[trikdacy]

Original owner here. Car special ordered, and picked up Oct-1993. About 15 years ago I replaced the original ECM unit with the Mopar High Performance unit. I also installed Thorley Ceramic headers, K&N Air intake, a Demon ignition kit and a MagnaFlow Street Series Cat-Back Performance Exhaust System. My Jeep is well maintained and runs great. I now decided to go back to the original ECM unit, because I am tired of listening to 2,000 RPM to maintain 55-60 mph. Unable to locate my original ECM in my "archives" I decide to purchase an ECM from Flagship One. Here's the problem I need help with. Even though the ECM is based on the VIN, there happens to be three different ECM's associated with the 1994 5.2l ZJ, no matter the VIN. Various web sites have one or all of the three ECM versions. Flagship One asked for the part number on the orginal ECM of which I do not have anymore. A few dealers did not have the info based on the age of my ZJ. I also called FIAT/Chrysler support, and they gave me the three part numbers for the ECM's not specifying which one is the correct one. The part #'s are 56028112, 56028112, and 56029302. Can I have an assist fellow members as to which part is the correct part?

 

[Mr. Mike]

Guys with Mopar performance ECUs all the time complained about taking their vehicle in for service and getting it back running like it was stock. The dealer as a matter of procedure would re flash the eprom with the latest Mopar firm ware wiping out the performance fuel and air curves. If you are never going to use the performance ECu just get it re flashed.
That said with 3.73 gears and 29 inch tall tires 2000RPM is normal, why not change back to stock exhaust?

 

[trikdacy]

I am changing my ECM to get back the original shifting, improved gas mileage, and lower RPM at a given speed. I now travel around 200+ miles a day. Zipping around the city is fine and fun with the High Performance ECM, and I like the sound and do not mind 10mpg in the city. It's the 3-4 hr. trips at 2000RPM I want to change. The exhaust is much quiter at even 1800 RPM's. I never brought it back to a Jeep dealer since my extended warranty ran out many years ago. I changed the ECM way after the warranty ran out. According to my detailed self kept logs there were some changes with the High Performance ECM. Prior to the high performance ECM my gas mileage was 23mpg at 1600RPM 55-60mph using regular grade gasoline. After changing the ECM my gas mileage went down to 17mpg at 2000rpm at 55-60mph using premium grade gasoline. I did this mileage check on the same road under the same conditions. With the High Performance ECM, the addition of the headers, air intake, ignition, and exhaust system my gas mileage went up to 21mpg at 2000rpm at 55-60mph using premium grade gasoline. After contacting the MOPAR people at FIAT/CHRYSLER they were kind enough to look up the original build in their offline data. MOPAR stated a replacement ECM # R6028113 which was originally 56028113 at the time of build is no longer manufactured. Being a retired systems engineer, speaking to the JEEP techs at JEEP local facilities left me feeling technically uneasy and just replacing the ECM would be more convenient, and retain the High Performance ECM as a spare. Flagship One will supply the "new" ECM. This is all fun to me, not a make or break. I do long for the day of my 1966 Nova with a 327 and it just had plugs and points.

 

[Mr. Mike]

Seems odd to me that RPMs went up at cruising speed with the performance ECM. The transmission not shifting into overdrive or the torque converter not locking up?

 

[trikdacy]

The change in RPM's have been present since the ECM change since 2014. Just today, now that it's warmer outside, I found that after my last trip to my local garage ,about a month ago, my passenger side vaccuum lines were either not connected, or reconnected wrong, and they left this rigid vaccum line off on the drivers side, and it wraped around my master cylinder. I am not sure if these things had any effect on my gas mileage, but I bet this did add to things ooperating differently the past mnonth. Once I connect all these lines up correctly, according to the service manual, I will update. When I depress the O/D Off switch to "on" the RPM's do go up. I use this in the snow & rain. How would I know if the torque converter is locking up? The above statements I made are still the same, but I have to connect all these lines before I do another update to this thread. Thanks for the info.

 

[Mr. Mike]

Torque converter lock up occurs when the trans shifts into overdrive when cruising. Some times it feels like it shifter into a higher gear. How were you even able to dive with vacuum lines off because that increases the idle speedso putting it into gear really thumps.Anyway good luck replacing the ECM and thanks for the replies.