Misfire woes
 

The car started missing and threw P0304 and P1316 codes. Installed new plugs,I changed out the # 4 coil pack, misfire and codes remain. Swapped the coil packs between # 3 and # 4 cylinders, Same codes and still missing. Just so I appear totally stupid (this has happened), the # 4 cylinder is on the passenger or right side of the engine, right? Not sure where to go from here, any suggestions?

Thanks,

It could be the injector

Attached is the cylinder numbering schemes. Number four is on Bank 2 (left side of vehicle when viewed from front seats).

Check the connectors to the injector and coil unit for damage.

Thanks NBCat. After looking at the diagrams, and reading your explanation I'm still a bit confused. The diagrams seem to indicate that the # 4 cylinder is the rearmost cylinder on the passenger side of the car, which is where I was working. Your narrative says: "Number four is on Bank 2 (left side of vehicle when viewed from front seats)" which would seem to indicate the rearmost cylinder on the driver's side of the car. I'd feel pretty stupid (but relieved) if all the work I put in was on the wrong bank!

Yes, on your engine 4 is on right rear.

My mistake, since your car has an AJ27, the number four cylinder is indeed on the RH side rear of Bank 1.

Check the spark plug for oil and fuel contamination.

Max, my 1999 x100 has been setting off the same code for years. I've gone through the same spark plug, coil pack you have. Still flashes same codes once in awhile. I just reach down and clear the codes with my scan gauge. I too have noticed in the past a little oil seepage around the plug area as you noted. Have not done anything about it thus far. These cars set off reduced performance at the drop of the hat. I had to laugh when just changing the air filter set the codes off till the angle became use to the new air...Let me know if the oil gaskets work. Lots of luck. Rich

I wouldn't care as much about the codes if the car wasn't running so badly. The # 4 cylinder (right side bank) now has a new coil pack, spark plug, and I changed out my damaged cam cover for a good used one with all of the proper gaskets and seals (there was oil in the spark holes). I checked the wiring to the # 4 plug and it seems fine as does all of the wiring in that area. I'm going to the left side bank and changing out all of the spark plugs there, too, so that the car will have a full set of new plugs.

This situation started about two weeks ago. The car was idling in a park lot and suddenly started missing. Fortunately, I was less than 10 minutes from home so I was able to limp back to my garage where I found it had thrown codes P0304 and P1316. It's also showing P1646 indicating a bad 02 sensor on the left bank, but I've had that for about a month now and the car ran fine. The battery is at least 5 years old and I can see that that might be the source of some of the codes, but doubt it could cause a dead miss. I guess the fuel injector is a possibility, and I'm going to pull the # 4 spark plug and try to see if there's been any combustion in occurring in that cylinder. After that, I'm totally and completely out of fresh ideas.

With P1646 it's already guessing how to fuel (*) so fix that and you've a chance to save the cat on that side and also make progress to what else may be (or is) wrong.

(*) it will avoid engine disaster, i.e. will avoid lean, and the only way it knows is to run rich - you're preventing it knowing when it is a little bit rich so it will go very rich!

Summary: it's not been running "fine" unless you like the above

For the 2000 XK8 The # 4 cylinder is the aft one on the right side viewed from the rear. On my 2000 the coils were actually numbered correctly on the coil. There is a lot of confusion in that area. I spent a lot of time moving coils around to confirm the number system. The one we have in the sticky is wrong for the 2000.

As RJ237 wrote, you probably have a bad injector on #4. If you have time, you can remove all the injectors and send them to a service for testing. They can check them and match them for better performance (if you are willing to replace a few to get them to match). Matching the injectors is a sneak way to really help performance. If one is bad, it follows that others may be on their way out also.

Good advice. After I swapped coil packs back and forth with no change, I ordered and installed a rebuilt injector on # 4 cylinder. I must have done something terribly wrong because now it barely runs at all. Feels like an overall lean condition; very rough idle (can't even tell if # 4 cylinder is still missing), stalls almost immediately (can't keep it running long enough to get a code off it). If pushed, it will rev up to 3,000 RPM briefly after which the revs drop and it stalls. My original cam cover had a damaged fitting for the hose that runs into the accordion connector to the throttle body so I bought a used one cover from ebay and changed the old one out while playing with the coil packs. Can't see how that would affect anything unless it's causing a vacuum leak somehow.

Going back to basics to try to figure it out. I know I have a upper O2 sensor on the left bank (the missing cylinder is on the right bank) and it previously ran okay despite that. Going to check the fuel pressure at the rail in case my fuel pump coincidentally decided to retire. After that, I may have to take it to a good Jag mechanic $$$$. Damnedest thing.

When symptoms become chaotic, it starts smelling like the ECU. The ECU controls both the spark and the injectors. If it has dementia, you will get chaos.

Something else to look at is the wiring for the coils and injectors. this stuff is plastic and can get heat damaged, so just moving it sometimes can damage it.

You may be right about the lean condition, there may be a leak in something that you disturbed. Try to trace your steps to see if something you touched broke.

Misfire Woes
 

I've been checking it with the cover over the coil packs removed on the right Bank. Wondering if this is the source of the massive vacuum leak. Knowing me, it could absolutely be something that stupid.

That cover is just to keep water out, and it often doesn't. Don't wash the engine.

I've already heard of the problems that washing the engine creates, so I'll skip that step. I'm going to finish what I started out to do and change the left bank spark plug, then re-assemble everything, do a hard re-set and start from scratch. I'm also planning to have the battery changed out; seems to be okay, but it hasn't been load tested and it's over 6 years old. And I'll repeat my long suffering mantra: "if the engineers that designed the engine were then forced to work on it in the car, it might have culminated in better access under the hood"!

Misfire Woes - UPDATE
 

The car still barely runs and is not driveable at all. It feels like it's running lean, popping back and needing to pump the gas to keep it running. At this point, I've changed the # 4 coil pack and injector as well as all of the spark plugs. Codes are 1646, 1316, 1304, 1306 and 1308 leading me to believe that it's a problem with the right (passenger side) bank. I've checked the entire intake path and am sure there are no obvious vacuum leaks. Two questions: could the bad O2 sensor be causing this havoc, and is it possible my ECU has more dementia than I do? I've disconnected the battery to do a hared reset, and will give it a try again tomorrow. If you've experienced any or all of these symptoms, please let me know what the problem was and how it got fixed.

Thanks.

On your 2000, 1-4 are on the right bank, 5-8 left, so it's both sides. Check the fuel pressure at the schrader valve.

It had occurred to me that it could be the fuel pump, but the initial code was 0304 so I assumed it was a single cylinder problem. Looking back, it could have been a failing fuel pump all along. I'll check it out tomorrow.

I'm not thinking just the pump, the filter could cause low pressure also.