Lean condition could also cause the header to glow. In theory a hole in the exhaust manifold could cause the main o2 sensor to be off, but that I'd think would cause a rich condition.

Either way, cats usually have a fairly long life. Something may have caused the cat to fail if it is indeed causing the issue, so you may not be done with the problem.

 

The cracked manifold would let air into the exhaust causing the o2 sensor to read lean and force the computer to run rich.

 

I doubt the crack would be large enough to make it glow red, though. That'd have to be a pretty large crack.

 

The po removed the cat and I haven't had the time or money to install a new one. The crack is at least 3 inches long.

 

Then the cats not the issue. It has nothing to do with your problem.

I'm thinking the crack isn't whats causing your problem, either.

I'm guessing that crack developed because of the overheating the manifold is going through.

You could try getting the crack welded, but I'm not sure that is a perm solution, I always hear the welding crackes again eventually.

But it wouldn't hurt to try.

I still fear that it'll be worthless to weld it, as I'm thinking the glowing red is what caused the crack, not the crack causing the glowing manifold.

 

I have nust found another crack 3 inches or more long

 

Timing could be off enough to open the exhaust valve a little before the explosion happens letting the explosion partially occur in the manifold runner.

I can't imagine what would cause the timing to be that far off.

I don't know how much the engine can adjust its own timing, if at all.

 

For the timing to be off that much the timing chain would have to slip I would think. Did anything happen before it started doing this?

 

Thats what I think as well, but who knows?

I still want to say that those cracks are developing because your manifold is getting as hot as it is.

I'm wondering what would cause that lean/rich of mixture and let the motor still keep running...

 

Is this a vehicle you drive daily? Did this problem of it running foul progress or just start and how long have you noticed it?

 

It started yesterday. My friend was the one driving it n he said it just all of a sudden happened. I cranked it up this morning and it wld rev like normal.

 

Check fuel pressure,compression and ignition timing. Gota start with the basics.

 

I really don't think we're getting the whole story here, so it's going to be impossible to tell you what's really the problem. You spoke of two symptoms, red hot exhaust manifold and wont rev above 3500 rpms- these are classic signs of a clogged exhaust. Is it possible your friend went off roading in your jeep and "crimpped" the exhaust on a rock or something? You are also saying that you know it's running rich- it's no wonder without running a cat, your O2 sensors are going to be trying to adjust for the improper readings.

I think it's time you just bite the bullet and replace the entire exhaust (new header, cat, O2 sensors, and fix any leaks/holes). After you do that then you can come back and tell us what's working and what isn't.

 

Not running a cat wont cause running problems. Just emissions issues. The upstream o2 reads air/fuel ratio. Downstream checks operation of cat.

 

Thx for the help but its fixed now. The distributor hold down came loose, causing the distributor to turn.