Ok, so I've had my 77 F-250 for about two weeks. And here's what's up:


1. When I got it, I got true duals on it. The guy noticed that it was missing at high RPMS. It also missed when cold. I assumed it was fuel related so me and my friend who is an ASE mechanic pulled the carb, rebuilt it and threw it back in. The miss got worse. We keep tuning the idle and stuff like that and it just keeps getting worse.

2. It runs perfect when it's cold and just been started, the warmer it gets, the more it wants to misfire. Eventually, after you shut it off and start it back up when it's been driven a certain amount of time, it will want to stall out, misfire a lot and also stall out when we put it in gear.

could the spark plugs be fouled from running too rich and need to be replaced? That's the easiest fix.

 

Have you pulled the plugs to inspect em yet?

Seen the choke working properly?

Checked vacuum and mech advance?

 

Nope. I don't know how to inspect if they're fouled, I just know that they can be fouled or not gapped correctly, etc.

 

If you have a Chilton's manual (if you don't, get one) it should have a diagram showing how to diagnose internal issues w spark plugs. I'm sure the same thing is available on the interwebz, and probably in living color w better pics.

 

I do have the manual for my truck, I'll go look at it later today

 

Cool.
Also, either Haynes or Chilton's (I forget which one, maybe both) has a pretty comprehensive step-by-step troubleshooting guide towards the back...it can be VERY handy.

 

Sounds like it could be an actual case of vapor lock, too. I emphasize "actual" because vapor lock seems to be one of those diagnoses that gets thrown around a lot...like having a "short".

 

It must be vapor lock. I went to AutoZone and bought the heat reflecting wrap, and wrapped the fuel line, and the problem didn't go away, but it certainly made the thing drivable.

 

That's a good start then. You may want to consider rerouting your fuel lines away from heat sources and possibly installing an in-line electric fuel pump....doesn't have to be an expensive racing unit, just a pusher installed before the mech unit. A regulator between the mech pump and the carb will help prevent flooding.

 

If you're going to install an electric fuel pump, bypass the mechanical. A failed diaphragm will allow fuel to spill inside the engine

If the plugs are wet or sooty, clean em or change them

As I found out after changing a lot of stuff, problems like you're describing can also be ignition control module. I replaced mine last week and the difference was incredible!

It's a good idea to keep a spare anyway. I bought genuine motorcraft on eBay for under $40

 

How difficult is the ICM to replace? It involves wiring, right?

 

Not hard at all...there are two plug-in connectors. One is two wire and the other is four wire. They're even keyed so you can't connect them upside-down!

The box itself is mounted high on the fender by three screws

 

If you're going to throw dollars at the vehicle instead of doing some troubleshooting as the others have said....such as what do the plugs tell you, is the timing right, vac advance ok, no vacuum leaks, etc, then, ok.

A new ICM is "plug and play." It's that ~ 4"x4" metal dealie on the left fenderwell close to the cowl. Heat is a big minkey wrench for these puppies. Some people put washers under the mounting holes for air flow. But, get a Motorcraft one, not the cheapo Chinee ones. I believe you have the one with the blue grommet.

 

Is that what that thing is...? What does it do?

 

I have no tools to check 90% of those things. ICM is pretty cheap and mine has seen better days. It's not even bolted all the way onto the fender.