2005 XJR. Check out the below reading of the O2 sensors whilst cruising at 60MPH. It's like they're reading nothing. Surely that looks wrong?


Here's other readings cruising at 60MPH: (no vacuum leak)

 

For my education - assuming an XJR is supercharged, shouldn't a supercharged engine show boost at 60 mph?

 

No.

 

Need more than just 'no' for education.

 

If I was accelerating past 60 then there would be boost for sure, that's why I mentioned it was cruising at 60, to show the engine is under minimal load. The fuel trims would be different too if I was accelerating etc.

 

As usual assumptions are not a good way to go. I figured that since the NA engine is 11 to 1 compression ratio and the Supercharged is only 9 to 1 there would always be boost to achieve the same as the NA one.

 

Does anyone know if these O2 sensor readings look normal?

 

absolutely not. They should not be flat lines. They should switch up and down

 

That's what I thought. It may explain why my fuel trims are very high then.

Does anyone know the part numbers I need to replace them?

 

before you do that I would go and check to make sure that number one they’re connected to the wiring harness so get underneath there and take a look. Make sure the wire is not melted against the engine or the exhaust. Make sure the wire is not cut. See if the original O2 sensors are in there or if some generic replacements are in there. See if the wires are splice like the do for generic replacements. I have an S type but I know that on my S-type there’s an actual fuse for the O2 sensors so you might want to check (mine are in the engine apartment) wherever your fuse block is. How many miles on your car?

 

Thanks for the advice. They are both wired in ok, as my mechanic swapped them Left to Right last time I had it up with him, and the LTFT values stayed the same. That makes me think they must be totally dead. The car has nearly 200k miles on it, but the previous owner got it serviced religiously, and spent a fortune on it keeping it in good order.

He's also fitted a 200 cell cat, big bore exhaust, +10% supercharger pulley mod plus loads more, so that might effect it too.

Where are the fuses?

 

The likelihood all four would go bad is pretty remote. You can check F33 and F34 in the front box however it could also be the relay that powers the O2 heaters - R12 - it would kill all four.

 

Yeah, I agree.

But wouldn't a faulty relay/fuses stop the car from going into Closed Loop mode though?

 

Your dead O2's should stop closed loop as well. To go into closed loop may only be a timer after startup. However I think it also flags bad heaters - although it may not on a basic OBD reader. You can check the heater circuits at the fuses. Two O2 heaters go to each 30 amp fuse. The resistance will be quite low - may be around 1 ohm or less.

 

Thanks for the advice.

I don't have any DTCs, apart from the P0171.

Very strange.

 

Slight update. I changed the displays from graphs to dials and I can see a bit of movement now, so went for another run, including driving round town and WOT at 70mph up a dual carriageway. The O2 sensors never show a positive current at any stage! You can see the max/min figures on the dials too.

Screenshot taken at idle after the above run.

 

Are you sure your reader is giving the correct results? Why is there an O2 S2 5? etc.

 

Yes, it's just the Torque App being its usual buggy self.

 

When I have used Torque it has never given me anything incorrect. If I get my car off the hoist today I will run Torque to verify it is not screwing up. I have SDD and OBDlink that I double/triple check at times, so far so good!

 

Thanks, that would be a great help!

I also have SDD, but never really used it as I was scared of it crashing and breaking something. Heard a few horror stories like that!