I see various ECMs for sale online, some saying it will need to have your VIN programmed into it for some reason. I also came across some mention of ECMs essentially loosing their program ? Can anyone explain this? On a related note, I saw some where some issue of a security feature needing to be addressed if you swap ECMs?
Reason I ask - I am doing a 4.0 conversion on my 2.5 TJ. Just bought an engine which came with its ECM (technically I guess it is called a PCM). If I use this ECM with the motor it came with - am I OK? Or is the ECM somehow getting some signal of the VIN of the vehicle and will need to have the vehicles VIN programmed in?.
That suggests then the ECM has programming in place for different configurations?
What if I no longer have what the vehicle had stock? - as in a 98 Grand Cherokee engine, with the ECM that was paired with that engine, and either a AW4 tranny (which has its own control module and did not come from the same vehicle the engine did) or a AX-15 if i can find one, all going into a 97 TJ which stock had 4 clyinder 5 speed.
I would assume the Jeep Powertrain Control Module (PCM) works like other Chrysler PCMs. I own a Dodge Durango and a lot of Durango and Dakota owners on the boards swap PCMs. I have had a couple of PCMs in mine. Yes there is a VIN programmed in the PCM. The VIN in the PCM will not cause any operational issues if it is installed in another vehicle. On the Durango/Dak, if you have a new PCM and a VIN is not programmed, the ABS dash lamps will illuminate. The one issue Durango/Dak is, if the PCM has been used in a vehicle with the factory security system, the PCM will not work in a vehicle that does not have the security system.
The computer is not going to loose it's program. There are parameters and adjustments the PCM makes by learning after the vehisle has been driven. Those learned parameters can be reset.
100% whenever you are welding, disconnect the computer.
Where wheel size, gear ratio etc stored on the Jeep? On the Durango/Dak it's in the Controller Anti-lock Brake (CAB). Obviously it's not there on the Jeep as not all models have anti-lock.
I think the main reason the VIN is programmed in is to make the vehicle "unique". VIN numbers are stamped all over the place, some encoded where you need special equipment to find them. This way if your vehicle gets stollen and stripped, they can trace the parts back to the seller through multiple buyers. This is what helped the FBI find the Oklahoma City bomber...from the VIN on the rear axle.
FWIW - on the older Cherokees at least, those using the AW4 tranny, there is a separate tranmission controller module. Later ones intergrated engine and tranny control into one module though.
Related question (sort of...maybe worth its own thread). I know in 1998 Jeep came out with the Smart Key theft deterent system. (I think this is the security topic I mentioned in my original post here) Not sure if ALL had it, or if only those with certain option groups did. I wonder if this is part of the need for VIN programming. Going further with this topic - The ECM that came with the engine donor for my 4.0 conversion is from a 98 Grand. I assume it is a SMart Key version. I also found a source for a ECM from a 98 TJ - dont know for sure if it had the Smart Key set up yet or not. If it does - how do you get around using a smart key equipped ECM in a non smart key vehicle?