Possible Fuel Pressure issue
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Senior User
Joined: Jun 2004
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From: Florida
Possible Fuel Pressure issue
Hey all, Finally got around to checking the fuel prsssure. Got 40 PSI with key on, engine off test connector to ground. WIth it running it was exactly 30 PSI. Pulled vaccum line off the Fuel Pressure regulator and it went up close to 40 PSI. My question is that 30 PSI seems a little low to me. This think has a miss for about a year now, and now its starting to stall if you turn the wheel, put it in reverse etc. It is running rich, and no codes. I have repaced, cap, rotor, plugs, wires, injectors, FPR, coil and fixed several little vaccum leaks, mostly in the AC lines.
Would low Fuel pressure cause a miss though? Im not sure what to do next other than start replacing fuel pumps.
Would low Fuel pressure cause a miss though? Im not sure what to do next other than start replacing fuel pumps.
Fleet Owner
Joined: Aug 2005
Posts: 23,668
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From: Easton,Ks
Your fuel pressure seems to be about 2 or 3 PSI low on both ends, maybe the gauge is off by that amount.
While cleaning injectors I first start to see a miss when it drops to about 26-28 PSI. The engine will die at about 22-24 PSI. This is all for a 302 engine but I think the 351 would be the same.
While cleaning injectors I first start to see a miss when it drops to about 26-28 PSI. The engine will die at about 22-24 PSI. This is all for a 302 engine but I think the 351 would be the same.
Thread Starter
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Senior User
Joined: Jun 2004
Posts: 205
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From: Florida
The injectors were replaced with accel injectors about 6 months ago from summit. The PSI readings i took were with a cold engine. It seems to get worse when it heats up so i will try reading it again after a test drive. It just seems low to me.
When I took the vacuum line off the FPR the exhaust smell was normal and seemed to run better. With it off it was 40 PSI. This thing is a 90 302, so I am hoping that I have an external High pressure pump maybe? Not sure what year they changed it. It sounds kind of sick.
When I took the vacuum line off the FPR the exhaust smell was normal and seemed to run better. With it off it was 40 PSI. This thing is a 90 302, so I am hoping that I have an external High pressure pump maybe? Not sure what year they changed it. It sounds kind of sick.
Fleet Owner
Joined: Aug 2005
Posts: 23,668
Likes: 301
From: Easton,Ks
In a 1990 F150 your fuel pumps are inside the tanks, no pump on the frame.
The tank pumps will put out from 95 to 100 PSI on a blocked head and your pressure is regulated down by the fuel pressure regulator. The fuel pressure regulator on the 302 normally with high vacuum at idle is around 32 to 33 PSI and at WOT 40 PSI. No Vacuum (hose off or not running with pin #6 of the VIP grounded) some regulators will go as high as 45 PSI.
As long as it goes to 40 PSI with the line off and the engine running I would think the pumps to be OK.
Either the fuel pressure regulator you put on has a weak spring or you gauge is reading low by 2 to 3 pounds.
If you get any more pressure than 45 PSI your O2 sensors will star giving error codes (too rich).
The tank pumps will put out from 95 to 100 PSI on a blocked head and your pressure is regulated down by the fuel pressure regulator. The fuel pressure regulator on the 302 normally with high vacuum at idle is around 32 to 33 PSI and at WOT 40 PSI. No Vacuum (hose off or not running with pin #6 of the VIP grounded) some regulators will go as high as 45 PSI.
As long as it goes to 40 PSI with the line off and the engine running I would think the pumps to be OK.
Either the fuel pressure regulator you put on has a weak spring or you gauge is reading low by 2 to 3 pounds.
If you get any more pressure than 45 PSI your O2 sensors will star giving error codes (too rich).
