Hey Guys,

Ive recently become the new owner of a 1994 F-150 Lightning. The truck has been sitting since July of last year, and I am currently in the process of bringing her back to life. Among many of the quirks this truck has, ive had to drill out the seized ignition lock cylinder (and broke the housing in the process, so it seems ill have to buy a new steering column.) Being a previous bullnose owner, im not too familiar with these OBS trucks, so bare with me.
I found out that I could start this truck with the ignition switch, located not too far down from the column. right off the bat I realized that as soon as switching on accessory power, I get no chime, no dash lights, no gauge check, nothing. I only get the battery/charging system light, and the sound of the fuel pump engaging. I also realized on/accessory doesn't let the wheel break loose from its lock, nor does it let me shift the truck out of park.
the truck still had about half a tank of old gas, so I threw in a can of octane booster, and started it up using the switch. Upon starting the truck, I realize the truck has a really rough idle. It idles, but it stumbles a lot. If I give the truck gas, the truck would die as it revved back down. after holding the idle at around 2000rpm for about 5 minutes the idle stabilized a bit, but still was a bit rough. im thinking of replacing a bunch of the old sensors on there like the IAC, MAP, TPS, etc.
The engine also has a sort of hissing sound, sound like a vacuum leak?? that would explain the stumbling idle, right?
Any help is appreciated. Thanks.

 

One thing at a time. IDT the octane booster is going to make up for the old gas. I would put fresh gas in it first, then deal with the hissing sound next. Have you checked for any codes?

 

X2...do not start blindly replacing sensors. You need to methodically diagnose the issues, then repair accordingly. Throwing the parts cannon at it usually results in a much thinner wallet and more issues that you introduced.

 

good point. funny enough, after this, i got the idle problem situated by messing with the screw underneath the throttle body. it idles fine even with the old gas. All that leaves me now is with that hissing sound. sounds like a vacuum leak coming from the center of the engine. I also ended causing myself another issue, lol. i ripped out an old cheap aftermarket antitheft/alarm module the PO had installed, and now the truck won’t start from the ignition switch. I’ve got to trace the wires and made sure i didn’t cut anything important now. I can also now steer the truck and shift it out of park. i simply moved the mechanism where the ignition switch where usually stick into and the steering wheel unlocked.

 

Take a fuel sample
Get the old gas out of there and try it again
Plan on replacing the fuel pump
Messing with the screw on the throttle body?
Plan on replacing that too now
Hard if not impossible to get one back adjusted where it needs to be

 

Ethanol blended fuel does not last very long. Chances are it could have damaged one or more injectors. You really need to get rid of that old gas and not continue to run it through the engine.

It seems like pulling the steering wheel to see what in the ignition cylinder and linkage was binding up would have been easier than drilling out the lock and damaging the column. You need to diagnose problems. Throwing new parts will add unknown variables into the mix.

If it sounds like a vacuum leak…it probably is. That is not an idle adjustment screw like on a carburetor. It is a throttle stop screw to keep the butterflies from closing too far and contacting the bore.

 

excuse my ignorance, i’m pretty sure i’ve just gotten a little bit too ahead of myself. i’ll start on the actual health of the engine and how it runs by draining the gas out before i damage the fuel pump anymore. then i’ll move on to all the electrical wizardry.

 

There is a good chance the gasket under the plenum is the problem. You will need a torx socket to get the center bolt out. If the gasket is the problem you will have to turn the stop screw back to where it was.

 

Hey guys,
in the past few days, i’ve drained both tanks and filled with fresh gas, and have done an oil change, along with new plugs wires and cap. after tons of snooping around there appears to be no vacuum leak in the engine. I also gained accessory power again by replacing a 10A fuse that was blown, and upon further reading, also went to my TCM. The truck still stumbles at idle, and will stumble even more when it’s in gear. When accelerating, the tranny will not shift unless i let off the throttle, and it will deliver a hard shift. I’ve been reading around forums and doing some research and most that have had these same symptoms found the TPS to be the main culprit. I have already cleaned out my IAC, and it relieved the idle just a bit. Is there any way i can test my TPS? I’ve already tried to pull codes but it appears the system isn’t throwing any. Insight?

 

Yes. You can test the TPS with an oscilloscope. You can also use a multimeter but it's more difficult to see a malfunction with it.