P0171 code help (1 Viewer)

[Zurbozz]

I bought a 96 lx450 recently and it’s had a p0171 code that I cannot seem to fix. So far I have cleaned the MAF, done the throttle body gasket, many vaccum lines & the intake hose, smoke tested it(no leaks), replaced the fuel filter and am at a loss as to where to go from here. Do you think best course of action would be to get the injectors cleaned/refurbished? Any guidance would be appreciated.

 

[Malleus]

Cleaning injectors may make you feel better about yourself, but it (most likely) won't solve any engine performance problems. I've seen injectors in a 1FZ-FE engine that were almost closed and the engine still ran like a well oiled sewing machine.

Not knowing any more about your truck than you've shared, I can't give you any advice, other than read the manual.

These are the steps in the school solution, in order:

If you don't have the manual, LMK and I'll post it in the Resources forum for you (and everyone else). @jonheld has previously posted a 1997 LX450 service manual and EWD. I don't know what (if any) differences there are between the two, but, if it was me, I'd want the version for my year model.

The pages above are from the 1996 LX450 manual (RM482U).

 

[Malleus]

Even though it's low on the list, my bet would be the ECT sensor, if the O2 sensor hasn't failed. Keep in mind that these manuals were written with dealer service technicians in mind, working on current model year trucks. This has a lot to do with the order of operations in the troubleshooting lists. There is simply no way that someone 35 years ago could have foreseen which components would last 4 decades and still not fail.

ECM board delamination problems and leaky capacitors, which are becoming more and more common as time goes by, are a case in point. During the 90s, practically the only way anyone would see a bad ECM is if there was an assembly problem, like a bad trace or cold joint. There was no way a board delamination or leaky cap would have happened back then.

Current wisdom helps out (somewhat) in these cases.

This comment doesn't apply, obviously, to common mechanical problems which have been well documented for a very long time. Engine internals, brakes and wheel bearings come to mind.

 

[LongDuck]

Check the air intake tube accordion section very closely. When these split, they allow unmetered air into the intake which has bypassed the AFM, causing the Lean Condition. Given this is a high vibration point, the accordion will crack in between the ridges (in the grooves) and when static without the engine running, it's hard to see any cracks.

Pretty common given the age, heat, and brittle rubberized plastics used for these.

 

[jonheld]

@jonheld has previously posted a 1997 LX450 service manual and EWD. I don't know what (if any) differences there are between the two, but, if it was me, I'd want the version for my year model.

The pages above are from the 1996 LX450 manual (RM482U).

Same engine with the same part number for the ECU (96-97).
There are only very minor differences between the 96/97 FZJ80 and the 96/97 LX450 in US spec. I use the 1996 FZJ80 FSM and EWD 99% of the time on my 97 LX450.