Engine running WIDE OPEN
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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
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
Senior User
Joined: Nov 2007
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From: Los Angeles, CA
Have you checked for an air leak?
The amount of fuel sent to the engine is not directly regulated by the blade in the TB. Any air leak will increase the engine speed. Also check the top to bottom intake manifold gasket. There are many threads about that check here.
I believe that the computer has a rev limit. I am not sure about your truck's year.
The amount of fuel sent to the engine is not directly regulated by the blade in the TB. Any air leak will increase the engine speed. Also check the top to bottom intake manifold gasket. There are many threads about that check here.
I believe that the computer has a rev limit. I am not sure about your truck's year.
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From: Denver Metro Area, CO
If it were merely a large air leak (vacuum leak) I would expect the engine to die as it's gonna be too lean of a mixture.
However, lots of air combined with lots of gasoline = full-throttle operation.
However, lots of air combined with lots of gasoline = full-throttle operation.
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Have you checked for an air leak?
The amount of fuel sent to the engine is not directly regulated by the blade in the TB. Any air leak will increase the engine speed. Also check the top to bottom intake manifold gasket. There are many threads about that check here.
I believe that the computer has a rev limit. I am not sure about your truck's year.
The amount of fuel sent to the engine is not directly regulated by the blade in the TB. Any air leak will increase the engine speed. Also check the top to bottom intake manifold gasket. There are many threads about that check here.
I believe that the computer has a rev limit. I am not sure about your truck's year.
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We did not unplug it during the cleaning. I have plugged and unplugged since the problem (revving wide open) began thinking that it might be the culprit. My understanding of this sensor is this just sends position info to other processes and does not control the actual engine rpm. Would u agree?
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As more air gets into the engine via an air leak, the O2 sensors detect the exhaust starting to lean out and the computer directs the fuel injectors to shoot more fuel in, resulting in the revving engine--the computer just thinks that you've put the accelerator down (it's really an "air" pedal, not a "gas" pedal!). The only thing I'm not sure about is how much the computer considers the input of the TPS in all this. My experience with a bad TPS was that the engine ran and revved fine in park, but the shift points were royally screwed up when I was rolling.
Jason
Jason
If just an air leak would cause this I would think that others would have experienced this and reported similar experience. I may have to replace the TPS and/or Air Bypass Valve to rule them out.
Cargo Master
Joined: Apr 2003
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From: Frequently frozen MN
I would suspect an electrical issue -- possibly with the throttle position sensor -- it 's telling the computer how much throttle is applied -- how fast you WANT to go.
Easy enpugh to ohm out the tps --but you may want to try to check the harness as well. If some of the cleaner got in the connector it could have caused a partial short.
One other possibility is the cruise control -- assuming you have one.
Not sure if there is a rev limiter in that year. I was driving an 80's era Ford once and just for giggles, I slipped the tranny into neutral while I had the cruise on. Engine started to wind out and I quickly killed the cruise
.
Good Luck,
hj
Easy enpugh to ohm out the tps --but you may want to try to check the harness as well. If some of the cleaner got in the connector it could have caused a partial short.
One other possibility is the cruise control -- assuming you have one.
Not sure if there is a rev limiter in that year. I was driving an 80's era Ford once and just for giggles, I slipped the tranny into neutral while I had the cruise on. Engine started to wind out and I quickly killed the cruise
. Good Luck,
hj
Fleet Owner
Joined: Oct 2005
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From: Kentucky
Disconnect the IAC, Idle Air Control valve. This will take the computer control out of the equation. If the idle RPM is still high/maxed out you have an unmetered air (vacuum leak) problem. Did you remove and clean the IAC while you were cleaning the throttle body?
For reference: Fuel Injection Technical Library » Idle Air Bypass (IAB)
For reference: Fuel Injection Technical Library » Idle Air Bypass (IAB)
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Problem solved
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
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
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.
Thanks again.
