87 mystery problem
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Joined: Dec 2004
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87 mystery problem
I have an 87 f-150 4x2 with a 5.0 engine. Recently it only wanted to start when holding the throttle WO. Iniated a self test and found ACT and ECT sensors out of range and replaced them, truck fired right up and ran great. Then it just stalled, and the fuel pumps would not run when key on. Shorted the test pin and pumps run and have 40 psi on the rail with no leak down. Went through the test procedures in a Haynes manual to check power and ground for relays and PCM, and all test check good. Still no pumps running, left it till this morning and it fired right up, going to drive it a bit and see what happens. I was wondering if PCM could have an intermittent open on ground. I have a 94 donor truck with a 5.8, not sure if the PCM is compatable though. Any ideas on what to do next? I'm going for a drive and will check back. Thanks for any advise.
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Joined: Jan 2001
Posts: 2,358
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From: Nebraska
I'd check for bad connections. If you can get it running, wiggle the fuel pump relay harness and connector, and any other connector related. I think 87 still has the direct ground to the battery for the PCM. I've seen these get bad connections causing problems too.
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New User
Joined: Dec 2004
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Just drove it for about 20 miles and it ran fine. Tryed wiggling the harness and relays and nothing so maybe it is fixed. yes the 87 has direct ground to battery, 2 black wires from pins 40 and 60 to neg bat cable. I'll keep an eye on it for a while, thanks for the reply.
