Crack but no start - JeepForum.com
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post #1 of 40 Old 08-13-2020, 06:31 AM Thread Starter
gdukeh
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Crack but no start

My 99 jeep grand Cherokee will crank but won't start. I tried turning key 3 times to get code but nothing came up didn't even say done like usual. The check gauges light stays on as well as a key with a 🚫 and a fuel light. Any help will be greatly appreciated.

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post #2 of 40 Old 08-13-2020, 09:00 AM
Bigrigr
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What engine do you have? check fuel pressure at the port on the fuel rail if its a V8

'00LMTD-4.7l,242hd,D30,D44A,3.73's,True-trac front,Spartan rear,4" short arm lift,JK'sW/32's
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post #3 of 40 Old 08-13-2020, 10:08 AM Thread Starter
gdukeh
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It a 4.0 straight 6
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post #4 of 40 Old 08-13-2020, 12:14 PM
Waterluvr
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Your PCM was on the way out, and now it's gone it's not powering up the ASD relay and the bus com circuit is shorted.

Take out the three 10mm bolts on the coolant tank and slide it forward you don't have to disconnect anything that will allow you to see the sticker on the pcm cabinet.

Take a picture of the part number sticker, go to the pick and pull yard and get another one and send me a pm I can flash it for you so it's plug and play drop in ready.

You have to match part numbers, the alpha suffix at the end of the part number can be anything in the (AE - AJ) range.
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post #5 of 40 Old 08-13-2020, 02:35 PM
snowbuggy
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I never heard of a PCM going bad until I got some jeeps. My 2001 battery went dead in a week and now I get the key light. This is just a parts vehicle but it is nice to be able to move it around. That's why I hate to put any more money in it. If I found another pcm and had waterluvr help me, does it have to be the same year PCM? I guess I can't just unplug the halo thing around the key switch huh?
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post #6 of 40 Old 08-13-2020, 03:33 PM Thread Starter
gdukeh
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Update....... i had it towed home today. Check engine light comes on after the key is in the ignition for a minute or two but still not throwing any codes on dash. We did get it started with starting fluid for a second. We are thinking no fuel to engine. With these symptoms correspond with a bad PCM as well. I tried to pm but wouldn't let me for some reason. Greatly appreciate the help. Thanks again.
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post #7 of 40 Old 08-13-2020, 06:11 PM
Mattyjm
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If it's not throwing any codes in the odometer by using the key dance trick, the next step would be to have a OBD scanner hooked up to see if the PCM is communicating at all. I don't think that yours is, and that's the beginning of your problem.

When it's not running, or not running properly, and there's no codes set and no communication whatsoever from your PCM, I'd say that's your problem. But, I'd still check to see if you're getting any fuel pressure. THEN, put a scanner on it.

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post #8 of 40 Old 08-13-2020, 07:13 PM
Waterluvr
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Quote:
Originally Posted by snowbuggy View Post
I never heard of a PCM going bad until I got some jeeps. My 2001 battery went dead in a week and now I get the key light. This is just a parts vehicle but it is nice to be able to move it around. That's why I hate to put any more money in it. If I found another pcm and had waterluvr help me, does it have to be the same year PCM? I guess I can't just unplug the halo thing around the key switch huh?
It has to be same year, part number is especially important due to hardware changes in the modules.

For example I see you drive a 2004, there was a much needed improvement to the fan low / high speed control relay function that an earlier module would not operate properly.

Always match the part number of the sticker on the pcm, at the very end there is a suffix with (AE-AJ) you can use anything in that range I reflash the software with updates to get them current.
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post #9 of 40 Old 08-13-2020, 07:34 PM Thread Starter
gdukeh
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Thank you very much. I will check it out tomorrow and let you know what i come up. Greatly appreciate the help.
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post #10 of 40 Old 08-14-2020, 07:23 AM
snowbuggy
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Quote:
Originally Posted by gdukeh View Post
Update....... i had it towed home today. Check engine light comes on after the key is in the ignition for a minute or two but still not throwing any codes on dash. We did get it started with starting fluid for a second. We are thinking no fuel to engine. With these symptoms correspond with a bad PCM as well. I tried to pm but wouldn't let me for some reason. Greatly appreciate the help. Thanks again.

With the key light on it should start and run great for about 2 seconds. I do believe the security system is shutting of the fuel.


thanks for the clarification waterluvr
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post #11 of 40 Old 08-14-2020, 08:01 AM
Waterluvr
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I'll give you guys an outline of how the pcm and skim security module function during the key on / crank / start sequence.

There are unique identifiers programmed into both of them, they are based on the VIN number and a skim security code in both modules and skim also has an RF frequency identifier programmed that is unique to each key.

Normal operation occurs when you turn the key and pass the on position, both modules power up and exchange information over the pci data bus and the skim pings the key via the antenna ring around the lock cylinder.

Provided all is well the skim see's a programmed key code and exchanges a digital handshake with the pcm module and off you go.

In the event somethings wrong, say an attempt is made to steal the Jeep by a scumbag that has a WJ key cylinder and key the Jeep will start for 2 seconds when the pcm powers up and then the skim will ping the pcm to shut down the ASD relay which will power off the fuel injectors and ignition coils.

If someone swapped the pcm's and tired to steal it so long as the module wasn't defective same thing would happen, you'd have a crank/start/run for 2 seconds and during that time the pcm and skim won't exchange the proper digital handshake and the pcm will kill the ASD relay.

The most common failures I see in Chrysler / Jeep pcm's is a crank no start condition due to internal board failure of the ASD relay circuit as it's a main voltage path on the circuit board and get's very hot during use.

Failed idle air control drivers are next on the list, they aren't as robust and live right next to the ASD relay circuit.
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post #12 of 40 Old 08-17-2020, 03:46 PM Thread Starter
gdukeh
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Quote:
Originally Posted by Mattyjm View Post
If it's not throwing any codes in the odometer by using the key dance trick, the next step would be to have a OBD scanner hooked up to see if the PCM is communicating at all. I don't think that yours is, and that's the beginning of your problem.

When it's not running, or not running properly, and there's no codes set and no communication whatsoever from your PCM, I'd say that's your problem. But, I'd still check to see if you're getting any fuel pressure. THEN, put a scanner on it.
Finally got a OBD hooked up and it wont link to vehicle?
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post #13 of 40 Old 08-17-2020, 06:18 PM
Waterluvr
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Originally Posted by gdukeh View Post
Finally got a OBD hooked up and it wont link to vehicle?
The pcm is not communicating over the bus to the data link connector where you plug a scanner in.
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post #14 of 40 Old 08-17-2020, 07:06 PM Thread Starter
gdukeh
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Originally Posted by Waterluvr View Post
Quote:
Originally Posted by gdukeh View Post
Finally got a OBD hooked up and it wont link to vehicle?
The pcm is not communicating over the bus to the data link connector where you plug a scanner in.
What do I do now?
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post #15 of 40 Old 08-17-2020, 07:51 PM Thread Starter
gdukeh
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Originally Posted by Waterluvr View Post
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Originally Posted by gdukeh View Post
Finally got a OBD hooked up and it wont link to vehicle?
The pcm is not communicating over the bus to the data link connector where you plug a scanner in.
What do I do now?
Bad PCM correct?
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