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Anyone knows anything about trucks?

by ThaPig

My brother has a Ford F 150 automatic, 5.8 liters and he is having a persistent problem.
Which surprises me because he knows A LOT about mechanics, so it's not often he is puzzled by an engine problem.

The truck is always stuck in high RPMs. He already checked everything. He changed the throttle and all the vacuums and it's not that. He has tried everything he has been recommended all over the Internet and the problem doesn't go away.

The last thing to try is a new computer, but it's kind of expansive and he would like to check all other possibilities before buying one.

Maybe someone here can think of something that could be causing that problem?

Viewed:	21 times
Added:	6 years, 2 months ago 19 Feb 2018 05:36 CET

10 Comments on this Journal

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Norithics

6 years, 2 months ago

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Hm, when I had that problem it was an air-intake issue, it wasn't quite sealed due to a crack in a valve.
I'd re-check the whole intake system if it were me.

ThaPig

6 years, 2 months ago

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@ Norithics

He did that already and didn't fix it.

mommavicky

6 years, 2 months ago

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It sounds like a computer issue to me. Ford's trucks have been having trouble with them. but im far from a expert.

ThaPig

6 years, 2 months ago

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@ mommavicky

Yeah that's what we think. But he is trying to discard all other possibilities before having to buy one.

Waccoon

6 years, 1 month ago

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Yeah, first things to come to mind are the MAF and oxygen sensors (which control air/fuel mixture) or the temperature sensor (since engines idle higher when the engine is cold). Short of that, it sounds like a computer problem.

Scotty has some recommendations for cheap diagnostic code readers which may be worth looking into. Those things are great for seasoned mechanics, and spending around $100 for a code reader sure beats $1,000+ on a computer that may not even be the problem -- or wasting days of your time going in circles.

https://www.youtube.com/watch?v=uMPeQh2Qq8E

ThaPig

6 years, 1 month ago

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Edited 6 years, 1 month ago by Owner

@ Waccoon

He already replaced the sensors.

The problem with the computer codes is that he took it to a few places and they can't find what's wrong with it. They said something like "cannot replicate problem". I'll send him the video anyways, it's a tool he may find useful.

AxleFurret

6 years, 1 month ago

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@ ThaPig

What year is it? We got a few cars with 302s and 351s in them but they are all pre-mid-1980s and carbureted... Like I'm fixing up a 1983 F-150 302 at the moment myself. So I don't know how much I can help, not being able to futz around with said vehicle myself.

If it isn't something mechanical like a dead or missing return spring or a pin that popped loose, it could be an electrical fault or the computer.

If he's trying to save money, get a new computer from a place that it can be returned easily if it doesn't fix the issue, like amazon or walmart or any of the big auto retailers. If it gets plugged in and the problem is instantly gone, then bingo you know what the problem is, if the problem persists, then you know it is something else.

My old VW would constantly throw strange error codes that "could not be replicated" and not even the dealership could figure it out because it didn't cause the car to run strange at all... Eventually found out the main grounding cable had rubbed against some metal and would cause an occasional issue that brought up the code.

My 65 Chrysler had a near constant misfire issue that was none of the usual culprits, found out instead that after upgrading to electronic ignition that the old mechanical voltage regulator couldn't keep up with the digital voltage and was fixed with a $15 digital voltage regulator.

ThaPig

6 years, 1 month ago

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Edited 6 years, 1 month ago by Owner

@ AxleFurret

Thanks for the insight. This one is from 1995 and the engine is the 351.

moyomongoose

6 years, 1 month ago

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I had that problem with my 1976 Dodge camper after I replaced a lot of old half rotted vacuum hoses. I found out what caused it was I had replaced two vacuum lines to the cruise control crisscrossed backward. Swapping those two hoses to where they belong fixed the problem.

ThaPig

6 years, 1 month ago

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@ moyomongoose

We are sure it's the computer by now. He replaced almost everything else.

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