91 4.0 in a 97

[JuicedDMax]

I had a 91 4.0 built for my then totaled 91 YJ, but after years of the slow rebuild I found a 97 for cheap with a beat engine. So I thought this would be perfect to swap my newly rebuilt power train into (rebuilt my transmission as well). Well the engine appears to run fine but keeps throwing the crankshaft position sensor code. I've replaced the sensor, distributor (which was bad) even replaced the computer. Code still comes up. In the past I could reset the computer right before I went through emissions, but now they caught onto that.

Does anyone know exactly what the difference is between the different years? Am I missing something, could it be addressed by swapping out the cam and timing chain set. Or are the engine designs totaly different?


I thought the only differences between the various years were all related to the electrical/engine management items not mechanical. Naturally I don't want to swap this engine out, its basicaly brand new.

 

[superj]

i thought the electrcal was the difference too, ecu, wiring, etc

 

[Bounty__Hunter]

It's quite possible the '91 an '97 use two different CPS sensors. You may have to modify the '97 sensor to fit the '91 bellhousing or modify the bellhousing.

 

[JuicedDMax]

I do have the 97 bellhousing on it with the 97 CPS. I put a new one in, code still comes back. I suppose that one could be faulty.

 

[Jester32]

The tone wheel on the flywheel is different for the different engine controllers as well

 

[jps4jeep]

might want to check the legality i nyour state, I doubt you will have issue since your swapping a 4.0 for another 4.0, and no one will notice, but in my state it is illegal to swap in an older motor into a newer vehicle and have it legally pass RMV inspection. again, I doubt anyone would notice though.

as mentioned, the 91 motor is ODBI the 97 is ODBII you will need to use all the 97 sensors, exhaust, ECM, ignition. etc.. I am not sure what year, but I know the TJ's were distributorless, can't recall if it was 97 though, this might pose an issue in your swap if it is, I think it was a year or two later that they went to coil on cyl. ignition, but someone else can verify this or not.

 

[Utah_jeepster]

The 97 through 99 or 2000 still had a distributor.

Sent from my Android using Jeepz

 

[jps4jeep]

Thx, didn't realize it was that late.

 

[JuicedDMax]

Jester32, would you know if swapping the flywheel outwould work or would it require a cam swap as well. I've kept everything from the 97 except the block.

 

[Jester32]

Should work. The cam is just a gear the cam sensor is driven by the cam just like the distributor. May be in the distributor on 97. The crank sensor signal is generated by the flywheel.

 

[Jester32]

Sorry the can just has a gear not is a gear. Hope I didn't confuse ya

 

[JuicedDMax]

Thanks,

I guess thats my next step, time to start searching for a flywheel.