FUEL PRESSURE QUESTION
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Freshman User
Joined: Oct 2015
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FUEL PRESSURE QUESTION
Testing my pressure with a gauge hooked up all seems well about 35 at idle jumps to 42-43 with vac hose off. jumps a bit when I give it gas then settles around 34-35. One thing I noticed is when I kill the motor the pressure drops to zero in maybe 10-15 seconds. This a leaky injector? Im hunting down a rough running issue
Fleet Owner
Joined: Aug 2005
Posts: 23,666
Likes: 301
From: Easton,Ks
Sounds like your fuel pressure gauge is off.
Sounds like you have a V8 so the spring in the fuel pressure gauge has a pressure of about 40lb (39.3lb) so you should not see a pressure above 40psi unless you have a 4.9L engine.
If your pressure are correct then you might have a bad FPR or pinched fuel return line.
High fuel pressure can cause your rough running.
You should have 30-32psi fuel pressure at idle with good engine vacuum.
Sounds like you have a V8 so the spring in the fuel pressure gauge has a pressure of about 40lb (39.3lb) so you should not see a pressure above 40psi unless you have a 4.9L engine.
If your pressure are correct then you might have a bad FPR or pinched fuel return line.
High fuel pressure can cause your rough running.
You should have 30-32psi fuel pressure at idle with good engine vacuum.
FTE Legend
Joined: Jun 2006
Posts: 31,930
Likes: 1,499
From: Ottawa, Ontario
39.5psi is the spec but manufacturing tolerances being what they are with regulators and fuel pressure gauges anything up to 45spi indicated for the V8s is OK IMO. From what I have seen measuring about 42psi is not uncommon.
The pressure bleeding off quickly could be a couple things, if you have a leaking injector that plug will be wet.
Other possibilities are a bad check valve inside the FDM module in the tank for '90+ trucks or a leaking switch valve on the frame for '89 and older gas trucks.
The pressure bleeding off quickly could be a couple things, if you have a leaking injector that plug will be wet.
Other possibilities are a bad check valve inside the FDM module in the tank for '90+ trucks or a leaking switch valve on the frame for '89 and older gas trucks.
Senior User
Joined: Dec 2010
Posts: 359
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From: Shafer, MN
Ford's spec for the 5.0 engine is fuel pressure at the rail between 33-44 is normal. (1996 5.0)
this is direct from ford as I work at a dealer and am currently dealing with a similar issue myself.
this is direct from ford as I work at a dealer and am currently dealing with a similar issue myself.
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