1990 f150 in trouble

hey i got a buddy and he has a 1990 302 ford f150 dont know the trans,but his truck is doin somethin that i have never seen before.the truck has a dead miss in it after runnin for about a min or a min and a half.the idle is way high and it runs rich.i think almost sure that a sensor is out somewhere, however i have no idea which it could be.Because of the high idle when it is in gear it will obviously get to goin real fast switch into second gear and keep goin.so when it is in gear and the brake is on u can tell the sob wants to get goin so it will raise up like a truck thats in 4low would do,then it will miss and when that happens the truck looks like u put it in park.so all in all im pretty sure its the eec or iac or some sensor like that but i dont know which to look at first.also test cant be run on it.so any help at all would be great thanks.sorry i posted in the wrong topic lol my bad.

95 buckin bronco said:

hey i got a buddy and he has a 1990 302 ford f150 dont know the trans,but his truck is doin somethin that i have never seen before.the truck has a dead miss in it after runnin for about a min or a min and a half.the idle is way high and it runs rich.i think almost sure that a sensor is out somewhere, however i have no idea which it could be.Because of the high idle when it is in gear it will obviously get to goin real fast switch into second gear and keep goin.so when it is in gear and the brake is on u can tell the sob wants to get goin so it will raise up like a truck thats in 4low would do,then it will miss and when that happens the truck looks like u put it in park.so all in all im pretty sure its the eec or iac or some sensor like that but i dont know which to look at first.also test cant be run on it.so any help at all would be great thanks.sorry i posted in the wrong topic lol my bad.

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Well, its obviously hard to diag it online.. But, a rich miss sounds like an injector hung open.. The PCM could do it, but you'll need to find out which cyl.. Maybe you could unplug each injector or plug wire, one at a time to determine which one does not make a difference.. At that point, if you ID one, you can take a test light to see if the PCM is commanding it, the light will be steady and not blink if its a PCM comand. If It's blinking, the injecotr may have physically stuck.. As for the idle, how high is "way high"??? The IAC can stick, but its a motor, not a sensor, it wont just open on its own, something is telling it to.. If the PCM driver is holding the injector open, it makes sense that the PCM caould also be commanding the IAC open.. I've seen a few bad PCM's doing weird things in that era truck, but I'd still check it as thoroughly as possible before throwing parts...

What do you mean a test cant be run? Will it not enter selftest or do you not have the tools?? A scan tool would help.....

Greg

No need for the fancy scan tool all you need is a short piece of wire,a pencil,paper and ability to count to ten. Do a search here for "self diagnisis" its really simple

Elmo said:

No need for the fancy scan tool all you need is a short piece of wire,a pencil,paper and ability to count to ten. Do a search here for "self diagnisis" its really simple

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Unfortunatly, a short peice of wire and pencil wont read sensor operation... Works fine as an "Autozone" style diag tool though.. I'm not knocking the recomendation, I've just seen many $$$$ wasted by throwing parts at codes rather than diagnosing them..

hey thanks i did read about that diagnosis thing awhile back.but it just wont read dont know but i will check that pcm.thanks again.

make sure the vacuum line is on the map sensor. if the vacumm line fell off, the engine will idle very high and the computer will think that you are at a very high load and it will be dumping fuel in. map sensor is located on the firewall to the passenger side, almost to the cowl. will have a three wire connector going to it and supposed to be a vacuum line going to the manifold

There should be a plaque certifying vehicles on the edge of the driver's door or door jam. There will be a tree that is listed in the registry. If the tree is a type limited-slip, the PIN code, one letter and one number. If the code is two digits, the difference is an open style