Diagnose my new Jeep Cherokee!

[klaucke]

You may have guessed it, I now own (another) Jeep Cherokee. I just picked up a 1994 model, w/ the standard 4.0L I-6 engine, manual trans, 4wd, no bells and no whistles, and 140k miles. Problem is, it runs like crap. It does start and run, but it sounds like it's misfiring.

Up until now, I've heard nothing but good things about Cherokee's, in fact, I own one that runs flawlessly at 150k miles. I've been thinking it might have a clogged catalytic converter... or of course it might be electrical. I popped the distrubutor cap and rotor off and cleaned up the terminals with some sand paper, and I installed new plugs. I'd rather not spend $75 on a new cap, rotor, and wires unless I'm sure thats the reason it's not running right. Perhaps it could be the computer, I've heard of this going bad on a friends 2001 model.

Have you guys heard of any chronic or common problems with this engine? I know my way around a motor for the most part, basically, I just need to diagnose this so I can fix it. Fixing is the easy part. I just don't to throw money at possible solutions, I'd rather fix the specific one and nothing else.

Sorry I left my digicam in a friends car, so I can't post a pic. I will later though. Thanks in advance for any insight!

[Teutonics]

You may want to try a search at Jeeps Unlimited Cherokee forum. My '93 had a clogged cat at 115k but the symptom was SEVERE engine knock under acceleration, and loss of power (i.e. would continuously kick down into passing gear).

Hope that helps!

[asphaltgambler]

Those engines are very reliable, evry tough. Ours has 205K on the clock and it drives and runs great.

I would suggest a reputable shop to find what the specific problem is. Shouldn't be more than a hour's labor. If the shop has good techs it's money well spent instead of just guessing.

[johnco]

a loose vacuum hose left of the airfilter, right above and behind the power steering pump in that multiple port connector, caused mine to run terrible. the hard plastic hose was cracked right where it slips into the rubber connector. it took me quite a while to find it.

[klaucke]

I've had a similar little vacuum hose come off on my '88, causing a high idle and poor running, however, this newer motor (the 4.0 High Output) doesn't have that little collector of a bunch of tubes. I think I'm going to check to see if the throttle position sensor is in spec, I've just read these are problematic. Thanks for the replys, I may just do what AsphaultGambler said and have a shop who deals with these everyday diagnose it, then I can fix it.

[JSDSKI]

Throttle body needs cleaning - use Berrymans. Check vacuum lines. TDC sensor is a common issue. Best advice is to go to someone who is used to the engine because it will cut down on diagnosis expense.

[Jims5543]

I would give it a tune up. Plugs / Wires / Cap / Rotor. Then change the fuel filter / Air Cleaner and any PCV valves. I do this to any used car I buy first. I also do the betls and hoses but that is just my preferance. I usually drop a couple hundred on it right off the bat and then not have to worry about maintenance for a while.

If you think you have a vacume leak you can spray brake cleaner and you will hear the engine surge when you spray the problem area.

[klaucke]

Jims, the car was only $500 bucks and I am not about to toss a couple more hundred at it for stuff that isn't bad. I've never seen a cap or rotor go bad, and good plug wires last a LONG time. Belts and hoses are soft and uncracked. The air cleaner is brand new, I plan to clean the PCV when I change the oil this weekend.

As far as the vacuum leak, I don't think this is one, doesn't sound or feel like it, its not idling high or low so much as it is rough and bucky. Instead of using brake cleaner, I like propane - no mess.

[928ram]

Most (all?) Chrysler products from that era have a built-in system failure diagnostic; some of the code will pinpoint an exact component failure, some will be a "somewhere in this system" failure.
If equipped, the codes are retreived by toggling the ignition on-off-on-off-on then reading the flashes on the dash (normally the "check engine" light). The flashes are read as 2 digit numbers then referenced to a chart; like 5 flashes then 5 flashes would be 55 which is the "end of diagnostic" code. I'm sure the cross-reference for the codes can be found online somewhere.

[VaSteve]

I have a 99 and bought the Haynes manual. I was browsing through it the other day and found that it has a nice troubleshooting section in the front. I think I will pick one up for my 911 now as well.

Anyhow, if you don't have it, here's the list of stuff to check on. BTW, jeepforums.com is really good for body kits and such, I found technical knowledge a little lacking. Well nothing is as good as this site..

Here's the list:
Engine misses as idle
1.Spark plugs faulty
2. Faulty plug wires.
3. Wet or damaged distributor
4. Short circuits in ignition, coil or spar plug wires
5. Sticking or faulty emissions system
6. Clogged fuel filter and/or foreign matter in fuel
7. Vacuum leaks.
8 Incorrect idle speed or idle mixture.
9.Incorrect ignition timing
10. low or uneven cylinder compression
11. Choke not operating properly
12. Clogged or dirty fuel injectors.

Good luck!

[Wolf1]

Originally posted by klaucke

I've been thinking it might have a clogged catalytic converter.

I popped the distrubutor cap and rotor off and cleaned up the terminals with some sand paper, and I installed new plugs.

Have you guys heard of any chronic or common problems with this engine?

I just don't to throw money at possible solutions, I'd rather fix the specific one and nothing else.

Most likely its NOT the catalytic converter. Normaly plugged converters will cause a general loss of power and poor performance.

Replacing the plugs was a good idea, did the old ones look suspicious? Were there any signs of fouling or extreme wear? It would probably be a good idea to change the wires, cap and rotor also.

Common problems on this engine are most commonly excessive blow-by. This will force a fair quantity of oil into the air filter box and saturate the filter.
Another common Chrysler problem is the MAP sensor, these tend to fail regularly.
Chrysler products also rely very heavily on the O2 sensor, a sluggish or defective sensor will really affect the driveability of these vehicles.

Try the self diagnostics as mentioned previously, it may help to narrow it down.

When you do finally solve the problem I would highly recommend cleaning the throttle body and IAC passages. Pay particular attention to the butterfly and its mating surfaces in the throttle body bore. Then reset the adaptives, I usually do this with a scan tool but disconnecting the battery should do the job as well.

If all else fails a trip to your favorite repair shop for diagnostics may be a good idea.

Good luck.......

[klaucke]

There is no "Check Engine" light on. The 4wd light doensn't work either, so I suppose it could the bulb, although I doubt it. So I don't think the self-diagnostics is an option. My friend works at a GM/Chevy/Pontiac/etc. dealership, where I might be working on it Sat (in the warm), so is it possible to scan using a tool they may have? Aren't the Snap-On scan tools universal for a certain port?

My plan is to first clean the throttle body and the small sensor on it, possibly what you called the IAC?

I started it up tonight and it didn't sound that bad, its more of a sound of a misfire, an almost hunting sound, rather than a bucking/shaking vehicle type misfire. I doubt it's the wires, although I have heard the caps and rotors are bad on these 4.0's (not sure I believe it).

The old plugs were Autolite (ugh, I hate autolites) and 1 or 2 Bosch. I've had my Jeep get a bad plug, so I replaced these straight up (out of character for me to replace anything on a daily driver). The plugs were not the light tan color I was hoping for, but weren't bad. Only a very very slight black carbon coating. Rotor, cap, and wires are money I just don't want to spend.

I've been doubting it was the cat, and I'm going to replace everything from the cat back tomorrow (its all rotted and needs replacing).

I'll report back tomorrow with my progress!

[Wolf1]

Originally posted by klaucke
Aren't the Snap-On scan tools universal for a certain port?

The Snap-on MT2500 or the Snap-on Solus will work for this.

[Staylo]

'94 is OBD1. The amber check engine light should flash if the 02 sensor is bad, but still worth checking. Mopar sells their own kick a$$ throttle body cleaner. Might want to warn your neighbors first. What transfer case is it?

[klaucke]

I cleaned the throttle body and IAC, it seemed to help. Looks like it was just a plug wire... I started pulling them off one at a time to see which one didn't make a difference. Only got shocked a couple times. I still need to do the exhaust, and I plan to do a fuel rail/fuel injection cleaning, cooling system flush (have to do a thermostat too), and of course change the oil. Turns out the whining I heard when I drove it home was just a huge lack of tranny fluid! No wonder the syncros feel beat.

[klaucke]

To answer your question, Staylo, its the NP-231 transfer case. I did a fuel rail cleaning, oil change, fixed the exhaust, however, it still idles rough. I'm going to try and check for some more vacuum leaks, however, I think the temp sensor is bad, so perhaps too much/ too little fuel is being metered at idle because the computer thinks the engine is hot or cold when it's not. My guage is wacky. Everything above idle seems smooth and normal.

For now, my tranny is leaking terribly, so I'll have to try and fix that. I think it might be the output seal (where the tranny meets the transfer case), however, it looks like it might be from the bolts where the tranny bolts to the crossmember. I'm sure I'll find out.

[Staylo]

Sounds like you are on the right track. I will bet that your tranny is leaking from the output seal.
As for the idle, continue to look for vacuum leaks. Cracked exhaust manifolds are not uncommon on the 4.0 I6. Check around the flanges well.
IIRC, the 231 command-trac is the base model PT 4x4, the light may not come on when engaged as it does with the 242 select-trac. Put it in PT and do some slow circles in a parking lot, you will know if it is engaging or not. Good luck.

[klaucke]

My tranny wasn't leaking from the output seal... IT WAS CRACKED. Thats right, someone sold me a car w/ a cracked transmission. Oh well, when given lemons, make lemonade: $250 bucks and a couple afternoons work = new 5-spd in my Cherokee. I dropped the tranny, transfer case, and front drive shaft all as one assembly, and installed the tranny alone, then bolted up the transfer and front drive shaft. Its a little tricky supporting that all when you're trying to bolt the cross member up.

Pics:
New tranny from a auto recycler:


Transfer case and front drive shaft, to be connected under the vehicle:


Bolted up to the bell housing, still supported by $15 yard sale tranny jack (this tool is invaluable for jobs like this, and when hooked up to an air impact wrench (instead of hand rachet) it's super quick up and down):


Other side:


And the $500 special (now more like $900 after fixing):


Believe it or not, it's now for sale, but I can sell it with a clear conscience. If it doesn't sell at 2300 or more, I'll just keep it till winter and have fun with it. Hope you guy enjoyed the pics, thanks for the prior help.

[johnco]

I just cranked up one of my jeeps that has not been run for a year or 2. It started fine but had a rough idle, like it was missing on a cylinder or 2. while checking injector connections, I bumped the plug for the sensor mounted on the firewall above the engine. problem solved! I replugged the connector and it runs perfect now. I may be wrong, but isn't that the map sensor? anyway, it doesn't miss anymore. just a loose connection.

[Vonzipper]

I really enjoy the Grand Cherokee, although I've done a few mods...