AT KOEO, I have 40psi AT IDLE, I have 30psi reving it up, i get around 40psi when I pinched the return, it shot up to 70+ psi. quickly. Is this thing bad? for a daily driver, is stock replacement fine, or go with an adjustable?

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04-03-2001, 07:00 PM	#2
jimberg Registered Member Join Date: Oct 1998 Location: Rogers, MN Posts: 2,089	Pressure goes down when engine vacuum increases, so yes, it should drop when the engine is at idle. Think of it this way, you have the cylinder trying to pull fuel into it and you have the fuel rails try to push fuel into the cylinders. The injector is the opening between the two. You want to maintain a constant relative pressure between the two since the injector is rated to let through a certain amount of fuel at a certain fuel pressure (39 psi). Since the cylinder is pulling hardest at idle, say at 10 psi, the fuel rail pressure needs to drop to 30 psi to maintain a constant relative pressure of 40 psi. Vacuum drops at WOT to nearly 0 so you need to push the fuel at 40psi. The pressure you set the FPR to maintain with the vacuum line disconnected is the pressure that the engine will try to maintain all throughout the RPM range. By the way, you should probably drop your fuel pressure to 38 psi. ------------------ 351W 89 Mustang GT Convertible

04-03-2001, 08:53 PM	#3
slo95 Registered Member Join Date: Dec 2000 Posts: 168	thanks, but I am now confused, not too difficult a task, mind you... I am trouble shooting some serious annoyances, and thought the FPR was to blame. it is stock, so no adjustments, right? Chiltons says to pinch the return, and if the psi jumps rapidly, replace the unit. Well, $50 bucks into it, and no difference. Time to start tossing $$ at the potential problems.

04-03-2001, 09:27 PM	#4
jimberg Registered Member Join Date: Oct 1998 Location: Rogers, MN Posts: 2,089	I read the other thread and I think your problem is that the EGR is stuck slightly open probably because of carbon deposits. It is possible for it to fail without getting codes. It's been 6 years which is about the time that mine went on me. The EGR is supposed to stay closed at WOT and idle which are the places you are having troubles. I think your FPR is fine and am not sure about the Chilton's pinch test. It doesn't make sense to me. Of course the pressure will shoot up if you pinch the return line. That's basically what the FPR does. ------------------ 351W 89 Mustang GT Convertible

04-03-2001, 09:50 PM	#5
slo95 Registered Member Join Date: Dec 2000 Posts: 168	thanks again for the help. I am at wit's end with this thing! the EGR was my first choice, with all the symptoms I am getting...but no codes. torque converter slippage, poor mpg - this, wow. 40 miles today on a half tank. no kidding., what else, erratic idle, surges, all that. I will get one tomorrow. whats another hundo, right? As for the Chilton's test, yeah, that was a nice little 50 dollar mis-print! oh well.

04-04-2001, 08:22 AM	#6
jimberg Registered Member Join Date: Oct 1998 Location: Rogers, MN Posts: 2,089	It shouldn't be that much, but who knows? Call around. My brother just got one for his Metro and it was $125. I think they are about $70 for the Mustang. You may want to try to clean the one you have. I think you said you did that in the other thread so I'm not sure if it's cleanable at this point. If you only did a basic cleaning, though, you may want to really focus on cleaning it to save the money. Concentrate on the valve opening. Find the best product you can for disolving carbon. You may even want it to soak, just doon't soak the diaphragm. Just to see for sure, you may want to bolt a plate over the holes where the EGR goes. You'll probably have to fabricate it, but it shouldn't be that big of a deal. If performance improves, you know that you can just get a new EGR and fix it. If it doesn't, you can eliminate the EGR as a problem. ------------------ 351W 89 Mustang GT Convertible

04-04-2001, 12:15 PM	#7
slo95 Registered Member Join Date: Dec 2000 Posts: 168	I sure appreciate the help. I just got another EGR gasket and plan on cleaning the one I have. The first cleaning, yes, it was light, because I didn't want to damage the diaphram. So I will also try blocking off the EGR with a plate.

04-04-2001, 02:16 PM	#8
LX XLR8R Dirk Diggler Join Date: Feb 1999 Location: SLOATSBURG, NY Posts: 1,931	do you still have all the emmisons one ur car??the reason i ask is cuz i havent had a egr valve on my car for 2 years..nor a AIB..i made plates to cover the holes ------------------ 1987 black notch(ex 4 banger) DSS 306 w/ main support...Elderbrock 6028 heads..gt-40 intake..24# injectors...70 mm tb..77 pro-m...accel 300+..mac full legnth..tremec w/ pro5oh...full MAC exhaust,off road h-pipe,long tubes, catback...ron davis radiator..subframes, control arms...CFDF II..o yea holley FPR sucks..dont buy one.. AIM=onesillynotch

04-04-2001, 04:00 PM	#9
slo95 Registered Member Join Date: Dec 2000 Posts: 168	yes, still have EGR and IAC valve.

04-04-2001, 07:01 PM	#10
jimberg Registered Member Join Date: Oct 1998 Location: Rogers, MN Posts: 2,089	You definitely don't want to give up your IAB valve. It actually gives you a little more air flow at WOT. [This message has been edited by jimberg (edited 04-04-2001).]

04-04-2001, 07:55 PM	#11
slo95 Registered Member Join Date: Dec 2000 Posts: 168	no, won't do that...actually just completely cleaned out the EGR valve, it was filthy. Sorry to say the few hours worth of work made no difference, although it idles a lot better, but still the nasty ping. at least I still have the hundred bucks - for something else! I also got a hi dollar fuel system cleaner, installed thru vacuum and everything, no difference.