i have a 2000 xj8 with about 130,000. it started going into restricted performance and has prevented me from driving it in any reliability since july of last year. i have replaced coils in the most recent troubleshooting because that is what the diagnostic computer is telling us to do. i have also put on several new hoses and sensors. it all started with it going into restricted performance when trying to turn the heat on. i would turn the car off and turn it back on and it would ren great. then it started with low coolant lights and i would add coolant to no avail. i replaced the reservoir sensor and the reservoir itself to no avial. i took it to the dealership and they said it needed a new water pump, that got replaced also. now this brings us to present and i have no idea what to do next because after replacing the coils it bounces back between the two saying that they are bad and they are both brand new. someone please help !!!!!!!!!!!!!!!!!!!!

 

Do you have any more specific information? Which cylinders are now coming up bad? On a 2000, I believe you have the two-pin coils. This setup uses ignition control modules (2 of them). They are wired to four cylinders each, but in a cross pattern (2 outer cylinders, 2 inner cylinders on the opposite bank).

So, if you're intermittently pulling P03xx codes, it could be one ignition control module and not the coils.

Yuma is pretty hot! Keep a close eye on everything "coolant related" on your car at all times.

 

3,7, then 2 and 8. it jumps around to different coils that have been tested good. we don't have any idea of what could be causing this problem. i have talked to someone else that thinks it may be the unit that controls the coils because the ghost gripe we can't pin down. if it is the control unit for the coils how would we test to make sure it is bad?

 

alright steve i see that you're thinking the same as the other guy is. how do i test to make sure this is the exact problem. i'm really sorry for not realizing you guys are talking about the same thing sooner.

 

This kind of random errorcode generation is quite common with microprocessor controlled mechanical equipment, as I learned when I used to repair compact-disc jukeboxes. It often works out to something POWERING the programmed logic controller (in cars ECU, TCU etc.) OR it's all glitched up due to something sparking.*
Check around the battery and ALL its associated charging circuitry. E.g., sulphated terminals, loose terminals, loose/corroded ground strap for battery AND engine, loose/corroded alternator power output terminal, connexions to starter motor, solenoid, etc. ANY connector that carries heavy current. Look to see the connector plugs to the various PLCs are fully home and not corroded (has been known for water to drip onto the ABS unit in Citroen C4s, eventually setting it, and the car on fire). Good electronic connectors are always gold-plated. One case I read from a forum only yesterday of a Jag. having all sorts of random problems just like yours. Everyone tearing out handfuls of hair. Eventually a very old mechanic pushed the ECU connector fully home -- end of problems.
I'm not saying this advice WILL fix your problem, but it's something to get out of the way before tackling the complicated stuff. As I used to tell my students at fault location, "go for the simple things first".
Leedsman.
*Anytime there is an electrical spark, even a subtle one, its creates an electromagnetic field which can induce damaging currents or induce dropped/stuck bits in a register/memory. In Europe there is a whole raft of legislation called "EMC" meaning ElectroMagnetic Compatibilty which covers the susceptibility of the equ. TO EMC radiation, AND its GENERATION of electromagnetic radiation. So it musn't be either sensitive to it, or generate it, within reason.

 

Fully support Leedsman's advice. In addition, and this is well known, the electronics on the X308s, XK8/Rs S-Types (all of them) are also sensitive to a "threshold voltage". If battery voltage routinely drops below about 12.1v, crazy random electrical "things" start to happen. If the battery really gets bad - drops to around 11.1v; 11.2v, then correspondingly really crazy electrical things happen....Electrical Ghosts.

I always assume (wrongly, of course) the basic stuff, like healthy battery and good electrical connections are a given.

On the ignition control modules, there are two, and they can be swapped to see if the interimttent coil failures chase the modules around. Probably the easiest "driveway" testing procedure.

 

always eliminate what works and focus on the rest. swap side to side and if that does not help. welll tell us the results and we can go from there