Hey folks! Looking for a little help with my 2005 LR3. I have a check engine light and at P0171 "lean bank one" code that I've been chasing for a month or so at this point. I have limited experience working on cars. I bought this as a project to learn on so anything I've "ruled out" or whatever should be taken with a grain of salt. I searched the forums here and saw some good tips but I think my situation is different from the ones that I saw.

The conditions: When it first presented, I assumed it was a suck open injector becuase I was getting a fuel smell. I removed and cleaned all the injectors and replaced the gaskets/seals. The problem persisted. Then I got smart and watched some videos on how to actually diagnose the code so I evaluated the fuel trims and saw that they dropped when revs increased (classic sign of vacuum leak). Bank 1 was hovering between 15-20% for LTFT at idle. Bank 2 was also a little high but not crazy. Like 7% or so. Both dropped at higher RPMs.
Repairs and results: I smoke tested and sprayed the engine bay with carb cleaner and got no results from either test so I cleaned and replaced all intake manifold gaskets since it seemed the most likely culprit. Afterwards, idle LTFT for bank 1 was is around 4%...massive improvement and seems to be within spec but honestly I'm not sure what "spec" is so maybe not? I thought I fixed the problem but the light came back on. I also replaced the PCV valve with a decent quality one from FCP Euro.

Other diagnostics performed: I did a O2 sensor voltage test, which seemed to indicate properly functioning 02 sensors. Voltage reacted appropriately to idle and engine revs through OBD scan. Maybe I did something wrong here but it seemed at least that both Bank 1 and Bank 2 sensors were reacting similarly so I ruled out O2 sensor isssues.

Current state and other notes: After driving around with the OBD scanner plugged in, it seems that Bank 1 LTFT jumps to 15%-16% when I let off the throttle. Could that alone be causing the code and CEL? It looks good when idling and accelerating, though. The other thing that looks odd to me is that throughout all my tests, STFT seemed to be fine but the LTFT was jumping around like crazy or registering a number for LTFT that I never saw in STFT. In videos I've seen LTFT is a very slow/gradual change based on an average of STFT but both STFT and LTFT appear to update constantly and, for Bank 1, it registers a higher number than I ever see in the STFT. That doesn't seem mathmatically possible. Am I missing something there? Sorry if this is confusing.

Any help would be appreciated. Thanks in advance!

 

Have you cleaned out or inspected O2 sensors? If they're covered in carbon build up (from running rich) up they may not properly read? It doesn't perfectly follow your symptoms but could be worth looking at. Thats the only thing I can think of but I'm not the most well versed in LR3s compared to other forum members.

 

My Lean Bank 1 P0171 turned out to be a leaking fuel injector o-ring. I had a shop replace injectors when my 07 was across the country. It was better for a while, but kept returning somewhat randomly.

I sprayed carb cleaner around the intake while idling and watching live fuel trims. When I sprayed around the Bank 1 side (passenger US models) I could see movement in Bank 1 fuel trim. I was convinced the intake was leaking, bought the gaskets and got ready for the repair. One last check before removing the intake, I sprayed directly at the injector ports and found 1 cylinder (#7 I think) had a leaky o-ring. I removed all the injectors, thoroughly cleaned the ports (previous shop did not) applied new injector o-rings and have not had a problem since.

The replacement o-rings had a very tight fit. Much better than what came with the aftermarket injectors that the shop used. I blame crappy aftermarket parts, specifically poor fitting o-rings.

Hope you get it resolved! It can be frustrating, but that somehow makes the final fix more rewarding.

 

You have done a ton of good diagnostic steps and thrown a few parts at it too.

I agree the values sound weird. If I have time I’ll check an LR3 to see if the LT fluctuate as much/more than ST.

Ive cured some mystery lean codes by doing a fuel rail/injector and intake cleaning. There are special tools for hooking up to the fuel rail with shop air and a cleaner like BG, set pressure at 65 psi, disable fuel pump, and run the vehicle for12-15 min/time for the can to run out.

same tool has an atomizer tip that goes in the intake using an intake cleaner, rev to 1k, with romps every 30 seconds or so to suck the cleaner through and blow out the exhaust.

good luck!