Ok just looking for advice.

My 2001 XKR 60K miles running fine here in california. BUT my long term fuel trims (LTFT) are 0.74% and 2.78% (bank 1). This would suggest an air leak between the super charger outlet and the inlet manifold?. But as this is a supercharged engine from where the inlet duct splits which is only after the super charger the system is actually under pressure 7.5psi so unlike the normally aspirated car air would not seep out. No visible signs of leaks and fuel pump regulator breather connected ok on that side.

I assume air leaks out from exhaust manifold/EGR pipe/ top joint cat converter (all these are before the top O2 sensor) would not cause FT variance.

Note STFT are ok. Car is well serviced i.e new sparks/MAF/Evap Valve/Rocker Vent tube (bank2) e.t.c in last 10K miles. No air leaks in before TB.

Any ideas or is 2% diff normal ?

Thanks in advance

 

You need to add the stft as well to get an overall figure.


2% deviation is not something I would spend time on to be honest.

 

OK thanks the STFT are -1.51 and -1.18

 

You will notice that the stfts can fluctuate, so for good readings its best to either have a graph of both stft/ltft per bank, or watch them closely.

With the values you show, its that a fuel trim of -0.77% and -1.6%, so perfectly ok.


Now even if you would have an small earlieak (ie >5% or even 10% fuel trim adjustments), due to the ecu adjusting the a/f ratio, you will pass the emissions tests. Overhere it is tested not at idle though, the engine needs to run about 2500 rpm, where the co and o2 is measured.

 

Funny you say that I just did the emission test last week and passed with flying colours. On passed tests they have used the rolling road test e.t.c but this time he just connect to the ECU a device that he left on the dash (so I assume it was wireless) let the car run for like 10 min with no driver, he spent the 10 min looking around under the hood paying particular attention to the driver side pic on the wing. Didnt even open the petrol cap. And that was it issued a passed cert with the DMV cert # and all categories pass. No reading given for CO, Nox, O2 I used to get these. Guess CA must have changed how they do these test on 2000> cars.

Yes STFT range between -/+ 1.5 and are the same for both sides when I get the engine warn and measure them over a 10 mile run. But LTFT always have that 2% diff on bank 1 range is usually 0 to 5% with a 2% diff between the banks. I'll leave it alone as car runs great and wait until I have to take the super charger out, as I know at some point that will need to be done!

I did have the throttle body out last year to replace a bolt on the EGR value that had dropped out (was sitting on the gear box back in 2004 jaguar did the EGR pipe TSB and had to re thread that bolt guess they did'nt tighten it up!). LTFT were higher but dropped 2-3% after I replace the bank 2 rocker breath and put the latest version of the Evap Valve in (the one inside the driver side wing).