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New ECM- Runs beautifully... for 3 seconds

T

tragiccomic1972

NAXJA Forum User
Location
Snow Camp NC
2000 XJ SE, 4.0, Auto 2wd

I bought this with a blown head gasket and a few other problems, meaning to fix it and keep it as a beater. It has fought me every step of the way.

Long story short, it needed an ECM (the one on the drivers side fender) I got the part number off the old one, went on ebay and got a used one with the same number. It starts and runs beautifully.... for 3 seconds at a time... anyone had this before? I need to get this thing going!
 
Sounds like a fuel pump issue. Search around, I'm not sure, but different circuits run the pump for the "start" (cranking) phase and the run phase. Relays?
 
The ECM you got was originally in a rig with security. The ECM is the same part number, but on first fireup with a new ECM if it finds the security module, it learns that and you can't make it 'unlearn' it. If your rig doesn't have a security module (came without the security option), then the ECM can't find it, and shuts down.

send it to sideways and have him reset it.

A friend of mine went through this with three different "new" ECM's from rockauto.com. Apparently they weren't actually 'new', since they would have skipped all the security crap if they'd found no security module on first fireup.
 
If the vehicle is equipped with sentrykey(gray oval key) the ECM and SKIM need to be matched, any time one is replaced the vin needs to be entered as well ad a 4 digit access code from the dealer.
 
What happens with the SKIM Is when the ecu powers up and it sees a SKIM on the CCD bus it enabled the security bit in the EE area of the ecu which can't be turned off, not by the dealer or any "ecu refurbishers". The 4 digit access code that XJ Jay is talking about is only if you already have a SKIM module and you need to learn new keys to the SKIM module or download the SKIM data into the ecu (for backup purposes). I could go into the details of how the SKIM module works and how to get around it, but that is not public knowledge.
 
sidewaysstarion said:
What happens with the SKIM Is when the ecu powers up and it sees a SKIM on the CCD bus it enabled the security bit in the EE area of the ecu which can't be turned off, not by the dealer or any "ecu refurbishers". The 4 digit access code that XJ Jay is talking about is only if you already have a SKIM module and you need to learn new keys to the SKIM module or download the SKIM data into the ecu (for backup purposes). I could go into the details of how the SKIM module works and how to get around it, but that is not public knowledge.
Click to expand...

An even better explanation. However, what is not clear... the dealer and ECM refurbishers cannot reset this bit, but you can? or it's a lost cause if you hook up an ECM on a rig with a SKIM and fire it up... that ECM is always tied to a vehicle with security after that?
 
NotMatt said:
An even better explanation. However, what is not clear... the dealer and ECM refurbishers cannot reset this bit, but you can? or it's a lost cause if you hook up an ECM on a rig with a SKIM and fire it up... that ECM is always tied to a vehicle with security after that?
Click to expand...

Well the bit lives deep in the ECU and in a protected area that Chrysler didn't want people to have access to. This is to prevent someone with a dealer scan tool from just breaking the ignition on a car, unplugging the skim and resetting the security and driving off. You have to remember that both the dealership scan tools and the ecu refurbishing tools are sold to the general public, so Chrysler didn't want to make it easy to bypass the the security in the ecu. If you were going to steal a car with a SKIM module and you had a dealership scan tool you could in theory get the 4 digit pin from Chrysler, learn a new key to the SKIM and drive off that way, but that takes a fair bit of time.
 
Makes complete sense, thanks for the extra explanation. It explains why my buddy had so much trouble with "new" ECM's (that were most likely refurbished units).
 
sidewaysstarion said:
If your friend already has a SKIM module in his jeep, and he gets a "refurbished ecu" then all he needs to do is make sure the VIN in the ECU matches the VIN on the jeep and it should all work.
Click to expand...

His problem was actually the same as the OP's... 93 grand cherokee (the rare one with no options, 4.0L and an AW4 trans), specified no security option when ordering the ECM. Three different "refurbished" ECM's arrived, he plugs them in and fires the rig up and it shuts down after three seconds. Each of the first 2 or 3 ECMS (can't remember the exact many times he had to send an ECM back) was searching for a non-existant SKIM module on his 93 grand with NO security... when it didn't find it, it shut the engine down.

Because these ECM's all came from vehicles that originally did have a SKIM module, the bit was set in all the ECM's he was sent even though they were "refurbished".
 
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