Looking at a 2001 XJ to buy. Current owner recently swapped the motor. Put a 97 motor in it. He says it's misfiring and throwing a code for the O2 sensors.

I'm not too familiar with these, but from all the research I've done online, it looks like in 01, they used the new exhaust manifold set up where they use two manifolds. One for cyls 1-3 and one for 3-6, with an O2 sensor on each, and an additional sensor downstream as well. From what I understand, that means the 01 had 4 sensors compared to 2 in the 97 models. If he didn't bother to use the 01 manifold and put the 97 on there, that should be the source of his codes and misfire, if I'm correct.

I'm here to ask if I'm correct in my assumptions, as well as to ask if there is a course of action besides swapping the appropriate year motor back into the vehicle. For example, would a set of 01 exhaust manifolds swap onto the 97 motor just fine with the correct amount of O2 sensors in place?

Thanks for your time and input!

 

I believe that you could be correct in that some of these issues could be cause of what he did or did not do when he put the '97 motor in.
The question is what exactly did he do.
Now remember that a '01 does not have a distributor also.
I am hoping he swapped the gear drive and the camshaft positioning sensor in place of the distributor from his old '01 motor.
There is not a coil in the traditional sense either.
It has what we call a coil rail, or bar, that goes right on all 6 spark plugs at once.
Hoping he took care of that too.
You have to find out what head and exhaust is on the motor. Exhaust is easy. Can tell just by looking.
You would have to figure out what head is on there too.
So the correct head would be 0331. A '97 I believe would be the 0630.
So if he used the '97 head but with the '01 exhaust did he use the adapter plate?

https://jeepexhaustadapter.com/

Exhaust ports are larger on the '97 head.
So as far as swapping in the correct motor goes don't think that would be necessary.
But what you will have to do or how much money you will have to spend is unknown until you know what he did.
I say go by a worst case scenario deal.
Assume you have to buy the adapter plate, a complete '01 exhaust (exhaust manifolds back), and 4 O2 sensors.
Can you live with that cost and with the work involved.
And that is assuming he swapped it too distributorless and is using a coil rail.

 

Is the ECU a 1997 or a 2001?

 

And starting in 2000, the downstream O2 sensors participate in determining air-fuel mix, so a 2001 ECU will be looking for that.

Word.

 

The 01 has a 2 piece exh manifold that has a cat and a pre and post o2 sensors in each segment so there are 4 o2 sensors and 2 cats all up in the manifolds above the downpipe connector. The head in the 01 is different than the 97 so the manifolds are not interchangeable .you can use the 97 block but you need to reuse the 0331 head and manifolds from the 01 . If you go with the 97 head and exh sysyem ....you must seriously modify the exh to make it match up to what the 01 computer is looking for. I have done this but it takes a lot of explaining and help from a good exh shop to make it work . In addition to the 97 dizzy and the 01 coil rail...i ran a coil rail eliminator coil pack when i made my 01 into a 98 Also a 97 exh manifold will not match up with the 01 downpipe...the 01 manifold is longer so you need to do some mods to make them all fit together..its a lot of work