Fuel Pressure Problem??

TWIN86GNS · 04-22-2005, 09:59 PM

I have had my car (GN #2) on the roads for the last couple of weeks and I have noticed an odd problem. When going WOT (about 18#'s of boost) I would get some knock, but only at WOT. I run good fuel (around 98 octane with a 100 octane chip) and I also have alcohol injection so I shouldn't be getting any knock at all, even at 22 or 23 #'s of boost!!

I put my Autometer Sport Comp (2 5/8") fuel pressure gauge under the wiper so I could see it while driving and I noticed that I had set the fuel pressure to 43#'s but with the vacuum line re-attached the FP did NOT drop?? I took it for a drive and the fuel pressure seemed to be about 45#'s but when I got into boost it would drop slightly to about 40 - 42#'s and stay there even if I hit 10 or 12 #'s of boost?? (I guess it is a good thing that I run good fuel and alcohol).

I just noticed this problem and I wondered if anyone has any idea of what the problem may be. I am going to change the fuel filter (shouldn't be the problem) and I am going to swap out my Accufab fpr for an AC Delco 239 regulator to see how it reacts. I hope to get out to the garage tomorrow to work on it but I have been very busy lately. Right now I am assuming it is a problem with my Accufab fpr that I bought in 1998 but I am open to listening to any ideas.

My basic build up is as follows, stock turbo, stock engine, K&N filter, 340 Walbro (installed last fall), hot wire kit, Accufab FPR, bluetop injectors, Jay Carter 100 octane chip and an Autometer 2 5/8" fuel pressure gauge on a 3' braided line so I can see it while driving.

Thanks in advance for any and all help and ideas.

forzfed · 04-22-2005, 10:22 PM

Sounds like the fpr. Unless you have a vac leak somewhere preventing the pressure from rising.

Ormand · 04-23-2005, 06:54 AM

Since the pressure doesn't go down with vacuum, or up with pressure, maybe the sensor line is blocked. Sure would be easier to fix than putting in a new FPR! I'd check the line before I pulled the FPR.

TurboDave · 04-23-2005, 07:41 AM

Is there good vacuum to the regulator. Doesn't sound like it's getting a good vacuum/boost signal.

ULYCYC · 04-23-2005, 01:28 PM

I blew a head gasket at Bristol from this. The steel vacuum/boost line was cracked at the hold down bolt on the intake. Pull the whole steel line set off and check for cracks.

TWIN86GNS · 04-23-2005, 10:07 PM

Thanks for the idea's guys but I don't *think* the line to the top of the regulator is the problem due to the fact that you can really feel the vacuum suck on your finger while the line is off of the top of the regulator. I will double check that line again, I had a problem with it back in about 1998 or 1999. My wife was out today so I was with my son for the day and I didn't make it out to the garage. I will let everyone know what I find out tomorrow.

I forgot to mention in my original post that you can adjust the pressure up, I took if from about 43 #'s (line off) up to about 58 or 60#'s line off. But when I was lowering the pressure I could NOT drop it below 43#'s, and it took a lot of adjustment to go from 45#'s down to 43#'s, I thought that was weird??

Once again thanks for all of your help and if anyone has anymore info or ideas I would appreciate it.

04-22-2005, 09:59 PM	#1 (permalink)
TWIN86GNS 2 GN's = No money!! Join Date: Sep 2000 Location: Keswick, Ontario, Canada Posts: 3,167	Fuel Pressure Problem?? I have had my car (GN #2) on the roads for the last couple of weeks and I have noticed an odd problem. When going WOT (about 18#'s of boost) I would get some knock, but only at WOT. I run good fuel (around 98 octane with a 100 octane chip) and I also have alcohol injection so I shouldn't be getting any knock at all, even at 22 or 23 #'s of boost!! I put my Autometer Sport Comp (2 5/8") fuel pressure gauge under the wiper so I could see it while driving and I noticed that I had set the fuel pressure to 43#'s but with the vacuum line re-attached the FP did NOT drop?? I took it for a drive and the fuel pressure seemed to be about 45#'s but when I got into boost it would drop slightly to about 40 - 42#'s and stay there even if I hit 10 or 12 #'s of boost?? (I guess it is a good thing that I run good fuel and alcohol). I just noticed this problem and I wondered if anyone has any idea of what the problem may be. I am going to change the fuel filter (shouldn't be the problem) and I am going to swap out my Accufab fpr for an AC Delco 239 regulator to see how it reacts. I hope to get out to the garage tomorrow to work on it but I have been very busy lately. Right now I am assuming it is a problem with my Accufab fpr that I bought in 1998 but I am open to listening to any ideas. My basic build up is as follows, stock turbo, stock engine, K&N filter, 340 Walbro (installed last fall), hot wire kit, Accufab FPR, bluetop injectors, Jay Carter 100 octane chip and an Autometer 2 5/8" fuel pressure gauge on a 3' braided line so I can see it while driving. Thanks in advance for any and all help and ideas. __________________ Paul Beal pbeal@sympatico.ca First official Canadian member of the DSR..... That's just how we roll. 1986 GN # 1 11.38 @ 120.25 mph with 1.501 60' 1986 GN # 2 13.25 @ 102.95 mph with 2.086 60'

04-23-2005, 06:54 AM	#3 (permalink)
Ormand Registered User Join Date: Nov 2001 Location: Raleigh, NC Posts: 2,098	Since the pressure doesn't go down with vacuum, or up with pressure, maybe the sensor line is blocked. Sure would be easier to fix than putting in a new FPR! I'd check the line before I pulled the FPR. __________________ George W-

04-23-2005, 07:41 AM	#4 (permalink)
TurboDave Cell Phone Doc Join Date: Sep 2000 Location: Sevierville, TN Posts: 1,438	Is there good vacuum to the regulator. Doesn't sound like it's getting a good vacuum/boost signal. __________________ TurboDave EWCS(SW) USN ret. Email Us Sevierville, TN TranslatorPro MAFless fuel, spark and boost management 86 GN11.67@117.51(MAFTPro on speed density w/boost & fuel pump control/Extender Pro,PLX-WB) (original owner) 87 GN 12.95@105.50(Stock) (second owner) 84 Z28 L69 (original owner) 01 Excursion LTD TTS"race" chip 7.3L PSD(power stroke diesel) Turbo 4X2 08 Honda Accord EX-L My Photo Gallery

04-23-2005, 01:28 PM	#5 (permalink)
ULYCYC Fuhgeddaboudit Join Date: Sep 2000 Location: Brooklyn, NY Posts: 16,195	I blew a head gasket at Bristol from this. The steel vacuum/boost line was cracked at the hold down bolt on the intake. Pull the whole steel line set off and check for cracks. __________________ ED BAKER 87-T, Maplight equipped rear view mirror.. 93 PARK AVE"SUPERCHARGED" BPG#1458 My Photo Page buickperformancegroup.com

04-23-2005, 10:07 PM	#6 (permalink)
TWIN86GNS 2 GN's = No money!! Join Date: Sep 2000 Location: Keswick, Ontario, Canada Posts: 3,167	Thanks for the idea's guys but I don't think the line to the top of the regulator is the problem due to the fact that you can really feel the vacuum suck on your finger while the line is off of the top of the regulator. I will double check that line again, I had a problem with it back in about 1998 or 1999. My wife was out today so I was with my son for the day and I didn't make it out to the garage. I will let everyone know what I find out tomorrow. I forgot to mention in my original post that you can adjust the pressure up, I took if from about 43 #'s (line off) up to about 58 or 60#'s line off. But when I was lowering the pressure I could NOT drop it below 43#'s, and it took a lot of adjustment to go from 45#'s down to 43#'s, I thought that was weird?? Once again thanks for all of your help and if anyone has anymore info or ideas I would appreciate it. __________________ Paul Beal pbeal@sympatico.ca First official Canadian member of the DSR..... That's just how we roll. 1986 GN # 1 11.38 @ 120.25 mph with 1.501 60' 1986 GN # 2 13.25 @ 102.95 mph with 2.086 60'

04-22-2005, 10:22 PM	#2 (permalink)
forzfed Registered User Join Date: Jul 2001 Location: Winterpeg Posts: 5,515	Sounds like the fpr. Unless you have a vac leak somewhere preventing the pressure from rising.

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