So on my 2004 xj8 with 136000 miles, i have been getting a p0171 code every so often. After i clear it, it usually takes about a week or more before it comes back up. The code is bank 1 being too lean which leads me to believe that there is an air leak somewhere. Anyone have any ideas on how to begin to search for the issue? I take it that this is also is whats causing my low gas mileage, im getting 13.6 miles to the gallon! Thanks guys!

 

Here is the full list of Possible Causes of P0171 on your model from the Jaguar DTC listing (see right hand column):



This should give you some more detail on where to investigate the source.

Graham

 

OK, as helpful as the dtc you gave is, i still dont know where to begin! I forgot to mention that i also get code p1111 if that helps

 

Check the plastic intake box. The resonator tubes on the bottom somethimes crack where they join the box.

 

It's most likely going to be the PCV valve. If only one bank is running lean like you described you can rule out fuel pump/fuel filter clogged/leaking air inlet tube/leaking throttle body gasket as this would affect both banks.
Unless you have a smoke machine, there's no real way to accurately pinpoint an unmetered air leak. You can try spraying brake clean or carb and choke cleaner around the intake and see if your rpm's raise. I doubt you will have an air leak at the intake though on one bank only.

 

P1111 just means the self diagnostics are complete. That is normal.

Remove the acoustic cover and take a good look at all the hoses and connections. Start the motor and listen/feel for any hose leaks.

Although rather rare, a cracked exhaust header pipe can also read as a lean condition. I would bet the problem is on the top side of the engine, though.

The mass air sensor is a common issue that you can likely also rule out, since you are not also getting a P174 (it would affect both banks).

 

Thanks for the info guys! The PCV valve does click and make sounds when i drive and slow down, but i thought this was normal. As for the air box, i thought it was this and checked it and nothing. There is a sound that occurs when i am driving and giving throttle that sounds like a choo choo train,it sounds like its coming from the passenger side (USA model). ANy ideas?

 

Is it supercharged or naturally aspirated? If you can your hands on a scan tool and monitor the long term and short term fuel trims at idle and report back here with the information that would be great.

 

Yes, but that would affect both banks and he would have a P0171 and P0174 at the same time.

 

Post #2 on this thread has the most useful information. I would evaluate the last column of that list and see what out of those suggestions you can tackle (process of elimination).

 

I will plug my scanner in and let you guys know about the fuel trim ratios. Furthermore, it is naturally aspirated. I shouldve mentioned that before, sorry!