Engine miss...

Got back from Tioga yesterday about 3 pm. Had a great time, more on that later. The Jeep performed flawlessly the whole way up, ~180+ miles, all weekend on the trails, and ALMOST the whole way home.
I was about 10 miles from home, on the interstate. Running about 60 mph, about 2200 rpm.
I suddenly fel an engine miss. Just one miss, kind of a lurch, then smooth for a few hundred yards. Then again, maybe twice in quick succession, then smooth again. I back off a bit, knowing my exit is 2 miles ahead. I'm thinking maybe I'm outta gas, but shouldn't be...
The miss continues. Not steady, but sporadic. It's not missing on every revolution, like a dead cylinder would. It seems to be more frequent when I try to accelerate or put a load on the engine. I make the exit, go to a gas station. I got out, sloshed the tank, plenty of gas. It starts and idles normally. I pull out, notice the sporadic miss, but I'm able to go. It lurches when it misses. I make it to the bypass, get out on that, and wind it out a bit. I wind it through some misses, maybe get it up to 2500 rpm... the fuel must have built up in the muffler from one or more cylinders not firing, then ignited like a rifle shot!
Wow, was that loud and unexpected!!
It seemed to run better aftwer that, for only a moment, then the miss came back. Needless to say I babied it the rest of the way home. It did one more exhaust explosion on the way home. It seemed the first time was in the pass side bank, the next in the drivers bank... but I'm not certain.
I managed to get it home and in the driveway.
I haven't had time to look at it, other than to look at the mufflers and see if they were still there.
The engine idles smoothly. doesn't start the miss until you feed gas.


The Jeep is covered in mud. Pics later. The engine and bay is a uniform mud brown, just like the outside, only not chunky. The distributor has a "hat" on it, from a Ford, keeps water off the cap.
I'll check the clear fuel filter first.
I'm going to check the wires, then pull the plugs and see what they look like. Check for any cracked porcelin or carbon traces. I'll pull the cap, look for any traces of arcing inside, wear on the contacts or rotor. I doubt any problem with the pertronix, again since it idles OK. I'll check the timing, but I doubt that since it idles smoothly.
I also doubt the carb, since it's clearly getting fuel when it misses, hence the exhaust explosions.

I'm thinking worst case could be sticking lifter or burnt valve. I don't hear any noise like a sticking lifter, so I'm thinking that's not likely.
What are the symptoms of a burnt valve? Even so, would that be sporadic? It would seem that would show up on every revolution and at idle.
BroncoJohnny said that after we both got gas, he had some rattling/clattering valves in his 302 when accelerating, he's thinking maybe bad gas... but mine ran perfect for 3 hours after getting that gas...

Looking for ideas/input suggestions...

Did I mention we had a blast in the mud??????????? :twisted:
Carnage report: A couple broken axle ujoints, one blown brake line.
My only carnage is some sheet metal rearrangement on the drivers fender when a tree got between my bumper and fender
Oh, the MasterFlow MF-1050 portable compressor aired up my tires from 19 psi to 30 psi in under 3 minutes per tire.

 

Maybe... would it appear that suddenly, after 3 continuous hours of running just fine? And a full weekend on the trails, and a 4 hour drive to get there on Thursday, with nary a miss?

Engine has ~80K. (It had some work done at some point, since it already has steel timing gears. That might have occurred when my brother grenaded the driveline at about 22K miles.)

 

Yup, sounds like a plug wire to me......

 

Thanks guys, for the good input. I hope to have a chance to take a look tonight...

 

Quick check last night, plug wires are intact and not touching anything bad, like a header...

I did take some time to clean off the glass fuel filter.
I found it odd that it was empty, and I did notice a stronger than usual fuel smell around the engine.
Fuel pump probably doesn't have 1K miles on it so I'm doubting a bad diaphragm.
I'll have to check fuel hoses/connections.
And I'll examine both filters carefully.

Coil is a reasonable guess, I had similar symptoms many years ago in a beetle, and it was the coil. I'm running a Jacobs coil, it's over 10 yrs old, mounted on the fender away from the engine heat.

Tonight after work I'll start washing it, try to get it clean enough to start working on it. At least get the big chunks off

 

I don't run a Jacobs ignition, just one of their stock-style 12V coils.

Just thinking a bit about this... based on our earlier discussions about Pertronix and ballast resistors, I took my ballast resistor out of the circuit in June. Maybe I should have left well enough alone since it ran fine before that and I didn't see any gains from dropping the BR out... maybe I roasted the coil ... :?