fuel pressure question
Thread Starter
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VT Chapter Ldr
Joined: Apr 2004
Posts: 96,096
Likes: 294
From: Orange, Vermont
fuel pressure question
I have a gauge hooked up to the shrader valve. It is a little hard to get a good reading because I am using an air filled gauge, not the glicerin filled, so the needle bounces pretty good with the pulses. Trying to average the pulses at idle it is around 50 psi but when driving it will drop down and can go as low as around 30 psi. Should it stay up at 50 no matter or is it suppose to drop? I would say the FPR is ok because of the pressure at idle but more like a fuel supply problem? What would cause it and how much to fix if it is the problem? Thanks.
Lead Driver
Joined: May 2007
Posts: 8,608
Likes: 13
From: Belair md
it will vary as the demand changes. you dont want it dropping too low, 45-50 is about the norm. you can shim the regulator with a bb to bump it up to 80 psi which happens to be the max "safe" limit in the ford manual. this will help out with the drop in pressure.
Thread Starter
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VT Chapter Ldr
Joined: Apr 2004
Posts: 96,096
Likes: 294
From: Orange, Vermont
So increasing the fuel pressure will help it keep up with the demand better? I was thinking it was a fuel supply problem which was resulting in the drop of psi. I need to get a glicerin filled one to get a better reading anyways.
Post Fiend
Joined: Mar 2006
Posts: 7,841
Likes: 0
From: Vacaville, Ca
The FPR shim is installing a BB under the spring inside the plunger on the Fuel Pressure Regulator. On the top of the FPR there is a 3/4" plug. Unscrew it, carfully remove the spring. Then use a magnet or needle nose pliers and remove the plunger. Install the BB inside the plunger, install the spring and install the assembly in the FPR. Be careful not to bend the spring when reinstalling the plug. This is one of the easier mods.
Check the fuel pressure before you install the BB. If it is over 60PSI you do not need to do this mod.
Check the fuel pressure before you install the BB. If it is over 60PSI you do not need to do this mod.
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Postmaster
Joined: Feb 2004
Posts: 3,266
Likes: 0
From: Levittown
If your gauge has a rubber hose, the old trick is to slowly pinch off the line
with needle nose pliers or something. It will give you the reading.
With a drop in pressure the bb is just going to buy you time. You have caught
an issue in the fuel system in its infant stage.
Your pressure fall is most likley from lack of volume.
61-62 psi is what most tuners use for a baseline fuel pressure.
.02
Bill
with needle nose pliers or something. It will give you the reading.
With a drop in pressure the bb is just going to buy you time. You have caught
an issue in the fuel system in its infant stage.
Your pressure fall is most likley from lack of volume.
61-62 psi is what most tuners use for a baseline fuel pressure.
.02
Bill
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Thread Starter
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VT Chapter Ldr
Joined: Apr 2004
Posts: 96,096
Likes: 294
From: Orange, Vermont
I will have to try pinching the line. That is what I was kind of thinking also because at idle the psi is in an acceptable range. I can try the bb and see what happens.
Postmaster
Joined: Feb 2004
Posts: 3,266
Likes: 0
From: Levittown
Not strange. His pressure drops.
Correct test is idle pressure 1st, then hold the throttle to the floor
for the 2nd pressure test. It should rise in the 2nd test.(mech pump)
(aftermarket chip removed for test)
Bill
Postmaster
Joined: Feb 2004
Posts: 3,266
Likes: 0
From: Levittown
Could be a restriction or air in the system, or failing pump.
80psi at idle is to high. Its added stress on the pump.
Bill
80psi at idle is to high. Its added stress on the pump.
Bill