I took my '04 XJR with 85k out of town last week and while I was away I felt the car running rough a few times. The check engine light came on and I pulled P0300-P0308, and P1316. I know P1316 means engine misfire exceeds emissions rate, and P0300 is multiple/random cylinder misfire. Then there are the codes for every cylinder. I cleared the codes, and the light came back on the next day. The car appeared to run fine on the interstate on the way home, without any rough running. That was only detectable as a slight surging at a steady 30mph. I felt nothing at 80mph. I got home and pulled the same codes, plus P1000 from clearing the codes the day before.

A search here found possible causes:

1. Cylinder compression low
2. Worn camshaft / broken valve spring(s)
3. Fuel delivery pressure (low / high)
4. Fuel injector(s) blocked / leaking
5. Fuel injector(s) continuously open
6. Fuel contamination
7. Fuel injector circuit fault(s) (Injector DTCs also flagged)
8. Spark plug failure / fouled / incorrect gap
9. ECM to ignition module primary circuit fault (Cylinder misfire detected DTC also flagged)
10. Ignition module ground circuit: open circuit, high resistance
11. Ignition module / coil failure

Since all 8 cylinders started misfiring at the same time, I would think it unlikely to be 1, 2, 4, 5, 8 or 11, as it must be something that affected all cylinders at the same time. I'm not sure, but I think 7, 9, and 10 would be unlikely for the same reason.

That would leave:
3. Fuel delivery pressure (low / high) - perhaps a failing fuel pump or clogged filter?
6. Fuel contamination - I bought fuel at the same place I always do, but that's not a guarantee.

I've seen a lot of threads about misfires, but I didn't find any where they all went at once.

 

I've now run two tanks of gas through the car since I got the error codes and they haven't returned. I'll probably still replace the fuel filter, but it looks like the culprit was fuel contamination. I guess I dodged a bullet there.

 

Yes, good job. Could have been that you got some water in the system or just fueled up at the wrong time. I try to avoid filling up any time that I see a tanker truck at the station because sometimes those can kick up some debris in the station's tanks. Either way, It's always nice to hear about any easy fix...

 

Good idea to replace the filter now. You'll probably see a lot of crud when you do.

 

I've gotten the codes three more times. I cleared the first one and it came back two weeks later. I cleared that one and it came back 5 minutes later. I cleared that and haven't had it happen over the last couple of weeks. The only thing I believe was common to all occurances is that the car was very low on gas. On at least two occasions the low fuel light was on. I rarely get it that low, so this week I tried letting to low fuel light come on again to see what happened, but no codes.

If it was a single cylinder that would be one thing, but every one? All at the same time?