Various/intermittant Cylinder Missfires Jeep Cherokee 4.0.

Looky what I found:

http://www.golenengineservice.com/documents/Jeep%204.6/4.6-270hp%20Jeep%20LB.pdf

4.6 stroker longblock for just under $4000. Ouch...

Just found another one for $3200

http://titanengines.com/jeep-4-6-4-7-stroker-forged-longblock-engine.html

 

1999 4.0 has a better breathing cylinder head if memory serves. Also the later head had cracking issues although I have yet to see one at our dealer cracked.
Misfires on your 01....does it set a misfire code? If its actually misfiring it will set a code. We had a lot of camshaft issues around those years. Wiping off lobes like an old 305 chevy. I cant see you driving it this long if it was a cam lobe though. Its pretty severe. I have had the odd one burn a valve from excessive carbon.
Normally the 4.0 is damn tough. I put a total of around 600000km between my 2 cherokees. No mechanical failures short of water pumps.
Check your vacuum at idle. Compression test. Normally I would do a running compression test but you have that pain in the ... coil rail. so thats not practical.
Vacuum guage is simple and tells a lot.

 

I've had the codes pulled several times, and it does show a misfire code. Each time I get it pulled, it shows a different cylinder misfiring. At first, it was 3 and 6. Then it was 2 and 5, and the latest was 3 and 5. As far as compression checks, I only had it checked one time. I've never checked compression before, don't even know how, to be honest. Anyway, it showed cylinder 3 to be low, almost nothing after first firing it up. After about 30 seconds it came up to around 95.

Never thought of the cam... The valves, yes. Is there any easy way to find out whether it's the cam, the valves, or the rings? That is, without taking the engine completely apart?

 

With the misfires moving around like that I suspect carbon issues. The cams I have seen are usually just one lobe and its completely gone. I would put the vacuum gauge on it.

http://www.secondchancegarage.com/public/186.cfm

 

Thanks for the link Darren!! That explains how to read a vacuum gauge perfectly.

I'll go and get one this weekend and see what I come up with.

 

I am rather impressed with the 4.2/4.0 i have in my CJ. I put a 4.0 head on the factory 4.2L block (you have to weld up some coolant ports and re mill the head flat) gotta have sefi when you are running moab carburetors can get you killed if your not careful

But honestly if I was doing it again I would have just gotten a 4.0 block and put a 4.2L crank and rods in with stock 4.0 pistons effectively making the motor a 4.5L. Here is some info for you on that

http://www.ajeepthing.com/stroker-motor.html

 

Ok I got the vacuum gauge and checked it out.

Here's a video of the gauge while idling, and a few good revs of the engine. Can anyone tell me if this is good? Seems like it to me.

http://youtu.be/pACxuIFX1sc

 

16-17 in seems about right, think thats where mines at idle. Vacuum will go almost to zero it hard and fast,so that's normal.

 

Ok so now why does it misfire sometimes?

And why does it feel like it has very little HP when punching it from a dead stop?

 

How many miles are on it? You know the term its a jeep thing that miss is one of those jeep things lol. Does yours make a knocking noise too? Mine and my roommate's does this and has since we've got them, sounds like a bad main bearing but mine's been going like this for 4 years now. If you figure it out please let me know, just one of those things I gave up on.

 

130,000 miles. It makes a knocking noise when it starts up and runs for awhile. I think it's the valves, though. The only other knocking noise I've noticed is when I'm stopped at a light, I hear a slight knocking coming from the back of the engine. At first I thought it was serious, but then I lightly pulled up on the 4 wheel drive shifter and the knocking ceased. Happens all the time and I just lightly pull up on that handle and it goes away. Weird lol!