Jeep GC 4.0 dies randomly while driving, no codes no MIL, computer? - JeepForum.com
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Unread 12-28-2009, 08:05 PM   #1
ron7000
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Join Date: Feb 2007
Location: CT
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Jeep GC 4.0 dies randomly while driving, no codes no MIL, computer?

hi, need some help before i throw parts at it.
2003 Jeep GC, 4.0L, 4wd selec-trac, 57000 miles, excellent condition, has run great till a week a few days ago.

will be driving on a local road anywhere from 20-50mph and the engine will start bucking and lose all power, and the dash gauge cluster will lose power also- the speedo will drop down to zero along with the tachometer and gas gauge. The best way to describe the loss of power and bucking is like if you turned the ignition key off while driving then before the engine completely stopped spinning turned it back to run, however when this problem happens the lights on the dash cluster never go out nor dim, just the gauges fluctuate from their current position to zero.

Now the first time this happened, the gas gauge read about 1/4 or slightly over, this was when wife was driving it. So i drove it and it was fine for almost a whole day... i figured maybe water in gas plus i was trying to duplicate the problem and couldn't. so now gas guage is under about 1/8 so as i'm driving to gas station the jeep bucks and loses power intermittently, but then comes back and i make it to the gas station. Fuel light never came on saying i was low in gas either. I put 19 gallons in the tank, i think it's a 20 gal tank.
So now i start thinking maybe it was out of gas and it was pumping air in the fuel line... so with a full tank of gas i put about 30 miles on it later that day with no problems. Also, the jeep was in about 2 years ago because the gas gauge wouldn't read at F when it was full, so dealer had dropped the tank and adjusted whatever, so now i'm figuring the gauge is off on the empty side. But yesterday and today with over 3/4 in the gas tank it did it again.

last nite wife got stuck coming home, jeep died, and when she went to restart the engine would NOT turn over when turning the key to start.
And battery is 100%. so she calls me and i get there in 15 minutes. flashers are still going, interior lights nice and bright. I start the jeep, starts right up like nothing was ever wrong, and i'm able to haul about 5 miles to home, jeep has full power. could not duplicate problem again last night.

tonight on way to store about 10 minutes after leaving home from a cold start it bucked and died as i was doing 35-40, so i coast and stop. try to restart and engine turns over but won't fire. so i turn key off, wait 30 seconds, engine starts up. now in neutral i can usually rev the engine and its fine but it started sputtering- when it's below 1000 rpm and you tap the gas pedal it'll sputter but then rev up to 2000 and sound smooth and normal, and i can rev it from 1500-3000 fine, but let it back down to 1000 then step on the gas and it would sputter. I was 3 miles from home and it took me about an hour to get back, mostly because i was trying to find some bounding conditions to the problem. Would lose power and buck a lot, would pull over let it idle for minute then try to go and would buck and have no power. turned engine off, waited 1-2 minutes, restarted but would buck & lose power within another minute. after at least 1/2 hour of that, i'm a block from home, i turn engine off, wait minute, restart, then drive about 4 miles with full power and no problems.
Got code scanner, no codes ever. Engine MIL light has never illuminated on the dash when this has happened.

the only other thing i can think of is the ASD (automatic shutdown) relay under the hood in the fuse box, i have the service manual and it says this relay supplies battery +12v to the fuel injectors and ignition coils, and maybe to O2 sensor heating elements, and it PCM controls it by switching the relay's ground circuit on/off. this is the only thing i can think of that might cause what i'm experiencing, although i'd expect the relay to fail outright and engine would not run.

I have also shaken and pulled all the wiring harnesses under the hood, the connections to the PCM, and the fuse box to see if it might be a loose connection and could not cause the idle to stumble.

any help greatly appreciated.

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2003 Jeep Grand Cherokee Laredo
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Unread 12-28-2009, 08:39 PM   #2
ron7000
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think i'm gonna try replacing the CPS sensor first.
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Unread 12-28-2009, 09:31 PM   #3
spikesnspurs
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sounds like the crank sensor to me....
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Unread 12-28-2009, 10:10 PM   #4
ZeeJay1997
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The relays are easy enough to eliminate by swapping. Swap fuel pump and ASD with two other relays. (horn, int wiper) . They can be intermittent because of carbon on the contacts.

You can try disconnecting o2 sensors to see if problem goes away. You could be looking at a bad CPS also. They sometimes they short out at random and cause PCM to reset. Give engine bay and under carriage a once over for wire bundles rubbing the frame or damage of any kind.

Sorry to say gauges dropping with no other visible power problems could indicate a bad PCM. If you have access to a scanner you can confirm by watching emissions monitors. If the PCM is resetting itself on the fly, the monitors will reset.
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Unread 12-28-2009, 10:52 PM   #5
ron7000
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need a clarification,
is there a crank position sensor on the 4.0L ? if so, where?
i'm reading my manual and see no mention of it for the 4.0L but it references it for the 4.7L v-8.

the cam position sensor is on top of the oil pump drive shaft, what looks like a slimmed-down distributor on the passenger side of the block.

should i be replacing the cam sensor (CMP) or the crank sensor (CPS) if there is one?
thanks,

nevermind, found CPS, it's hidden under the fuel delivery section of the manual, go figure.
and it goes by CKP,
mounted to the transmission bellhousing at the left/rear side of engine block, sounds like fun to get to.
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Last edited by ron7000; 12-28-2009 at 11:15 PM..
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Unread 12-28-2009, 10:58 PM   #6
spikesnspurs
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its located on the top of the bell houseing on the drivers side ...
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Unread 01-06-2010, 09:07 PM   #7
ron7000
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replaced cps, still dies


to change the crankshaft position sensor (CKP) on a 2003 Jeep Grand Cherokee laredo, with the 4.0L cylinder and 4wd, i had to take the intake air box off the throttle body which was easy and i could reach down and touch the ckp on the trans bellhousing on the driver's side. this is how you pull it out and drop the new one in.
from underneath i had to undo the transmission shifter bracket and cable, the cable end on the shift linkage just pushes off but takes a bit of force, the bracket is held on by 1 bolt needing a 10mm socket and the big bolt was 18mm i think. with that out of the way and a good light to see up to the ckp, that's held on by a bolt needing an 11mm socket. I have a 6", 3", and 1.5" extensions for 1/4" and 3/8" size sockets (craftsman socket set), the way to get at the ckp bolt was using the 11mm socket in 1/4" size, with a 1/4" universal after it followed by the 6", 3", and 1.5" extensions in 1/4" size then using a 1/4 to 3/8 adapter followed by my 6" and 3" extensions in 3/8 size. That allowed me to undo the ckp bolt and retighten it. Getting the bolt back in wasn't easy with the front driveshaft in the way but wasn't too bad, and i was not able to get the wire shield back on with the new ckp sensor. There was absolutely no way to get at the bolt from the top with any kind of tool, not on mine, it was too close to the firewall/body. The ckp has about 8" of wiring which lays across the bellhousing to the passenger side where it plugs in, had to undo 3 or 4 wiring connectors to loosen the wiring bundle which was all on top of the ckp plug.
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Last edited by ron7000; 01-06-2010 at 09:53 PM..
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Unread 01-21-2010, 02:29 PM   #8
ron7000
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well turns out I had replaced a crank sensor and vehicle speed sensor for nothing
after bringing it to the dealer eventually thinking it was the SKIM module and needing them to use their DRB scan tool to check,
the mechanic found the main wiring harness that runs from the PCM around the top back side of the engine (inline-6 4.0L) to the injector rail, had been sitting on the rear driver side valve cover stud and after 7 years/50k miles the vibration had allowed the stud to poke into the harness and short to ground three wires. That's what was causing the entire problem. At first the stalling out seemed random, then prior to bringing it to the dealer it would die within 3 minutes of starting it up.

During the diagnostic at the dealer, it died on them just like it had on me, they tried scanning the computer but found when it was dying that the computer was also being reset so no codes were being stored. And the way the mechanic explained that it was a short in the harness gave me the impression they've seen this before. It should be a TSB, because it was the way the jeep was built at the factory and is a definite problem, it will happen to everyone I think eventually if the wiring harness it tight around the valve cover and is touching on the valve cover studs.

After repairing the 3 wires, the harness was taped up and a piece of 1/4" rubber fuel hose was placed over the protruding driver's side rear valve cover stud so it doesn't wear through again.

I recommend anyone with the 4.0L inline-6 check the wiring harness running around the back of the engine and make sure it's not sitting on anything that can wear into it.
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Unread 01-21-2010, 10:37 PM   #9
rooster51
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Solid copy, will do. Exellent find.
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Unread 02-01-2010, 10:20 PM   #10
Hopperstien
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I think mine did this exact thing today. It bumped once and then just died while going down the road about 35. Coasted to the red light and cranked right back up, and was able to drive home. It instantly threw a code though. Was going to get it read on Wednesday, now I am going to have to check this wiring harnes situation out to see if it is the same.
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Unread 03-12-2010, 09:18 AM   #11
Sand8
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2003 Jeep stalls while driving

My Jeep just started stalling a few weeks ago.

My friend, a master mechanic, has gone mad trying to solve the problem without codes or putting in new parts! He has washed his hands of the problem!

After stalling, it takes 30 minutes - 2 hours before it restarts.

I was just about to try to make an appointment to replace the Crankshaft Position Sensor - Will check for worn spots first.
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Unread 03-12-2010, 10:59 AM   #12
KillaKam79
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My 99 is doing the samething. It would just shut off randomly, not often though. I was going to get the CPS tested to see if that was the problem. If not I will check the wiring. Also after like 30 min of driving and hitting stop & go traffic the Jeep would become slugish while excelerating. I did a tune up, change plugs, spark plugs, air filter, fuel filter, replace all 4 shocks, replace 2 front axle.

Last edited by KillaKam79; 03-12-2010 at 11:16 AM..
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Unread 03-12-2010, 07:06 PM   #13
Sand8
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Thanks, I am going to get the CPS tested first thing Monday.
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Unread 03-12-2010, 07:08 PM   #14
Sand8
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2003 Jeep Stalling full details - Ideas, please!

My Jeep Grand Cherokee Laredo started stalling while driving a few weeks ago. No codes. It takes an hour or so before it restarts. It does not lose electrical. The engine shuts off. It stalls on shorter distances now than when the problem surfaced.
A good friend, a master mechanic, got frustrated after trying for more than a week to narrow it down. He just washed his hands of my Jeep and went back to working for paying customers.
Monday morning, I am taking it to another mechanic, who works with my friend, and have him test the Crankshaft Position Sensor.
Anyone with the same problem and success in fixing it?
I am not sure my stalling behaves like the usual CPS stall…

Here is the long story…..
Late February, my perfectly reliable 2003 Jeep Grand Cherokee Laredo stalls while driving 65 mph. After an hour, it starts. I add Heet and drive 40 miles home, no problem.
Adding Heet does not solve it. A few days later, the Jeep stalls while driving 40 mph, after doing errands in town and a 45 minute massage. It takes more than an hour before it starts, then I drive to a Conoco and add quality gas.
It seems reliable, then a day or so later, it stalls again, this time 35 miles from home. It is freezing cold and turning dark. After nearly 2 hours I call AAA to tow my car to a friend’s house. He is a master mechanic. It starts.
We determine it is not a fuel problem. He shows me how to test by spraying carb cleaner. He later tries that test.
He puts everything he knows into trouble shooting this.
March 6, Friend pulls the computer. He wrote me:
Pulled computer, there is no way the screws can touch anything,
the inside is encapsulated, there are no burned spots, dark spots or
irregularities visible. Where Jeep mounted the computer muck from the
tire gets thrown on the computer, I am going to reseal computer and clean
the area around the mounting and inspect the wires and connectors.
Tomorrow I will try hot tests to see if I can duplicate failure. if that
don't work we are back to square one, unless cleaning connectors and Ecm
area fixed it.

March 7, I go to pick it up and it stalls in front of his shop. Delighted, my friend grabs voltage meters and analyzes everything. No codes. He drives me home and keeps the Jeep.

He drives it with tools, tests it when it stalls, and cannot find anything. He has to leave it a couple of times and gets rides with friends.
March 9 I send him pieces of advice about similar Jeeps, ideas that it might be the Crankshaft Position Sensor.
He checks for frayed electrical. Does not see anything. He assembles and installs a by-pass cable, it has no effect.
March 10, he emails me:
Sandra
* * * *Things keep pointing at Crank position sensor even though I have
no codes, I *can not get to it, my shoulder won't let me, I am going to
get the part and have another mechanic I know install it,. I can't tie up
his bay while I run back and forth trying to test it, so am going to
remove it from equation, I am running out of time other work is backing
up, sensor is around $45.00 and outside labor is around $45.00 .

But 4 hours later, with no explanation, he writes that he is sending the part back and canceling the appointment with the other mechanic.

*I no longer can do anything for your Jeep. I am out of time, I
canceled my appointment with Mike and will return the part I bought, I
probably lost one customer doing this, I have at least six hours chasing
this down of which I am not billing for. I left a sheet of things I did
on the front seat and the check you wrote the other day. Maybe your
roommates mechanic can do this without buying any parts, I am not that
good so, give him a try. The keys are in it. * * * * * * * * * * JD

Completely frustrated, he turns the Jeep back over to me and washes his hands of the problem on March 11.
Here is what he put on the list:
Will stall after driving for 4 miles then letting set roughly 1 hour.
1. Fuel pressure good
2. Seems to loose +12 V ignition & injectors.
3. Cleaned ECM connector/opened ECM - nothing irregular, Resealed.
4. No codes - just got a O2 circuit value code.
6. Swapped ASD relay no change.
7. Heated components with heat gun, no failures.
8. Pulled relay box, inspected connectors.
9. If ASD shuts down, it should set code.
I suspect bad crank sensor and due to location I can not test or bad power connection.
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Unread 03-12-2010, 07:49 PM   #15
perfectcircle
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1999 WJ 
 
Join Date: May 2008
Location: , Tennessee
Posts: 844
Replace crank sensor with a MOPAR replacement. With some patience you can do it yourself. Most mechanics around here would be happy to throw parts at it until it fixes the issues haha. the crank sensor is common, second is the cam sensor but with the stalling i'd go with crank. You'll get dirty, you need to stretch first, but you can do it in your driveway. Not sure what his shoulder has to do with it, he could have lowered the cross member and got at it with a few long extensions..either way, pm me if you want more info
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