just noticed my fuel pressure is dropping to 30 psi while cruising at 55 mph.if i accelerate it will climb a few lbs.It will increase with boost. I only noticed this because i got lots of knock at partial throttle .A few days earlier i was running 22psi of boost with NO knock. . If i go out now it will be 40 psi but will drop after i drive it awhile. This is a fuel pump from Full Throttle with less than 1000 miles on it.Also has hotwire on it. Any ideas?
fuel pressure dropping
- Thread starter racer5252
- Start date
TurboTom72
Boost Addict
- Joined
- Jul 8, 2006
How long ago was that pump purchased? There was issues withn the Walboro pumps a while back. I changed mine as a precaution and got one of the bad ones. Not driving the car more than a couple hundred miles a season, it took a while before it failed. Changed out with a pump from Red Armstrong, and no trouble for several years now.
TurboTom72
Boost Addict
- Joined
- Jul 8, 2006
Updated, as in after the recall? I'd still throw a guage on the car and verify the 1 to 1 rise in fuel pressure. Checking voltage at the pump isn't a bad idea either. How old is the fuel filter? Was the car running good and this just started all of a sudden?
yes, it was after the recall.I do have a hood mounted fuel pressure guage and it does raise 1 to 1. I have never noticed before that it goes down to 30 psi at cruising speed. Today the lowest it would go is 34psi. Still lots of knock. Yes, this started all of the sudden
TurboTom72
Boost Addict
- Joined
- Jul 8, 2006
Are you just running the scanmaster, or do you have a powerlogger? Maybe start taking some log files or checking your ecm data readings for issues.
This sounds like a pump going bad after it gets some heat.
TurboTom72
Boost Addict
- Joined
- Jul 8, 2006
X2 on the fuel pump being flakey. That's what the 20 questions were about. Just trying to get all the facts first. That's basically what my recalled pump was doing before it finally started shitting the bed completely.
Mike Licht
I was here first
- Joined
- May 23, 2001
First of all check that pump pressure goes up one to one with boost. Base FP setting + whatever boost you are running. If it does, most likely the pump is fine. Do you have a hot wire kit? It is not impossible if the base pressure is set to say 42 for the cruise vacuum to pull it down. What is your block learn at cruise?
fuel pressure seems to be raising 1 to 1. but it starts knocking at half throttle. I do have a hotwire kit. Key on getting 11.6 volts to the pump. i did notice when i turn key on i hear the pump run then stop but fp gauge is still at 0 psi until i start it. bl at cruise is 122
Well just installed a complete stainless steel fuel pump assembly from Racetronics and it is still doing the same thing. I did notice the fuel pressure drops to 0 after sitting overnight. I put a new accufab adjustable FP gage in last year. Do these go bad? Any other ideas?
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Have you checked for kinks in your fuel line? The previous owner of my car had a mechanic change out the intake manifold gasket and put a pretty severe kink in the inlet fuel supply line. I would get 3 to 4 degrees of Knock Retard until I changed out the fuel line then all the knock went away.
This sums it up to me. If the fp rise is right and depending on your base setting, 30psi isn't that low under decelerating vacuum. What is your base psi? I think you have another issue causing knock. Have you check alky pressure under boost yet? My alky pumps only last 2-3 years and I use it a lot. If they sit, the alky pumps go bad even sooner.
The pump should stop after a key on before start, but you should see fp at that time. That could just be a bad checkvalve though, not a big deal to me. Your BL is good too so look elsewhere for your knock issue.
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