Is it best to adjust Fuel Pressure on a hot or cold engine?
Thread Starter
Supreme Member

Joined: Jan 2000
Posts: 1,180
Likes: 82
From: Mississauga, Ontario Canada
Car: 1987 GTA
Engine: 5.7
Transmission: T5WC
Axle/Gears: 3:27
Is it best to adjust Fuel Pressure on a hot or cold engine?
Or does it even matter? I had to replace the diagphram and now my FP seems a little high and turning the screw makes little differnce. As a matter of fact Im pretty sure the screw is backed right off and the FP is just under 60 psi. Aftet the engine warms up it gets down to around 52-55 vacuum hose off.
I also just installed a 255 Lph pump. I'm not sure if I have issues with the fuel pressure gauge. Its a liquid filled Marshell. The pressure on shutdown drops to 25psi quite quickly then sits there for a whle before dropping right off.
Yesterday when I blew the diagphram, I notice there was still quite a bit of pressure under the cap 40 minutes latter with the guage at 0. I had to pinch off the vacuum line because fuel was spraying out of it hard.
I also just installed a 255 Lph pump. I'm not sure if I have issues with the fuel pressure gauge. Its a liquid filled Marshell. The pressure on shutdown drops to 25psi quite quickly then sits there for a whle before dropping right off.
Yesterday when I blew the diagphram, I notice there was still quite a bit of pressure under the cap 40 minutes latter with the guage at 0. I had to pinch off the vacuum line because fuel was spraying out of it hard.
Supreme Member

Joined: Jan 2003
Posts: 2,043
Likes: 3
From: San Diego
Car: 1994 Trans Am
Engine: LT1
Transmission: Auto
Axle/Gears: 3.23
Re: Is it best to adjust Fuel Pressure on a hot or cold engine?
Doesn't matter. You just got a new fuel pump so the pressure is staying high which is good.
Did you make a AFPR out of the one you had, or did you buy a new diaphragm? I just replaced mine with a Holley a few months ago because the stock unit was spiking it up to 55psi and I was getting vapors in my house at night.
Did you make a AFPR out of the one you had, or did you buy a new diaphragm? I just replaced mine with a Holley a few months ago because the stock unit was spiking it up to 55psi and I was getting vapors in my house at night.
Thread Starter
Supreme Member

Joined: Jan 2000
Posts: 1,180
Likes: 82
From: Mississauga, Ontario Canada
Car: 1987 GTA
Engine: 5.7
Transmission: T5WC
Axle/Gears: 3:27
Re: Is it best to adjust Fuel Pressure on a hot or cold engine?
Doesn't matter. You just got a new fuel pump so the pressure is staying high which is good.
Did you make a AFPR out of the one you had, or did you buy a new diaphragm? I just replaced mine with a Holley a few months ago because the stock unit was spiking it up to 55psi and I was getting vapors in my house at night.
Did you make a AFPR out of the one you had, or did you buy a new diaphragm? I just replaced mine with a Holley a few months ago because the stock unit was spiking it up to 55psi and I was getting vapors in my house at night.
Supreme Member

Joined: Jan 2003
Posts: 2,043
Likes: 3
From: San Diego
Car: 1994 Trans Am
Engine: LT1
Transmission: Auto
Axle/Gears: 3.23
Re: Is it best to adjust Fuel Pressure on a hot or cold engine?
Sounds like maybe, something didn't seat right when you did it. I didn't want to go through the hassle of what your going through so I just bought a holley and slapped it on. No issues.
Thread Starter
Supreme Member

Joined: Jan 2000
Posts: 1,180
Likes: 82
From: Mississauga, Ontario Canada
Car: 1987 GTA
Engine: 5.7
Transmission: T5WC
Axle/Gears: 3:27
Re: Is it best to adjust Fuel Pressure on a hot or cold engine?
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