Fuel pressure readings?
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Fleet Mechanic
Joined: Jul 2004
Posts: 1,552
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From: va
Fuel pressure readings?
1987 f150 4.9 EFI
What's the fuel pressure suppose to be at with key on but not running? How about while running? If I get a good reading with key on not running and can't start the truck. Is that ok or do I need it to run? Thanks guys
What's the fuel pressure suppose to be at with key on but not running? How about while running? If I get a good reading with key on not running and can't start the truck. Is that ok or do I need it to run? Thanks guys
Elder User
Joined: Feb 2004
Posts: 855
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From: Ocean Park WA
Chilton manual says 13-17 psi, it will only run for I think 5-10 seconds when you first turn on the key and then stops till you get oil pressure (IE craanking the engine). You can jumper the relay and test the pressure that way also and it should read higher by a couple of pounds.
Senior User
Joined: Sep 2003
Posts: 223
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From: York, PA
EFI engines will be 35-45 psi, key on engine off, pressure should not drop off because the pump has a check valve in it to keep pressure up so starting is easier, with engine running, pressure is going to be closer to 35 psi, snap throttle and it shoiuld go to 45 psi just for an instant, pull off the fuel regulator vacuum tube and pressure should go to 45 psi. Broken Wire
Elder User
Joined: Feb 2004
Posts: 855
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From: Ocean Park WA
My Chiltons has two differnt values on two differnt pages 13-17 and 39-40 with 30 at idle. The higher does sound better. Try installing a jumper from the yellow to dark green with yellow at the relay and see if the pump runs.
