Early this year my 2000 XKR developed a misfire and codes indicated a couple of suspect coils. I renewed all 8 coils (Chinese) and all was sweet, for a time.
Last week I start the car up and it immediately went to "restricted performance" mode and logged error codes P0356, P0357, P0351, P0354, P1367, and P1646. Running on 4 cylinders. I did not have time to deal with it immediately but I was able to research the possible causes over the next couple of days online.
Plenty of hits on this exact combination of codes to be had ranging from bad ECM's due to leaking caps, a TSB regarding a need for a ECM reflash within my VIN range and other not pleasant to think about causes and solutions.
Weekend gave me time to have a look. ECM looked like new internally and no open circuits in the harness but I did find a short between the ground and ignition feedback for group 1. Further checking showed number 1A (P0351) coil has failed with an internal short between the ground pin and the ECM feedback pin resulting in the shutting down of all 4 coils in group 1 (P1367). The remaining P1646 is a symptom of the other errors rather than a problem in itself.
Replaced the bad coil on number 1 and started and ran sweet BUT now I was getting "gearbox fault" and logged error P0753. Luckily I had a replacement conductor plate etc. ready for this time (known issue on the MB boxes) so I now have a freshly serviced gearbox as well.
Next few drives might need to be solo just in case I have more surprises in store.

 

Great detective work!
John

 

Well done and happy motoring....

 

So just to ask since I have pretty much the same codes, but on the other 4 cylinders, does yours have two pins on the coils or more? I'm not sure what year they changed them. What kinda reading did you get on your bad coil? When I checked my coils I got something around .2 ohm between the pins on all the coils, however I couldn't get any of them to read from either pin and the tip where the spring connects for the spark plug. It still runs on 4 cylinders, so I thought if they all read the same then they were either all bad or all good. And since it ran off and on, then on 4 I figured it probably meant they were all good. Just curious

 

l have the 4 pin coils which incorporate an idividual coil module in each coil. The earlier 2 pin coils use a seperate coil module for each group of 4 cylinders. If yours are 2 pin you may have a failed coil module back on the firewall. I think the change was at the move to aj27 which happened in 2000 for the xkr but was earlier for xk8.
I found it pointless trying to make anything of readings between one pin and the next other than looking for open circuit or dead short.
(Just checked your profile, if '97 xk8 is car in question l would assume coils are 2 pin and likely culprit will be coil module.)

 

Ok gotcha. Yes mine are 2 pin and I do have the 2 ignition modules. I tried swapping the modules and cleared the codes, then the same codes came back. Then I tried moving my coils and plugs around after checking them, cleared the codes, then the same codes came back. I actually sent my ecu out already, but I thought I'd ask, just to see how you checked, just in case it still does it when it comes back. I looked in my ecu too and I thought it "looked" fine, but I have had boards that have had issues that looked ok before

 

Just a late follow up regarding the gearbox fault l had here.
After changing out the conductor plate l still had the fault. Some more continuity checks showed open circuit in the 'A' solonoid circuit. Long story short GB2 plug was only just barely mated and was not locked up. Male pins looked like Christmas trees. Cleaned them all up and mated plug securely and all fixed.
l have never been near that plug in 5 years of ownership so been apart and not back properly in previous life and l had no doubt disturbed it just enough tracking down the ignition issues to lose contact on the one pin.
Goes to show assuming cause of any fault without checking is not good,
During the gearbox service l discovered a displaced O ring blocking the dipstick/fill tube which explains why l could never get the dip stick in far enough to check level. I also found correct fluid level was reached with 1 litre less fluid than was drained at beginning of work. Never had any gearbox issues in the past due to this overfilling.