1998 XJR 233K miles

I looked briefly in a search of this forumn. I replaced both upstream Denso air/fuel ratio sensors when I got the heads back on and running. About 3 months and 20 miles ago. The problem, I'm really want to keep the car. My question... Do the dowmstream sensors have any fuel ratio input to the computer other than what it's reading from the catalytic convertor for Efficiency?? I know that it only had two wires on each so it couldn't

 

The downstream sensors just check/monitor the catalyst efficiency.

bob

 

AJ26S do not have downstream sensors.

 

Maybe... but I think they are also used for fine-trimming the fuel.

JTIS is a little unclear for this era car as if I'm looking at the right part it says:

Oxygen Sensor (O2S)

are positioned downstream of the catalytic convertor

has the ability to generate a voltage signal proportional to the oxygen content of the exhaust gases leaving the catalytic convertor

provides feedback information to the ECM used to calculate fuel delivery

(JTIS is clearer for later model cars, removing the doubt.)

 

They may (probably do) have them in USA etc.

 

The U.S. cars have downstream 2 wire oxygen sensors. Both N/A and S/C'd cars do.

The reason I ask this question is because my LT fuel trims are a little on the lean side. The car having such high miles and age I just wasn't sure if the downstream sensors would possibly richen the mixture a bit or not. I don't mind paying $150 for 2 Denso downstream sensors, I just wanted to do it knowing that it would adjust my LT fuel trims. I also do know that being 2 wire will have a much lazier response than heated upstream sensors. Other than just driving the car long distance to see if the LT adjusts, I'm going to convert the old style MAF to the newer style sensor and relocate the pins in the connector and see if that also changes it.

I'm still interested in hearing if anybody else has any input pertaining to this. Thank you!

 

"The reason I ask this question is because my LT fuel trims are a little on the lean side." [Addicted2boost]

I am interested in clarification on this question as well. I have done a few rounds of smoke testing and currently can find NO vacuum leaks, yet my fuel trims run a little lean with randoms jumps to very lean. I am wondering if replacing the upstream and possibly the downstream O2 sensors could solve the problem. If the downstream are not as critical for fuel trims, I'd like to save a few short term dollars and just replace the upstream sensors. (03 XJR)

 

http://www.jagrepair.com/images/Trai...ual-9-5-01.pdf


pages 86-89

 

Harvest, having f a fresh set of upstream sensors will improve performance and gas mileage. It wouldn't be a waste of $ to change those out.

Thanks XJR-99 for the clarification within that link.

 

If you are running E-10, then it will be expected that your trims will be a little positive. Positive is what you mean when you say lean, right?

 

Yes, positive (adding fuel) is what I meant by lean. I tweaked my XJ8 with smoke tests and a used MAF until the trims ended up right around zero all the time. I was hoping to accomplish the same with my XJR. I have improved the trims somewhat, but still haven't gotten them down to the low numbers I accomplished on the XJ8.

They both of course run E 10 gasoline, but I never knew that created positive fuel trims. That's very interesting. I have learned something today.

Edit: Sorry, I thought the comment was directed at me. Of course it was directed to the OP. By the way Addicted2boost, I ordered 2 new upstream oxygen sensors; they will be delivered on Monday and installed on Tuesday.

 

Not running E-10, just 93 octane. Yes, you are correct about the positive reading and it's lean. Between 10% — 15% positive scale. The short trims do very little compensation to adjust this. I really just need to perform a hard reset to zero out the fuel tables and go on a long drive to see what it says.