Cabledog

2000 grand Cherokee 240,000 miles
It sat for a week last month went to start it. It acted like it running on 3 cylinders black smoke was coming out of tail pipe. No codes on reader. I did find it had an intake leak vacuum was 12 inches of mercury. Replaced intake gasket now has 17 inches of mercury. Still runs extremely rich ST/LT +32% still no codes Did compression test all cylinders 130 plus or minus 5 lbs Wet was 145 checked coil for spark, all ports checked good, checked injectors with noir lights all good, replaced injectors for good measure. Timing at idle is 10 degrees and 35 at 2500 rpm. Changed cam sensor and crank sensor. Still no change. The header pipe and Cat are new along with O2 up stream and down. Checked for issue on PCI bus and modules. Isolated each one, no change. Talked with a mechanic that works on Jeeps, he had no suggestions !!!
I have one thing I want check the timing
chain might have jumped. Any ideas on how test would be great. No timing marks to reference and not sure were the Cam sensor should be at TDC.
Also checked grounds and all connections into PCM all appear good. One additional thing I did notice the voltage gauge is not working, Had battery load tested checked good voltage is 13.5 with a 50 amp charge coming from alternator.

dzywicki

This is the XJ (cherokee) forum, but since it's the same 4.0, I'll give this a shot. You will definitely need to do some searching. On the 4.0 motor, you have timing marks on the timing cover. If you have never taken the timing cover off, the marks are most likely covered in a thick coat of grime and unreadable. You can see by looking to the upper right of the vibration damper. Once you get that cleaned off, you'll need to see where it says 0. You will need to turn the crank until you see a notch. Once you find the notch, mark it with some white paint. To turn the crankshaft: remove the electric fan and then get a socket on the front of the crankshaft. You will only want to turn it clockwise.
Turn the crank until the notch lines up with the 0. There are two times this happens. During TDC at the end of the compression stroke and at the end of the exhaust stroke. You want the end of the compressions stroke. I use a compression gauge in cylinder 1 to know if it's compression or exhaust.
Once you find TDC on the compression stroke, the distributor rotor should be pointing to the cap terminal of cylinder 1. Making sure the the distributor is aligned correctly is a different search.
To check if the timing chain has jumped (highly unlikely), would require removing the timing cover chain and lining up the marks on the cam and crank sprocket.
Since you have good compression, I doubt you have a timing problem. Was it running correctly prior to sitting? With those ST/FT numbers, it seems like a problem with your O2 sensors. What brand O2 sensors did you use and how long ago were they changed?
Check the plugs too, to make sure they aren't fouled. If it's running that rich, they can get fouled. I had that happen once. You can also read the plugs when you have them out to see what's going on in all 6 cylinders.

extrashaky

He doesn't have a distributor. The 2000 4.0L is a coil rail motor.

Torque will show me pending codes that haven't tripped the CEL yet. Can you see pending codes with your scanner?

On the coil rail motor, timing is handled by the computer. You don't adjust the timing on these motors the way you would by rotating the distributor on an earlier motor. Rotating the cam sensor doesn't adjust timing. If you move it, the computer will just adjust to its new position.

HOWEVER, although the computer adjusts timing on the fly, the signal from the cam sensor can get so far outside normal parameters that the computer doesn't know what to do with it, and this can happen if the timing chain has jumped. What you want to do in that case is to reindex the cam position sensor. The top of the oil pump drive under the cam sensor has an indexing hole in it that should be lined up at TDC, and you can line it up using a toothpick. It's a pretty easy procedure, but instead of rewriting it, I'll just give you a link:

http://www.jeepforum.com/forum/f11/h...ensor-1145301/

One caveat: If you have an aftermarket oil pump drive, there's a good chance it will NOT have the toothpick indexing hole because it came with a little cap you use to align it instead. If you look in there and don't find a hole, you can order a replacement alignment cap.

Did you replace the O2 sensors at the same time you installed the header and cats? If so, you may need to replace your upstream sensors again. As a new header breaks in, it can burn off gases that foul the O2 sensors. When I installed my header, sure enough my new O2 sensors crapped out on me within 200 miles of driving. I had read about the phenomenon and was already expecting it to happen, so it was no big deal.

Don't let the fact that you don't have a CEL fool you. O2 sensors are little liars that will often be failing but will still tell the engine computer, "Oh, I'm fine, nothing to worry about."

A few other things come to mind.

Your motor is subject to the valve rotation TSB linked here:

http://www.wjjeeps.com/tsb/tsb_wj_0900303.pdf

The earlier coil rail motors were known to have an issue with the valves not rotating properly at high RPM, resulting in carbon deposits that then didn't let the valves close properly. A leak down test will detect it, but a simpler compression test may not. The TSB requires you to clean the combustion chambers with Mopar Combustion Chamber Cleaner and then manually rotate the valves.

With this in mind, before attempting to perform the TSB, you may get immediate results out of the simple steam cleaning procedure described here:

https://www.cherokeeforum.com/f30/st...-4-0-a-226299/

That's basically the same thing as using the Mopar Combustion Chamber Cleaner, just with water instead of chemicals. The steam cleaning procedure may clear out enough carbon that you don't need to physically rotate the valves. If the problem comes back, you can always get in there with a valve spring compressor later.

These motors have some other spring issues, so you might also consider pulling the valve cover off and just inspecting for damage. My persistent cylinder 6 misfire turned out to be a broken spring. The spring was causing it to run rich and lean alternately, resulting in a bizarre half-black, half-tan plug.

Bugout4x4

Fantastic knowledge shared here... Thank you.

cruiser54

I moved this thread to Grand Cherokee tech....

dave1123

You about covered it, Shaky! I KNOW I'd seen that FSB somewhere before, but couldn't put my finger on it! You can reduce that carbon buildup by installing an oil catch can in the CCV line, which I'm about to do.