I thought all mid yr 99s to 01s had the 0331 head on them? also an issue most might not know about, in late 99 when the company started to slack on the 4.0 (as u can see cracking heads and what not) but theres another thing that occured when this happened....heat soak...this occurs if you lets say drive from your house, shut your Xj off, run in a store to grab something quick and come back to start your vehicle...quick off and ons...they didnt insulate the injectors on 00s and 01s in the tj, wj and xjs...not all get it...my first didnt get it almost at all this new one gets it all the time...it occurs because the injector gets so hot with no insulation that fuel vaporizes inside them ...believe me when i say u feel like your XJ is going to self distruct...shaking, unstable rpms, loud weird exhaust noise, electric fan cranking away all for about 20 seconds then back to prefect normal running temp and operation...the way to fix this problem is to take heat wrap (sheilding) and insulate your injector... the problem motly occurs with the number 3 injector but wrap all of them to be on the safe side..better yet tell the dealership about this and see if they will do it for u (that is if ur buying it from a dealership)...the part number is 56028371aa and the picture that comes up with this number when imputted (is that a word??) in the dealers computer will not correspond to what im telling you (should look like a plug wire holder clamp) but trust me it is..
this is another reason to stay away from 00 and 01s
good luck hunting....
Andrew
p.s. pm me if u want the directions on how to do it in case you buy private, or the stealership won't do it for you
o and dont listen to these guys about red and white being better they lie, dark green is the way to go...your XJ will feel like its part of the trees around it and further solidifies its nature to be, well, with nature