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Old 06-10-2013, 12:50 AM
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02 4.7 fails to crank

I have a WJ GC limited 4.7 with 210k km owned since new and always serviced by same dealer. GC was delivered in Sydney Australia. About 18 mths ago, GC suddenly failed to crank on a hot day, but recovered when engine cooled. This problem has continued to now and is getting worse. My dealer has had the GC many times and on each occasion "can't fault it" and also reports each time that no "fault codes" have been recorded by the computer. The dealer has removed the console to check the gear selector etc, but says no probs here.

I have replaced the battery with another (both genuine mopar) and have had an independent auto electrician replace the battery leads - all to no avail. The auto elec has reported that when the problem occurs however, there is NO NEGATIVE SIGNAL on the negative battery lead. Other than this, he can't fault the GC either, despite much pulling and pushing leads and terminals under the hood and dash.

Over time, I have come up with some observations that may assist in problem solving - and one bizarre one.

Problem occurs only when engine (and GC)is hot - and worsens in hotter ambient temps.

Problem never occurs first thing in morning.

All dash lights and gages always normal-GC simply won't crank.

When problem occurs, there are no clicks or noises of any kind.

After warming GC in morning, problem may occur every start for whole day. It will only rectify after parking for a whole night.

Now for the bizarre bit that has all the specialists doubly stumped. When the GC doesn't crank, if I hold the key at the "start" position (against the spring loading) and if I STAMP ON THE BRAKE PEDAL at the same time, it will often suddenly crank and start normally! Weird, huh?

Unfortunately, this onle works in 95% of cases - in the rest I have to tow the GC or drive my wife's Honda!

Please help me with this continuing drama as it really has reached the point where I can't rely on GC any more.
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Old 06-10-2013, 02:04 AM
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Re: 02 4.7 fails to crank

sounds like the starter itself. or i have read that there is a yellow wire that goes down to the starter that is known to corrode at the connections
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Old 06-10-2013, 04:22 AM
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Thanks
I'll get it checked out.

Looking for as many suggestions as possible so I can give all to my dealer to keep them busy for a week or so!
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Old 06-10-2013, 05:00 AM
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Re: 02 4.7 fails to crank

i dont know how much money you have put out so far but it sounds like alot were it me i think i would start looking for a new mechanic or do alot of reading and start figureing out how to do some of these things by yourself, its not rocket science when it wont start it should be checked for power at the starter theres really only a few things it could be but youre connection to stomping on the brake pedal and it working could be leading to the ignition switch(not the lock cylinder) but the actual switch that is usually mounted down near the firewall on the steering column
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Old 06-10-2013, 06:18 AM
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Thanks again. Actually $ outlay is not great as nobody has succeeded.

Re your idea of the ignition switch, is it located in the cabin or on engine side of firewall? Is it a repairable part or a throw away job?
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Old 06-10-2013, 03:08 PM
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Re: 02 4.7 fails to crank

cabinside/ throwaway
and im not 100% sure on the info i gave you but typically the switch is activated by a metal rod that slides within the switch. the metal rod is moved by the key being turned in the lock cylinder

ok well it looks like im wrong its in the column afterall heres a pic 01 02 03 04 Jeep Grand Cherokee Ignition Switch | eBay
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Old 06-10-2013, 05:43 PM
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Thanks. Do you think a faulty ig switch might be affected by eng bay temps?
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Old 06-10-2013, 06:10 PM
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Re: 02 4.7 fails to crank

The fact that the dash lights are normal, shows that the battery wires are ok. If there was a wire problem, the lights would dim when trying to start.
Ignition switch could be the problem, but also the transmission range sensor inside the tranny (part of the TRS/solenoid block). This last one only makes a ground path for the starter relay in park and Neutral. If the shift cable is not completely well rigged, this problem could happen as well. Just wiggle a bit with the shift lever or even move it out of Park and see if it will start then. The high tranny temp could be the influencing factor.
To be sure that the ignition switch is not the problem, you could remove the starter relay from the Power Distribution Center and measure with a multimeter between slot 86 and ground, while someone tries to start. You should measure 12V, if its not there, the ignition switch could be the problem.
You could also jumper point 30 with 87, which should activate the starter solenoid and the starter motor should turn. If not, the starter motor or solenoid (which is part of the starter motor), is faulty.
Also you could check the TRS if its switching to ground. Measure from point 85 to ground (on the same starter relay slots) with the multimeter in ohms, it should give continuity or a very low resistance. Ofcourse all these measurements should be done when the problem is there.
Last the problem could be with the starter relay, just swap it with one other similar relay and try again.
Success with the trouble shooting and let us know what you find.
For your reference the wiring diagram for the starting system.
Attached Files
File Type: pdf starting circuit.pdf (178.4 KB, 2 views)
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Old 06-10-2013, 08:04 PM
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Thanks for the very in depth analysis. I have previously tried moving the shift lever several times but no success.

I am curious why many people don't zero in on starter or associated solenoid? I may be imaginating this but I swear that when the problem occurs then I step on the brake, that I have noticed the crank speed is slightly lower than normal!

I am more inclined to try my auto electrician on this but he has having no luck with wiring diagrams - I guess it's logical that dealer and Jeep Australia aren't interested in helping an outsider! Are such diagrams available to the general public?
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Old 06-10-2013, 10:30 PM
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Re: 02 4.7 fails to crank

With the wiring schematic i attached before, a mechanic should be able to discover if the problem is the ignition switch, the transmission TRS switch, the starter relay or the starter motor.
But the fact that there is no click at all, should rule out the starter motor in the first place. The starter relay in the power distribution center under the hood should make a clicking sound, even if the starter is faulty. It is a small relay, so it doesnīt make much noise, but you can hear it with the hood open.
If it realy doesnīt click, then the problem is or the ignition switch, the TRS pack or wiring.
That you say that when the problem is there and you step on the brake, that the crank speed is lower, could still have to do with the actual problem. There is something not ok and by pressing the brake pedal you are not solving the problem.
You also say that when you stamp on the brake pedal that it sometimes starts normally? When you press the pedal in a normal way it wonīt? Maybe by pressing the pedal with force, you shake the jeep a bit, which vibration acts on the failing part?
But only by measuring at the moment the problem is there, you should be able to eliminate the possibilities and find the failing part. Donīt know if you can do any measurements yourself, but when the problem is there again, open the hood and let someone listen at the power distribution center to be sure if the starter relay clicks or not. When you know this for sure, you can eliminate several possibilities already.
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Old 06-11-2013, 01:01 AM
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Thanks again. I don't seem to have received the schematic you refer to but it would be very valuable. Could you please send again?

I recall we changed the starter relay but didn't solve prob. I understand all your suggestions need to be checked and I intend to provide all your suggestions to my elec - hopefully with the schematic.

One major difficulty is that the mechs have not been able to reproduce the prob and my auto elec has seen it only once. I believe it doesn't seem to occur by just idling the engine - it seems to require actually DRIVING the GC-makes prob detection hard when vehicle is in pieces on the shop floor!
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Old 06-11-2013, 05:29 AM
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Re: 02 4.7 fails to crank

The schematic is attached to my first message, just below the text.
Here it is again.
For the trouble shooting to know if the problem is the ignition switch, the TRS or the starter (or the related wiring), only the starter relay has to be removed and measured from the relay slots, so that can be done at any moment the problem shows up. If you know how to handle a multimeter, you could do this yourself.
Only be carefull when putting a jumper wire between slots 30-87, because if the starter motor/solenoid is not the problem, it will kick in, independent of the gear lever position and the ignition switch, and the engine can start when the ignition switch is in run. Also there probably be some sparks when making this jumper connection.
Attached Files
File Type: pdf starting circuit.pdf (178.4 KB, 9 views)
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