CasualMechanic...Your compliment is what makes the magazine and forums gratifying...Thanks! Response to the 2.5L TBI coverage has been significant and meaningful...
The flywheel on the 2.5L TBI and MPI engines, as you know, provides the crankshaft position pulse. This is accomplished by a set of carefully positioned "teeth" that set up a field as the flywheel rotates. The odd "tooth out" helps the ECU or PCM determine the top-dead-center (TDC) position of #1 piston and the corresponding crankshaft position. The sensor at the top of the clutch housing is a pickup that interacts with this clocked set of cogs on the flywheel.
Every other rotation of the crankshaft, #1 piston is up to fire. As for ignition, though, the ECU or PCM is simply looking for a reference to TDC: The rest of the spark timing and fuel management is controlled by the computer itself. On your TBI engine and the MPI engine, an ignition distributor directs the controlled spark to each of the distributor cap spark leads, using a typical rotor. Like a conventional distributor, the distributor shaft gets driven by the camshaft.
You actually have two concerns: 1) whether the TDC signal is the same (pickup and flywheel wise), and 2) will the TBI distributor interface with the PCM and other components. The second point simply clarifies whether you need to change out the distributor as well.
Here's the rundown on the parts...Beginning with the distributor, the TBI distributor is not the same as the MPI distributor. You need the MPI distributor for this conversion...As for the flywheel, again you find a different part number for 1991-up MPI engines: Mopar 53005526. Your OE flywheel for the TBI engine is a Mopar 33002408. The TBI flywheel is no longer available from Mopar, the 1991 up flywheel is still available. Here are the Jeep models using the TBI type flywheel, none is newer than 1990:
The 53005526 MPI 2.5L flywheel has two counterpart flywheels: 53020578 and 53010555AA. Jeep coverage is wide, from 1991-2002 in 2.5L MPI applications. (The late TJ 2.4L four uses another flywheel type.) There is a difference between the TBI and MPI flywheels, and it's good that you have the donor flywheel.
If I were doing this job on a 2WD Comanche MJ, I would simply remove the transmission and clutch housing to access the clutch assembly and flywheel—unless you prefer removing the engine to install the MPI parts. The engine is relatively short and easy to support while removing the transmission, there's enough room to tilt the engine slightly for access to the clutch housing bolts, and the flywheel is readily accessible at that point. The factory method for changing out the flywheel is just a few steps beyond a clutch cover and disk replacement, and this might be a smart time to renew the clutch assembly.
Without a transfer case, you only have the rear driveline to remove, the Aisin AX4 is relatively easy to remove, and you're there. Make sure the used flywheel has a flat, crack free and usable clutch surface. If the flywheel needs machining, find a capable shop that understands the Jeep/AMC flywheel designs and has proper tooling for the surfacing.
Let us know what the actual difference is between these two flywheels, it should be apparent. A couple of photos would be very helpful, CasualMechanic...Thanks!
Everyone is here for more questions on your project...You will also need the higher output fuel pump that I discuss in the recent/ongoing YJ Wrangler Jeep 2.5L TBI troubleshooting forum exchange: