HI,
I wonder if anyone can help me to sort out my PO174 problem please?

2001 XKR 148,000 miles.

Car starts easily no matter what weather, no matter how long it has been sitting. Seems to run smooth.

Presuming the codes and MIL have been reset, the car starts fine as stated. There are no lights on and no codes or pending codes. When the car hits it operating temperature it throws code PO174 (Bank 2 Lean), the MIL light comes on and it goes into Restricted Performance. If I drive it around for a few miles, or rev it to the 3000RPM RP limiter, RP light goes out and car runs fine (but rich). It will stay that way until it is allowed to cool below operating temp and then the process repeats (ie goes into RP)

The MAF is new. It has also had one from a working car tried on it and it does not make any difference. It is only PO174 (not both sides) that gets thrown.

The car is running rich, not lean and mileage (not surprisingly) is poor.

SHRTFT1% cold is +3.1 with range of -0.8 to +0.8 through warm up
LONGFT1% is -7.6 falling to -4.7 when fully hot under load.

SHRFT2% is +25.0 ( I think that is the max that it can be provided with).
LONGFT2% is 19.5.

It does not sound like a vacuum leak to me as it is only one side. I have checked though and haven't found anything.

I have the other typical data readings but sure what might help people advise me.

Clearly the car believes that it needs to dump extra fuel for bank 2, and fuel trims seem to demonstrate that is happening. Where should I start looking keeping in mind it never throws a Bank 1 lean code.
Thanks,
Perry

 

How about the O2 sensor for bank 2? They do not last forever and 148k miles is getting close to forever. They also affect fuel trim . . . a lot.

Surprising that there is not other codes set ICW the RP.

 

You might also have a charge air cooler seal leak. There a TSB on this, attached.

Try to isolate the problem by watching the trims for instabilty while spraying various areas of the intake with carb cleaner.

 

Thanks for advice. I will try the air cooler seals first and then bite the bullet and go with the O2 sensors. Thanks

 

Having checked everything possible for vacuum leaks, I decided to replace Bank 2 Upstream HO2Sensor.

This seems to have solved the problems: the old fuel trim data was:
SHRTFT1% cold +3.1 with range of -0.8 to +0.8 through warm up
LONGFT1% -7.6 falling to -4.7 when fully hot under load.

SHRFT2% +25.0 ( I think that is the max that it can be provided with).
LONGFT2% +19.5.

New Data:
SHRTFT1% -0.8 TO +0.8
LONGFT1% -1.6 TO -2.4

SHRTFT2% -0.8 TO +0.8
LONGFT2% -2.4 TO -3.2

I don't think I need to be concerned at those levels given age and mileage, but if any one feels different please comment.

If it helps others, I did the job myself. It is not very technical, just fiddly. I put the car on ramps and had a look from the bottom and whilst the downstream O2 sensor looks doable, even my slender arms can't get at the Upstream sensor without removing exhaust. I opted to work from the top:
1. Siphon coolant from expansion tank, I got about 2 litres out this way.
2. remove clip securing coolant tank sensor and pull out sensor wire.
3. remove the torx screw for the expansion tank and hoses (4 in total, one underneath, one at the top facing fire wall, one to the side of the engine and that runs under up the middle to the radiator). The expansion tank should lift/ slide away. If your coolant drips from hoses just cork them up.
4. remove three torx head screws holding heat shield in place. They are very awkward to get at. This was the most time consuming part of the process for me. I just could not get a good purchase on them.
5. move the heat shield out of the way.
6. separate the grey connector for the O2 sensor. Tie a string to the part of the wire attached to the O2 sensor. This will allow you to drop it through so it is not in the way of removing the sensor and if you keep the string in place you can retrace the route when reassembling.
7. It is a tight squeeze but I managed to remove and replace the sensor using a standard 22mm open end wrench. Once you crack it loose, it seems to unthread easily as expected.

Reassembly is just a reversal of the above,

Thanks for everyone's help, regards, Perry