System too lean? Changed spark plugs

[bfunk1414]

Got a system too lean CEL light not long ago. Went off by itself, came back, replaced spark plugs but still there. Any ideas what could it be? I do need the N80 as I speak but doubt that that could be why.

Coils were good when I changed spark plugs, no misfire either.

[aluthman]

It could actually be the N80, since that can affect fuel trims. It could also be a number of other things. Start by replacing the N80 if you had planned on doing it anyway.

[4rings2turbos]

Vacuum leak too, right? Have a friend with a D2 S8 with both banks running lean and have never had the issue so I have no experience. I did have an N80 go bad on my C5 though and it threw a code.

[bfunk1414]

It could actually be the N80, since that can affect fuel trims. It could also be a number of other things. Start by replacing the N80 if you had planned on doing it anyway.

Gotcha. I'll do that tomorrow

Vacuum leak too, right? Have a friend with a D2 S8 with both banks running lean and have never had the issue so I have no experience. I did have an N80 go bad on my C5 though and it threw a code.

I wouldn't say a vacuum leak.

[aluthman]

Yep, it could all be due to a bad N80.

[bfunk1414]

Yep, it could all be due to a bad N80.

Let's hope so. This is my baby. Don't like to see it sick lol.
I've also noticed loss of rpms from time to time. It hits 600 and usual is 730 to 780

[aluthman]

N80 can also affect the idle.

[bfunk1414]

N80 can also affect the idle.

Beautiful. Hopefully that fixes all. Also, I've been following up with your engine build. Sucks u r in CT, I would've offer to help for free lol. Not like I would be of much help tho. I'm a rookie at these stuffs.

[MrBigglesworth]

What are you actual learned fuel trim values? Are you lean at idle or throttle?

[swaggerwagon]

That's an N80. I had the same codes. I finally gave in and bought the N80 at the dealer when I was pumping gas and my car wouldn't start afterwards unless I pumped the pedal.

[bfunk1414]

What are you actual learned fuel trim values? Are you lean at idle or throttle?

Either or. I doesn't tell me exactly when it's lean. I have a basic OBD reader

[bfunk1414]

That's an N80. I had the same codes. I finally gave in and bought the N80 at the dealer when I was pumping gas and my car wouldn't start afterwards unless I pumped the pedal.

About to find out if that was it. Omw to the dealership now lol. Hope this is it.

[aluthman]

About to find out if that was it. Omw to the dealership now lol. Hope this is it.

Hopefully just to buy an N80? It's stupid easy to change out yourself.

[bfunk1414]

That's an N80. I had the same codes. I finally gave in and bought the N80 at the dealer when I was pumping gas and my car wouldn't start afterwards unless I pumped the pedal.

Hopefully just to buy an N80? It's stupid easy to change out yourself.

Replaced now. Cleared codes and drove for about 10 miles. No CEL yet but seems like I need a PCV as well. But it does run better

Thanks everyone for your input!

[swaggerwagon]

How does it seem you need a PCV?

[bfunk1414]

How does it seem you need a PCV?

There like a clicking sound coming from it. It used to be louder before I changed the N80 but still there. It's coming from the like the top of the circled part of the PCV. Also, it seems like the tend to go bad by now. I'm at 95k miles.

[Silveravant]

If the spark plugs were bad it would be too rich. Misfires.

[wding2000]

As I just read this thread this morning, this (or similar) happened to me this afternoon. Car started idle rough, like misfiring, then after a couple of minutes, seemed normal at 800 rpm, even though I recalled my normal idle should be at 750 rpm. Drove ten miles, stopped, restart seemed normal at 800 rpm. After five mile driving, CEL thrown. Pulled codes after getting home:
- P0171: system too lean
- P0304: cylinder 4 misfire

Plan to switch no 4 coil and spark plug to see if misfire moves with it. Questions: if it were coil or plug, could it causes P0171? or is it due to N80? but I do not have any EVAP codes thrown. If lean fuel could also cause misfiring? Thanks

[wding2000]

Forgot to mention: the car is 08, and has close to 60k miles.

[bfunk1414]

As I just read this thread this morning, this (or similar) happened to me this afternoon. Car started idle rough, like misfiring, then after a couple of minutes, seemed normal at 800 rpm, even though I recalled my normal idle should be at 750 rpm. Drove ten miles, stopped, restart seemed normal at 800 rpm. After five mile driving, CEL thrown. Pulled codes after getting home:
- P0171: system too lean
- P0304: cylinder 4 misfire

Plan to switch no 4 coil and spark plug to see if misfire moves with it. Questions: if it were coil or plug, could it causes P0171? or is it due to N80? but I do not have any EVAP codes thrown. If lean fuel could also cause misfiring? Thanks

Not sure on that end. Hopefully someone will reply with the right info

[aluthman]

As I just read this thread this morning, this (or similar) happened to me this afternoon. Car started idle rough, like misfiring, then after a couple of minutes, seemed normal at 800 rpm, even though I recalled my normal idle should be at 750 rpm. Drove ten miles, stopped, restart seemed normal at 800 rpm. After five mile driving, CEL thrown. Pulled codes after getting home:
- P0171: system too lean
- P0304: cylinder 4 misfire

Plan to switch no 4 coil and spark plug to see if misfire moves with it. Questions: if it were coil or plug, could it causes P0171? or is it due to N80? but I do not have any EVAP codes thrown. If lean fuel could also cause misfiring? Thanks

Swap the coil and plug as planned to see if it moves. If it stays with cyl. #4, you may have a bad injector.

[wding2000]

Swap the coil and plug as planned to see if it moves. If it stays with cyl. #4, you may have a bad injector.

Cleared codes and took test run, after 10 miles, CEL back on. So there is something, not false alarm.

Proceed to switch coil/plug last night, I did notice #4 plug was loose, looser than other three - maybe I was afraid cross threading to torque it right before. Swap #3 and #4, and torqued to less than 20 ft-lb (spec says 22) - guess still concerned about cross threading , but definitely tighter than before. Initial idle start has misfiring on all four, test run, all smooth. This morning cold start, no misfiring. Hopefully the issue is the loose plug.

As for system lean, will pay attention in next several days.

[wding2000]

I did pull the log. LTFT was 15.625% and STFT was constantly at 18%. This is after I cleared code, made 10 miles run and had CEL back on. If I run longer, I would guess LTFT would be at 18%. After I switch plug, it is now at 14.0625%. Is it still too high and supposed to be around +/-10%? I will make longer run then pull log again.

Another observation: Fuel/Air ratio seems good at 0.99 mostly, except for a period of 8 sec, it goes up to 1.99, while O2 reading at 0 V. I cannot make out what that means - O2 sensor fails to read out (?). Out of 20 minute log, there are about 20 seconds 0f O2 at 0.

[wding2000]

Log screen shot

[wding2000]

As for N80, from log, I do see Commanded evaporative purge (%) has values from time to time from 0%, 1% to as high as 20% even 70% in a couple of instances. Not sure what that means, but at least it is doing something. However, both Absolute evap system vapor pressure (Pa) and Evap system vapor pressure (Pa) - not sure these are not reported or my OBD reader does not support reading these.

[aluthman]

I'm leaning towards an o2 sensor. I've heard that you can take them out and soak them in acetone to clean them, although I've never done it. What did your plugs look like? White, tan, black? That would be an indicator as to whether you are actually running that lean or if a bad o2 sensor is just making the ecu think it is.

[wding2000]

Thanks for your help, Adam. The tip is kind of white/grey, the top of thread is black and I can wipe out carbon. Sorry the picture is not very focused.

[aluthman]

That looks normal. I think you have an o2 sensor issue.

[wding2000]

Thanks. I will look into this. Even though no O2 codes, it is definitely aging.

[aluthman]

The lean code can be considered an O2 code.

[MrBigglesworth]

How did you get on fixing your issue?

[bfunk1414]

How did you get on fixing your issue?

Spark plugs and the N80. The N80 did the most results since apparently it affects many different things in the car. Even the RPMs

Sent from my SAMSUNG-SM-G890A using Tapatalk

[wding2000]

How did you get on fixing your issue?

Report back to the group. In my case, we thought it was my O2 B1S2 sensor. Actually I was not sure it is pre-cat or post-cat, as B1S1 reading (mA) has corresponding spikes, thus which causes which. Around the same time, I noticed I had oil leak around filter housing - I knew it is oil cooler and/or filter housing gaskets. Since I was due for an oil change any way, I thought I would seaform fuel tank and crankcase, change gaskets and oil/filter, then put on new O2 sensor (in that order), so as to keep new O2 from any seaform contamination (I know they claim O2 sensor safe, but still).

Now 400 miles after gaskets/oil/filter change, CEL never come back! Pull a log, LTFT is at about 6-7%. I guess I am good now. However, I am puzzled how oil cooler/filter housing gasket leak can throw LTFT off and P0171 CEL on.

Take a closer look at B1S2, I still see the occasional 0V reading. It seem my O2 may still need a change, but it does not seem it is as bad as throw LTFT off and CEL on. I will continue monitor it.

[wding2000]

FT and O2 B1S2 plots