The usual suspects, common problems with the XJ and what *usually* fixes it.

Time and time again I see threads come up on the same subjects, hopefully we can get together a post with enough keywords in it that this one compendium of troubleshooting will come up on a search result easily.


So, let's try to A.) keep on topic, and B.) try to use wording that will make this post easily searchable. try to remember that 3 character words will not be found by the vBulletin search engine.

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Probelm #1: No spark.

Most likely cause: failure of the Crankshaft position sensor, commonly referred to as the CPS or CKPS. Inspect wiring to the sensor (which is located on the upper drivers side of the transmission bell housing) for melted or damaged wires, inspect connector(s) for corrosion or damage, test resistance and voltage with digital multi-meter. Replace if out of spec. Hopefully someone will post the CPS testing procedures for the renix and HO versions of the CPS.

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Problem #2: turn the key, nothing happens.


Most likely cause: corrosion inside the Neutral Safety Switch, commonly referred to as the NSS. This sensor is located on the passenger side of the transmission, and tells the ECU that the transmission is in either "park" or "neutral" and it is OK to start the engine. Telltale sign that the NSS is starting to fail is the loss of reverse lights as corrosion builds up inside the switch itself. A quick fix is usually to start the engine with the transmission in neutral, but sometimes that will not work either. On 96 and earlier models the NSS can be bypassed by splicing together the two centermost wires in the connector that are on the row opposite the clip that holds the connector together (WARNING: This will make the engine able to start in any gear position, be aware that this will cause the vehicle to move suddenly when the key is turned if the gear selector is not in "P" or "N"). On 98 and later models the NSS cannot be bypassed as the engine computer uses input from the NSS to determine what gear to put the transmission in. Hopefully someone will link to the NSS cleaning/rebuilding procedure. Replacing it is also an option but it is somewhat expensive to do so.

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Please feel free to add to this thread, if it gets enough good info put into it maybe we can get it made into a sticky. Also if you've noticed any errors or misinformation report the post to a mod to have it corrected.


:cheers:

GrimmJeeper said:

Problem #2: turn the key, nothing happens.
. On 96 and earlier models the NSS can be bypassed by splicing together the two centermost wires in the connector that are on the row opposite the clip that holds the connector together (WARNING: This will make the engine able to start in any gear position, be aware that this will cause the vehicle to move suddenly when the key is turned if the gear selector is not in "P" or "N").

Click to expand...

A quick method of getting a '90 and earlier (Renix) to start without digging into the greasy nether regions of your Jeep is to run a ground wire from the ground terminal of the starter relay to the battery neg. post or any good ground. The neutral safety switch is a ground switch for this circuit, so with it by-passed it will still start in any gear-- caution and common sense are still necessary.

One of the many rattles and clunks may be loose leaf spring clamps. There's a FSB (NUMBER: 02-03-99) on the problem dealing with leaf spring camps wearing out:

"A new leaf spring retainer clamp, p/n 05014495AA, has been released. This clamp wraps around the spring to keep the individual leafs aligned and assembled when the spring is removed from the vehicle. This part has not been available separately in the past. It should be used in situations where the original clamp is loose on the spring and is rattling or has become separated from the spring."

I made new ones using 1/4 X 1-1/2" flat stock and stainless 1/4" bolts and nylon lock nuts.

Sorry, no pictures, but for the NSS:
On the transmission's passenger side you will see a fin-like structure with a lot of wires and one shifting cable coming out of it. Stamped metal, 1/2" thick, a 90 degree wedge mounted on a center pivot.
First, disconnect the steel cable from the pivot.
Second, remove the nut securing the NSS to the body.
Third, remove the NSS from the transmission. On my rig, this was very difficult. Be persistent, use the needed profanity, wiggle it & pray you don't break the switch on the way out. It can be done.
Fourth, spray down the screws on the switch body with PB Blaster or similar penetrating oil. Eat a sandwhich, give your partner a roll in the hay, smoke a cig, whatever - just let the oil do its stuff. You don't want to strip a screw.
Using a good quality screwdriver to minimize stripping, remove the screws holding the NSS together. Put them in a tupperware or a small baggie so you don't lose them.
Using electricial contact cleaner & an old tooth brush, clean all the junk & copper dust out of the NSS. Do this over a clean well contained surface so you don't lose the little springs and copper contacts. You'll need them all to re assemble.
Once you have it adequately clean, you can spray it all down with WD-40 like I did and reassemble. Or you can use dielectric grease like some other folks do and then reassemble it. I just shot it with WD40 and put it back together (reverse of removal) and have had no troubles the last couple years.

thermal failure / no spark /. 91-2000
Ie starts when cold, runs fine till up to running temp then starts to cut out when driving, gets worse with time then, will not start/ spark when hot. If left to cool will start and run.
suspect in this order:
#1 Crank sensor
#2 coil
#3 cam sensor, (in the bottom of the dizzy).
With the crank sensor and coil, spray with water when hot, you are not going any where anyway, see if it will start. can also work with the cam sensor but because it is in closed in the hot dizzy housing results can be less obvious.
when you get home test all the components electrically, resistance and voltage output for the crank and cam, after you let it run in the driveway till it has cut out. (prick of a job& requires 2 people)
Has spark and will not start after warm/ running for a while- check fuel pressure.
grate post on the crank sensor:
http://www.naxja.org/forum/showpost.php?p=245069237&postcount=3

Rainman said:

thermal failure / no spark /. 91-2000
Ie starts when cold, runs fine till up to running temp then starts to cut out when driving, gets worse with time then, will not start/ spark when hot. If left to cool will start and run.
suspect in this order:
#1 Crank sensor
#2 coil
#3 cam sensor, (in the bottom of the dizzy).
With the crank sensor and coil, spray with water when hot, you are not going any where anyway, see if it will start. can also work with the cam sensor but because it is in closed in the hot dizzy housing results can be less obvious.
when you get home test all the components electrically, resistance and voltage output for the crank and cam, after you let it run in the driveway till it has cut out. (prick of a job& requires 2 people)
Has spark and will not start after warm/ running for a while- check fuel pressure.
grate post on the crank sensor:
http://www.naxja.org/forum/showpost.php?p=245069237&postcount=3

Click to expand...

also known as "Heat soak" right?

My understanding was heat soak happens to a component after the engine is off, residual heat from the engine soaks into a component. like the injector issue in the later xj's.
this thermal fail happens when the engine is on and running, i'm not a mechanic / engineer just my understanding is all, may be someone who does know will chime in? .

thanks for the contribution, regardless. :cheers:

HEATER/AIR only blows through defrost vents.

I see this posted at least once a week. The default for the HVAC system with no or compromised vacuum is for the vents to go to the defrost mode...even if you don't have defrost selected. You may not even notice that it's just blowing through the defrost vents, it's just not blowing through any other vents.

You have a vacuum leak. Most common leak site is along the passenger fender to the vacuum reservoir. Cracked and/or broken lines. You could have a crack in the reservoir or there could be a leak inside the dash (less common).

Replace any sketchy vac lines on the passenger side. You can use bulk line which is cheeeap and existing fittings (unless they're toast too). These lines generally don't cause any running or driveability issues. Make sure the source vacuum is attached to the intake manifold. If you think your HVAC vacuum is somehow related to brake vacuum or emissions vacuum...no...different system.

...and if you think accessing the vac reservoir behind the bumper is a PITA, relocate the reservoir to the engine compartment. Less line, easier to get to.

Problem: Going over uneven bumps or while turning, you hear a loud click, pop, clunk or otherwise undesirable noise.
Diagnosis: With the car in park and emergency brake on (or rear wheels chocked), have an assistant start the car and turn the wheels slowly back and forth. Look at & carefully place a hand on the track bar (the bar running from driver's side wheel well area to the axle on the passenger's side) and feel, look & listen for movement. There should be almost none at all.
If there is movement, esp, associated with noise, replace it. Axle side bushings are available separately in rubber or polyurethane at rockauto.com
Also check the bracket, which bolts to the body. These frequently come loose even after loc-tite in my experience and can be welded to the unibody with no ill effect. Just make sure the taper where the track bar attaches is in good condition before you tack it down.
If no movement in the track bar, grab each side of the sway bar independently and attempt w/ man-strength to move it up or down. It can be tough, but you may find that a sway link which looks solid is in fact broken. Noisy as hell.

Still no luck? Most likely thing now is U-joints. Turn off the engine for this one.
Lift the car so the front wheels are off the ground. Support car with jack stands. You may need to do one side at a time, depending on your jack / lift situation.
Grab a u-joint firmly in hand and attempt to twist it back & forth, rapidly reversing directions. You are attempting to diagnose relative motion between the two parts of the axle shaft, inner & outer. Some small movement before the splines engage is normal (if small) but the U-joint should lock the two halves of the shaft EXACTLY in sync with each other. Any play indicates a worn joint, and if you are performing the test & the joint has play, it is likely to be your problem.

Airbag light...no cruise control, no horn

Fix = Replace clockspring.

RENIX 6cyl. High temp reading with no external sign of overheating. Check sending unit on the top of the rear of head. Mine failed giving high (220*) reading.
RENIX low/no oil pressure reading with no external sign of low pressure. Again check sending unit above oil filter. (I was warned here a common failure and should be replaced with a factory part)