Fuel Pressure Question
Thread Starter
Pro
Joined: Jan 2004
Posts: 503
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From: Forney Texas
Fuel Pressure Question
I have a 90 with a forged 383 running 8 lbs of boost, 60 lb injectors, Walbro fuel pump with the factory FPR. The 383/injectors have about 5,000 miles on them. The fuel pump has about 10,000 miles on it. I think that should set the stage for my questions.
The problem is stumbling between off idle up to 2500 rpm. I ran a data log and the car is running very lean -- BLM's around 180. The car up to a couple of weeks ago was running slightly rich -- BLM's around 122. I have the FSM and have not begun to troubleshoot using the GM procedures. Here is what I have done and what I have observed.
Car @ idle -- FPR no vacuum line attached -- 40 psi
Car @ idle -- FPR vacuum line attached -- 30 psi
Applied vacuum to the FPR using a hand held pump. Pulled -5 psi and the FPR held the pressure. This leads me to believe the FPR diaphragm is good. Also, no gas in vacuum line.
Any ideas what would be the least time consuming troubleshooting approach? Anyone with a similar experience? All ideas are welcome.
Thanks in advance.
90Indy
The problem is stumbling between off idle up to 2500 rpm. I ran a data log and the car is running very lean -- BLM's around 180. The car up to a couple of weeks ago was running slightly rich -- BLM's around 122. I have the FSM and have not begun to troubleshoot using the GM procedures. Here is what I have done and what I have observed.
Car @ idle -- FPR no vacuum line attached -- 40 psi
Car @ idle -- FPR vacuum line attached -- 30 psi
Applied vacuum to the FPR using a hand held pump. Pulled -5 psi and the FPR held the pressure. This leads me to believe the FPR diaphragm is good. Also, no gas in vacuum line.
Any ideas what would be the least time consuming troubleshooting approach? Anyone with a similar experience? All ideas are welcome.
Thanks in advance.
90Indy
Thread Starter
Pro
Joined: Jan 2004
Posts: 503
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From: Forney Texas
90Indy
Thread Starter
Pro
Joined: Jan 2004
Posts: 503
Likes: 0
From: Forney Texas
I plan on using my hand held vacuum/pressure tester tonight and see how the FPR reacts to small changes in negative/positive pressures. If what I am thinking is right, the FPR is faulty, I should be able to see the abnormal fuel pressure readings. You have to keep in mind that nothing on this set up was altered and the car was running slightly rich less than 100 miles ago. This tells me that something operational has to have changed.
90Indy
Team Owner
Joined: Jul 2004
Posts: 28,381
Likes: 3,262
From: Hartford WI
Yes there is. Just because it doesn't leak doesn't mean the spring is in good condition. If it is weak, it allows fuel pressure to bleed off resulting in low fuel pressure.
Thread Starter
Pro
Joined: Jan 2004
Posts: 503
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From: Forney Texas
90Indy
Drifting
Joined: Oct 2006
Posts: 1,554
Likes: 13
From: Romeoville IL
If you have a vacuum gauge I would check the engine vacuum as well, Leak down test could be handy as well. those could point you towards other problems (ones you would like not to discover). If you are getting a lot of blow by, it could be causing you problems as well.
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Safety Car
Joined: Aug 2009
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From: Melbourne, Victoria, Australia
Hi i have an 85 vette with a vortech intercooled supercharger 8 psi boost i have my stock injectors and have the stock mass airflow sensor in the return side to the inlet manifold
have set the fuel press to 50 psi and it has run great for the past 3 years .. have some bad injectors now which i have to replace . anyway they are 24lbs injectors and have a high flow inline fuel pump also so maybe put the original or slightly bigger injectors in and perhaps an adjustable fuel press regulator set it 45 or 55 psi and it should help .. also try the tps set it 0.60vdc
hope it helps !
gerards
gerard
have set the fuel press to 50 psi and it has run great for the past 3 years .. have some bad injectors now which i have to replace . anyway they are 24lbs injectors and have a high flow inline fuel pump also so maybe put the original or slightly bigger injectors in and perhaps an adjustable fuel press regulator set it 45 or 55 psi and it should help .. also try the tps set it 0.60vdc
hope it helps !
gerards
gerard