This has me stumped, please help if you have solved this befrore. I have an older (1994) F-150 with 190K on it. I bought it new and have taken good care of her. Doesnt burn oil. Runs great sometimes then all of a sudden it runs like you unplugged a sparkplug wire or a major vacume line, then (many times) after shutting it down and then restarting it runs fine again.

I already did the following:
-new plugs and wires and rotor/cap (no change)
-new 02 sensor (no change) had a code for this in the computer
-new ingnition modual (no change)
-new exhaust canister solenoid (no change) had a code for this one too

My mechanic says he connected it to a different coil and had no change, (I did suspect this) I may buy a new one just for grins

The mechanic says the computer checks out good on his tester too, I was thinking I needed a new puter, but he says no

What am I missing?

 

The 1994 dosent offer a data stream for a regular scan tool, so its really hard to pinpoint the problem on them. I would reccomend taking it to Ford. They can get a data stream and see what sensor is messing up. In the mean time.. Attach a fuel pressure gauge to the truck and watch it when the problem happens. Does it continue to run rough when the truck is put in park?

 

No, it runs fine at start and idle 99% of the time, every once in awhile in the middle of a really bad spell it may have a slowed idle that isint as smooth as normal, but this has only happened a couple times.

I too am starting to suspect fuel rather than electrical.....Ive been focused on electrical for quite some time

 

I don't see a fuel filter on there. is it stopped up?

 

I just ordered a throttle positon sensor. The book I have says if a sensor is failing the computer substitutes pre programed input as a bandaid to keep it alive so you dont get stranded. That feels like what is happening. There is only one other sensor left that I know of besides the throttle position and that is the intake air temp. I plan on changing that one next. Is there another Im missing?

I dont want to take it to FORD, our Dealer isint the greatest here

 

test the TPS before thowing parts at it.. Should be able to read .9 closed throttle to about 4.8 volts WOT. It should be a smooth transition from open to closed.

 

Just a follow-up. Today I found out what has been wrong. Even though my mechanic said the computer tested good, I swapped computers with a friend that has an identical truck, problem solves, and his ran like crud.

as we were getting ready to swap them back the plastic shoulder on the radiator gave out and fluid spewed all over, so its a new puter and a new radiator........and all will be well again.

Thanks for the help......will let you know how the instal goes

 

Glad everything worked out for ya!

 

Just a quick note. New(rebuilt) computer installed today and new radiator, that thing decided to crap out right now too, anyway, that fixed the running terrible sometimes problem, the computer.

As far as electrical there are a couple sensors that didnt get changed; most did. Im thinking one of two things had to happen...either the computer just went bad, or something caused it to go bad.

What was changed that had a code was 02 sensor, exhaust cannister sensor, then the ignition module tested bad and was replaced. I also replaced the throttle position indicator sensor just for fun. So, heres my question........if something caused the computer to go bad, what are the chances I have replaced the culprit. Im hoping the ingnition module would be the most likely culprit. What say you? TIA

 

I guess it just went bad by itself. It's was pretty old. I know that there's a lot of computers older and still running, but it just happends.