1985 Bronco....Need help

[Mike Meese]

Hi, I am new here. Just bought an 85 Bronco 351w, ran good until the idle went through roof while I was driving it. Had to shut it down for fear of blowing the motor.....

 

[love_my_bronco]

was it parked or what happened when the idle shot up? driving. did it jump on its own or was it like you just stepped on the gas and it didnt go back down?

 

[Mike Meese]

was it parked or what happened when the idle shot up? driving. did it jump on its own or was it like you just stepped on the gas and it didnt go back down?

I was driving it and I stepped on the gas and it just went crazy, I had to shut it off and now when I start it it still does it.

 

[love_my_bronco]

hmm could be accelerator pump but not entirly sure on that.. sounds to me something is locking up.. hmm anyone else have some ideas? i'm gonna look it up see what might cause it bud

 

[BroncoJoe19]

Could something gotten up and stuck in your throttle linkage?

Could your carpet slid up on your gas peddle?

IF none of the above, look for a vacuum leak.

Checking for vacuum leaks.

Some of the sensors and some of the actuators either read the amount of vacuum, or use vacuum to move controls, therefore it is important to the proper functioning of the engine that your vacuum system is fully intact. Otherwise one may get codes falsely indicating that there is a problem with a controller/actuator, or a sensor when in reality it is caused by a lack of vacuum.

Look at your rubber vacuum hoses (they are about 1/4 - 3/8 inches in diameter, if they are dry rotted or cracked, replace them. IF they slip on/off of their connectors too easily, they may have stretched out a little bit, cut the ends off, and put them back on.

You may listen for a leak. Sometimes using a cut off piece of garden hose is a good aid to listen with. Sometimes a cardboard tube (like from gift wrapping paper) is helpful. Just remember that whenever you stick your head inside a running engine compartment, that you are not wearing any loose clothing or jewelry that can get caught.

Another suggestion is to use a spray can of carb cleaner and spray around the bottom of the intake manifold, and the base of the throttle body assembly. IF there is a leak, you should hear a change in your engine.

 

[Mike Meese]

Could something gotten up and stuck in your throttle linkage?

Could your carpet slid up on your gas peddle?

My carpet is out of the way, and I checked for any cracked hoses. The carb is a motorcraft but I am not sure how to get to the accelerator pump to check it.

 

[Yardape]

With the truck off work the throttle from closed to wide open, is it sticking at all?

 

[shift1313]

is there tension on the throttle cable? i would start by pulling the cable off and starting the truck. Check to make sure the linkage moves freely. can you take a pic of the carb or pull some numbers off it so we know what you have?

 

[BroncoJoe19]

The accellerator pump wouldn't cause this.

Also check to make sure they don't slide off easily. (the vacuum hoses)

 

[Mike Meese]

The accellerator pump wouldn't cause this.
Also check to make sure they don't slide off easily.

The linkage looks fine and the pedal works like it always has. It is a motorcraft carb # E5TEZA A5C14

 

[shift1313]

like joe said, if the accel pump was stuck and your throttle butterflies were closed you would just flood the truck maybe. Without the extra air it wouldnt be pulling anything to make the idle skyrocket. You either have an air leak(base of the carb, at the head, vac lines. Or maybe somehow your distributor came loose and went way advanced. check the distributor to make sure its not free to rotate

 

[RBuffordTJ]

Hi, I am new here. Just bought an 85 Bronco 351w, ran good until the idle went through roof while I was driving it. Had to shut it down for fear of blowing the motor.....

This might sound a little stupid but check it out because the same thing happened to me in an old pickup I had some years back. The spring on the throttle linkage popped at the bend. When I lifted the breather it looked fine until I bumped it on accident and noticed the problem. Just pull it and make sure it didn't pop.

If your pedal is not laying on the floor it should be ok but check to be sure. Scared the crap out of me when it happened.

Rick in Orlando

 

[love_my_bronco]

hmm. just a question how could vacum lines cause high idle? i've never heard of it doing something like that. guess i gotta start learnin more.. what should i look for in case?

 

[Mike Meese]

Well I unhoked the throttle cable and tried to start it and the carb shot flames out and caught on fire.

 

[love_my_bronco]

the only other time i have seen something like that is if your timing is off.. but a good amount. what was destroyed. have you checked your timing since?

 

[Mike Meese]

the only other time i have seen something like that is if your timing is off.. but a good amount. what was destroyed. have you checked your timing since?

I can not get it started, the flames did not do any damage but now it will not start

 

[Yardape]

I would start with your timing.

 

[Seabronc]

I wasn't able to interpret "going crazy" in the initial post, but as Yardape said, the backfiring sounds like timing and from the sound of it your timing gear and/or chain may be suspect. My first thought when I read the initial post was timing chain jumping teeth on the sprocket.

If running crazy meant it went red line, then I would suspect something in the linkage so the butterfly/s were wide open.

Good luck,

>-

 

[Yardape]

I wasn't able to interpret "going crazy" in the initial post, but as Yardape said, the backfiring sounds like timing and from the sound of it your timing gear and/or chain may be suspect. My first thought when I read the initial post was timing chain jumping teeth on the sprocket.
If running crazy meant it went red line, then I would suspect something in the linkage so the butterfly/s were wide open.

Good luck,

>-

I was wondering if for some reason the wide open throttle caused the chain to skip a tooth. I cant see timing causing the wot that you described.