Fuel, spark, no start.
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Fuel, spark, no start.
Hello all. I have an 87 F150 with the 4.9. I'm getting fuel and spark. The fuel pumps run constantly with the key on. I know this points to a bad computer, but from what I've read on here,if its the computer, the pumps will shut off if you unplug it. I unplugged the computer and the pumps keep running. Any ideas? Thanks.
Post Fiend
Joined: Apr 2002
Posts: 19,311
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From: Waterloo, Iowa
Welcome to FTE
Sorry I can't be more help. I will say bad grounds and connections can mimic more expensive or complex problems. Always worth investigating before throwing parts at it.
Also your truck (or the computer) is at the age where some of the internal components are well past their expected lifespan. Electrolytic capacitors. These should be replaced regardless, they aren't expensive. This may be part of the issue (guessing). Hopefully somebody will be along with more than generalized advice and troubleshooting.
Ted
Sorry I can't be more help. I will say bad grounds and connections can mimic more expensive or complex problems. Always worth investigating before throwing parts at it.
Also your truck (or the computer) is at the age where some of the internal components are well past their expected lifespan. Electrolytic capacitors. These should be replaced regardless, they aren't expensive. This may be part of the issue (guessing). Hopefully somebody will be along with more than generalized advice and troubleshooting.
Ted
Lead Driver
Joined: Jul 2007
Posts: 7,868
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From: Rhode Island
If you disconnected the main 60 pin computer connector and the fuel pump still runs with the key on, either your fuel pump relay is stuck on, or you have a fairly major wiring fault somewhere.
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Thanks guys for all of your input. I was thinking the same thing about a wiring issue. The truck is not my daily driver so it does sit a lot. So if it doesn't shut off the pumps whatever I unplug the computer, can I eliminate that as a possibility. I have opened up the computer and there are no burn marks and everything looks pretty good.
Post Fiend
Joined: Apr 2002
Posts: 19,311
Likes: 97
From: Waterloo, Iowa
Looking at capacitors isn't really a valid test. They should be replaced based upon their age alone. If they leak visibly they are obviously defective but, the reverse doesn't mean that they are OK by any stretch. And we're talking a half hour and $5 worth of new parts.
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