Does my Cherokee have a computer?

[dutchjeep]

Ok, well I thought cars like the cherokee were all mechanics (and that's usually all I ever care about on a car), now I read in an exhaust manifold thread (the big one I think) that after changing the cracked manifold for a non-cracked specimen you would either have to reset the 'computer' or let the car adjust itself over several hundreds of miles to get everything in optima shape. I'm about to do exactly that (exchanging the cracked for the non-cracked that is) so I figured it might be useful give some considerations to the computerized world of car maintenance.

So here's my questions (at least I think they are, it is always hard to know what you don't understand):

1) how do I reset the 'computer' (or: where/what is it?)?
2) when do you do that (or: when not to do that!?)?
3) please update me on the jargon here, how do you call these computer components in the cherokee?

My cherokee is a '92 limited 4dr, 4wd with the 4.0l line6 engine. All the help to any of my questions is more than welcome. Thanks --Tim

 

[anony91xj]

Yes, your Cherokee has a computer. It's electronically fuel injected, it needs one.

You don't have to reset anything when you replace the exhaust manifold. If you want to reset it though, just disconnect the battery for a couple minutes and reconnect it.

 

[TiRod]

The computer is called . . . a computer. Or an Electonic Control Module (ECM,) black box, or, when broke (rarely) a @#$%%&*!
The other parts are a Crankshaft Position Sensor, Coolant Temperature Sensor, Manifold Air Pressure sensor, Pickup Coil, EGR valve solenoid, O2 Sensor, Knock sensor, and whatever else someone remembers.

They are all parts of the Renix, Chryco OBDI, and OBDII computer systems which interpret the signals to calculate about what amount the of air the engine is consuming in the ambient environment and how much fuel to inject, with a feedback from the O2 to keep it clean. Yours should give trouble codes that can help narrow down diagnosis for repair - but the codes don't mean the part is broke. Further testing is required to maintain your wallet's integrity. The first tool you should get is a good Volt Ohm meter to check these parts and eliminate the dreaded "I've changed everything" non repair.

 

[dutchjeep]

He, that's great. I have a half-decent multimeter so should be all set . So where do I read these computer trouble reports? How do I interpret the computer output? Is that human-readable or is that codes that I need to know what they mean? Thanks!

 

[HeightsHoustonXJ]

Haha, I can vouch that they have computers. In fact, my 97 XJ has a computer that is made out of pure gold and is diamond crusted on the inside. At least I think it is based on how much it cost to replace last year.

 

[Rescue xj]

He called his jeep a car :shiver:

 

[SCW]

He called his jeep a car :shiver:

Mine's a station wagon. With a computer even!

 

[Matthew Currie]

He, that's great. I have a half-decent multimeter so should be all set . So where do I read these computer trouble reports? How do I interpret the computer output? Is that human-readable or is that codes that I need to know what they mean? Thanks!

For your vintage, turn ignition key on - off - on - off -on, then leave on. the Check engine light will flash a series of two-digit codes. "55" is the default starting code to tell you that the system is reading. "12" says the battery has recently been disconnected. All other codes have a meaning. You can get the codes from various sources. Post back here, or try

http://www.allpar.com/fix/codes.html.

Not all the codes are absolutely accurate. Sometimes a problem will affect something else and throw a misleading code, but it is a good place to start. A trouble code, including "12," will stay stored for approximately 50 cold starts before it goes away, but if you fix a problem that was setting the check engine light, it should stop as soon as it's fixed.

The computer (called, by the way, the "PCM" officially by Chrysler/Jeep for this vintage) does not have a sophisticated learning mode, so you need not worry about resetting or teaching it bad habits, etc. Just fix the problem and go. Reset with a battery disconnect to clear the stored codes if you're not sure whether a problem is really fixed.

Cult status notwithstanding, my Jeep is a car too, albeit a very rugged, utilitarian, special sort of one. It has four doors, a roof, power accessories and a radio and a back seat. When I need the services of a car, that is the vehicle I use. When I need to haul rocks or plow snow or throw garbage in the back, I have a truck for that.

 

[Saudade]

Cult status notwithstanding, my Jeep is a car too, albeit a very rugged, utilitarian, special sort of one. It has four doors, a roof, power accessories and a radio and a back seat. When I need the services of a car, that is the vehicle I use. When I need to haul rocks or plow snow or throw garbage in the back, I have a truck for that.

I bought my Jeep because it is a Jeep. However, it's really just Dad's taxi. I haul my kids, groceries, go to Dr appointments, etc., with an occasional trip to HD or Loew's for some small stuff. If I need to haul big stuff, help someone move, or carry really "messy" stuff, I use my little Nissan P/U.

 

[dutchjeep]

I bought mine because my wife told me to. And -- as is often true to my regret -- she was right! It is one *&^% of a car. It's a car nonetheless. No matter the namegiving (I need to distinguish it from my truck) I think we all share about the same feelings for it. Maybe for different reasons but that's ok!

Great input! Thanks all, learned a lot!

 

[TiRod]

I had a truck, then I tried to use the Jeep to haul stuff, but the firewood and concrete pavers keep bending up the chrome strips in back. A 5x8 trailer solved that problem.

Now I have a six wheel truck with center pivot.