Dominic Sorresso

I usually watch my ZT-2 WB as my motor warms up. Of course it will run somewhat rich as it warms up in O/L. Then it will head for 14.7:1 as it transitions into C/L. However, for a brief few seconds, AFR will go lean, as in 16-17:1. Then AFR will richen up back to stoich and pretty much stay there. Although every once in a while, the WB will report a lean 16:1. Not sure why.
Nothing telltale as far as motor running. I do have porting and more aggressive camshafts.

RBob

iTrader: (1)

Can it be cured by increasing the closed loop enable temperature? I needed to do that on one vehicle, just by 5* C or so. The engine would stumble a bit upon entering closed loop and would last 30 - 45 seconds. Then cleared up.

Upping the enable temperature fixed it.

If that doesn't do it then it may be that the proportional gain is too high at that point. Which could be removing too much fuel when it sees the O2 reading is rich.

RBob.

Dominic Sorresso

Hey RBob,

Hadn't thought about the Prop Gain. I'll try increasing the C/L enable. It was at 57C and I am bumping it to 65.
Perhaps the Prop Gain also explains why I see AFR going to 16:1 very intermittently when at idle and trailing throttle cruise.

Dominic Sorresso

RBob,

Tried the increase in C/L Enable Temp, but if anything the lean condition as it goes into C/L actually appeared to last longer than previous. Think I'll try the Prop Gain next.

Dominic Sorresso

RBob,

Still playing w this. Just a thought. Would it happen to have anything to do w the TF as it transitions and any delay in the PG? Is Closed Throttle Idle SA active in O/L?

ULTM8Z

No to hijack the thread... but am I reading RBob correctly that the prop gain is basically how strongly the ECM reacts to the O2 sensor?

I need to have these types of things broken down into very simple language so I can understand it.

Dominic Sorresso

If you use a Wideband, you will note how the AF switches flips from rich to lean and back again. Its never a static 14.7. Prop Gain varies the AFR for the purpose of maintaining the converter.
I am sure that Rbob will jump in with a much better and more accurate explanation.

Dominic Sorresso

RBob,

Think I am getting closer to dealing w this. Part of the answer may be that if your O/L warmup is too rich, it may cause the ECM to pull fuel as it transitions to C/L and overshoot temporarily. So I looked at the stock bin and saw that O/L Enrichment v CTS was significantly leaner than the table I was using. I used the enrichment curve from the stock chip and it settled into C/L without the lean spike I was seeing. That was at ~ 65C. Then at 74C I got a brief spike in lean which stabilized within 5 sec or so. So it appears that you may want to get the O/L idle closer to correct stoich or the transition may be too great and it gets overcompensated for.
Thoughts?

RBob

iTrader: (1)

Good possibility that having the AFR closer to stoich on the transition to C/l is better. One thing to keep in mind is that you are running all sixteen injectors together. This makes the fueling corrections double the actual fuel change for a change in injector PW.

RBob.

Dominic Sorresso

Rbob,

Only 8 of the 16 injectors are operational at Closed Throttle (typically below 1.9% TPS).

RBob

iTrader: (1)

Are you saying that the open to closed loop transition anomaly only occurs during closed throttle?

RBob.

Dominic Sorresso

Yes, this was one of those "things" people like us chase because we can or must. Its only during warmup when it flips over from O/L to C/L.
BTW, just played around some more adding some additional fuel at the 40-55kPa and 4-600rpm cells. Also dropped the O/L v CTS % another 5% from the
32-68C. So it was coming very close to stoich before it went C/L and this time no spike in the AFR when it did that. One other thing this appeared to tame was an oscillating idle when freewheeling w Closed Throttle.

Dominic Sorresso

Ok, so I keep playing around w this because it also seems to be having an affect on my "free wheeling" decel oscillation. With bigger cams, I have used Traxion's
method of lowering the O2 window at idle. This helps avoid the rich idle people experience w larger cams. I decided to raise that a bit thinking perhaps the spike in AFR was the ECM attempting to reach that level as part of the O2 window. So I bumped that window up by about 8%. I dropped the PGain one count as well. The idle seems to be tamer and I am not seeing the lean spikes nearly as often.