SteveTCook

Hi guys, like the Title says, my brother's Scrambler's 4.2 6-cyl is misfiring on the front 3 cylinders. It's not electrical, it's not a clogged up intake manifold. Could be something wonky with the carburetor, but we cleaned it and made sure that the gaskets were all in the right order & such. Any ideas?

OverlandZJ

You cant have a fuel related misfire unless it's injected..

Inspect the plugs and wires?

2WDUnderachiever

+1 on the plugs and wires.
And the distributor...
And the coil.

SteveTCook

After determining that the front 3 cylinders weren't firing, he removed the plugs one at a time and watched them spark while running the engine. They're definitely sparking, which is why he ruled out the electrical system. Can you explain how it might still be the culprit?

2WDUnderachiever

It can't be, but if you're trying to be a smartass, then drop the act, because you didn't give us this much detail to begin with... The burden of description is on you, since you're the one asking for help.
If you weren't being a smartass, sorry for the outburst.

That being said, if it's carbureted and the plugs are firing, then this is interesting... Maybe it's running rich and fouling the spark plugs? But he'd see that when he takes them out, plus it's unlikely that it would happen to a specific three plugs each time.
Or the head gasket could be blown between the three cylinders.
Or the valves could be sticking, or the valvesprings could be broken.

Long story short -- pull the valve cover, and maybe the head, and get back to us.

SteveTCook

1) I wasn't being a smartass, I was giving the details of why we had ruled out the electrical system in case somebody thought that wasn't enough to rule it out.
2) Cool your jets
3) Now to convince him to pull the valve cover. It has a liquid gasket, so it's gonna be a B to pull off.

2WDUnderachiever

Sorry to be a jerk... Just didn't know whether you were trying to be a smartass or not.
In my life, when you hear "can you explain..." or "well then how do you explain..." it's never a good thing; sorry, I didn't know what your attitude was, and I assumed the worst. And when you assume, you make an *** of you and me. My bad.

I know me apologizing to you is stupid, as it wasn't even a big deal to begin with, but I just read about a member here who died years ago, and was an awesome guy who wouldn't have been a jerk while giving advice, and I want to be more like him. So... Sorry.

Good luck convincing your friend to pull his valve cover gasket... Just hope he doesn't have to pull the head, eventually.
By the way, a razor blade should help you with that gasket... Though a paint scraper might help more.
A little bit of research says that acetone (nail polish remover) will too.
Be careful about getting that stuff on the paint, though.

SteveTCook

Thanks for the advice.

SteveTCook

Haven't pulled the valve cover yet, but we did do a compression test on it today, here's the results:

Cyl PSI
1 115
2 122
3 115
4 113
5 120
6 115

Any thoughts?

chuck1225

Well, I don't believe that it is a head gasket then. It could still be valves not opening. At the moment, that seems to be the most likely problem. I just hope that he hasn't broken a cam or something. I read somewhere that those old engines don't like the newer engine oils as much, due to some things that they have changed around in the oil formulas. Anyway, good luck with the scrambler! You oughta throw up a few pics of it.

2WDUnderachiever

^X2 on what he said about it likely being the valves and not the head gasket.

SteveTCook

So would the next logical step still be to pull the valve cover off, then run it and make sure all of the rocker arms are being actuated? Is it safe to run the motor with no valve cover?

Here's a pic of the Jeep in Moab a few years ago with my other brother (not the one who owns it now) and my Dad:

chuck1225

Yes and yes. Just be a little careful. I haven't run one of those engines specifically, but every other engine I've pulled the valve cover off of you can run it without the cover in place. And NICE Jeep!!!