Hello All,
I have replaced the upstream oxygen sensor on my 1998 XK8 due to Short & Long Term Fuel Trim for B1 being way off, showing 19.5% (Short Fuel Trim) and 14.8% (Long Fuel Trim) on live data with Oxygen sensor B1S1 output showing constantly 0.000V compared to Long Term Fuel Trim for B2 showing -4.7% with a B2S1 sensor being in a normal wave range between 0.111V to 0.090V.
When I got the old sensor out it had a lot of carbon built-up so my first thought was that's because the sensor has failed and caused the fuel management of B1 go rich. Later it occurred to me what if I have a leaking injector and that caused the sensor to have the carbon built-up and consequently failed because of that. However I had no MIL-light coming on or codes showing, the car was driving normal, no driving issues. The only reason I started looking into it was that the right exhaust-tip was more black than the left side and I could smell exhaust fumes when standing behind the car. Also gas milage wasn't that great.
After installing a new upstream sensor everything went back to normal, no more smell, voltage readings of the new sensor were within range. However I am still uncertain whether I have cured the problem. What if I have a leaking injector will it cause the new sensor to get carbon built-up and fail again? Also am I running to lean now on B1 due to a possibly leaking injector the sensor would sense a too rich condition and will cut down on fuel for B1? Or am I thinking inside a box?
Another question I have: Do I have to do a "hard reset" to let the ECU to re-adjust the Long Term Fuel Trim for B1 or will it do it by itself just by doing the drive-cycles without a hard-reset?
Btw I ordered a Denso 2344720 sensor from Rockauto as a direct replacement for the originally installed Denso 065500-9970 (LJA1682AE) after checking a cross-reference chart.
Thanks in advance for any suggestions & advice

 

It will adjust fuel trims (it does it all the time). If you wish you can zero them by disconnecting the battery - but be aware that (same as doing an OBD codes clear) will clear the OBD monitors (used for such as smog check but also until they set again many codes can't flag).

I'd just monitor the trims, especially at idle with a hot engine, to see if they're good (say within 5% of zero).

 

JagV8 thank you so much ! I wasn't aware of that it will also clear the OBD monitors. I just did another test run with the iCarsoft Diagnostic reader at idle:

Engine Coolant Temp. = 97°C
Short Term Fuel Trim B1 = -1.6%
Long Term Fuel Trim B1 = -8.6%
Short Term Fuel Trim B2 = -2.3%
Long Term Fuel Trim B2 =. -5.5%
Engine RPM = 659rpm
Asolute Throttle Position = 2.4%
Oxygen Sensor Output Voltage (B1-S1) = 0.085V
Short Term Fuel Trim B1-S1) = 0.0%
Oxygen Sensor Output Voltage (B2-S1) = 0.535V
Short Term Fuel Trim (B2-S1) = -2.3%

It looks about right or what do you think?

Again your advice is greatly appreciated!

 

With both short and long term trims negative, the ECM is injecting LESS fuel than it otherwise should as per the input of the sensors. IOW, the sensors are telling the ECM to inject a quantity of fuel, and the feedback/trim system is telling it to back some of it out. It is the "opposite" of an air leak in a sense. You have excess fuel.

With it happening on both banks, it is usually a sign of a failed air flow meter. You can try and clean it with the recommended procedure (spray the cavity multiple times, etc.), but keep your expectations low.

A very dirty air filter could also do this.

Another option is a failed purge valve, constantly leaking fuel fumes from the fuel tank. There would probably be a code for that.

Leaking injector is possible. I believe it normally soaks the cylinder, leaks past the rings and end up in the engine oil where it can be detected (smell it). If it is stuck open, you should not be able to maintain fuel pressure in the rail for long after you shut the engine off.

Best of luck, keep us posted.

 

Thank you fmertz for your advice. I have to look into that.
I can rule out the air-filter I've replaced it recently. I have no codes showing so far. I will check the air-flow meter, the purge valve and check fuel pressure in the rails after shut-down. Probably working on it on the weekend.
I will post the results.

 

Always good to check the air filter anyway, new or not. Mice and Squirrels love to nest in a clean air filter.

Z

 

+/- 5 is ideal but pick and choose your battles it's an old car. you trip rich\lean at like -18.5/+18.5 % on the 27 and later.

 

good point! When I replaced the B1 upstream sensor I removed the air-duct but didn't remove the air-filter box or looked inside because I renewed the filter not that long ago. Will have to take a look. Thanks for the hint!

 

thank you xalty for your input! I guess you are referring to the Long Term Fuel Trim not the Short Term Fuel Trim?

@JagV8 and @xalty I just reviewed my previous readings before I changed the B1-S1 sensor, unfortunately on the test run after renewing the B1-S1 sensor I have posted earlier, I did not record the "Air Float Rate from Mass Air-Flow Sensor". I will do that on my the next test run. The values should give me an idea whether something is wrong with it?

Engine at Idle: 652 rpm
Calculated LOAD Value: 16.9%
Engine Coolant Temp: 98°C
Short Term Fuel Trim B1: 19.5% (!)
Long Term Fuel Trim B1: 14.8%(!)
Short Term Fuel Trim B2: 0.0%
Long Term Fuel Trim B2: -4.7%
Air Flow Rate from Mass Air Flow Sensor: 4.41g/s
Absolut Throttle Position: 2.4%
Oxygen Sensor Output (B1-S1): 0.000V (the faulty one - always stayed on 0.000V output)
Short Term Fuel Trim (B1-S1) : 19.5% (!)
Oxygen Sensor Output (B2-S1) : 0.075V
Short Term Fuel Trim (B2-S1) : 0.0%

Thanks to All for advising so far!

I will post any new results

 

..in addition to my last post..I forgot to include @fmertz sorry about that since your detailed explanation is very helpful!

 

You need working O2 sensors. It can't get the right trim without them.

(You also need the other things posted of course, such as clean MAF, and it's nice to have a fair air filter.)

Once those are OK, if you have a large +ve trim give it a rev to about 2500 and if the trim(s) head lower very soon then you pretty much must have an air leak. (Don't over rev, don't do it for long, it's not kind.)

 

@JagV8 thank you for your reply. The values I have posted last were the values BEFORE I replaced the B1-S1 Oxygen-Sensor just as a reference and to include MAF readings. I also should mention that my ’98 XK8 is an European version with no downstream oxygen sensors installed.

Here’s an update of what I have done so far and created a little work-report.

· replaced B1-S1 Sensor, Voltage output with new one now within given range
· examined Air-Filter, Air-Filter Box & Air-Duct, checks clean, examined Air-Duct for cracks and leaks, especially around shroud, no discrepancies.
· Examined both breather-tubes, no discrepancies
· Examined engine-oil for fuel contamination in regards to possibility of injector(s) leaking, no fuel smell, oil looks clean
· Found Oil-Filler Cap not tight enough, re-tightend
· Checked O-Ring on engine oil dipstick, no discrepancies

Performed test run @idle:
Fuel system 1 status: CL
Fuel system 2 status. CL
Calculated LOAD value: 16.5%
Eng. Coolant Temp: 99°C
Short Term Fuel Trim B1: 1.6%
Long Term Fuel Trim B1: -4.7%
Short Term Fuel Trim B2: -0.8%
Long Term Fuel Trim B2: -1.6%
Engine Speed: 637 RPM
Air Flow Rate from MAS: 4.07g/s
Oxygen Sensor output V (B1-S1): 0.580V
Short Term Fuel Trim (B1-S1): 0.0%
Oxygen Sensor output V (B2-S1): 0.305V
Short Term Fuel Trim (B2-S1): 0.0%

Performed second test run as outlined by JagV8 revving engine up to 2500 RPM and monitored fuel trims.
Fuel system 1 status: CL
Fuel system 2 status. CL
Calculated LOAD value: 14%
Eng. Coolant Temp: 97°C
Short Term Fuel Trim B1: -2.3%
Long Term Fuel Trim B1: -0.8%
Short Term Fuel Trim B2: 0.0%
Long Term Fuel Trim B2: 0.8%
Engine Speed: 2557 RPM
Air Flow Rate from MAS: 14.12g/s
Oxygen Sensor output V (B1-S1): 0.105V
Short Term Fuel Trim (B1-S1): -1.6%
Oxygen Sensor output V (B2-S1): 0.240V
Short Term Fuel Trim (B2-S1): -2.3%

Short Term Fuel Trim B1 went from +1.6% @idle to -2.3% @2557 rpm
Long Term Fuel Trim B1 went from -4.7% @idle to -0.8% @2557 rpm

Short Term Fuel Trim B2 went from -0.8% @idle to 0.0% @ 2557 rpm
Long Term Fuel Trim B2 went from -1.6% @idle to +0.8% @2557 rpm

Are these Fuel Trim values within limits in respect to a possible air-leak - especially for B1?

Also comparing the MAF readings to a chart I found at JagRepairs.com, my readings are lower than given but it seems like the values are still within tolerance.
Below I have inserted the chart:

Jaguar Repair MAFS Readings
MAFS
Do you have a scantool or just a code reader?? If you can read Mass Air Flow, or find someone who can, use the attached pic as a guide. Read your Mass Air Flow under the four conditions. If the idle readings vary more than about 1 g/sec, or the high RPM readings vary more than about 3-4 g/sec, then the Mass Air Flow is suspect. If your MAF reports more than the chart figure, Rich System Codes can be set.
[img]blob:https://www.jaguarforums.com/820928e0-f4ee-4dbd-a782-0076284ac6ba[/img]

Any suggestions are highly appreciated, again thank you for any advice!

 

Your new idle readings look good, unless they are still changing over multiple runs i.e. unless the learning hasn't finished. So far, no problems or have I missed a concern you have?

With good idle readings you probably didn't need to rev but those look good too.

 

@JagV8 Thank you for checking - my only concern was to make sure I'm not running lean. I did more test runs @idle and also @ 2500 rpm with driving cycles in between. No changes.

Again, thanks to everybody being involved!