Oil pressure/pump problem
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Senior User
Joined: Dec 2004
Posts: 100
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From: Emlenton, PA
Oil pressure/pump problem
77 F-150 351M. When I first bought the truck the oil gauge in the dash would show pressure when the key was on and stay at the same reading when I'd fire her up. Today however I noticed when I stopped and the engine dropped to idle the needle went down to L and pegged. So I shifted to park and gave it some R's and the needle moved back up. Could it be a bad sending unit? Or is the pump shot? Has anyone had experience with this low RPM's and the oil pressure falling off? I would think for as long as I ran it when the gauge was "sticking" the motor would have been toast long ago. It does use oil like a fiend though.
Junior User
Joined: Jul 2004
Posts: 90
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From: houston, tx
i had the same problem, i just replaced my pump and put in a mechanical gauge and now my pressure is up and running good, but i have a strait-6 so i had to un bolt my motor mounts, rase the engine about 8 inches just to get my oil pan off.
New User
Joined: Jan 2008
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Your problem is engine related to the 351M .
Thread will be moved to the 335 engine series forum.
Please READ ....the Read First: threads in the 73-79 forum.
The sending unit is hardly the best way to get oil pressure.
Put a mechanical gauge on to know for sure.
The 351M was bad for the oiling system.
Thread will be moved to the 335 engine series forum.
Please READ ....the Read First: threads in the 73-79 forum.
The sending unit is hardly the best way to get oil pressure.
Put a mechanical gauge on to know for sure.
The 351M was bad for the oiling system.
Posting Guru
Joined: Dec 2003
Posts: 1,391
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From: South Central Boise
My guess would be the sending unit and the wiring. Check your rocker arms to see if they have wet oil on them. If yes, then your pump is ok. You can even get a new gauge set with senders from walmart for like $15. The oil gauge should read zero before engine startup and should move up to the middle position while running. If yours eats oil like a motha you should definately know how much pressure you have at all times. No oil = no more engine.
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Senior User
Joined: Dec 2004
Posts: 100
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From: Emlenton, PA
Well, the good part: I found my oil leak. It was leakin' like a seive out of the sending unit where they're pressed together. The bad part: I put in a new sending unit and it did the same thing. SO, I ripped the new sending unit off and put on the mech. gauge. It reads 40lbs at sart-up (at idle)but when the oil is warm it reads maybe 7 at idle. Should I have oil running directly to the new gauge? My mechanic says I should?? Whadda you guys know about it? I did order a new pump today, a high flow. I believe the pressure should be about 20 idle and around 45-50 WOT. Any comments are appreciated!!
