Diesel mech needs help with gasser :(
 

Guys, this is so embarrassing :o I borrowed a friends 89 F250 bucket truck to help in putting up some trusses for a roof-over. When I picked it up, it ran great, now not so much so. :'(
It is a EFI 460. It will only run if you constantly move the accelerator pedal, sorta like keeping a carbed engine running with the accelerator pump when the jets are stopped up. I have replaced the fuel filter and checked the fuel pressure, it is 38 PSI as it should be. I can find no vacuum leaks, nor any wires chewed by mice, or anything that looks out of the ordinary.
I hope someone here can give me a few clues, I have posted in the 460 forum and also the 48-56 forum and have gotten suggestions, but nothing to resolve the problem.
Any help will be appreciated and all wise cracks and dumb looks are expected :-roll

Have you removed cleaned and lubed the idle air control valve?

It's a cylindrical device using two bolts holding it on the intake manifold near the throttle body, with a two wire electrical connector. Take it off. Hit the inside with some WD-40, then cycle the valve a few times with a pair of needle nose pliers. They are around $50 at the parts store, but I have yet to encounter one that couldn't be saved.....

First thing that comes to mind for me is the Throttle Position Sensor..

You should be able to test that with a ohm meter if we can come up with what the correct values should be.

Yep, pulled, looked, cleaned, lubed, no change :(

I considered the TPS, but it doesn't seem like it would act like this. Most I have seen (and that was very few) would usually cause a surge at idle or have a flat spot in them. I guess I could Ohm it through the travel and see if it is consistent.
I pulled the codes and the only one that could cause a problem shouldn't keep it from running at all. The engine coolant sensor was out of parameters, but that usually causes a rich mixture.

Plastic gas tank or steel? Maybe the pick-up foot is full of crap.

Steel tanks, but the fuel pressure stay right at 38 PSI as it should, so I don't think it's a fuel delivery problem.
Noticed something else last night while messing with it, sometimes it will hit as soon as I start to crank it and then at other times it will just turn over and not hit at all. Let off the key and turn it again and it'll start. :-huh

So it doesn't run with your foot at one position on the pedal, you have to pump it to keep it running?

Exactly, if you stop moving the pedal, it dies. No sputtering or fading out, just dead :-rip Also it seems like it really only runs in the first third of the pedal travel, more than that and it starves out. I haven't checked on the price of a TPS, but I'm leaning towards that being the problem.

How about the MAP sensor Jeff? I've had them act just like you are saying ,gotta keep pumping the throttle to just to keep it running.

Inspected the coil packs? I had a Olds in the garage a while back that was acting like it had a fuel problem, but in reality had shorted in the connector at the coil pack and fried it.

Took a while to find that one.

I had a big long write up for you that I thought I posted this morning but I guess I must have closed the browser before I sent it. I'll be way more brief this time. WHen I first read the thread, I immediately thought of IAC because I have had so many stick. However, they only affect idle and kick out as soon as you apply throttle. Next would be a major vacuum leak. It would be hard to find any vacuum leak if you have to constantly rev the motor to keep it running so you may look at the bigger vacuum hoses (like the pvc valve and brake booster hoses) to see if anything might have popped loose or dry rotted apart.

Being that the truck belongs to your friend, you don't want to throw alot of part or money at it so I would check everything that doesn't cost anything. I think you need to check your ignition system. It doesn't take very long to pop the distributor cap loose and check it and the rotor for corrosion. I would NOT take the ignition wires off more than one at a time so you don't mess up the firing order. Look over the wires for a burnt spark plug wire or frayed melted harness. And common issue with high mileage vehicles that sit around a lot is worn valve guides can drain oil into the cylinder causing the spark plugs to fowl out. I would check several spark plugs for good measure. Only a couple are pia to remove so pick a few easy ones and pull them to look at them. If you are running lean, they will be clean, if you are running really rich and not burning due to a bad coil or ignition problem, they may smell like gas. I don't think the 460 ever saw coil packs.

Next I would do the TPS check with a multimeter. It doesn't take very long. I personally don't think this is the problem, but its free to check if you already own a multimeter (VOM). As far as MAP sensors go, I don't think they can be checked without some special tools like an oscilloscope. If you lucky enough to have another vehicle with one or a friend with one, you might try swapping out to see if it makes any difference. Alot of Ford MAP sensors are interchangeable. If you are going to be close to Fort Smith, I have one you can barrow.

Sorry to be so long getting back guys, but a special little lady has taken most of my free time lately :)
Finally got time to check a few things, ignition seems to be fine, plugs aren't fouled and dist cap looks good. In checking things today I noticed if I unhook the vacuum line to the MAP sensor, it will attempt to idle, but still die if the accelerator is not being moved.
I have found no major vacuum leaks and no chewed wires either.

Ding, ding, ding...... Dave gets the cookie! :-X04
Plugged in a MAP sensor from a 3.8 V6 out of a Cougar and it runs! Not sure if it is correct or not, but it seems to run pretty good. I just love it when something I threw on the shelf because I might need it someday turns out to save me a $$$ }>
Thanks guys for all of the replies :-wink

WOO HOO. Now go celebrate with the Girl Friend. That Shed has waited this long so it can wait a bit longer.

I'll agree, it's way too hot to mess with the shed right now anyway! :-X04