Newly rebuilt engine (long block) purchased thru Autozone.. cranked fine on first try..
The problem.. occasional miss at idle, upon slight acceleration or holding any speed .. engine stumbles & stutters, but when accelerating a good bit, the engine smooths out..

Timing is correct, manifold and vac. advance vacuum tests fine.

I have since replaced the fuel pump, coil, carb, pickup coil in distributor, plugs, wires, dist. cap/rotor, fuel line, air filter, fuel filter. .. Problem still exists..

Egr valve was blocked of when I bought it.. left it that way and it ran like a top for a few years.. til it threw a rod..

Problem started with the new engine..

78 F100.. 300 6 cyl. no air injection

Hep me hep me!!!

 

First off WELCOME TO FTE! Do you have a manual or automatic transmission , when you say that the manifold and vac. advance tested fine what do you mean?

 

Thanks for the welcome...

It has a manual 3 speed..

the manifold and vacuum advance tested good with a vacuum test gauge.

I might also clear up that when I accelerate kinda heavily is when it smooths out.. through the acceleration... then when it reaches the speed wherever I hold the gas pedal, it misfires in a bad way..

 

OK what was the reading on the vacuum gauge , how many inches at idle and what does the needle do when running does it bounce around wiggle or anything at all that would indicate a problem? I think you have a vaccum leak either at the carb to manifold or (more likely) at the intake to head , try re-torque the intake/exhaust combo manifold again and see it that helps .
I really think that is the problem I dont think it is an ignition problem. How is the carburetor set up?

 

Is the actual distributor new?
Having bad.worn out drive bushings can cause a rough idle/miss and bad emissions. (weird, but I learned it in my tech classes)
WrenchHead

 

I am currently having the same problem with me 302. I know it is on my right side due to my duel exhaust sys. I have replaced the complete ignition sys from the control box to the plugs to include a new holley two barrel carb. I have retorqued the intake but not the exhaust side, I'll try it when I get home but how would this cause a stumble?

I have pulled all the egr stuff off to include the spacer and the problem is persistant. I have also tryed retorquing the rocker arms and non moved, and watched the valve springs with no binding and they appear to open fully without actually pulling the head I can not tell.

I havn't tryed the vacume check yet, what should I look for? were do I connect it to and what should my reading be? I can pick up one on the way home. thnx in advance.

 

If you still have an EGR "plate" under the carb or in the intake manifold it may be leaking internally, caused from years of erosion by the exhaust gasses that pass through it. This can happen even if you have blocked it off.