Engine running WIDE OPEN

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Apr 28, 2013 | 08:20 PM

Tommky

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Engine running WIDE OPEN

I need help please. I have a 1986 F-150 302 with EFI. Cleaned throttle body which was gunked up very bad. Very few items to remove to disconnect body to clean it so very little was done. Excited about running it after cleaning to see if runs any better. To my amazement, engine revs wide open with RPM needle pegging out. Have to turn ignition off immediately as fear of blowing it.

Unhooked battery for 30+ minutes hoping it was some kind of memory setting. No change. Also unplugged Air Bypass valve, no change. Butterflies seem to move easily with no binding. What in the world could I have done that would cause engine to rev to max? Please share ideas if you have any.

Thanks

Apr 28, 2013 | 08:36 PM

ctubutis

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From: Denver Metro Area, CO

I would guess you installed the throttle body and/or linkage incorrectly.

Can you operate the linkage by hand under the hood and visually see what it's doing? Begin there.

Apr 28, 2013 | 09:12 PM

Tommky

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We didn't really disconnect the linkage, just laid it back. I took the two bolts loose that holds the linkage to the top of the intake manifold. The butterflies move manually and when applying the accelerator. The butterflies are about 90% closed with the engine off. Is that where you would expect them to be? As you apply the accelerator, the become more open. That would be how they should move isn't it? I have not tried to see if they move when starting the engine as it is revving so high.

Apr 28, 2013 | 09:17 PM

Rico47635

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From: Rockport, IN

The throttle is either stuck open or the butterflies have broken loose and been sucked into the intake. I've had both happen before, but fortunately only once with the butterflies getting sucked into the engine. Hope you get it figured out.

Apr 28, 2013 | 09:39 PM

ctubutis

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From: Denver Metro Area, CO

"Giving it gas" means opening the throttle, which means allowing the engine to suck in more air and more gasoline.

Yes, throttle plates opening up once the engine is running can cause this problem.

I'm sorry, didn't mean you should have the engine running when you look at the operation of the linkage and plates....

Apr 29, 2013 | 07:42 PM

Tommky

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Problem Solved

Quote:

Originally Posted by Tommky

Thanks to everyone for your helpful comments. The problem was due to the butterfly plates not being reinstalled properly. They would rotate but only so far. They could not fully close and that was the main problem in causing it to rev wide open. Several of you made comments that were very close and it just took another close look to figure it out.

My son has been driving the truck and he is the real enthusiast, just not having the knowledge and experience to take on cleaning the gunk out of the throttle body. After the project "blew up" I had to try and learn how it worked. We had a nice discussion on lessons learned.

- ctubutis - you were on it right out of the gate - thanks

Thanks again.