Been chasing a fiendish intermittent 'Restricted Performance' light and finally got it plugged into an ODB2 sensor to have a look at the live data and one of the O2 sensors looks dead.

O2 2 Bank 1 - 0.010 (did not change while blipping throttle)
O2 2 Bank 2 - 0.750
Wide O2 S1 B1 - 136.55
Wide O2 S1 B2 - 126.70

Just wondering if any of you wise Jag wizards knew which sensor this is, where it's located and how to replace it?
I am pretty mechanically minded and willing to tackle most stuff.

Thanks in advance

Alex

(btw - 1999 XJR 4.0 UK build [so right hand drive if people want to talk sides/cylinder banks])

 

Assume you're posting voltage ranges??

Unfortunately, not knowing all conditions of your tests could render and incomplete or inaccurate recommendation. Secondly, given that what appears to be the oddball (O2 2 Bank 1 0.010) doesn't necessarily mean this sensor is bad as the the O2 sensors downstream only measure what has already been cleaned by the Catalytic converter. Downstream O2 sensors tend to fluctuate very little. That said:

1. The bank indications are the same whether you are in the UK or anywhere else. From the CAR SEAT looking out the windshield - Bank 1 is the rightside; bank 2 is the leftside.
2. Each side has 2 O2 sensors - one before the Cat, and one after. The upstream one is referred to as 1, the downstream as 2.
3. So - if you're viewing the .010 value O2 sesnor as the culprit, look for it underneath the car, right side, after the cat converter.
4. Be careful removing these. There was a TSB out on frozen O2 sensors in AJV8s. Use WD40 on the threads, let soak, use a proper O2 sensor socket. If VERY tough to loosen up, gradually work back and forth until the WD40 has a chance to penetrate the threads. If you strong arm it you might pull the threads out of the pipe...then you'll be in big trouble!

 

Thanks for the reply Stevetech,

having had a look at the position of the sensors I don't think I can get any of my tools into position so I think i'll just run it into an exhaust specialist and get them to fit the new one. Probably wouldn't cost much more than buying the tools needed to only use them once or twice.

Cheers

Alex

 

Just a thought - I had both upstream O2 sensors go on my '99 XJ8 Sovereign without any RPL at all - I had them replaced. Some months later, when I did eventually get an intermittent RPL it was due to an intermittently defective coil on one of the cylinders. Are you certain you aren't getting any misfire or coil codes?

Jim

 

If I am keeping a car for a while, I'll replace O2 sensors at about 80K, even if they have not acted up. O2 sensors wear over time like spark plugs do. The coating dissolves and can send a narrower or erratic voltage range causing STFT and LTFT to be impacted, usually in the rich range, meaning gas mileage starts to suffer.

 

Thanks for the input guys, any cunning way to test coils (esp possibly intermittent problem ones).
Would a packed up O2 sensor cause the fuel trims to run positive or negative (rich or lean, I don't know which was positive or negative corresponds to) as I plugged it into a live data scanner and the trim was -2.
As for a coil problem it threw a misfire code on cylinder two and sure enough the plug was loose so I re-attached it and disconnected the battery for 10 mins (sure I read on here somewhere this resets the computer) and low and behold it ran fine, always seems more eager after this 'reset' as I guess it goes back to default fuel mapping before I assume 'leaning' the mix. Then as i was parking up low and behold the 'rpl' light comes back on. Just invested in my own OBD2 scanner so i'll try swapping coils if it still throws a coil error.
But i'm also keen to sort the lambda problem as it is so much more fun when not running what i assume is lean. Do they tend to fail together or individually? I was looking at investing in some high flow cats, when cash flow allows, so was going to change all 4 when those went in (all in favour of preventative maintanence)

Cheers

Alex

 

Sorry, forgot to ask. What does STFT and LTFT stand for?

Alex

 

LTFT - Long Term Fuel Trim
STFT - Short Term Fuel Trim.

If you're reading a - 2, that means the ECU is trying to correct for a rich cylinder condition. You just say "trim" though. You cannot read STFT and make any sense out of it for "driveway diagnosis" as STFT oscillates constantly. You need to read LTFT which is an averaging out or smoothing of the STFT.

Second - if you have a bad coil, or even an intermittent one, a fault code will set. However, O2 sensors can go pretty far out of normal range before they exceed a threshold that sets a fault code. And, the ECU remedy for that stray range would be a reaction to fuel delivery, just as you're seeing. Same thing with the MAFS, which is another primary input to FT.

If you want to driveway test a coil. With engine off, unplug the coil lead. Start the engine (warm engine), see the fault code set, read it, verify it is the coil you unplugged, shut off the ignition, plug coil back in, reset the fault code. You should also feel/see a difference in idling with a coil lead unplugged.

 

Thanks again for the reply steve,

Once my scanner gets here i'll investigate the coil properly.

Out of interest any ideas what would be causing the fueling to be compensating as it is? Is this likely to be the lambda or something else?

Many thanks

Alex