Just replaced the coil and ignition module in my 1977 F250. Now after it warms up it looses power and starts sputtering. I know it's getting fuel so that points me toward the timing. It idles fine and runs good throughout 2nd gear and low rpm in 3rd. As long as I stay below say 30 mph it runs ok. Vac leak? Torn vac diaphram? Please help.

 

To be sure it's getting enough fuel you need to put a fuel psi gauge on it. Pumps can go bad & not leak a drop but only be putting out, say 3psi or so, not enough to put any kind of a load on it without it sputtering.

 

If the problem developed right after you replaced parts then those parts are suspect. I would swap the ignition module to see if that changes anything. Then swap the plug wires if not.

And, speaking of plug wires, you did change them one at a time so there was no way to mis-wire it - right? If not, check your firing order.

 

Parts that have been changed. Entire fuel system from tank to carb.and rebuilt it. Ran fine until it started to miss going up hill. Changed the coil. Once again ran fine until yesterday. Drove it for about 30 min then all of the sudden during acceleration through 3rd it started to buck and sputter until it died. Replaced the ICM and it seem to run a little better. I really appreciate the help

 

Can you give us a sense of how long it "ran fine until it started to miss going up hill"? Was this a day or months? Ditto after you changed the coil. It looks like the changes you've made haven't gotten to the problem, although it is possible that if the times it ran well were many months then maybe it is a new problem.

Typically, missing under load at low RPM is poor spark getting to the plugs. That could be a bad coil giving poor spark, or bad wires/cap/rotor allowing the spark to go elsewhere than the plug it was supposed to go to. Or, it might be the pickup in the distributor, which can cause the timing to change or, in some cases, even go away. And, that usually happens when the engine gets warm. So, since you seem to have covered the other ignition components I'd replace the pickup.

But, it can be a fuel problem, although if so it is a lean condition rather than a rich condition. In other words it might be a vacuum leak but probably not a bad power valve as the power valve will give an overly rich condition.

Still, I'd finish the ignition system off before going to the fuel system as vacuum leaks don't usually change with engine temp and ignition can.

 

Just a few days in between occurances. Ignition parts that are left would be plugs, wires, cap, and button. Possibly a distributor.

 

I misunderstood. If you've not replaced the plugs, wires, cap, and rotor I'd do that now. The cap, rotor, and wires are the most logical suspects. Next would be the plugs. And I really doubt it is the whole distributor, but it can easily be the pickup, so do that after the plugs.

 

Gary you referred to the pickup. What are you calling the pick up?

 

In the distributor there is a pickup that connects to the DS module. The reluctor that is on the distributor's shaft triggers the pickup, which triggers the ignition. The pickup sometimes fails and quite often it fails when the engine gets hot.

 

Ok latest and greatest. Just replaced the distributor, plugs, wires, and voltage regulator and now she runs like a raped ape. Thanks for the help.

 

Good job.

 

Ok so after replacing the entire file system and the entire ignition system I am having the same problem. Seems as if the ignition is turning off and back on at the top of third and in fourth gear.

 

Boy, am I confused:

?

Are you trying to say that everything seemed to behave fine after the Grand Parts Replacement but the same problem returned 5 days later?

If so, have you looked into your ignition switch at all? You say it seems like the ignition is turning off... well, maybe it is....

 

Yes after the new parts it ran awesome. Now it runs good through 2nd gear so I shift to 3rd and it seems to run fine until I get to the top end of third and entire 4th gear it acts as if it is losing ignition. I let off the gas down shift to third and it does it all over again until it completely dies.

 

You say it acts like it is losing ignition (which, to me, means total removal of power from the ignition system) but I'm thinking it's not and you're being fooled...

Have you looked at your base timing and ignition timing advance? What is the base timing, and what is the total and when does it come in?