### Taking no credit, just reposting since post#1 has been /dev/nulled.
### Pulled from the Wayback Machine, dated 10/29/2013.
### Original author - JasonStebbins
Common ZJ Problems / Tutorial On How To Fix Them
I was inspired to do this by another thread "12 Things To Do When Your ZJ Stalls" posted by ZeeJay1997.
1. Erratic shifting/Long shifts/High revs
There are a few things that can cause these transmissions to act crazy. Start by checking the fluid. The transmissions are very picky about being even a little bit low. Have the Jeep running warm in neutral. You will not get the proper reading in park or when it is cold.
Second, adjust the TV/Kickdown transmission cable. It is located directly next to the throttle cable above the valve cover. A kickdown cable with too much slack or too tight will result in early/late shifting and can damage the transmission. Here is a great write-up on how to adjust it.
Third, change the filter and put in fresh fluid. A clogged filter or burnt ATF+4 will not cooperate very well with the system. The filter is held on by three Torx T-20 bolts.
Fourth, swap out the Governor Pressure Sensor and Shift Solenoid. These sensors commonly go bad and can cause problems that will make you think you need a transmission rebuild. They are easily accessible by dropping the pan. I replaced my Solenoid with the upgraded Borg Warner unit.
Fifth, completely replace the TV/Kickdown cable. I have read on the forum that people have done this with success. It is a few feet long and can stretch out over time. Also check where it connects to the transmission as the connects can come loose/become disconnected.
Sixth, test and replace the TPS (Throttle Position Sensor). This sensor is directly linked from the transmission to the PCM and will cause shifting issues if the voltage is incorrect or the sensor is faulty.
Seventh, have the bands adjusted. This is a bit more in depth and should only be done if you are confident in your skills. Mis-adjusting these bands can do more bad then good if not done properly.
2. Erratic/High-Low Idle
Clean and remove the IAC (Idle Air Control). This little guy can cause the Jeep to run rough if there is carbon or dirt build up on the needle. It should be cleaned regularly as part of regular maintenance. It is held on by two Torx T-20 bolts. It is located on the side of the throttle body. Don't forget to clean inside the housing it mounts into. Here is a great write-up on how to remove and clean the IAC.
Second, remove the air intake tube and thoroughly clean the throttle body and butterfly. This can get dirty with carbon build up and grime just like the IAC. Spray carburetor cleaner or SeaFoam on and around the throttle body and wipe it clean. Running seafoam through the intake while running can also clean out they system. I do this every couple months.
Third, check for vaccuum leaks. This can be done by putting soap and water in a spray bottle and applying on all hoses. A pinhole or crack will bubble letting you know it is dry rotted or damaged.
Fourth, check and/or replace injector o-rings.
3. Dome Lights Stay On
Start by checking the dimmer switch next to the headlight switch. It activates all interior lights if it is pushed up all the way and can get bumped easily when getting in or out of the Jeep.
Second, check all fuses in the kick panel and under the hood. This process only takes about five minutes and a lot of the time you may find a blown fuse that could control other accessories as well as the interior lights.
Third, check all four of the black door "buttons" that are attached to the body of the vehicle. These can commonly get stuck in or get unplugged from the sensor. Sometimes they may need an O-ring to keep them from being pushed in too far. There is also one in the cargo area, I'm not exactly sure of the location.
Fourth, check the relays in the fuse panel. A faulty relay will not trigger the lights to go of after the allotted time. Swapping in a working relay is the easiest way to rule out a faulty switch.
4. Rear End Clunk
There are a lot of things that can cause this. Start by checking the U-joints on the drive shaft. Any excess movement in the joint is bad. Do this by grabbing the shaft directly in front/behind the joint and chocking it in each direction.
Second, make sure your caliper bolts are tight. Loose bolts will allow the caliper to move back and fourth on the knuckle and make an unwanted noise. Since you are already back there, make sure the grooves on the knuckle where the brake pads mount are not worn out. This will cause the pad brackets to slide back and fourth.
Third, check the condition of your upper and lower control arm bushings. The upper bushings seem to get neglected and once the rubber is completely worn, the metal sleeve will make contact with the arm.
Fourth, remove the rear drive shaft and fill the slip joint with grease. The slip joint is where the splined part of the shaft connects to the transfer case. The grease will dry out/squeeze out over time and will make metal on metal contact/excess movement. I use Lucas heavy duty grease.
Fifth, check the condition of your shock mount/bushings. Like any other bushing, once the rubber becomes too dry rotted/crushed, it will allow the metals to make contact with each other.
Sixth, check the condition of your transmission mount. It is a large piece of rubber wrapped in steel and once it wears out, it will allow a lot of movement in the drivetrain. It is a pretty easy replacement. Remove the cross member and hold up the transmission with jack stands. There are four bolts that hold it on. I replaced mine with the Anchor brand.
Seventh, check your exhaust hangers and bushings. You would be surprised how many people think they have a mechanical issue when it turns out to be the exhaust pipe banging on the sway bar or oil pan.
Eighth, inspect and replace the transfer case chain. This happened in my first ZJ. The chain stretched out and would clunk from a dead stop before it tightened up and engaged.
5. Front End Clunk
Start by checking the sway bar links and bushings. They are the easiest and cheapest place to start. Any up and down movement is bad. That means the ball inside has come loose. The sway bar wallows out the bushings over time.
Second, check the tie rod end and drag link end for a bad joint. Up and down movement is a bad thing.
Third, check the track bar. The bushing on the axle side can wear out or the undersized bolt can wallow out the hole allowing the bar to move back and fourth. The ball joint end can also fail just like any other.
Fourth, check the ball joints. A dead giveaway for a bad ball joint are collapsed boots or loose steering.
Fifth, check the U-joints on the axle. Chock the axle up and down to check movement in both directions.
Sixth, check the U-joints in the drive shaft. The double cardan unit contains two joints that work with a ball/spring mechanism inside. Here is a great write-up on how to rebuild the double cardan assembly.
6. Knocking On Cold Starts
If you have the 4.0L you probably have piston slap. It comes equipped with it from the factory, so just get used to it.
Second, inspect the flex plate. It is part of the transmisson in between the tranny and oil pan. Remove the three bolts holding on the inspection cover and you will have access to these bolts. There are four bolts that hold it on and commonly come loose or wallow out the holes causing a knocking/clanking sound. Remove the bolts and apply thread lock and tigten them back down. The flex plate itself can also get cracked and will need to be replaced altogether.
Third, replace the spark plugs. Bad detonation due to fouled plugs can cause a scary sound as well.
7. Sagging/Thumping/Uneven Door
Everybody loves this. You will be hard pressed to find a driver's ZJ door that doesn't have this problem. The door pins that hold the hinges on eventually go bad and will cause the door to sag and thud when it opens/closes. The super cool pin striping plus up and down door movement is the easiest way to notice the problem. Here is a great write-up on how to replace the pins.
8. No Intermittent Wipers/Won't Go Back "Home"
This is a very annoying problem. Start by checking fuses in the kick panel and under the hood.
Second, replace the intermittent wiper control module velcroed under the driver side dash or under the removable grille under the windshield. It is a little black box and the wires run to the steering wheel or wiper motor. Also test and replace the intermittent wiper relay in PDC (Power Distribution Center).
Third, replace the multi-function switch. I had to replace mine twice. The steering wheel bezel is held on by three T-25 torx bolts. The switch is held on by two tamper proof T-25 torx bolts.
Fourth, replace the wiper motor. It is located under the removable grille under the windshield.
9. One Or More Power Windows Not Working/Off Track
Start by making sure the master window lock is off. You would be surprised.
Second, the most common issue for these symptoms are the wires in the driver's door jamb. When the door is opened all the way the wires get stretched past their limit and break. Take off the door panel and remove the large black clip near the hinges that holds the wires in place. Pull the wires out as far as you can and check for exposed/broken wires. In my case a yellow wire was broke and that was my problem for the passenger front window.
Third, check the wiring in the other three doors using the same technique.
Fourth, replace the window switch. Take off the door panel and remove the two phillips screws that hold on the small black box that the switch is attached to. Swap in a working switch to rule it out. Trial and error is a good thing.
Fifth, take off the panel and verify the window is still in the track. I had to crimp the bracket back together in order for my window to stay in the track. A bad motor or regulator may need to be replaced as well.
10. Coolant Leak
Start by checking the radiator hoses. They dry rot and can get damaged from constant heating/cooling. If replacing the lower hose, make sure to re-install the spring inside so it does not collapse. I would replace the OEM alligator clamps with the worm type to ensure a tight connection.
Second, inspect and replace the thermostat/water pump gasket. If the water pump is leaking from the weep hole, it's time to replace the whole unit. There is also a hard line running from the driver's side of the pump to the block that has an O-ring that can fail over time.
Third, inspect the radiator. Broken/smashed fins or cracks in the sidewalls will cause a leak.
Fourth, inspect the hose that runs from the radiator cap to the reservoir. Mine managed to wiggle loose and was seeping fluid and then the fan blew it everywhere, making it hard to pinpoint where it was coming from.
Fifth, inspect the timing chain cover gasket. This leak is hard to diagnose because of the location.
Sixth, inspect the transmission cooler lines that attach to the radiator. The quick disconnects are plastic and eventually wear out. I used some Copper RTV and smeared it all around the connection point with great results.
Seventh, check your oil. If it looks like a milkshake, you have a blown head gasket. Sucks to be you.
11. Transmission Fluid Leak
Start by checking the steel lines that run from the radiator. One of mine near the "frame" rail got cracked while wheeling and was spewing fluid. I cut about one inch off the line and replaced it with high pressure fuel hose with worm clamps. Been going strong for almost four years now.
Second, inspect and replace the transmission pan gasket. Don't be intimidated to drop the pan. It's a matter of 13? bolts, but you will smell pretty for the next few days. When re-installing the pan, do not over torque the bolts. They only require a minor tightening or else you will warp the pan and create more problems.
Third, inspect the transmission output seal where it connects to the transfer case. This repair is more advanced and should only be performed if you are confident in your skills.
Fourth, check the plastic connectors that snap into the radiator. The elbow of the hoses can also become brittle and spring a leak.
12. Sloppy Steering/Wandering
Start by checking the steering box adjustment. Here is the TSB on how to do so.
Second, check the condition of the ball joints. Worn or broken ball joints not only will cause loose steering, but also is not safe to drive.
Third, have a trustworthy friend turn the steering wheel back and fourth to full lock in both directions. Look for slop in any of the front end components.
Fourth, burp the power steering system. Do this by removing the cap and with the engine running, turn the wheel back and fourth several times to full lock in both directions.
13. Overheating Issues
Start by replacing your thermostat and water pump. They are easy wrenching and the parts are cheap. 195 degree thermostat.
Second, check and replace the fan clutch. Chuck the fan back and fourth. Any movement is bad and can cause wear on the water pump bearing. Also, if the fan spins more then a third of the way around cold, it needs replaced.
Third, flush the coolant system. There is a plug at the bottom of the radiator that makes this an easy process. Please don't do this while engine is warm.
Fourth, replace the radiator cap with a new 18 pound cap. The spring can become faulty and cause improper flow. Coolant bubbling in the reservoir is a good way to tell if the cap needs replaced.
Fifth, clean both sides of the radiator. Mud/bug/debris filled fins will not allow proper cooling.
Sixth, burp the cooling system. If there is air in the system it will wreak havoc on the flow. Do this by parking on a steep incline and let the engine run from a cold start for the few minutes with the cap off.
Seventh, for slight overheating at cruise you're looking at a clogged catalytic converter. Low engine vacuum at cruise and high back pressure caused by the clogged exhaust leads to a build-up of heat and pressure in the engine.
14. Oil Leak
If you own a ZJ, you know all too well about oil leaks. The three notorious leaks are caused by bad valve cover gaskets, the oil filter adapter and the rear main seal.
The valve cover gasket is a very easy replacement. The only hard part is clearing the firewall to remove the cover and tightening the rearest bolts on re-installation. You might as well replace the PCV valves while you have the cover off. The oil filter adapter has three O-rings that dry rot and cause the leak. You can tell if they are bad if your starter and oil filter are covered in oil. You will need a T-60 torx to remove the adapter. The rear main seal is a bigger job, requiring the oil pan to be removed to gain access. Here are two great write-ups on the oil filter adapter and rear main seal.
15. Clicking On Sharp Turns
This is a bad CV axle. To replace the axle, you will need a 36mm nut to remove the axle nut, a 12 point socket to remove the three hub assembly bolts and a 10mm socket to remove the caliper. The axle just slides out. I used a Shop-Vac to clean out the axle tubes.
16. Parasitic Drain
Start by checking fuse #7 in the kick panel. This seems to be the most common problem.
Second, remove the BCM (Body Control Module) and repair the solder joints. This black box under the driver's dash controls most of the interior electronics and can cause all sorts of strange problems including battery drain. The instrument/gauge cluster is commonly causes this drain due to a faulty BCM. If it can't be repaired, replace the entire unit.
The grommet for the rear wiper on the hatch enjoys letting water in and faults the switch, also causing a drain.
17. Groaning/Whining Upon Acceleration/Deceleration
This is usually caused by bad carrier bearings or gears in the front or rear differential. Unfortunately this is an advanced job since there are exact preloads and shimming required.
18. Belt Squeal/Chirp
This is personally the most annoying problem I have encountered. Start by replacing the serpentine belt. Stay away from the cheap belts that are sold at your local parts store. I went with the Bando brand. They are the OEM manufacturer for belts for most vehicle makes and models. The GoodYear Gatorback belt also has excellent reviews on this forum.
Second, check the tightness of the belt if you have the 4.0L There are so many people that throw money at their ZJ because of a loose belt. To tighten the belt, loosen the 15mm bolt on the idler pulley below the power steering pump. Then tighten down the long 15mm bolt behind/to the left of the pump. Re-tighten the 15mm bolt on the idler pulley and you are done. There should be around 1/4" of play in the longest part of the belt.
Third, replace one or more of the idler pulleys. The bearings commonly go bad and they are simple and cheap to replace with a 15mm socket.
Fourth, check and replace the alternator pulley or A/C compressor pulley. The bearings can go bad like any other and will cause an annoying squeal.
Stay away from belt dressing. I use motor oil during the summer to keep the belt from dry rotting and cracking.
Fifth, watch the belt while revving the engine. If you notice the pulley portion of the harmonic balancer moving in and out, check the rubber grommet for excessive wear or damage. Inspection of the grommet will show that it may be on it's way to coming apart. The isolating rubber will be bulging out and may be able to be peeled off. This is not a good thing. With a short harmonic balancer puller, it can be pulled out without removing the radiator.
19. Sluggish/Bogging Down/Stalling
There are several things that can cause these symptoms. Start by checking the fuel pressure at the rail. I bought a kit on eBay for $35.00 shipped or you can rent one from your local auto parts store. It should be 48psi +/- 5 on the 1996-1998 models and and about 32psi on the earlier models. A clogged filter or failing fuel pump will cause running problems.
Second, replace the upstream oxygen sensor. If the sensor is giving off incorrect readings the fuel/air ratio will be incorrect and your ZJ will run rich or lean.
Third, replace the catalytic converter. A clogged or collapsed converter will restrict air flow and reduce back pressure causing sputtering/stalling issues.
20. No Air/Only Certain Speeds
Start by replacing the blower motor resistor. It is a small unit to the left of the blower motor made of some type of ceramic/porcelain material. They often burn out causing no air or low/high speed only.
Second, replace the blower motor. It is held on by three Phillips screws. I take mine out once a year and clean all the leaves and debris that build up in the filter.
Third, replace the climate control unit. The soldering can sometimes be repaired but usually the unit shorts out or fails completely.
Fourth, a broken vacuum line at the firewall tee next to the A/C lines is a common cause of air blowing only out the defroster vents.
21. Tailgate Won't Open/Rattles
We all love this one. Remove the door panel and locate all the rods near the locking/latching mechanism. The long threaded rod should be clipped into the small white piece of plastic. It commonly falls out and this is what the outside handle connects to, activating the mechanism. While your in there, check to make sure it is well greased. Mine was all dried out and starting to rust.
As for the rattling, start by replacing the tail gate stoppers/bumpers located on the left and right side of the door. Dorman part #45390. I get a set once a year off Summit Racing. They seem to crush and rot fairly quickly around here with six months of winter. You can also adjust how far out or in the stoppers sit by using a 10mm? wrench and tightening/loosening the bolt. I've learned that if you tighten them too much, this will also cause the tailgate to stay shut.
22. Heated Seat Repair
The actual problem occurs in the wiring inside the seat cover. This sounds like an unfixable problem but it's surprisingly easy to get at. There are two heating elements (small thin wires looped through the seat cushion) in the seat. The one that breaks is the one on the outside edge of the seat. This makes perfect sense if you think about it. Every time you get in and out of the Jeep you put a lot of wear and tear on that outside edge. There are two heavy gauge wires coming up into the seat and they are soldered to the thin wires about 2/3rds of the way back from the front of the seat. In both cases, the break in the thin wire was within a few inches of the solder joint.
Before you get started with this verify that this is the actual problem with your seats. Find the relay under the seat and remove it and test for continuity between the black/orange and brown/black wires. If it tests good then the break may be in another element. The wiring diagram at the end of this article may help. They are wired in series so if one breaks the other won't work either. Odds are pretty good the problem is in the seat. Here is a great write-up on how to repair your heated seats.
23. Replace That Sagging Headliner
Chances are your headliner is sagging in your ZJ. Whether it's under the windshield or above your driver's window, it will eventually happen to all of us. Instead of using thumb tacks to hold it up, you might as well replace the entire thing with the OEM unit or aftermarket fabric of your choice. I have seen some pretty cool headliners including RealTree fabric and custom Jeep logo fabric on the forum. Here is a great write-up on how to remove and replace the headliner.
24. Headlights Flickering/Interior Dimming Issues
Do your headlights have a tendency to flicker or your instrument gauge/VIC/Hvac controls dim feature go whacko? This is caused by a faulty headlight switch. The soldering can go bad or the terminals can burn out. Here's a great write-up on how to fix this issue.
Re-soldering the VIC can also fix the (Coolant Temp Sensor) problem that a lot of people run into.
Re-soldering the PCM can also cause stalling/starting/running issues.
25. Rear Wiper Motor Dead/No Delay
Does your rear wiper motor work? Mine either. The rear motor seizes because water leaks into the shaft of the wiper arm, corroding it. The motor will slow down over time and do one of two things; burn itself out or move partly then stop. I just took mine off and put a rubber plug in the hole. But if you enjoy using it and don't want to spend a small fortune on an OEM Mopar replacement, here's a great write-up on how to diagnose and repair yours.
26. ABS Light On
I prefer not to have ABS on my Jeep, but for anyone that does here are some common causes for the light. Start by checking all four wheel sensors and magnets next to the tone rings on the axles. The wiring and lines can break, especially if you go wheeling a lot. My right front passenger harness was broke in half upon inspection.
Second, replace the ABS module under the hood. www.RockAuto.com
has Cardone brand remanufactured ones for around $100 after the core.
Third, check all the fuses. If I remember correctly, there are two or three MAXI fuses under the hood and one or two in the kick panel. Even if the fuses are good, check to make sure the contact posts are clean.
Fourth, test the Hydraulic Control Unit (HCU) mounted near the driver's fender wall/firewall area. Removing the air box assembly and windshield washer reservoir will give you access to the HCU. Replace if necessary.
Fifth, check under the rear seat to ensure the relay/box is plugged in. Also test and replace the ABS pump under the hood.
27. Heated Seat/Power Mirror Memory Repair
Inside the mirror there is a sensor that tracks where it sits and this gets dirty and it screws up. Here is the fix.
Put the window down, as its easier to work. Take the mirror and tilt it down all the way. Carefully pull up on the mirror and it will unsnap from the housing. Lay it down on the door with a rag under it so as not to scratch the door. If you look there are four little tabs hooked into the plastic frame that the mirror attached to. Take a small flat screwdriver and carefully unhook/pry them out. Once you have them unhooked take and carefully put your fingers behind the frame and pull it off the pivot in the center of the motor assembly. Once that is off take and remove the torx screws holding the motor to the mirror frame. Holding it flat,take out the rest of the screws. There are two more under the little rubber "condom" that goes over the 4 little arms.Now VERY carefully separate the 2 halves. Make sure the arms stay in the motor!! Once you have the arms off you will see the little "fingers" against the little resistor strip. VERY carefully, and not mixing up the arms, take them out ,clean off the old grease from the strips in the motor and then clean up the "fingers" being careful as they are very easily bent. Bend them out a bit so they have good contact and then regrease them with dielectric grease.
28. Death Wobble
First, check both ends of the track bar. The ball joint end can fail or the bolt on the axle end can wallow out the hole allowing movement.
Second, check all the tie rod ends for damaged boots or play.
Third, get an alignment.
Fourth, check upper and lower control arm bushings, sway bar links and sway bar bushings.
Fifth, make sure nothing is bent. The tie rod, track bar, sway bar and drag link.
Sixth, replace your warped rotors.
Seventh, check for play in your ball joints.