Accurate WB reading?

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I have a 2000 S10 ZR2 with a stock L33 and flashed 0411. Cats are in with NB O2 bungs on both banks. WB bung is on bank 2 near the NB bung. HPTuners MPVI2 with AEM 30-0310 UEGO.

The WB sensor reads 1.3 Lambda at idle and 1.5+ under load then maxes out at 2.0 on deceleration. Makes no difference if I force closed loop by disconnecting the NB O2 sensors - reads and runs the same. Plugs are not showing any unusual signs of lean or rich but misfire current/history both show frequent misfires on all cylinders (more so on 3 and 4 for some reason). Occasional P0172 code (bank 2 too rich). I've checked for vacuum leaks and I have no reason to think I have bad injectors. AEM WB checks out with open air calibration. The truck runs but runs poorly. My aim was to touch up the tune but can't get past the crazy high EQ numbers. I can share a short log if that helps with diagnosis.

What am I overlooking to have such high EQ readings?

[5FDP]

Do you fuel trims report the same thing as thew wideband?

Are those super high like +25% all the time?

Are you running the correct fuel pressure too?


I've run wideband sensors after the cat converter and before the converter and never see anything like you are describing. Except the decel being lean because that is normal if DFCO is still working.

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Trims are all over the place. Bank 1 long is near 0%, bank 1 short is +2-3%. Bank 2 long is -5% and short is -2 to +3%. So, no, not reflecting what I see on WB readings. I'm glad you pointed out fuel trims; another thing to cross-reference. Also bummed to see they vary so much from bank to bank and they suggest the WB is off.

Fuel pressure is managed by a C5 Corvette filter/regulator. Pump is the OE in-tank S10. Fuel rail reads 54psi. GM says 58-62psi is needed to run a non-return LS. If the question is is my fuel pressure high enough, then it almost is. If the question is the pressure too high and too much fuel is being injected, I don't think so. I had a spare injector and replaced #3 because it most frequently misfired but that hasn't made a difference. Still misses on #3 most often.

A few more points: it runs cold. 70mph at 2200rpm it sits at 194F with 185F thermostat. Low ECT because it is running so fat? Also, MAF hertz vs air mass graph shows missing info at some RPM when the engine is warm. I've cleaned the MAF but see no difference. So it missed because the MAF reads bad and misfires because it's so rich?

Wide band sensor is completely separate from the ECM on my setup. This generation of ECU does not have a WB channel. I wanted to learn to tune and Lambda seemed right. The WB has no influence on the ECM; it's just gathering info at the tailpipe. My ECU is catching something that's not right and defaulting to some sort of limp or protection mode. Spitballing here. I'm open to any and all suggestions.

[5FDP]

Those fuel trims are pretty normal to be honest. Anything that is within 3-5% of zero on either bank is good. They will never be the same either, the short term trims will always bounce around and the long term trims kinda follow where the short term trims spend most of their time.

With those trims, it's not really running rich or lean. It's doing a good job of keeping things in line.

Yes, that fuel pressure should be okay. So long as it can keep up at full throttle and no drop below that 54psi at high rpm.


You can always try moving the wideband to one of the o2 sensor bungs to see if it stops reading so lean like you said above. Maybe there is a pin hole leak or something that it's seeing or a leak at a slip joint if you have that.

Also 194F degrees is a perfect temp for a LS engine, no problems there.


As for the misfire, did you move the coils or wires around? How about the entire bank of coils to make sure that harness isn't a problem.

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Moving the WB sensor to a NB bung doesn't make a noticeable difference. I did find - with the help of my shop vac and a feather - a pin hole leak that may have been skewing my numbers. I've patched the hole with a dollop of high temp JB Weld for now. I messed with fuel trims and it runs better. So that's a start but without knowing for sure I don't have a leak or bad sensor I'm afraid to tune solely with NB info.

I've chased the misfires by replacing coil packs, plugs, wires, and injectors. The quick way to do this was with miscellaneous parts I have on hand, not new parts, so I'm at risk of replacing bad parts with bad parts. So far no major improvements with the changing of parts.

At the moment I still have occasional misfires - as measured by the current and history PID - and I have 1.4+ lambda WB readings. Both of these bug me so and I'll keep searching for answers.