ok so on my 96 xj i did the key on off thing and got a code #31, i read that this is either the ac clutch or the evap control circuit. my ac doesnt work so i cut the hose and all to clear up the engine bay a little this code was on there from before i think but not sure, it had an o2 code then i replace that and reset the computer and the light was still on this is wat came up when i checked it again. would this code be showing up if i disco my ac stuff or where is a good place to start running this issue down. recently had a new to me non HO engine put in, i had a HO before and it does kinda seem less powerful, and gas mileage is like 12-13 mpg. i need exhaust work done also so that could be part of the power issue. any help would be much appreciated guys!

 

The A/C clutch isn't monitored in that system, at least not that I can recall. 31 is an evap problem. Charcoal canister, vapor lines, purge system- something in there.

 

since it is a 96, getting the actual OBDII code would bring to a quicker conclusion than chasing the problem down the old way.

 

I agree. The two digit code is easy to retrieve with the "key-on, key-off" technique, but the FULL code is always the way to go. You'll need either a code reader or a scan tool to get that. Or go to a parts store like Autozone where they will read the codes for free.