Well, having just had a new made in Japan Eurospare brand coil installed in cylinder 6 while I was having other work done at the independent British car repair shop I've been frequenting (and it has been frequent.....), and needing to make a 400 km round trip this past weekend, what better vehicle to take than my XJR? So I did. It ran well until it started to stumble a little at part throttle with the cruise control on. I had it up to 160 kph for a brief time and it ran well. However, on the return trip the CEL light lit, and I averaged 16 litres/100 km fuel consumption: yikes! (this is 14.8 US mpg or 17.8 Imperial mpg) I was mostly cruising at 115 kph.

So, do I have another bad coil? Or is it a coil PLUS a bad oxygen sensor? Or does the P1138 code light up because the oxygen sensor detects a rich mixture because of the incomplete ignition of cylinder 6? I hate to keep replacing coils if the problem is also a bad Oxygen Sensor. How do I check the Oxygen Sensors?

I'd rather trouble shoot this myself for a bit before I cave in and take it back to the mechanic once again.

Any help with this interpretation is much appreciated!

 

Anyone?

 

Hmmmm cant help specifically I'm afraid.

I can sympathise having had to fit 2 or 3 02 Lambda sensors in the past 6 months, albeit not on a Jag I must say.

Symptoms were really poor performance, chugging / stuttering / lack of power when pressing the gas pedal and seriously bad mpg.

Hopefully some of the guys in the know, tech type guru's will be along to help shortly....In the meantime this reply helps to bump it and keep it live for you.

Good luck

 

I'd suggest that the O2 Sensor code could be caused by the misfire but I don't see how a misfire code could be caused by a faulty O2 sensor.

The 0306 code says that Cyl 6 is still your problem. If that coil has just been replaced check the wiring and connector. Then swap that coil with one of the other cylinders and see if the misfire follows the coil.

Have plugs been checked?

 

Thanks for the bump and your experiences Jim. Thanks b1mcp. It makes the most sense to me also that the O2 sensor code comes from incomplete combustion from misfiring cyl 6. I've never had to replace an O2 sensor so I wasn't sure.

Yes, I was starting to wonder about the wiring and plug. The plugs were replaced in January and only have about 3000 miles on them. (The car is funny: the km/miles switch on the dash does nothing. It's a US vehicle so the odometer is in miles, but the trip computer reads everything in metric). Those wiring harnesses certainly look flimsy considering the vibration and heat they must get be getting on top of the engine. Considering how much trouble I've had with cylinder 6 the plug may be fouled so I'll give it a clean.

Good point about switching the coils too. I'll switch them, clear the codes and see what happens. I just want it to run right! I've spent a ton of money on this car, way more than it's worth really, but when it runs right it's sooooo much fun! I love the torque, the smoothness, the ready power, the comfortable but controlled suspension quality, and the beautiful British interior. The XJR is much more fun than the XJ6 I had previously. This one also drives beautifully at 220 kph. I'll post back once I get it sorted. Thanks gents!