Intermittent P0171 CEL code 1996 LX 450 (1 Viewer)

[FJsexty]

Hey everyone,

I've been using this site for years but this is my first actual post. I recently bought a very clean stock 1996 LX 450 with 182,000 miles. Last week the check engine light came on and i pulled it up on my code reader and got P0171 system too lean (bank 1). I read through some of the threads on here about that code but none seem to fit my exact problem. I can clear the code and it can sit in the driveway all day at idle and code wont come on. I can even drive it around at different speeds/accelerations and it still wont come on. It seems to be very random when the CEL comes on. Only after about 20 minutes or so of driving is when i will get the code. I inspected the MAF and throttle bottle and it was spotless. I checked continuity as per FSM and sensor was in limits. I changed bank 1 sensor 1 (upstream) O2 sensor. All of the hoses and intake lines are new. I did notice with the light on the truck hesitates more on start up. Sometimes i have to crank it twice in order to start. I am leaning towards a fuel pressure issue and have a fuel filter on order. Any other suggestions would be much appreciated. Thank you

 

[Maozebong]

do you have access to a scan tool with live data?

you can check for vacuum leaks by spraying with parts cleaner around the intake and watching short term fuel trim % for changes.

 

[FJsexty]

do you have access to a scan tool with live data?

you can check for vacuum leaks by spraying with parts cleaner around the intake and watching short term fuel trim % for changes.

I have a scan tool but it doesn't show live data. I did try the spray technique and listened for a change in engine idle but nothing was heard.

 

[Maozebong]

I have a scan tool but it doesn't show live data. I did try the spray technique and listened for a change in engine idle but nothing was heard.

get a bluetooth obd2 connector and an app called ‘torque’ that reads live data. you need to see what the ecu is seeing or you’re just guessing.

the change is too subtle for the human ear to pick up, but the o2 sensor is fine enough to pickup any fuel getting sucked in thru a vac leak, you’d see it in the live data. if that didn’t work you could temporarily pinch off the return line to spike fuel pressure and watch the short term fuel trim data and help to eliminate which part of fuel/spark/air is effecting the A/F ratio.

 

[FJsexty]

get a bluetooth obd2 connector and an app called ‘torque’ that reads live data. you need to see what the ecu is seeing or you’re just guessing.

the change is too subtle for the human ear to pick up, but the o2 sensor is fine enough to pickup any fuel getting sucked in thru a vac leak, you’d see it in the live data. if that didn’t work you could temporarily pinch off the return line to spike fuel pressure and watch the short term fuel trim data and help to eliminate which part of fuel/spark/air is effecting the A/F ratio.

Ok thanks for the info. I was looking into one but was concerned some of the newer scan tools wont be able to talk an ECU from 1996. Do you own one and if so which one? I'll read through some of the details online and see which ones are compatible. I'm sure a good scan gauge will help me down the road with other issues as well. Thank you for the advice.

 

[Maozebong]

Ok thanks for the info. I was looking into one but was concerned some of the newer scan tools wont be able to talk an ECU from 1996. Do you own one and if so which one? I'll read through some of the details online and see which ones are compatible. I'm sure a good scan gauge will help me down the road with other issues as well. Thank you for the advice.

i bought a generic obd2 dongle for 20$ on amazon, and it works with my 95 so it will work with yours. don’t remember the brand.

i also own a launch c123, autel maxisys pro, and a couple others. the 20$ dongle will do everything you need.

 

[FJsexty]

i bought a generic obd2 dongle for 20$ on amazon, and it works with my 95 so it will work with yours. don’t remember the brand.

i also own a launch c123, autel maxisys pro, and a couple others. the 20$ dongle will do everything you need.

ok great. I ordered one today on Amazon. Should be here next week. Thanks again

 

[alia176]

Curious if a resolution was found.