start prob. please help!

[afjeep2082]

alright I did some searching and found few few answers but not enought to satisfy me to the point of tearing the jeep up quite yet. first off I have a 1993 cherokee sport,4.0L, auto trannny, fairly new motor (roughly 20,000 miles on it).

My problem is I was driving to the store and out of no where the engine dies..I still have eletrics but no engine. I got it to a safe place and tryed to re-start it, the engine will crank but as it cranks it intermittently backfires both through the intake and exhaust manifolds, it seems like at times it wants to start but it never starts. I did have a fault code 41, but I think it's an old code that never got cleared. Through my searching I thought maby I threw the timing chain, so to check I manualy turned the motor and watched to see if the distributor rotor turned aswell, and it did. So I'm not sure how possable it is that the chain could have all-of-a-sudden skipped a tooth or something. I'm hopeing it won't be down for more then a week since it's a DD...so if you guys have anyideas let me know asap! thanks..

 

[n5xl]

First, you need to verify that your coil is fine. Do an ohm check on it and see how it does. Make sure that your CPS is plugged in securely and the wires are not melted. If that checks ok, you might want to verify that the rotor on the distributor is pointing to number 1, when number 1 is on TDC on the compression stroke.

 

[afjeep2082]

I checked it out with a spare coil that I have and it did the same....wires and such are good. I know what your saying about the distributor but can it just all of a sudden move out of location?

 

[old_man]

The most common fault in this situation will be the cps. Don't worry about a skipped tooth or chain. That causes a whole different set of symptoms and is so rare as to not figure into the possibilities..

 

[afjeep2082]

yeah, i would have thought the cps as well but it is pretty much new...about 3 months old and when it went out it just cranked and that was it, mine has a nasty intermittent backfire now when I crank the engine..doesn't sound good whatever it is.

 

[afjeep2082]

Figured out the problem! Turns out the distributor gear was striped, causeing the rotor not to rotate. My next question would be how does this happen?

 

[8Mud]

Are the gear teeth chewed up? If so the distributor gear is only half of your problem, the gear drive on the cam is likely chewed up also.
I've never seen this on an XJ, but the most common cause is a broken gear tooth that jammed in the gears and pretty much tore up everything else.
There is usually a shear pin holding the gear on the distributor shaft that will shear before things get torn up too bad (hopefully).
If the hold down for the distributor is loose, it can cause gear tooth damage.

 

[afjeep2082]

the hold down was loose so I suppose that was the problem....I did inspect the cam gear and it looked fine

 

[afjeep2082]

I have another qwuestion when installing my new distributor, since obviously the rotor position on mine isn't reliable to use as a referance mark (because it was sliping) can I use a compression gauge to determine tdc? I tryed with my thumb but it's so cold outside I can't feel anything anyways. and if I can how do i read it? I also found a top dead center locator tool ( http://froogle.google.com/froogle_c...G=Search+Froogle&lmode=&addr=&scoring=p&hl=en)
), I understand how it works but is there adjustment needed on the tool for different engines?

 

[8Mud]

I put the compression gauge on number one and turn the motor over by hand until to starts to build compression, then line up the timing mark. The timing mark is on the inner part of the harmonic balancer and hard to see, I usually extend it to the outer ring with a crayon, then align it. If your not sure, do it again a few times till your confident you have TDC compression number 1.
Turning the motor over by hand doesn't produce much compression, so if your results are questionable, you can blip the key to start and watch the compression gauge. It usually takes a couple of tries, as it will invariably go past TDC, before you can get the starter stopped.
My TDC indicator tool is a slight curved piece of welding rod stuck down the spark plug hole, you can tell within 0.020-0.030" if it's at TDC, or not. But all this actually does is double check your timing marks.
Turning the motor backward by the harmonic balancer center bolt, can loosen the bolt (I do it, but very gently). Removing all of the plugs, makes turning by hand a whole lot easier. If you go past TDC, back up a ways and make the last movement to TDC alignment clockwise, looking at the front of the motor or go through the sequence again. There is play in the timing chain (and other places) and it's possible to be quit a ways off, if you try to align the timing marks turning *against* the standard rotation of the motor. You want to turn and align the timing marks, turning the same direction as standard rotation of the motor.