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Thread: fried PCM maybe? HELP!!

  1. #1
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    Question fried PCM maybe? HELP!!

    Hey there, I'm a newbie here and really need some help. My local dealer is being an ass about my issue. I hope someone here can help. Here goes...I've got a '96 Grand Cherokee Laredo, automatic, 4.7 liter straight 6. Bought it from an older gentleman in November of '09. Hear me out before saying,' well duh, there's your problem'. I had a 1000 watt stereo system professionally installed in December. I also had a 40 farad capacitor installed to help protect the charging system just in case. I discovered after everything went to sh** that 40 farads was overkill. Anyway, about a month after the install, things started going all wonky. I was heading north to visit family when it hit the fan. While I was driving I heard a chime go 'bing' and looked at the gauge cluster. The 'check gauges' light comes on and the batt. indicator dropped to zero, so I killed anything electrical just is case; the stereo,lights, and the heater; it was a damn cold drive home. I wasn't pushing the stereo. It was low enough that I was able to carry on a conversation at normal volume, so I know the stereo wasn't pulling any juice. I turned around and made the 2 1/2 hour drive without incident. Got home, turned it off, waited about 30 sec. then went to start it: dead. I disconnected the whole stereo, bought a new batt. and put it in. Started right up. Ran for about a week then while going to the store it happened again, same thing. Battery indicator went to zero, 'check gauges' comes on. I go home, turn it off, wait 30 sec., and try to start it. It starts. Indicator is normal. Within 5-10 mins. it happens again. Every time it would start, drive about 10 mins. then the indicator dies and the gauge light comes on. About 3 weeks ago, the lights and all started dimming while driving. Got it home just as it died. This tells me the alternator isn't charging the battery. Well, I pulled the alt. out yesterday and brought it to Autozone so they could test it...100% functional. I presume this leaves only 2 more options: wiring on the fritz or the PCM is fried. I can replace the parts myself, that's not a big deal. But the local dealer tells me that they are the only ones that can test the PCM. What do I do? I am on an extremely fixed budget so I can't afford to bring it anywhere. The cheapest PCM I've found is $200. The dealer told me $400-500 through them. At these prices I'm dead in the water for another 2-3 months. Any input would be much appreciated. Now, you'll have to excuse me, I need to go crank my amp and wail on my guitar

    D
    Last edited by cypher74; 03-17-2010 at 10:20 AM.

  2. #2
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    Quote Originally Posted by cypher74 View Post
    Hey there, I'm a newbie here and really need some help. My local dealer is being an ass about my issue. I hope someone here can help. Here goes...I've got a '96 Grand Cherokee Laredo, automatic, 4.7 liter straight 6. Bought it from an older gentleman in November of '09. Hear me out before saying,' well duh, there's your problem'. I had a 1000 watt stereo system professionally installed in December. I also had a 40 farad capacitor installed to help protect the charging system just in case. I discovered after everything went to sh** that 40 farads was overkill. Anyway, about a month after the install, things started going all wonky. I was heading north to visit family when it hit the fan. While I was driving I heard a chime go 'bing' and looked at the gauge cluster. The 'check gauges' light comes on and the batt. indicator dropped to zero, so I killed anything electrical just is case; the stereo,lights, and the heater; it was a damn cold drive home. I wasn't pushing the stereo. It was low enough that I was able to carry on a conversation at normal volume, so I know the stereo wasn't pulling any juice. I turned around and made the 2 1/2 hour drive without incident. Got home, turned it off, waited about 30 sec. then went to start it: dead. I disconnected the whole stereo, bought a new batt. and put it in. Started right up. Ran for about a week then while going to the store it happened again, same thing. Battery indicator went to zero, 'check gauges' comes on. I go home, turn it off, wait 30 sec., and try to start it. It starts. Indicator is normal. Within 5-10 mins. it happens again. Every time it would start, drive about 10 mins. then the indicator dies and the gauge light comes on. About 3 weeks ago, the lights and all started dimming while driving. Got it home just as it died. This tells me the alternator isn't charging the battery. Well, I pulled the alt. out yesterday and brought it to Autozone so they could test it...100% functional. I presume this leaves only 2 more options: wiring on the fritz or the PCM is fried. I can replace the parts myself, that's not a big deal. But the local dealer tells me that they are the only ones that can test the PCM. What do I do? I am on an extremely fixed budget so I can't afford to bring it anywhere. The cheapest PCM I've found is $200. The dealer told me $400-500 through them. At these prices I'm dead in the water for another 2-3 months. Any input would be much appreciated. Now, you'll have to excuse me, I need to go crank my amp and wail on my guitar

    D
    i have the factory scan tool and can test your pc

  3. #3
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    I can replace the parts myself, that's not a big deal. But the local dealer tells me that they are the only ones that can test the PCM. What do I do?
    Take extra 60.00 your gonna save and join our club it will be the best 60 bucks you have ever spent.


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    it could possibly be a loose belt. if the belt is too loose it wont turn the alternator enough to charge the battery. also check to see if the belt tensioner is stuck.
    98 TJ 3.5" R.E. lift,super30/35 kits, Alloy axle shafts, Auburn Ected lockers F/R,Warn rocker guards, winch, rear bumper, Smitty front bumper, AA sye, tom woods shaft, 33" MTZ's on soft 8's, optima yellow top.

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    Have mt check the pcm is a good start. Could be that or just a bad ground from the engine to the block ect. Some of the grands are also known for ignition switch problems also. Next time it happens jiggle the key and see what happens. Grounds can get coroded over time and will need to be cleaned up. Check the fuse pannels also to make sure there clean and not coroded. Best of luck.
    93zj 5.2 with factory skid plates. Dynomax muffler, open intake, american racing rims, front tow hooks and side band cb. 3.5 RE lift as of 1/6/10. lets not forget I got branded to. 31 bfg's
    Dan

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    Talking Thx for the input

    Thanks for the input guys. Mastertek2000, thanks for the offer for the test but I'm up in Fall River. I'm going to roll underneath and see if anything is loose. I checked the belt, all's nice 'n tight. Did the key jiggle thing...nada. BUT...I made an interesting discovery yesterday. I don't know what it is yet, but...right above the PCM, there are 3 looms of wires. Two big looms and one smaller one. The 2 larger ones are connected to the fire wall. The smaller 2 prong loom is connected to...?? I'm not finding the female end of the connection so I'm just going to move the coolant tank out of the way and poke around. Hopefully I'll find the problem. Oh what a happy day that will be. Hey Ltrain, what club?? You piqued my intersest...

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    Quote Originally Posted by cypher74 View Post
    Thanks for the input guys. Mastertek2000, thanks for the offer for the test but I'm up in Fall River. I'm going to roll underneath and see if anything is loose. I checked the belt, all's nice 'n tight. Did the key jiggle thing...nada. BUT...I made an interesting discovery yesterday. I don't know what it is yet, but...right above the PCM, there are 3 looms of wires. Two big looms and one smaller one. The 2 larger ones are connected to the fire wall. The smaller 2 prong loom is connected to...?? I'm not finding the female end of the connection so I'm just going to move the coolant tank out of the way and poke around. Hopefully I'll find the problem. Oh what a happy day that will be. Hey Ltrain, what club?? You piqued my intersest...
    our home base USAJEEPOWNERS .inc is in New Bedford

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    Do you have a 4.7 V8 or 4.7 straight 6? A stock straight 6 is a 4.0 but if you have a 4.7 straight 6 then its a stroker motor, in this case the PCMs need to be re-flashed and can give you trouble sometimes. I've seen whacky readings with reprogrammed units. Also dont always trust bringing it to an Autozone type place because sometimes the issues are sporatic and they only test it quick.
    97 TJ - not much is factory - currently being finished!

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    Default I'm losin' it...

    Hey Bump, my bad about the engine. It is a 4.0 straight six, not a 4.7. I've checked the grounds that I can find and nothing is disconnected. I moved the coolant reservoir to see if I could figure out where that 'extra' loom of wires goes and there is just nothing there for it to connect to. So, since I don't have a tester, I tried to do it the way the Haynes manual suggests; by turning the key to on then off 2x then leave it in the on position and wait for the 'check engine' light to start blinking. So I did, and counted the number of blinks. One problem...I didn't get the same number of blinks on any of the 4 times I did this. Now I have to throw the damn battery in backpack again and bring it to have it charged up before it completely discharges. Anymore ideas would be great! Thanks for reading.
    "we the unwilling led by the unknowing, are doing the impossible for the ungrateful. we have been doing so much for so long with so little, we are now capable of doing anything with nothing"

    unknown

  10. #10
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    On a 96 you should have a test port under the dash on the drivers side. Any Advance or Autozone should be able to plug in and test for codes. I had a charging issue with mine and the alternator bench tested good but when I put it back in no go. So I put in a new one and now all is well. The charging system is controlled threw the pcm on the grands. The pcm is very sensitive to the voltage and amps the alt is putting out. Also any Advance or Autozone can test the charging system in the Jeep. Alt should be putting out 14-15 volts.
    93zj 5.2 with factory skid plates. Dynomax muffler, open intake, american racing rims, front tow hooks and side band cb. 3.5 RE lift as of 1/6/10. lets not forget I got branded to. 31 bfg's
    Dan

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