So my car is a 2000 XJ8 With about 112,000 miles. Engine light and restricted performance came on, had code checked said it was a misfire on cylinder 6. Transmission fault came on a few months after that and it wouldn't engage into drive. Took it to mechanic. Mechanic says transmission fluid is clean, smells normal. Code he pulled was same as before, cylinder misfire and then P1722 for stall speed for the tranny. Got it back and now there is a misfire on cylinders 1,2,3, and 4, after putting three brand new coils in. Mind you I had spark plugs changed about two months ago as well. What could be causing now random misfires? Is it a computer issue? A short? Please help me.

 

You really should stay with one post for the same issue and I'm going to tell you pretty much the same thing as the other thread. Put Jaguar in front of your "P" code and do a web search, codes such as that are manufacturer specific and you'll get a more direct area of where to look and what to do. If this mechanic is the same AAMCO place, then my previous answer stands. You really should find a local indy to do a deep diagnostic on such.
You can do a search in the task bar above, putting in all your codes at once and see what is retrieved. You obviously have the codes or wouldn't know your cylinder misfires. But, one area I would start is your plug gap. You don't just pull them out of the box and toss them in, they need to be gapped even if they say they are pregapped, they should be checked.

 

You need to get a cheap code reader -- Amazon has them for $30. I know some buy from HF. Reset the codes and see what codes come back first. Did you mechanic reset the codes?

It rare to have two coils fail at one time -- unless there is a history of this problem. Jaguar has no history. Do you still have the old coils? Normally, when one Cyl has a misfire it's the coil or less frequent ...... oil fouling the coil/plug connection. Switching out the coil to another cylinder is the normal check -- to see if the code moves.

It's not unusual for multi misfire codes to pop up if you run the engine with a missfire in one Cyl ... that's why you need to reset the codes.

How is the engine running? -- is the transmission working? Also - never drive if the CEL is blinking.

 

In a previous thread yeldogt, the OP said they took it to AAMCO for the repairs. I think that's the mechanic issue. I really think regapping the plugs will be a big help, plus checking to be sure the connections were properly attached to the coils.

 

I see that now.

I'm also not sure if he drove around with the light on for a few months and the engine missing ... if so .. the transmission is most likely not related to the earlier issues.

 

Given that the misfires are all on one bank, leads me to believe it is a timing issue. Have the secondary timing chain tensioners been updated?

Second, check the wiring all the way back from each of the coils on the right bank.