Fuel pressure question?
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Tuned
Joined: Aug 2007
Posts: 287
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Fuel pressure question?
1988 F250 351 5.8l
Would there be any problem running my truck with the FPR vacuum hose disconnected?
With the vacuum line to the FPR connected I read 32 PSI fuel pressure with a fluctuating manifold vacuum around 17" +/-. The motor just doesn't get enough fuel to idle smooth and sometimes shakes pretty bad. If I increase fuel pressure to 36 PSI it smooths out fine and the manifold vacuum goes to 19 1/2" steady.
Without FPR vacuum disconnected I have 40 PSI fuel pressure, smooth idle, 19 1/2" vacuum. Truck runs outstanding at all speeds although I don't know if my fuel economy is adversely effected.
I found an adjustable stock replacement FPR for $90.00 from Steeda. That's quite a bit to pay (not to mention the very annoying, almost impossible to get at (3) allen screws holding the FPR to the fuel rail) if there isn't a downside to just running my current FPR with the vacuum off.
I would appreciate any thoughts?
Would there be any problem running my truck with the FPR vacuum hose disconnected?
With the vacuum line to the FPR connected I read 32 PSI fuel pressure with a fluctuating manifold vacuum around 17" +/-. The motor just doesn't get enough fuel to idle smooth and sometimes shakes pretty bad. If I increase fuel pressure to 36 PSI it smooths out fine and the manifold vacuum goes to 19 1/2" steady.
Without FPR vacuum disconnected I have 40 PSI fuel pressure, smooth idle, 19 1/2" vacuum. Truck runs outstanding at all speeds although I don't know if my fuel economy is adversely effected.
I found an adjustable stock replacement FPR for $90.00 from Steeda. That's quite a bit to pay (not to mention the very annoying, almost impossible to get at (3) allen screws holding the FPR to the fuel rail) if there isn't a downside to just running my current FPR with the vacuum off.
I would appreciate any thoughts?
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Tuned
Joined: Aug 2007
Posts: 287
Likes: 1
Thanks for the late night post!
I've learned never to say never with this truck but to the best of my ( and other mechanics) abilities I'm confident that I don't have a vacuum leak.
The engine is a reman. and not modified. I changed the lower manifold gasket once and the upper twice just in case. Capped off all of the plenum tees and blocked off the EGR with no change. The lines of the vacuum resevoir and brake booster hold vacuum for hours after the engine is off. The injectors are 19lbs and new. Injector seats were cleaned up and the lubed O-rings pressed in nicely.
The codes are 11 for both engine off and on. Trucks starts great but will eventually work its way down to 17 1/2 +/- of vacuum if the stock FPR is hooked up with the vacuum line. With the line off I see 19 1/2 vacuum.
Does the "regulated" FPR give any advantage to the efficiency of the engine.
The engine is a reman. and not modified. I changed the lower manifold gasket once and the upper twice just in case. Capped off all of the plenum tees and blocked off the EGR with no change. The lines of the vacuum resevoir and brake booster hold vacuum for hours after the engine is off. The injectors are 19lbs and new. Injector seats were cleaned up and the lubed O-rings pressed in nicely.
The codes are 11 for both engine off and on. Trucks starts great but will eventually work its way down to 17 1/2 +/- of vacuum if the stock FPR is hooked up with the vacuum line. With the line off I see 19 1/2 vacuum.
Does the "regulated" FPR give any advantage to the efficiency of the engine.
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Joined: Dec 2001
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From: Louisville,Ky.
It keeps it from running too rich under light loads.
Another thing to check is to remove the EGR valve and make sure it is closing completely. I have seen them get carboned up and not shut causing a lean condition.
Another thing to check is to remove the EGR valve and make sure it is closing completely. I have seen them get carboned up and not shut causing a lean condition.
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