ECU questions - JeepForum.com
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post #1 of 11 Old 01-22-2020, 07:40 PM Thread Starter
Submariner
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ECU questions

To change the ecu(computer) does it need to be programed for the VIN that it is going in?

Shop told my boy that his computer is bad and he needs a new one that is porgrammed for HIS VIN. he cannot get one from another 99 cherokee to just do a plug and play.

Are they blowing smoke up his A$$ or what?

What is the story on swapping ECU?

I did not think that it would be anything but a plug and play as long as you are going from 99 cherokee to a 99 cherokee, maybe a 98 or 00, 0r 01,

What is the right answer guys.


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post #2 of 11 Old 01-22-2020, 08:05 PM
car6car
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del

04 Grand (dead)
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post #3 of 11 Old 01-23-2020, 05:50 AM
CJ7-Tim
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Dude, you gotta stop posting BS.

The XJ Cherokee has no BCM, and the only part that is involved in this swap is the ECU itself.


If a 1997-2001 Cherokee owner needs to replace the ECU, a junkyard ECU with the exact same part number will run. If the donor XJ and the recipient XJ are the same model year, and the same engine + transmission, no re-programming necessary. The only thing one must do is verify that the donor XJ Cherokee did not have the Chip-in-Key SKIS anti-theft option enabled. Often 98 and 99 XJ ECU's will interchange with no issues. If the Cherokee has to pass a smog test, and the test involves a VIN check of the ECU then re-programming would be necessary to pass the test, but not to run and drive.

Keep in mind that many repair shops or mechanics that are not very good at diagnostics and will often blame the ECU for problems or malfunctions that they cannot diagnose. Replacement of the ECU should only be considered after a thorough and in-depth diagnostics and trouble shooting of the Check Engine Light trouble codes as well as the more common and more likely malfunctions.
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post #4 of 11 Old 01-23-2020, 09:07 AM
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As always I hate to condemn a PCM. Yeah anal I know BUT I gotta ask -
Tell us the issue that has them wanting to replsce the PCM?
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When I see the price of OEM I think aftermarket.
When I see the quality of aftermarket I think OEM.
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post #5 of 11 Old 01-23-2020, 09:30 AM
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My Mom's Oldsmobile went through a few ECM's. We always just got a junkyard unit and took it to a local Clearway Auto parts store. They re-flashed it with all the latest upgrades for $100.

Mark in Queens- Home of Spiderman and the Ramones
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post #6 of 11 Old 01-27-2020, 12:24 PM Thread Starter
Submariner
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ok guys it is like this.
Cherokee starts up no problem
gets warm idles ok, then run down the road, get about 1800 rpm and it stutters, coughs, back fires.

change the plug, changed the sensor on the flywheel, Changed the distributor, cap, rotor, wires, Maybe it would be easier to say what we did not change on the dang thing. Ecu has been changed . I am at a loss on what to do next except start changing the harness out.

Suggestions would be nice.

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post #7 of 11 Old 01-27-2020, 12:44 PM
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No codes? Put a scan tool on it. It should be lighting up with symptoms like that.

Mark in Queens- Home of Spiderman and the Ramones
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post #8 of 11 Old 01-27-2020, 04:34 PM
jtec
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no codes you are checking even if the light is OFF?
IDEALLY a scanner we can see live data. 99 is OBDII lots to see.

BUT if no codes lets look at things ECM does not monitor
FUEL pressure. you need a gauge. post PSI.
Exhaust back pressure - a vacuum gauge or a back pressure tester.
Loosen the gas cap - did you hear a rush of air?
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When I see the price of OEM I think aftermarket.
When I see the quality of aftermarket I think OEM.
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post #9 of 11 Old 01-27-2020, 05:00 PM
CJ7-Tim
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Test and diagnose before buying parts. Because Oldsmobile didn't build any Jeeps, the ECU is probably fine.


As suggested, check for any active or pending CEL Trouble Codes. Use an OBD-II reader to monitor the Live Data. Based on the limited diagnostics and symptoms briefly described, one might suppose that the issues occur when the ECU switches from open loop warm-up mode to closed loop running mode. Test the O2 sensors, inspect their fuses, wire harnesses, and wire plugs. Test the Coolant Temperature Sensor. Test the Coil.
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post #10 of 11 Old 01-28-2020, 08:02 AM
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post #11 of 11 Old 01-28-2020, 06:57 PM
NavyJeepGuy
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flagship one has pre-programmed ecu's for his Jeep. He DOES need to provide the VIN for it, and they will put all updates into it as well.
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