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Unread 06-16-2008, 06:28 PM   #1
shay737
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info for ecm/ecu 98cherokee sport.

i believe my ecu went bad and im trying to find some info. iv had a couple different people tell me different things. the first is if i buy a ecu from a junk yard from the exact same vehicle i will have to have it reflased for my vin number, then the dealership told me that the vin numbers are stored permanenlty in the ecu and i will have to buy a new ecu to get it running again which is about 600 dollars. can anyone give me some info on this. thanks

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Unread 06-16-2008, 07:23 PM   #2
CJ7-Tim
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First, explain why you think the ECU/ECM is bad. What symptoms are experiencing ? What have you tested and what parts have been replaced ?

I know a local Cherokee owner that in fact had a failed ECU/ECM and purchased a replacement ($150) from the junkyard that was for the same model year and the same engine/transmission. He installed it and drove away. He did not have it re-flashed.

There are sellers on eBay that recondition and re-flash ECU/ECM to match your VIN code. IIRC the cost is less than $200.
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Unread 06-17-2008, 05:35 AM   #3
shay737
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ecu

one day it would not start up so i started doing some looking and found the fuel pump was not running so i changed it out...still nothing with some more looking i found the spark plugs were not getting any power. i bought a used ecu from a junk yard but nothing, thats when i started having people tell me that you had to have it reflashed. then yesterday i had a service tech at one of the jeep dealers tell me i will have to put a new one in. thanks for the help.
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Unread 06-17-2008, 09:08 AM   #4
CJ7-Tim
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Check all the fuses both inside and under the hood in the Power Distribution Canter (PDC). Swap the Relays around see if the fuel pump relay is bad or sticky.

Was the ECM you purchased from the same model year ?
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Unread 06-17-2008, 09:59 AM   #5
shay737
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i have already tried all the fuses and relays. the ecu i bought is from the exact same year and model jeep.
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Unread 06-17-2008, 10:10 AM   #6
jrn1023
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Have you checked for a Check Engine code? On my '98 this past winter, the engine would not start. Cranked but no fire. I replaced the CPS to no avail. I replaced the coil as there was no spark. But that did nothing. Changed the ECU still no go. Finally ran out and purchased an OBDII reader which told me the Cam Shaft Position sensor was bad. Replace and the engine started right up.

Once the engine was running again, I put the junk yard ECU back in and it still ran fine. No flashing of VIN required. Fortunately the junk yard would take the ECU back minus a restocking fee as I did not need it after all. But it definitely would have work without re-flashing.

Another moral to this story, there are numerous sensors that when bad will not allow for the engine to start. These sensors basically tell the ecu to cut power to fuel pump and ignition coil causing no fuel/spark symptoms. So exhaust your search looking for bad sensors before jumping to the ECU conclusion like I did.
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Unread 06-17-2008, 10:43 AM   #7
CharBroiled
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as jrn found out, you dont need to flash the correct VIN in the ECU for it to run. only reason to flash the correct VIN is some states may pull the VIN from the ECU and compare it against the actual vin number on the chassis during inspection. varies state by state.

some late model stuff (2005+? not sure probably varies by make) have VINs stored in several modules in the car and they all will ask each other if the VIN matches.. no match, no start. some radios also check VINs to see if there are in the correct vehicle as an anti theft measure. but thats for later years than any XJ was made.
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Unread 06-17-2008, 11:11 AM   #8
chondamx
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No reflashing needed to run, it is not your ECU that is bad...pull some codes. I had the same thing happen to me and I bought another ECU for my '98 and I plugged it up after I got the Jeep running and it still started and ran on the new ECU.

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Unread 06-17-2008, 03:21 PM   #9
shay737
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well iv given in and taken it to a shop now. they said they were unable to get any codes because there ecu is not getting any power.
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Unread 06-20-2008, 05:13 AM   #10
shay737
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got it running, it was the cps. thanks for the advise.
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