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2002 - Replacing a CkPS. TDC on #1?

Old 04-28-2019, 06:35 PM
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Default 2002 - Replacing a CkPS. TDC on #1?

Well, I did it. I pulled the trigger on a 2002 Grand for the wife to run around in. It's a remarkably clean machine, inside and out. Minimal rust. It has the SelecTrac transfer case, so I need to learn more about that.

One small problem - the PO described it as having a problem with stalling occasionally, for no apparent reason, but it always restarted right away. (Probably why I got such a clean vehicle for a great price.) Sound familiar? So, of course, once I left his house, just before pulling on to the main highway, it died and would NOT restart. Tow time.

I tested the CkPS today (yeah, it's bad), but I had to remove it to get enough slack to get to the connector. Then I read that I should have put cylinder 1 to TDC before pulling it.

So, here I am with the CkPS out of the engine and I have no idea where cylinder #1 is at the moment.

Do I have a problem? OR can I just proceed with getting #1 to TDC and then install the new sensor?

----------------------------------------

EDIT TO ADD:

I'm posting this for anyone else who has the same question.

I picked up the sensor this morning at the dealer. $186 out the door! Ouch. But, it runs.

I checked while I was there. It is the CAM position sensor that needs to have #1 cylinder at TDC. That's not relevant to the CkPS. Doesn't matter.

Last edited by BlueRidgeMark; 04-29-2019 at 10:59 AM.
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Old 04-30-2019, 04:51 AM
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Don't fret about it. Just install it and the computer will sort it out. It's the cam sensor that needs to be timed. Even that will be okay as long as you don't pull it out of the block and just change the sensor on top. There's a series of windows on the flexplate that the crank sensor reads to tell when a piston is near top center. I think there's 3 windows at each station and the computer measures the time between the windows to determine crank speed and sets the spark advance accordingly. It also uses things like vacuum, TPS position, intake temp, and engine temp to control mixture. In other words, the crank sensor tells the computer when to fire the plugs and the cam sensor tells it which plugs to fire. BTW, this engine uses the "waste spark" system where 2 plugs fire at the same time. One on compression and one on exhaust, every revolution. There are only 3 coils in the coil pack and are controlled by digital drivers in the computer.

As far as I'm concerned, the 242 Selectrac transfer case is the best one used in jeeps. 2WD is self explanatory, 4WD Part Time should only be used on loose or slippery surfaces, 4WD Full Time can be used at any time, Neutral is used for towing the jeep and also to facilitate getting into low range, and Low Range is a "Granny" gear for more torque in the tough stuff at low speed. Low tops out at about 30 mph max. Low is not synchronized and gear to shaft speeds have to be matched carefully. Read your owners manual for the proper techniques to use low range or I'm sure the guys here will give you their opinions on how to shift into low. You can shift from 2WD to 4WD "on the fly" at any speed just by lifting your foot off the throttle and moving the shifter "briskly." I've done it at 60 mph when I've seen wind-blown snow on the road ahead.

IDK why I'm telling you this about low range if you have experience with XJ's and the 231. Guess I didn't read your profile.

Last edited by dave1123; 04-30-2019 at 04:56 AM.
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Old 04-30-2019, 09:05 PM
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Thanks for the info about the Selectrac, Dave. Since I'm on my 4th Cherokee, besides the several I drove for an employer years ago, I'm up to speed on the 231, but the Selectrac is new to me. I have vaguely heard about it, but that's it. Your info is helpful.

The waste-spark system is new to me, too. I have been aware of it from discussions here, but haven't owned one before. I really like the simplicity of a distributor, or maybe it's not the simplicity, maybe it's just what I'm used to. But, either way, time and technology marcheth on.
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Old 05-01-2019, 10:59 AM
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About the Full Time selection. When my rear axle blew up, it popped the 242 out of 2WD. I nursed it home in Full Time 4WD, then after replacing the rear axle, it wouldn't go back into 2WD. It was still catching the edge of the Part Time gears so I drove it all winter (6 months) in Full Time until I could replace the t/case. It was probably just a bent shift fork, but it's was my DD so I couldn't tie it up long enough to investigate. I didn't have my XJ then as a backup.

Yeah, the coil rail makes it difficult to check for spark. It's so much easier to pull off a plug wire, but you'll never screw up the firing order! LOL! The bad part about it is they have a tendency to short internally, usually the long connector between #1 and #6. A straight block engine is unique in the fact that 2 pistons are at top center at the same time so #1 and #6 fire together, #5 and #2, #3 and #4 also. Using waste spark reduces emissions and the complexity of the ignition system. You only need 3 coils and 3 drivers in the PCM. Waste spark is not new. Briggs & Stratton and Tecumseh used it on their 4-stroke single. That's why they "bark."

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Old 05-01-2019, 08:17 PM
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Well, well, well! Ain't you just a fountain of oddball info!

It's good stuff. Thanks.
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Old 05-02-2019, 05:45 AM
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Yeah, I used to **** off my friends playing Trivia too.
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