F150 Check Engine

dhermesc · Aug 1, 2011

I have 1991 F150 with the 5.0 engine - 133K miles. It sits a lot and only gets driven once in the while on weekends. On Saturday (in 104+ heat) I noticed the check engine light would come on when ever I lifted completely off the accelerator - like when I coasted into a lower speed limit and stopped at a stop light. As soon as I accelerated it would go off again. According to the owners manual the "Check Engine" light is only for eletronics - not emissions. The oil and temp gauges stayed in the normal range when this was happening. Any idea what this was?

ericlb · Aug 1, 2011

my money is on the oxygen sensor, if you havent changed it recently, lifting the throttle would cause a 'rich' reading on the sensor if its partially plugged up, which would turn on the lite

RLA · Aug 1, 2011

Go with what Eric is telling you.. Sense it
doesn't get driven alott it could also be
sooted up with carbon it could be shooting
a lean code as well.. You could try cleaning
it with gumout but chances are you'll end up
replacing it.. It's either EGR Or EGO thats
the problem....

Jiles · Aug 1, 2011

My first thought would be low coolant level

earlschieb · Aug 1, 2011

Also sounds like an egr problem, if it goes off on acceleration.

CWL · Aug 1, 2011

I had a '92 ranger that did that. It ended up being the oxygen sensor.

NEBeef · Aug 1, 2011

Why are you guessing at it, go get the code(s) read. You're paying for the computer anyway, why not use it to help you figure out what's going on?

But I guess if you want to you can just throw parts at it and hope you get lucky...

dhermesc · Aug 1, 2011

About $100 to get the codes read by a Ford dealer. Its an OBD computer - not the OBDII computer that most people have the code reader for (like Autozone).

CWL · Aug 1, 2011

Also the OBD isn't as informative as the OBDII. Will it even store a code if the check engine light doesn't stay on?

Jiles · Aug 1, 2011

Over the years that I have worked on vehicle, I can't remember the times there was an intermitant problem, or light, that was caused by a bad commection.
During load and coasting, the engine moves slightly. Can this cause your problem?? Very possible and just takes some unpluging, inspection and reconnecting. Takes time!

NEBeef · Aug 1, 2011

I'm pretty sure the OBD-I will store intermittent codes, but I could be wrong. But all but the cheapest readers will do ODB-I if you have the right cable - Autozone or one of the other chain stores should be able to do ODB-I

RedRoundhead · Aug 1, 2011

Is the EGR crosspipe rusted out? That is what had happened to me. The EGR crosspipe gaskets like to get brittle and blow out,too. I pulled my pipe off, and capped the EGR ports with home made gaskets,and then put the pipe back on to seal it. Worked well for me. Best of luck!

jackinok · Aug 2, 2011

another place to check,loose battery connections.pulling the power of a ac,and just the heat in general will make connections do some weird stuff.

F150 Check Engine

dhermesc

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ericlb

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RLA

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Jiles

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earlschieb

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CWL

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NEBeef

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dhermesc

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CWL

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Jiles

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NEBeef

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RedRoundhead

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jackinok

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