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Already searched: Timing chain question?!?!

JeepDawg

NAXJA Forum User
Location
New Jersey
1985 XJ, 2.5 4cyl 160,000 mi.

My jeep has been stumbling, shutting off, acting up, etc....but at the same time, it idles beautifully! Also, I can drive it for short distances....and I feel like I'm in XJ heaven! But invariably, it acts up!

I changed the fuel pump, fuel filter, dropped in a K&N filter, and ran like two bottles of Techron through it.

Then after all this.....along with having the vacuum lines checked....it began with this new behavior.

A mechanic told me that it was the timing chain....in which case it may require more work than I'm capable/prepared to do. Is there any way to verify this? I read something about taking off the distributor cap....but could you be more explicit? I'm a beginner... Also, how hard is it to get something like this fixed?

I've invested blood, sweat, & tears into this thing... Since it's become unreliable....and it's our only car.....I'm looking for another XJ. But I'm debating about keeping it as a project... I've had so much work done....and the interior is immaculate! Do you think it can be brought back to life? Anyone have success stories....where their XJ became trouble free again.....after all the work?

OK...I realize a lot of questions. My mind is going in a million directions at once. First things first....the timing chain.. Many thanks!!!
 
A quick way to check -

1) Take the distributor cap off.

2) Turn the crank nose bolt backwards (should be anticlockwise) just a bit.

3) Reverse your ratchet to turn clockwise. WATCH THE ROTOR - mark the distributor housing if you have to! SLOWLY turn the crank nose bolt forwards until the rotor just starts to move, noting how much you have to turn the thing.

Ideally, you should see the rotor start turning right away - realistically, having the rotor start turning after you turn the crank 3-5 degrees is acceptable.

HOW THIS WORKS - when you turned the crankshaft backwards just a bit, you put the "slack" in the timing chain where it would be taken up driving normally. Also, since you don't know the resting condition of the chain, you are ensuring that ALL of the slack ends up on the "drive" side of the chain, so you are seeing ALL of it, and not just part of it. The distributor rotor turns once the camshaft starts to turn, and the camshaft starts to turn once you've taken up all the slack in the chain.

This is not quite accurate, but it allows you to assess the condition of the timing chain without tearing down the front part of the engine...

5-90
 
JeepDawg said:
1985 XJ, 2.5 4cyl 160,000 mi.

My jeep has been stumbling, shutting off, acting up, etc....but at the same time, it idles beautifully! Also, I can drive it for short distances....and I feel like I'm in XJ heaven! But invariably, it acts up!

Mechanical parts of the engine rarely cause erratic behavior in your engine such as what you describe (vaguely, I might add, be more specific). If your timing chain was indeed loose, I suppose it could cause enough timing problems to cause stumbling, shutting off, etc., but I think I would be looking into some of those electrical gizmos that control a lot of those types of things. CPS, TPS, MAP sensor, these are all things that control how that engine runs. I would start hunting around for those types of things, but that's just me.
 
Yah - but not knowing how old the electronics are - the timing chain is probably original - and since some "shop monkey" told him it was the timing chain, I though I'd give him a way to check that first.

Besides, I've seen odd things happen with old timing chains - although the RENIX engine management system is quite adaptable. I once turn the distributor in my 87 180* EACH WAY while the engine was idling, and you wouldn't know it from the sound. Timing wandered all over the place, but it idled nice and smooth.

It's probalby not the timing chain, but I hadn't thought much about what it COULD be just yet... CPS is usually an "all or nothing" affair, and the engine can actually run without the SYNC sensor.

More symptomology, please?

5-90
 
Thanks for the insight thus far... But isn't Renix 87-90? I don't have fuel injection. It's a carbureted engine...

The symptoms are as I described. It idles really well.....but it stumbles somewhere in 3rd gear. I really don't have much time lately.....which is why I went to this mechanic. But I'm going to check the spark plugs.....just to see..... Is it possible that bad spark plugs could cause this type of problem?
 
RENIX was used until the end of the 1990MY on AMC engines in the XJ and MJ - if it didn't control fuel injection, it still controlled ignition and timing. So, you should still have RENIX. Take a close look at your ignition module - it should be divorced from the engine, the coil should be mounted directly to it, and you might even see "RENIX" cast or stamped into it.

GM V6-60 engines were all OBD-I complaint, RENIX was/is not.

Spark plugs? Iffy. Does it only do this in 3d gear?

While you're about it, I'd probably check the distributor cap - inside and out - for "carbon tracking," which could cause high-voltage leakage and loss of power or difficulty accelerating. Just a thought - but I'd also see if the problem could be replicated in ALL gear ranges, or even in Neutral (automatic/manual) or Park (automatic only.)

5-90
 
lol....we all get so used to working on the 4.0 that we forget that the early xj's were carburated.Speaking of did you clean the carb?
Wow that sounds weird if you say it out loud!!
 
Stick or auto? This is a carbureted engine and there are not a whole heck of a lot of sensors and electronics to check out, certainly compared to later 4.0 systems.

I have the same engine w/5-speed in my '85 and had similar symptoms (as reported so far) a year and a half ago at 270,000 miles. I was preparing to replace the carburetor anyway so went ahead and did that along with distributor and fuel pump. No change. During this time the timing chain and tensioner also went south but in my case there was no question about the chain with the noise clearly coming from the front of the engine. I changed these out, again with no cure. I did find water in the bowl a couple of times and added several bottles of Heet. Long story short, after about four months of intermittant problems, I was in town one morning when hesitation started again. I stopped at the parts house, got a second or third new fuel filter, installed it on the spot and haven't had a problem since. I can only assume I got a really bad tank of gas with a lot of water originally but don't know if this is logical given the length of time it went on. One day during this period I drove ~180 miles city and highway with absolutely no problems until nearly home. Stopped for a train and when starting forward, the engine choked, hesitated and nearly died for several minutes on the side of the road before clearing up and running normally several miles on home. Forgive the long ramble but you asked for a success story and I just wanted to give you one scenario.

In any event, I agree with RedHeepOjeep that the timing chain is not the likely culprit.

Have you checked EGR and O2 sensor? I believe that a bad EGR would primarily affect idle but someone correct me if I'm wrong. Also, as far as you know does it have the original (or replacement) Carter YFA carburetor?

Await further symptoms.

Bob
 
im going trough the same crap w/ my 88xj...it stumpled and had blow back into the airintake. I replaced the plugs, wires, rotor button, cap, coilpack, throttle positioning sensor, crank positioning sensor, fuel filter, fuel pump, and battery..then ran like brand new for one night...would not start next day. unhooked the battery to reset comp to see if it was sensor prob, wasnt. so tomm im cutting the cat off the exaust.. i think its clogged, its the original and i smell sulfer some in the air( it smells like rotten eggs) mine is fuel injected, but i just wanted to give you an idea of probably what not to do to save you money. if this doesnt work for me tomm ill let you know, i hope for your and mine sakes that its not the timing chain. that gets $$$
 
No question about the o2 sensor -- there is one.

I've never heard this referred to as a Renix system. I don't know if there were any variations during the model year but my coil is not mounted to the ignition module (a Wells unit mounted on top of the wheelwell near the starter relay). The coil is the classic round design that has been around forever mounted on the wheelwell near the distributor.

I believe the ECU on these 84-85 MJs and XJs was for most practical purposes used after warm up and when not at WOT to control the feedback to the various carburetors (Carter in the XJ) using input from the o2 sensor. I've changed to a Weber carb and taken the computer completely out of the fuel/ignition systems. (Just to make a point, I am not particularly proud of losing the attendant pollution control functions but this truck currently sees limited use and I want to ultimately convert to an EFI system .)

Third gear only? A choke that is not opening completely will cause poor performance above idle. If there is any question about this, you can tie it open with a bit of wire and see how it runs. To state the obvious, just be sure you don't drop something down the carb throat. Checking the wiring has been covered several times on the forum, by Old_Man in particular, but essentially you want to make sure there is good contact at the carburetor with the wire that runs from the relay near the starter relay. I went through this and finally discovered the relay had failed.
 
Thanks everyone for your thoughts and insight!!! Yes, it has a replaced Carter YFA carb. It's also a manual trans.

Recently, it started acting up in all gears... But then yesterday, it acted fine.....although I only drove it a short distance. I'll try some fuel system and carb cleaner....to see if that has an effect....and I'll try to check all the wiring/sensors....
 
FWIW, I've got a sloppy timing chain (or bad tensioner) on my 87 2.5 MJ, 170K miles on it. It's been clattering for about the last 25K miles. Lotsa blowby, but it still pulls good:)

Mine had similar symptoms as yours a while back after I had it off the road for over a year.....would start good, idle fine, and run great but randomly cut off/stumbled. I traced it down to the o2 sensor, so I swapped it out for a new one, but it still acted up unless I disconnected it, then it ran fine. So I ran with it discoed for about a month or so, and one day on a whim I reconnected it and it's been fine since :dunno:

Don't quite know what was exactly wrong (I hate that!) but it runs, still. Next time yours goes into a fit, if you can, try to disco the sensor to see if that clears it up.

HTH,
Jeff
 
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