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  #1  
Old 11-23-2015, 07:38 AM
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Exclamation 2000 Jeep Grand Cherokee Crank No Start

Hi,

I have a 2000 Jeep Grand Cherokee with a 4.0L with a no start, no spark condition. I also have a fuel and voltage gauge that is NOT reading correctly, however I did do a gauge check, hold in the trip reset and turn the key on and they all worked. I took the coil pack rail off and grounded a spark plug and there was no spark there. I unplugged the Crank Position sensor (CKP) and the gauges still read nothing. I read that that is a quick test to determine if the sensor is bad, however can it still be bad? (Should I just replace it anyways? I read one guy said his CKP made his new computer junk right away and I don’t want that to happen if I try a new computer, Or one out of my friends Jeep) There was fuel getting to the rail, however I did not check the pressure because with no spark I figured it didn’t matter if there was fuel there or not.

The ASD relay is also buzzing the whole time the key is on, I replaced it with a different relay that was the same and the buzzing was still there.

Does anyone know of anything else to check?

I am wondering if my ECM is bad or got wrecked somehow, Is there a way to tell if that is bad?


Thank you for the help in advance!!

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  #2  
Old 11-23-2015, 07:54 AM
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Re: 2000 Jeep Grand Cherokee Crank No Start

Welcome to the garage.
A shorted crank sensor will bring down the 5V supply from the PCM and prevent it from starting. Also the PCI bus will be down, so no volt nor fuel indication. Never heard that a bad crank sensor will damage the PCM, but who knows.The ASD relay is switched via the PCM, so if it buzzes, it should be the PCM which is causing this. I would check all grounds and remove/clean/dry/re-install the connectors from the PCM. Disconnect the negative battery lead before messing with the PCM.
But a good change that the PCM itself is faulty.
Besides the crank sensor, also the cam sensor and MAP sensor share the same 5V supply and can all cause a no start condition when shorted. Just remove the connector from each and see if the fuel/volt gauge come back to live.
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Old 11-23-2015, 08:14 AM
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Re: 2000 Jeep Grand Cherokee Crank No Start

If none of the gauges come back then you would try a different computer?

I just talked to the previous owner and he said his daughter could have hooked the jumper cables up wrong when she tried to jump it. I know this could wreck the computer but are there other things I should replace too?

I know hooking the jumper cables up wrong is not good but please if there is anything you would check with any of these issues just state it!!!

Thank you again!
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Old 11-23-2015, 01:33 PM
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Re: 2000 Jeep Grand Cherokee Crank No Start

So did you buy the jeep like this, not running? Inverting the polarity indeed can blow up some electronics, but difficult to say which will go first. Since the ASD relay is buzzing, i would expect at least a problem in the PCM. I would check very well the wire bundles, to see if there is no melted isolation or even completely burnt wire(s).
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Old 11-23-2015, 01:56 PM
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Re: 2000 Jeep Grand Cherokee Crank No Start

I did buy it like this, he never said the reversed polarity before but it was a cheap Jeep. I will look at wiring tonight, however everything I can find has worked so far on the interior of the jeep, except the fuel and voltage gauge.


I will look at the wires tonight, but like you said before trying to unplug those sensors if I can not find burnt wires or anything that looks suspicious would you try a new computer?
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Old 11-23-2015, 05:26 PM
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Exclamation Re: 2000 Jeep Grand Cherokee Crank No Start

Like I said his daughter COULD have, he never said she did or didn't because he wasn't there and his daughter didn't do it she got help, so that might not even be the problem but I wanted to bring it up just to get everything out there I know.

I have done some reading and it says there are common shorts above the transmission, behind the rear of the engine and sometimes the O2 sensor grounds out. Anyone confirm this?
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Old 11-23-2015, 09:18 PM
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Re: 2000 Jeep Grand Cherokee Crank No Start

I tested for voltage at the coil rail and there is roughly 0.5V and I believe there should be 12V. Does anyone know where to start?

I do have 5V at the cam position sensor, crank position sensor and MAP sensor. I checked for bare wires and didn't find anything.

The ASD relay still sits there and buzzes. I have the crank position sensor unhooked and nothing changes, even if I go through and unhook the cam position and MAP sensor.

But like I said I don't have voltage to the coils so nothing will happen, I checked the resistances of the coils and they checked out good. What else can I do?? I need help
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Old 11-24-2015, 05:57 AM
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Re: 2000 Jeep Grand Cherokee Crank No Start

The coil and the injectors are all fed via the ASD relay and should have 12V with ignition in run. When not started within 3 seconds, the ASD relay will fall of again.
That you have 5V at the crank sensor, shows that there is no short in one of the sensors.
The 4.0 has a common problem with shorting wire where it runs around the cylinder head, but i never heard of a buzzing ASD relay in such a case.
At this point i really would suspect the PCM to be faulty. There are several cases known of internal corrosion in the PCM which causes internal shorts.
A faulty O2 sensor will not prevent the engine from starting. When the O2 heater is shorted, it will blow fuse 16 in the PDC under the hood, but still run. When the sensor itself doesnīt perform well, it will influence the mpg or will make the engine run rough once its warmed up, but should still start normally.
Normally you can get fault codes out of the PCM using the key dance: ignition switch off-run three times and leave in run at the third time. The odometer will show DONE or any fault code(s). But since the PCM is not sending any info, this most probably will also not work.
You did check the fuses 6, 19 and 26 in the PDC and fuse 12 on the junction block?
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  #9  
Old 11-24-2015, 07:28 AM
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Re: 2000 Jeep Grand Cherokee Crank No Start

I checked all the fuses in the PDC and they are good, I don't know where fuse 12 is on the junction block? Or I don't know what you call the junction block.

I will try the key dance tonight and see if anything comes up but like you said it probably won't. I plugged in my scanner last night and found out it won't connect to the PCM. (I know my scanner should connect because I have scanned my friends Jeep that is the exact same year, so it is not the scanner)

I am going to just changed the Crank sensor tonight as well just so I can rule that out but I'm sure nothing will change unless it's grounding out internally.

I was wondering if I try a new PCM it can't damage that PCM can it? (Lets say my jeep has a short or something it won't blow the the PCM) I am wondering because if that is not the case I can just borrow one from my friend and see if that fixes it.
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Old 11-24-2015, 08:28 AM
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Re: 2000 Jeep Grand Cherokee Crank No Start

Jeep is calling the junction block the fuse/relay block which sits under the steering wheel area.
That the sanner canīt connect to the PCM is also a sign that the PCM is faulty. For sure the key dance will not work then.
Didnīt try it myself, but others already opened up the PCM and found corrosion from the casing, causing internal shorts to the PCM.
If you have 5V available when the crank sensor is plugged in, then it is a waist of money and time to change it, but that is up to you.
You can try the PCM from your friends jeep, eventhough it probably will not stay running for more then 3 seconds, since the PCM is not programmed to the SKIM (at least, if your jeep has the security key system). But if it runs for three seconds, then you know for sure that the PCM is the problem.
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  #11  
Old 11-24-2015, 10:13 AM
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Re: 2000 Jeep Grand Cherokee Crank No Start

Frank I would like to thank you for all your help, I will try the new PCM this weekend and let you know what I find!

My last two questions before I try this is there is no way plugging in a different computer to my non-running jeep can wreck his computer can it? And even if it doesn't run with a different computer if the ASD relay quits buzzing wouldn't that be enough to say that the PCM is bad?

Thank you again very very much!
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Old 11-24-2015, 03:19 PM
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Re: 2000 Jeep Grand Cherokee Crank No Start

Normally a shorted crank sensor or any other sensor on the 5V supply will bring the 5V supply down, but will do no harm to the PCM itself. So you should be save to test an other PCM. The engine should run for some seconds, even if the PCM is not programmed with the SKIM secret code, but will shut down. That should be enough to proof that the PCM is the culprit. But since the PCM switches the ASD relay, the problem must be in there.
Did you already remove the PCM and inspected the casing for deformation or corrosion signs on the outside?
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