Ive read a lot on the fourm about this code and roughly know what the short list of culprits might be, so got a good idea what, but don't know for sure. A potted history of recent events:

1. Everything running perfectly for past couple of years
2. Recent full service (incl fuel filter, trans oil/filter, front pads)
3. Within 50 miles CEL comes on
4. Hook up to OBD2/app and the P0171 code is now showing
5. Restricted Perf comes on and off every now and then
6. Cleaned MAF sensor with res free electrical cleaner (was really clean anyhow)
7. Took off air intake between MAF and TB, cleaned and checked for cracks (NOTHING)
8. Cleaned TB with CRC cleaner - was a bit mucky I suppose
9. Checked for leaks all over the shop with soapy water sprayer w engine on (no change in revs AT ALL)
10. Did hard reset and cleared the fault codes.
11. 50 miles or so later CEL back on with P0171!!!!!!!!!

Ran a diagnostic with Torque Pro (only went a few miles, and have not done that many since hard reset). Results:

1. Fuel pres 54.8psi
2. Intake 4.5psi
3. MAF 4.8g/s
4. STFT1 -2.3%
5. STFT2 0%
6. LTFT1 18%
7. LTFT2 16.4%
8. Volts 13.2
9. O2S1Eq 1.0
10. Av CO2 485g/km
11. Vacuum 208in/Hg
12. O2 1x2 0.8v
13. O2 2x2 0.6v
14. Boost -10.2psi

Now, I have NO idea what any of the above means, so am hoping the wise ones of you good folk out there can help me pin point what the issue is.

Worth mentioning I've been getting some slight surging now at low revs with little throttle (nothing at speed), plus some weird sweet smells from engine immediately after start up.

All help greatly appreciated.
Jules

 

Just do the LTFTs at idle & about 2500rpm, engine hot, parked. If they head towards zero you've an air leak (which is what the code is suggesting).

 

Idle:
LTFT1 18
LTFT2 16.4

2500 revs:
LTFT1 4.3
LTFT2 3.1

I guess this confirms an air leak somewhere? Could faulty spark plugs (misfires) also cause this tho as the sensors are seeing extra air?

 

I think you would notice the misfire if you had one.


Looks like it is time for the homemade smoke machine.

 

Classic air leak. I think you'd need every plug/coil to equally misfire and yet be undetected as misfir codes to replicate it - i.e. ain't gonna happen.

Looks like the leak is similar bank-to-bank so may well be something shared.

Smoke - looks a good idea!

 

I've had several over the past few days...!

 

Ok, not sure whether to laugh or cry!

Convinced this was an air leak and not being savvy enough to rig up the smoke test, I booked the cat in to the garage - was due in this Wednesday - and had already started busking on the streets in readiness for some horrendeous bill. As I do lots, had been searching the forum and I stumbled across a thread from our XJR friends who had similar issues, which gave a list of 'obvious' things to check. One of which was the o ring on the dip stick and another was to check the oil filler cap. So in hope I trundled out to do the checks and the dip stick seal was fine, but..... THE OIL FILLER CAP WAS ONLY HALF DONE UP!!!! Re sealed it and went out for a few miles drive with my Torque app on. Got back and the LTFT had fallen from 19.5 on both banks to 6.5 and 7, and they did not drop when I was in park and got to 2.5k revs!

Could this be the reason??? If so obviously im really happy and I will monitor closely over the next few days. If it is, then said garage wont be seeing me again any time soon!

Thanks again to those folk who offered up help here.
Jules

 

Yes, of course it can be and from your readings could well have been.