Pcm leaning Idle

[Weatheralls Auto]

Just want to double check;
I think this is normal,
At idle my Wideband is reading 21-22, Pcm O2 reading fairly lean as well.

I have been thinking this is just the PCMs way of reducing fuel consumption etc?

When I first started tuning and noticed I replaced the HO2s, no change, so I swapped out the Wideband for a new one and it was the same.

This is when I assumed it was normal.

Am I correct in this?

I guess I could change it in TinyTuners maybe, under
Fuel-Open/Closed Looped-O2 Sensor Rich/Lean Threshold

But is it necessary?

Mainly want to double check that this occurrence is normal?

[robertisaar]

definitely not normal... the EPA has had GM by the balls since the 80s when it comes to AFRs... anytime you're not in open loop due to a cold motor, or are in PE or the cat is overtemp, then you are going to be stuck at 14.7:1... unless you can change the stoich AFR in the tune, in which case it SHOULD be wherever you set it to. what does the STFT and LTFT say at idle?

[Weatheralls Auto]

Well they were like - 10 to -15 but I had been tuning that down, have them around +1 to -1 now

Why would Pcm be cutting fuel if WB see very lean? Seems to be only at Idle?

Unless not enough flow by WB due to a Plugged Cat maybe?

[robertisaar]

flow shouldn't matter to a wideband... and are you saying that you have the wideband AFTER the cat? seems like it would be best up in the original position and emulating a narrowband for the PCM.

[Weatheralls Auto]

No No, WB is in down pipe, approx 10" from stock HO2s.
By restricted flow, I meant Narrow band would see Rich while Wide band see Lean? Thus PCM thinking rich and leaning it out even though she is already lean?

But Honestly, I had thought about a restricted Cat earlier, but Map increase to 50 - 60 with 25% TP, on most vehicles with a plugged cat I see they would jump right up to 85-95 quite quick?

[robertisaar]

you couldn't actually idle at a 21:1 AFR idle... you'd be lucky to pass 16.5:1 and not have it surge/misfire itself into stalling.

[Weatheralls Auto]

It is really weird, its only at idle, when cruising I get fluxuating 12-16 and WOT 9 (have not tuned WOT yet)

[Weatheralls Auto]

Well this really SUX
I can not trust my WB.

I have been doing some reading about airpockets etcs, and see that I should put the WB on the slowest rate and not instant reading.

So I do this, Now at idle is about 17-18 still off, when cruising it is steady 14.6 to 14.8

WOT 12.5 (big change from 9.8 with out any tune changes)

I am going to rewire and pay close attention to the grounds, not sure if this will make it better or not.

[robertisaar]

yeah, it does sound like a "lack of buffer" issue... and it doesn't need it anywhere other than idle due to the increase in airflow.

[Weatheralls Auto]

If I couldnt rely on it at Idle wouldnt really bother me to much, I would just tune with Narrow anyways.

But since I set the buffer to slowest, read rate, my WOT numbers went from 9.8 to 12.5.

So I imaging if I set the refresh rate in the middle, my WOT reading would be in the middle.

So what number is correct? lol,

At least now I know the issue lies with the WB, but frustrating now that I can not trust it.

I put sensor half way down the down pipe @ 9 O'clock, it came with a DEEP bung but I did shave it down abit, not sure if the depth in the pipe would be causing this?

[robertisaar]

as long as that slowest read rate actually takes the sensor value and averages it before displaying it, then it would be fine, just a bit slow to react.

but it makes no sense that it read incredibly lean at idle when it was stoich, and incredibly rich at WOT, when it was likely more around 12.5:1.... or at least it doesn't to me. i'm not a WB fan... they are effected too much by spark advance and location for me to trust them.

when in doubt, do plug cuts.

[Weatheralls Auto]

I had some time this aft. and wanted to re/re all the mounts to put on thread locker now that everything has settled.


Did not rewire yet, but decided to remove the down pipe, and look at bung.

The bung that came with my Gauge was very deep (said to protect if in a spot that was too hot) I had ground down a bit in initial install but was still deeper than normal.

So I cut it down, leveled it and made sure threads were good.

I just recheck and now its idling from 14.4 to 14.8 and seems to follow the narrow band.

All in all, I guess it was just that the sensor was not in the flow enough.
Why such a deep bung if it wouldn't work though? I don't know but sure am glad to now see the WB and NB correlating at Idle!!

[robertisaar]

that deep bung would probably be useful if you were trying to track AFRs for individual cylinders, or if you have HIGH EGTs, but it sounds like you'll do just fine with the shorter setup.