I have an 84 CJ7 with a 304 upgrade. My jeep will randomly start runnig very rough, like all cylinders aren't hitting. I will barely idle and often won't. I have to keep my foot on the accelerator to keep the idle up enough to get home. The odd thing is, I may start it tomorrow and it be fine. I may drive it a couple of hundred miles before it does it again or I might only get a few miles. It is very random. I have replace the ignition module, plugs, plug wires, coil, distributor and rotor cap. I replaced fuel filter. Any suggestions?

Fuel pump???

Timing chain??

Have you replaced the distributor, or the distributor cap? Sometimes the play in the distributor bushings is enough to cause weird miss fire, or the pickup coil is bad. With how random it is, and how it runs fine in between, I bet it is electrical. It sounds like the only thing you haven't replaced is the hall effect sensor. Check out the side to side play on the metal pin wheel, and check the gap clearance between the pin wheel and sensor. If you have no play and the gap is something around .020-.045 you could try replacing the hall effect sensor.

If you think it is carburetor, next time it sputters, try giving it a little shot of ether, or pulling the vacuum line to the brake booster. if either of those work it could be carburetor.

Do you still have the original wingnut for the carb? I've had trouble with the stupid horseshoe connector on the coil (I cut the ends off and wired it direct with an '81 Dodge coil which ran MUCH better due to higher voltage)
Do you have a ground wire from the body to the motor/battery? If it broke off, these issues will happen (module overheats due to lack of voltage)

CArnuk
Higher voltage coils don't make an engine run BETTER. If the coil you replaced was a bad one the engine might have reverted to running NORMALLY...but if the coil you replaced was a good one it couldn't possibly run any better.
High voltage coils jump the gap in the plug at the same voltage as lower voltage coils... It is the nature of the beast.
Higher voltage coils are needed when the pressure they must discharge under is higher.. so high that a lower voltage coil cannot fire.
As long as the coil is working as designed, the coil that comes on an engine cannot be improved on! Unless of course other changes to the engine have raised the pressure at which the coil intends to discharge.
Big JIm <img src="/forums/images/graemlins/pfft.gif" alt="" />

Thanks for all the advice. Looks like I have an afternoon project.

Does the rough running follow the weather at all? ie it rains, you drive through a puddle and splash water on the distributor or something and then it runs rough until everything dries out?

Sean

Head gasket. Sucks, pull the heads off.