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Unread 09-15-2009, 01:54 AM   #1
Ved
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The dreaded engine randomly shuts off while driving problem.

I have been experiencing the dreaded "engine randomly shuts off while driving" problem that seems to plague a lot of Jeep owners with high mileage. However, I'm not getting any codes that would indicate any problems(Just code 12) No check engine light... Nothing.

I feel like I'm chasing a gremlin. Replaced fuel filter/Dist cap & rotor/Plugs & wires... etc After hours of reading/phone calls, and Google, I am lead to believe that it's either the CPS, Shutdown Relay, or the fuel pump... So my next step is the CPS.

I'm a bit confused about something though. There is the Crankshaft Position sensor located on the bell housing on the driver's side... However, what is that sensor that is located at the Crankshaft vibration damper pulley? Ya know, the one near the marks for checking the timing with a timing light?

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Unread 09-15-2009, 02:10 AM   #2
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Before you dig into anything else too deeply, check the power feed from your battery to the PDC.

I know, I know - the alternator feeds directly into the PDC. But, if that connexion is going silly on you, it can cause trouble.

Same sort of thing happened on my 87XJ - the feed lead from the battery to the starter motor relay screwpost (primary distribution point - AMC didn't use a PDC...) had corroded enough to cause vibration to finish the job, and enough vibration would cause the cable to lose contact internally. Sometimes it would vibrate back into place and the engine would start up again, sometimes not - but it would usually start right back up after I coasted over.

I finally figured it out by idling the engine and playing with the wiring, which is how you look for an intermittent. As soon as I wiggled the distro feeder lead, it would konk off. I did it again to confirm, and the lead separated totally - so I made new leads, put on new clamps, and everything's Jake.

Let me know if you need help with lead replacement, if it comes to that.
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Unread 09-15-2009, 02:36 AM   #3
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Thanks for the advice. I'll take a look at that as soon as the sun comes up and let ya know my findings. I did ponder the thought of a loose wire or bad connection vibrating, but because of the randomness, and lack of pattern in when it shuts off kept me looking elsewhere. I can be doing 60mph, or just pulling out of the driveway, or stopping when it dies. There is literally no pattern to it.

Poor old girl has 215,000 on her, but thanks to the indestructible L6, she is still as strong as an ox... The idle is a bit rough/low when at a stop but otherwise, starts up fine, and gets 18-19MPG on average. I really can't complain. But Iv'e chased many gremlins on my Jeeps and I get very stabby when It ends up being the last thing I check after countless hours of labor, parts, and head scratching... I'm still not convinced that Jeep stands for "Just Empty Every Pocket", but I'm getting close lol
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Unread 09-15-2009, 03:18 AM   #4
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This Could be an easy one for me to answer for you, but before I speak. I need to have you fill out your Profile At least give us A Year and model.

L-6 I only know I-6
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Unread 09-15-2009, 04:59 AM   #5
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Sorry it's an I-6 in my Grand Limited.. The L6 is in my 95 Cherokee.

Just so you know. This is an L6 - Jeep*242 Engine (L6, 242 cid, 4.0L)
Car Restoration - Jeep Engine - 91 - 95, L6, 4.0, 242, Long Block


The Jeep in question is a 94 Grand Cherokee Limited with a straight 6 (4x4).

I have 4 jeeps, so I am not sure as to what one I should put as my main in my profile.

Last edited by Ved; 09-15-2009 at 05:15 AM..
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Unread 09-15-2009, 06:09 AM   #6
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Erm...

There are actually three variations on the inline six used by Jeep...

The oldest is the "L6" - this was a flathead six. Both valves were in the engine block, and the cylinder head was a flat bit of cast iron.

The middle version was the "F6" - one valve in the block, one in the head (I believe the intake valve was in the block, but don't hold me to it.)

The current version we've got - the OverHead Valve (OHV) version, is the I6. The I6 may also be OverHead Camshaft (like the old Kaiser 230ci "Tornado" OHC I6 - which was way ahead of its time in 1961-1963!) like we're seeing in several car lines these days. The OHC varants are typically either SOHC (one camshaft) or DOHC (two camshafts - one for intake and one for exhaust, usually.)

One particular oddity about the Tornado was the complexity of the camshaft - they managed to drive both the intake and exhaust valve for a given cylinder off of the same camshaft lobe! I still want to see the grind on that cam...
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Unread 09-15-2009, 10:14 AM   #7
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OK I think I just gave myself a headache.

I've been researching for a few hours due to the rain preventing me from working on the Jeep much today, and some info I have been reading is confusing.

The Crank Position sensor is on the bell housing right? and the CAMshaft sensor is on the distributor right?

From what I gather, they work together... but, if the CAM position sensor was going bad, would it cause the engine to shutdown while driving as well? Because from what I read, if the cam pos sensor craps out, then it wouldn't start at all, so should I just keep with the speculation that its the Crank sensor thats the issue? Because whatever it is, it's intermittent, and I'm thinking it could possibly be thermal failure of the part.

I checked the alt and battery right before it rained and they are fine. I also checked the feed wire to the PDC as 5-90 suggested, and it looked good, and wiggling it around had no effect.

However, I did find the connector for the Crank sensor rests just below the oil tube, and it was covered in oil, so I unpluged it, and found oil inside.... I sprayed both ends generously with carb cleaner and then blew them out with my compressor. I'm going to take it for a test drive in a few hours to the store and have my uncle follow me just in case.. but I'm doubtful cleaning the connector solved it.
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Unread 09-15-2009, 12:33 PM   #8
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I was having a similar problem in my wj and self diagnosed it as the fuel pump and ended up eating a lot of money trying to figure it out after changing the pump and realizing that wasnt the problem. Eventually took it to my mechanic and he instantly suggest crank sensor and its been going good ever since.
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Unread 09-15-2009, 02:33 PM   #9
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*Update*

Well, I just took it for a test drive and it stalled again about 4 miles up the road, however, instead of immediately pulling over, I decided to put my foot in the pedal, and the engine fired right back up and I went on driving.

Before when it stalled out, I just pulled right over in fear that if I did anything else I could possibly damage something, but this time I just gave her some gas, and like a light switch it fired right back up.

I hope this helps narrow down any possible causes... Throttle position sensor? Crank position sensor? MAP sensor?

Suggestions?

Last edited by Ved; 09-15-2009 at 02:49 PM..
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Unread 09-15-2009, 11:35 PM   #10
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Unread 09-15-2009, 11:50 PM   #11
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Just a thought. Are your dummy lights coming on when it stalls? Im was thinking maybe the ignition switch ate it. I had the same problem in a different vehicle where it would shut down and sometimes come back on.
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Unread 09-18-2009, 06:53 PM   #12
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I went ahead and ordered a CPS. Should be here some time next week. I hope that does it.
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Unread 09-18-2009, 11:16 PM   #13
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Hey guys...My daughter has a '96 ZJ and it started stalling on her a few weeks ago. We had a mechanic look at it and he ended up changing out the Crank Position Sensor and the MAP sensor. Well, it ran good for one week...then started to stall again whenever it felt like it. Another mechanic looked at it and said it was a fuel problem, so he changed the fuel filter and had her get a new gas cap. Well that didn't work either. So, I've been doing a ton of reading online and several people said that it's the PCM (?)/main computer thing. They said that there are two small screws that hold the PCM together and they are apparently too long and are grounding out something? I didn't believe that because I figured if that was the issue, it would have been stalling out long ago. So, before we spend anymore money, I figured I'd give that a try (the two screws thing). Well, I backed the two small screws out, put a 3/8 think washer on them, screwed them back into the PCM and guess what? The Jeep's been driving great! It's been only four days since I did that, but so far so good! I'll believe that when I see it go for several weeks before I'll say that was the problem. But, it's worth giving a try before you buy more sensors, fuel pumps, filters and all that stuff. It literally took me ten minutes to do and it's running great! Go figure......

If that doesn't work, we're buying a new PCM and having it programmed to her ZJ and we'll take it from there.

Good luck!
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Unread 09-19-2009, 03:28 AM   #14
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I actually planned on giving that a try in the morning SamzJeep.

The CPS I ordered is already in transit, so I've got some time to spare while waiting, so I figured I'd give it a try. This Jeep has gotten progressively worse to the point now I cant even go more than 4-5 miles without it stalling out.

I'll let you know my results.

*Ive already disabled the stock security system as it has been known to fail and cause stall outs, so I might as well do as much "free" fixes that I can until the CPS comes in*
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Unread 09-19-2009, 10:21 AM   #15
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OK I've read about this "backing the screws out of the ECM" fix, but I am not seeing these magic screws.

This is what mine looks like http://www.autopart.com/gifs/A1/79-8313.jpg

After removing that plastic cover, the entire board is immersed in a silicone material, and I don't see any screws that could be grounding out on the board as I have read in many other posts.
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