I have an 87 F150, 351w, 4bbl holley 4180c (factory), c-6 automatic (pretty sure), 4X4, Dual tanks, tilt, cruise, aftemarket stereo and keyless entry alarm.
Regular cab, 8ft bed. The truck was repainted by a local Ford dealership, who then sold it as it to me. (white and light brown) Approximately 100 miles after I bought it the rear differential eploded at 30 mph. My neighbor and I replaced it with a nearly new one from a similar truck in a wrecking yard. ($70.00)

Here's what it's doing. It starts fine. The factory electric choke on the carb works, and opens after a minute or so. Seems to idle fine. When I'm driving, in drive, if I give it more than just a little gas, 8 out of 10 times it will cut out and bogg down, sometimes completely quitting (which is bad on the freeway!). If I let up on the gas, sometimes it will back-fire and let loose a huge white cloud (fuel I think) from both duel exhaust (also bad on the freeway!). Sometimes when I let up, it just starts running again, but I only have that little bit of throttle to play with, and have to feather it to keep it running to get home.

I thought immediately, power valve. So I replaced the power valve in the carburetor. I actaully replaced it twice, I tried a different one just to see if it ran better or worse, but it made no difference, so I put a standard one back in. I have also rebuilt the carburaetor. I supsected myself and took it back off top make sure I hadn't missed anything. Everything was fine. I check the timning, it's good. Replaced the plugs, wires, cap, ignition control module (left fender), coil (replaced with a standard coil instead of the one with the "c-clip" connector because it kept falling off).

Recently, I decided this might be a vacuum/tranny problem because it almost feels like it's trying to down shift (passing gear) when it happens.

This could be a direct result of my neighbor and I removing all of the emissions crap from the engine compartment. It had a smog pump, but no catalytic converter. Someone put dual exhausts on it and just tossed the converter, so the smog pump froze up! There were little green and red and blue plastic tubes running everywhere....gone. Smog pump...gone. All vacuum lines except 3 or 4 that were needed...gone.

So there it is. Any help would be greatly appreciated.

Clint (aka UH60L)

P.S.: This truck came with crappy one piece 4X4 hubs that broke, and I converted the axles, spindles, bearings, and rotors to a '89, and installed Warn hubs, but this shouldn't have had any effect on the current problem.

 

Sounds to me like you have a problem with your accelerator pump circuit and a small exhaust leak, probably at a collector.

What is the vacuum at idle? What is the fuel pressure? If you eliminated the EGR system, your combustion chambers are running too hot. How is your ignition advance controlled? Did you plug the smog ports in the backs of the heads?

 

I'm gonna sound really inexperienced here and ask what a "collector" is? By the way I have a valve on the left exhaust manifold that closes when it's cold.

As far as the vacuum pressure and fuel pressure, I haven't checked either because I don't own the necessary gauges. I'll see if my neighbor has them and let you know what I find.

Yes, the EGR valve is disconnected. How do I alleviate the overheating chambers?

My distributor has vacuum advance.

Pretty much anything that was connected that we disconnected got a cap on it when we were through. There was one piece at the back that is like a big valve that was screwed into the exhaust, it broke off, and we couldn't get the remains out, so I put a plug in it.

The overheating thing kinda makes sense. When the engine is cold it doesn't usually act up, but after it's warmed up it almost always does. That could probably cause a backfire-like effect even if the timing was correct.

I'll check those pressures and post them here asap.

Thanks,
Clint (aka UH60L)

 

I never did get the proper equipment to check fuel pressure and vacuum. I did however figure out that the ports on the back of the heads are connected to the thing I thought was part of the exhaust manifold, and that the plug in it was loose. Thus, in theory, I was losing compression through that little manifold between the heads. I tightenned the plug, and it hasn't done it again since, so I am assuming that was it. I am going to remove the plug and weld a plate over the openning.

Let me know if you think this might not be it, but I think I fixed it. I'll find out I guess, driving it 400 miles to elk camp on friday.