I am almost at my wits end with this. The original problem started when my 2002 XK8 dropped a valve seat on the left hand side, bank# 2, cylinder #5. I replaced the head with a used one. I was particularly concerned that I got the valve timing right, but I guess I did OK. The engine started up and actually sounds better, quieter, than it did before the replacement. Then the problems start. The first error code I got was P305, missing on cylinder #5. Oddly that was the cylinder that had the bad valve seal. So I checked the coil pack on that cylinder and it was dead. Strange, but oh well, no big deal. I bought a new coil and that took care of that problem. After driving it to the gas station for a tank full of fresh fuel the check engine light came on and it showed several codes, one of which was P306, the next cylinder in line. Sure enough that coil pack was dead now. So I ordered a new full set of coil packs and replaced number 6. That took care of #6.
Now the engine sounded pretty good again, for a few miles. Then the check engine light again. Using my Autoengenuity scanner I discovered that the upstream O2 sensor on the number 1 bank was weak, maybe dead. So I replaced all O2 sensors on both sides (4 sensors). I also checked carefully for any vacuum leaks, and I checked to make sure my fuel pressure was correct. The fuel pressure reads around 38lbs when idling and goes to around 42lbs when the vacuum hose to the regulator is removed. I also cleaned the mass air sensor.
These are the current codes: P300, P305 (again) P307, P1316,P171, and P174. My thinking is that because it is telling me that both banks are running lean, that might be the root of the other problems. The short and long term fuel trims seem to be trying to compensate up until the engine goes into closed loop, then it falls on its face.
What have missed? Can anyone help me get this old cat back on the road? Spring is here and I would love to take my wife and put the top down and cruise. It was last July that we had the valve seat problem and I have been working on this thing off and on ever since. It is beginning to take root in my garage.

 

I've moved your question from General Tech Help to X100 forum. Members here with the same model will be able to help and are more likely to see it here.

Graham

 

you threw parts at the problem and now the car runs like garbage

unplug the air fuel sensors and run the car in open loop fault. did you use denso?

 

Well, I guess from what I wrote you might think I " just threw parts at the problem". But in my defense I have been trying my best to follow the leads given me by the error codes. It may surprise you to learn that they don't always indicate what you might think. I bench tested the coil packs that showed bad and indeed they were , so I replaced them. I checked out the O2 sensor using the propane heating method and sure enough one of them showed almost no output. So, I replaced all 4 of them too. A lot of what I tried , I learned from this forum and ,of course, YouTube.
I will try your suggestion about unplugging the sensors to see if that allows it to run better. But of course that is not a long term solution.

 

If you bought a set of new coils try new ones in B1 and B3.
Several years ago l had a coil fail in such a way it affected several others and threw a bunch of other emissions related codes as a result. Fixing just the coils got rid of all the errors.

 

One suggestion on any older car is check the intake plastic bellows VERY carefully. Over time and use they can and will develop cracks in places you can never see!
Now you have been working on the engine and I bet you have taken the intake stuff off and on at least several times?
Remove ALL the intake plastic and really go over it in fine detail. This costs no money and maybe you will find something?

Just an easy thing to try right now before spending additional money. I think you have done good troubleshooting and repair but it is an old car at this point!

Which brings up my next point? ALL the rubber vacuum hoses as well as ALL the cooling hoses are now toast and EVERYTHING should be replaced!
Glad to see you replaced all the coils but what about the plugs? You did not post mileage so not sure but they are due at 100K miles.
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Well, it just gets better and better. My scanner tells me that the Catalytic convertor on side#2 has failed.(passenger side) The only replacement that I can find is from a company in Canada. But they won't ship to California. They have a premium version for about 3 times the price, but it also is not legal in Ca. Sources like Rock Auto don't have anything legal in Ca either. I have looked at YouTube videos about home grown fixes using everything from laquer thinner to hot soapy water. None of these look like a sure thing as far as bringing the cat back to life. Maybe I can find one from a salvage yard somewhere. I have not tried that yet. I know it is just an "old car" now. But I hate to give up on it after so much work and expense I have into it. But there has to be a point where you quit throwing good money after bad.

 

Try finding a way to the catalytic converter shipped to a location out of state?

 

To be perfectly honest, l am not sure l would be placing quite so much faith in my scanner.
You may indeed have a bad CAT but with all the problems you are having it may well be just a symptom of one of those upstream issues. Misfires seem to result in direct cause codes and a whole bagful of indirect codes.

 

Hate to hear about the catalytic converter problem! They are so expensive. But do fix the other problems because as posted above it might still be OK after the engine starts running properly.
I am not a fan but have you tried Cataclean?

Kind of a miracle in a bottle but at $25 it "may" get you thru an inspection?

Here is another one called Solder It.
Cheaper at around $12 a can.
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It seems strange that a bunch of parts would cascade fail after some work done. As baxtor says, you could have a bad cat, but it's too expensive a part just to change on spec.

Could there be an issue with the wiring harness on that side since it's been disturbed?

Note that the ECM will inhibit closed loop fuelling on B bank while it detects a misfire on that side.

 

OBD can let an owner see the CL status of each bank to see if that's happening.

 

Thank you everyone that responded. I remember when I originally posted almost a year ago about my Jag being "suddenly sick". At that time i had no idea what the actual problem was. As it turned out it was a valve seat that dropped out of cylinder number 5. I had driven the car several miles after that happened in order to get my wife and I back home from a remote spot. Someone at that time said "I hope you didn't damage the catalytic convertor(s)". I thought surely not that on top of everything else. Well, it seems we are down to that. I have replaced the damaged head, the plugs, several coil packs, all four O2 sensors. The scanner I have shows real time data on multiple channels. What it shows me is that on bank 2 the voltage is switching up and down as it is supposed to do, the O2 output on that side is around .35 volts and it responds to throttle action. On bank number 1 the output of the O2 sensor is almost zero, it does not switch. It will give a "blip" when the throttle is activated ,but only briefly.
I have ordered a new cat from the Canadian company and I am having it shipped to a friend who does not live in California. I will let you know how this works out, fingers crossed.

 

I'm half a world away from you and we have our own supply/cost issues to deal with down here, but l really feel for Californians sometimes regarding rules and regulation.

 

you put 2 new air fuel sensors in now the car runs like garbage, then at the same time you threw 2 new oxygen sensors in and now you have a cat efficiency code

put two and two together

 

Here is the latest regarding my problem(s) with my 2002 XK8. I finally swallowed my pride and hired a professional mechanic to come to my shop and help me diagnose the car. He has a stellar reputation in our area for being able to root out problems that allude us "back yard" wannabe,s. I have a hard time asking for help, but I know when I have reached my limits.
He has a much better scanner than I have, I think it was an Autel. The first thing we found was that my scanner had been mixing up the banks, telling me it was bank number one when the problem(s) were actually on bank number two. That was a bummer! We reset the error codes and drove the car until it went into closed loop several times. His scanner showed the lean code, p0174 on bank two. This is the drivers side of the engine. He tested the output of the O2 sensors, (good), the cam timing(good) the long and short term fuel trims. It indicates that on bank number two the short term signals for more fuel, then goes to too much fuel and "over compensates" by going lean. The result is a lean condition on bank number two which results in misfires. We checked the vacuum (ok), the fuel pressure (ok). He suspected maybe a leaking injector, but a leakdown test did not indicate that either. We pulled a plug on bank 2 and it showed indications of running very lean. Using a smoke generator we tested for vacuum leaks, nothing shows. The car runs "okay" until it goes into closed loop. Yes, it could be driven that way, but eventually I will have to pass a smog test here in California, so that is not a long term solution.
He finally had to admit that he was out of ideas. In a way I feel vindicated, but of course I am left with the problems. Although he didn't fix the problems I feel I got my moneys worth by watching how he went about diagnosing the car. Except for my screwed up scanner I had followed pretty much the same procedures he used. So I don't know where that leaves me. I have been chasing this for almost a year now and I am getting tired. I hate to sell it for a parts car, but it may come to that. Any ideas?

 

Sorry to hear the car is giving you soo much trouble. A couple of thoughts, and maybe you have already tried these.
Have you run a compression test on all of the cylinders?
If you are supsicous of a part, like the coil, injectors, or O2 sensor, swap them to the other bank. If your DTC moves to the new location with the parts, the part is the issue, if not there is a different problem.

As mentioned check the wiring on the suspect bank, grounds especially. Possibly compare measurements to the other bank. If not maybe ask if someone here can confirm your measurement on a good running car.

Last thought, could it be failing capacitors, or just plain failing ECM?

 

+1 on checking wiring harness - specifically look at the harness for the coils - found mine to have several leads where the insulation had become brittle over time/heat and flaked off the wire - temp fix was to wrap each lead with electrical tape and will look at eventually replacing the harness

 

Are you still getting a P0305?
Possibly a leaky inlet manifold seal on that cylinder if so, but I'd definitely do the easy checks first.

 

After exhausting all the easy tests that I or the professional could think of doing, I decided to go back to basics. I ran a compression test with the engine warm. I was surprised to find that bank #2 had only 90 lbs across the 4 cylinders on that side. (the side I replaced the head on) On bank #1 it has 125 lbs. All even, but low. So I removed the left side valve cover and checked the valve clearance. The book calls for .18mm to .2mm on the intake and .23mm to .27 on the exhaust. All were in tolerance. Then I used my leak down tester to check the cylinder leakage. Thinking maybe the valves were bad. Not so, all cylinders read under 10% leakage.
Is it possible that a cylinder head off of a different model of this engine, say a sedan, was substituted for my replacement. The head came from a local wrecking yard, not a real Jaguar specialist source. If so is it possible that it fits , but has a slightly different combustion chamber volume? My "pro" says "maybe you got a thicker head gasket on that side. I think that is grasping at straws.