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Lr3 4.4 p0172 p0175

12228 Views 4 Replies 3 Participants Last post by  LVDaytripper
I have a tough one here. 2006 LR3 4.4, 112,000 mi. Vehicle exhibits minor rough idle otherwise no drivability issues.

Originally kicked several codes indicating evap leak. Tested with smoke machine; EGR valve leaking; replaced. About 3 days later P0175 (Rich bank 2). Scanner showed very low barometric pressure (in Hg) and very low air flow (g/s). Replaced MAF and MAP sensors, now appear to read appropriately. A few days later, P0175 again.

Snap On Solus scanner also shows sporadic misfire in cylinder 8 (bank 2). Move cylinder 8 spark plug to cylinder 2 and cylinder 8 coil pack to cylinder 6. Reset and recheck; P0175 again after 100-200 miles, but misfire does not follow. Spark plugs look good, showing no indication of rich running; plugs were replaced at around 90,000.

Scanner shows LT fuel trim B1 normal, B2 negative teens. Excess fuel pressure ruled out due to only affecting one bank. Scanner also shows all 8 injector pulse widths more or less identical. Swapped bank 2 injectors over to bank 1; check engine light appears again on bank 2 only.

Scanner shows vehicle reaching closed loop on both banks more or less simultaneously. Yesterday replaced upstream bank 2 oxygen sensor; no effect. Then reinstalled old oxygen sensor bank 2 and installed new bank 1 upstream oxygen sensor, also no effect. Vehicle is no longer showing misfires, however.

Vehicle has not been at the dealer since 55,000 miles, so could be a reflash of ECU issue.

After research last night on how to interpret fuel trim plots, I need to rerun some scans (the light now comes on almost instantly, so getting a freeze frame of the fault is easy), redo the smoke test to double check for leaks, verify reasonable coolant temperature sender readings. But otherwise it appears my next option is give it to the dealer for a $230 diagnostic fee plus parts replacement I could do myself (I own an independent shop).

What am I missing?
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I have the same codes, with no drive-ability issues.
Does your Snap On Solus have the option to clear all engine adaptation values? Reason I asked is recently I was having issues with clearing my Lean Banks 1 and 2 codes even after I replaced my O2 and MAF sensors, PCV valves and air intake seals. Codes kept coming back after driving for 20 mins or 10 miles but truck was running smooth with no issues. I read about the adaptation values but my scanner did not have the option so I got another one which had. Upon receiving it, went to hook it up and cleared all engine adaptation values and to this day, codes never returned and its been a few months now.
I believe that the ecu refers back to the stored adaptation values and when it senses the old ones with the issue, it throws the codes back up since it has not learned the new values yet.
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