AFR confusion

[bjmsam]

The tailpipe WB02 sniffer reads very lean while the NB02s read very rich. What's going on here?

Time	O2vR	O2vF	Knock	RPM	TPS	Timing	Load	IPW	IDC	Boost
284.53	0.29	0.14	0	1813	24	30	34	3.33	5.03	-6.04
284.76	0.8	0.84	0	1813	24	30	33	3.07	4.64	-6.04
284.94	0.66	0.7	0	1813	23	30	33	3.33	5.03	-5.85
285.19	0.66	0.8	0	1813	24	31	33	3.07	4.64	-6.04
285.37	0.78	0.53	0	1813	24	31	33	3.33	5.03	-6.04
285.63	0.16	0.16	0	1813	24	31	33	3.33	5.03	-6.04
285.81	0.35	0.84	0	1844	28	31	38	4.1	6.29	-6.04
286.05	0.29	0.23	0	1875	49	25	59	5.12	8	-0.37
286.25	0.82	0.86	0	1906	63	23	64	5.38	8.54	0.57
286.52	0.76	0.82	0	1969	82	22	69	5.89	9.66	1.51
286.73	0.8	0.84	0	2031	85	22	74	6.14	10.4	2.27
287	0.2	0.88	0	2094	88	21	79	6.66	11.61	3.21
287.22	0.1	0.88	0	2156	89	22	83	8.19	14.72	4.16
287.49	0.1	0.88	0	2250	91	21	88	8.96	16.8	5.29
287.72	0.68	0.9	0	2344	93	21	92	9.73	19	6.24
288	0.84	0.92	0	2438	93	22	98	10.5	21.32	7.37
288.23	0.88	0.92	0	2531	93	22	102	11.26	23.76	8.31
288.53	0.88	0.94	0	2656	93	20	110	12.54	27.77	9.45
288.78	0.88	0.94	0	2781	94	18	117	13.82	32.04	10.96
289.05	0.9	0.94	0	2906	94	17	128	14.59	35.34	12.47
289.3	0.9	0.94	1	3063	94	16	134	15.36	39.2	13.79
289.62	0.9	0.94	0	3250	94	17	138	16.13	43.68	15.3
289.89	0.9	0.94	0	3406	94	17	140	16.13	45.78	16.24
290.19	0.92	0.94	0	3594	94	16	138	16.64	49.83	16.24
290.46	0.92	0.94	0	3750	94	14	142	17.15	53.6	16.24
290.79	0.92	0.96	0	3938	94	13	141	17.92	58.8	17.19
291.07	0.94	0.96	0	4094	94	12	148	18.69	63.75	16.24
291.4	0.94	0.96	0	4281	96	13	148	18.94	67.59	15.87
291.7	0.96	0.96	0	4438	96	14	148	19.2	71	15.68
292.04	0.96	0.96	0	4656	96	16	148	19.2	74.5	15.11
292.35	0.96	0.96	0	4813	96	18	149	19.2	77	14.73
292.71	0.96	0.96	0	5000	96	21	149	19.46	81.07	14.92
293.04	0.96	0.96	0	5188	96	20	151	19.71	85.21	15.68
293.42	0.96	0.96	0	5375	96	20	149	19.46	87.15	14.73
293.78	0.98	0.96	0	5531	96	20	149	19.71	90.86	14.92
294.17	0.98	0.98	0	5719	96	21	148	19.46	92.72	15.49
294.55	0.98	0.96	0	5906	96	23	147	18.94	93.24	15.3
294.97	0.96	0.98	0	6188	96	23	144	18.69	96.36	15.68
295.36	0.98	0.98	0	6375	96	25	142	18.43	97.92	15.68
295.82	0.98	0.98	0	6531	45	25	56	0.51	2.79	15.49

[Erick]

WB > NB
but.. Ive been on a dyno that had a tailpipe sniffer that was innacurate and even the guy stated he needed to replace it. At the time I didnt need to go off it, but it was free with the dyno run

[bjmsam]

Yes, I realize that a wideband in the downpipe is preferable to the stock narrowbands, but I am skeptical of this tailpipe sniffer, as the majority of cars dynoed today registered equally low at high RPMs (AFR remained above 12 for only one car, which happened to be the only one with its hood closed during the run, in case that's relevant). Note that I'm taking the dyno operator's word for it that low AFR numbers are lean and high AFR numbers are rich; I always thought it was the other way around (air / fuel), but it's his equipment and I have no experience with WBO2s. If I'm right and he's wrong, then this is all moot and I missed an opportunity to dial in the fuel.

My long-term fuel trims always hover right around 100 and IDCs typically peak below 90%, so I don't suspect fuel starvation. I don't know why IDCs and NBO2 voltages were so high during this session, but the dyno operator's interpretation of WBO2 readings discouraged me from leaning things out. My NBO2 sensors are a month old and I was told the WB02 has been used only a few times. I have an aftermarket single to dual exhaust with main cat intact (more complete burn?), and the WB02 was inserted into one of the four outlets as shown in the video below.

I logged my trip home from the dyno and IDCs and NBO2 readings were back to normal (<90% max and .94 max, respectively). I don't get it.

[bjmsam]

According to these charts on Jeff's page, I was right and the dyno operator was mistaken.



Here are the logged NBO2 voltages with the filmed WBO2 AFR values:

RPM	O2vR	O2vF	WBO2 AFR
2531	0.88	0.92	14.5
2656	0.88	0.94	14.2
2781	0.88	0.94	13.8
2906	0.90	0.94	13.3
3063	0.90	0.94	12.9
3250	0.90	0.94	12.7
3406	0.90	0.94	12.5
3594	0.92	0.94	12.3
3750	0.92	0.94	12.2
3938	0.92	0.96	12.2
4094	0.94	0.96	11.8
4281	0.94	0.96	11.7
4438	0.96	0.96	11.4
4656	0.96	0.96	11.0
4813	0.96	0.96	10.8
5000	0.96	0.96	10.8
5188	0.96	0.96	10.9
5375	0.96	0.96	10.7
5531	0.98	0.96	10.7
5719	0.98	0.98	10.6
5906	0.98	0.96	10.4
6188	0.96	0.98	10.5
6375	0.98	0.98	10.4
6531	0.98	0.98	10.2

The readings are normal according to Matt's map:

[BlackStealth]

Originally Posted by bjmsam

Note that I'm taking the dyno operator's word for it that low AFR numbers are lean and high AFR numbers are rich

Low voltage numbers on narrowband o2s indicate a lean AFR, so maybe that's where he got confused. When talking about wideband o2s, low AFR numbers always indicate rich.

[bjmsam]

Originally Posted by BlackStealth

Low voltage numbers on narrowband o2s indicate a low AFR, so maybe that's where he got confused. When talking about wideband o2s, low AFR numbers always indicate rich.

Aren't NBO2 voltages low when the mixture is lean, which would be a high AFR?

[BlackStealth]

Hah you're right, even I slipped up.

[3Sfever]

Originally Posted by bjmsam

I have an aftermarket single to dual exhaust with main cat intact (more complete burn?),

Now you know your catalytic converter works!

Considering one of the main functions of a catalytic converter is to oxidize any remaining hydrocarbons, my guess is that it would be very normal for a cat equipped car to have lean O2 at the tailpipe.

The excess fuel and oxygen that exited the engine became water and carbon dioxide at the cat.

Hopefully someone with real-world experience can verify that.

.

[bjmsam]

Sounds reasonable, but the mixture was definitely rich. The ECU was likely dumping fuel due to high charge temps (there was a fan pointed at the radiator but inadequate flow through the SMICs). A similar situation is described here.

[keithmac]

Stock management is pretty stupid, I don`t think it will have any form of heat soak correction programmed into it. If you were knocking badly due to the heat then maybe it would richen the mixture up but I think it just pulls boost pressure and timing normally?.

If the Rolling Road operator doesn`t know rich from lean on a wideband the run away!.