Hello fellow Jaguar fans. Any chance anyone has ideas on next steps to help me diagnose a P0171 (System too lean bank 1) code on my 2003 XKR supercharged 4.2 with 72K miles? I have found many threads on this topic and tried many troubleshooting steps from these threads. I have learned a lot but have been unable to isolate anything specific causing my out-of-ordinary fuel trims. Here is what I have been able to find out so far:

The engine runs smooth and has plenty of power. From a driving perspective, I do not notice anything unusual.
I have reset the code twice, and each time, after a few drive cycles, only P0171 comes back. P0174 does NOT show.

I have performed a smoke test at the intake and initially found a small leak at the throttle body gasket. This has been fixed, and I repeated a smoke test and found no leaks, but the code returned. The car has a clean, relatively new air filter.

Fuel trims: I watched short-term fuel trims and they seem farily stable around zero when the car is idling. If I increase RPMs while the car is parked, they bounce around a little, but still single digits (under 10 either direction). If I accelerate (under load) the fuel trims quickly max out at +25 and stay there until I finish accelerating.

Fuel pressure: Fuel pressure is consistent around 55PSI when idling, increasing RPMs and under acceleration and under load, including wide-open throttle under load. I believe this means my fuel pump, filter, and regulator are probably not the problem -- am I correct?

Vaccum: Vaccum seems to drop as fuel trims rise (i.e. under acceleration). 23psi when idling, 8psi under load at 50% throttle, 3psi under load at wide open throttle. Considering that the smoke test did not show any leaks, any idea what this means?

MAF: At idle, my MAF reading is about 6 g/s. At wide-open throttle under load, my MAF reading is around 180 g/s. Is this normal?

A friend suggests that I pull the plugs on bank 1 and see how they look. Maybe I will try that next.

Any ideas on next steps? Thanks in advance!

 

The o2 sensor is reading lean and the ECM is trying to compensate for this by adding fuel (maxing out at 25%)

Possible causes for this after reading what you have done so far...

O2 sensor working but incorrectly reporting.
Air leak around the o2 sensor (come loose and needs nipping up).
Exhaust manifold gasket leak.
A crack in the exhaust manifold.

Obviously relating to bank 1.....i take it your bank 2 fuel trims are ok and with in spec.

Other more experienced diagnostic members like JAG V8 and OTHERS may have more viable suggestions for your Po171 code.

Good luck.

 

What are the LTFTs (hot engine, parked) at idle & about 2500rpm?

I see you've watched STFTs, which is useful if the LTFTs indicate a leak but we don't know yet if they do.

It may help to regard P0171 as being caused by any of the things Jaguar list i.e. not necessarily a leak - which is why LTFTs at those engine speeds are so useful.

 

If it was not so damned hard to do, you could swap the bank 1 HO2S with the bank2 and see if the fault follows?

bob

 

Thanks everyone for the great suggestions/questions.

I bought some MAF sensor cleaner, pulled the MAF sensor, cleaned, air dried, and put it back. I then disconnected the battery and shorted the leads for a reset. The code still showed when I powered up, so I cleared it. I made 3 seperate on/off trips, each time to full operating temperature, so far the code has not returned, and does not show as pending. I noticed that under load, at wide open throttle, the MAF reading is now over 300 g/s -- much better than the 180 from before.

After a few trips, and with the car at full operating temperature, I captured both short and long term fuel trims for banks 1 and 2. Here's what I saw:

Parked, Idling around 650rpm:
STFT1 and STFT2 both were stable between -2 and -3
LTFT1 was stable at +11
LTFT2 was stable at +10

Parked, 2500 RPM:
STFT1 bouncing between +7 and +11
STFT2 bouncing between +5 and +9
LTFT1 and LTFT2 both stable at +8

Driving on the road:
STFT1 has big swings from -10 to +20 depending on acceleration, most of the time between -2 and +10.
STFT2 pattern was consistent with STFT1, roughly 1 percent lower.
LTFT1 hovered around +10, with a few drops to +4 or +8 depending on acceleration
LTFT2 pattern was consistent with LTFT1, roughly 1 percent lower.

I'm glad to see that bank 1 and 2 seem to be seeing similar behavior, but the big swings in STFT seem concerning.

Does this data help identify anything?

 

Your LTFT's at park seam to indicate an air leak relating to both banks...
At 650rpm you would expect LTFT to be under +5% (you have +10....+11)

At 2500rpm your LTFT's drop (indicating air leak)

Both banks have similar high LTFT's,..So i think this can rule out my post 2 possible causes.....
One of our members recommends cleaning the MAF more than just once....actually i think he said it took three cleans to get his MAF reporting correctly.

You have Motorcarman and JagV8 responding to your thread,Both greatly experienced in diagnostic's and will have a grater understanding of your fuel trim's.

Good luck.

 

It may well be that when it flags P0171 it is very close to P0174 as well. You can find out this way: wait for the code then read the freeze frame data.

The 2500 STFTs may mean it is still moving the LTFTs but see what the above shows.

 

See if you can do a smoke test of the entire crank case to detect other leaks (dip stick, all those Norma connectors, etc.) just in case the intake smoke did not quite reach.

The fact that the cleaning of the AFM helped means you would likely benefit from a new one. You probably already know, but the small "pill" on the side is the air temp sensor, the actual AFM is recessed and needs a GOOD soak to be clean. To be honest, cleaning the AFM is good routine maintenance, but probably will not fix it is you have symptoms of failure. Cheap to try, though. Unfortunately, the XKR AFM are more pricey. It has been pointed out before that the sealing condition of the o-ring around the base of the AFM is CRITICAL. Double check it is there, and in great shape.

Other possibility is that there is a crack in the plastic intake tube/snorkel that reveals itself under load, as the engine rocks. They are easy to remove and inspect. Double check all the accordion sections and resonators for wear and cracks. Also, I seem to remember the supercharger has seals that can slip under load. There is apparently a later design with better clamping capabilities and less likely to develop air leaks.

Best of luck, keep us posted.

PS: Remember that fuel trims are a matrix of numbers dedicated to a range of rpm and load.

 

Update:

I pulled the MAF sensor and gave it a second, very thorough cleaning and air dry. I also performed a thorough visual inspection of the plastic intake accordion tube (no problems found).

Also, I performed a smoke test on the crankcase. I double-checked there was plenty of smoke in the crankcase by temporarily opening the oil cap, PCV, etc. No leaks found in the crankcase, and I gave it a very thorough look, but I did find something. When looking all around for leaks, I happened to notice one of the bolts on the intake elbow was not fully seated. When I checked it, sure enough, it was only finger tight. I tightened this up. This did not show as a leak during my intake smoke test but maybe it was a contributor to my issues.

I took the car on a couple more trips, full on/off cycle, and full operating temperature. No codes, and no pending codes, other than P1000 (diagnostic test incomplete).

Fuel trims look better at full operating temperature:

Parked, idle:
STFT1: 0
LTFT1: 7.81
STFT2: 0
STFT2: 7.81

Parked, 2500RPM:
STFT1: 2.34
LTFT1: 8.59
STFT2: 2.34
LTFT2: 7.81

Also, the swings in STFT when driving under load are not as dramatic as I was first seeing.

So -- to recap -- thus far I have done the following:

1. Fixed small leak at throttle body gasket (found with a smoke test)
2. Thoroughly cleaned MAF sensor
3. Tightened loose bolt at intake elbow (found with visual inspection)

I think these fuel trims are acceptable to me, and I'm glad that there is consistency between banks 1 and 2. If fuel trims for both banks rise above acceptable thresholds in the near future, I think my next step will be to look at freeze frame data, and possibly install a new MAF sensor, but for now (fingers crossed) I think our work here is done.

Thanks to help from everyone on this thread, up to this point, I was able to diagnose and troubleshoot this issue for the low cost of a can of MAF sensor cleaner ($9 USD) and a DIY smoke machine ($5 USD in incense sticks and some spare parts).

Thanks everyone for the excellent help!

 

Those LTFTs are quite high. I feel not enough to panic.

As they're quite alike you'd be looking at a common cause.

Not an air leak (they don't drop when revved).

So... MAF is a suspect.

I'd probably just live with it or even look for a cheap used MAF over the weeks ahead...

 

Your LTFT's now dont suggest an air leak... (all sorted)

If you do a hard reset, it will reset the fuel trims and they may not go back up so high,
or you can let them sort their selves out but this will take longer.

If after a reset they go back as they are now, then it looks like another maf clean or as suggested start looking for a new maf.

Glad to see you have made really good progress with your P0171 code.