Commanded AFR changed?

[jonnycatz]

I noticed this morning as I was driving that my scanner was continuously at 13.62 for AFR commanded ratio high res and entering PE mode it would drop to 11.5. Commanded EQ ratio (SAE) is still at 1.00 though. A couple days ago while scanning, I was seeing AFR commaned high res at 14.5 and PE mode was dropping to about 12.2, both as desired. The only thing I have changed between these scans is I redone the MAF calibration for low frequency and I changed the MAP kPa PE enable value from 55kPa to 40 kPa. Any ideas?

[vltrb-0]

I noticed this morning as I was driving that my scanner was continuously at 13.62 for AFR commanded ratio high res and entering PE mode it would drop to 11.5. Commanded EQ ratio (SAE) is still at 1.00 though. A couple days ago while scanning, I was seeing AFR commaned high res at 14.5 and PE mode was dropping to about 12.2, both as desired. The only thing I have changed between these scans is I redone the MAF calibration for low frequency and I changed the MAP kPa PE enable value from 55kPa to 40 kPa. Any ideas?

conditions would also alter your equivalence ratios, best thing to do is scan and log and post differences

[4evervette]

what car do u have .. is it flex fuel truck ?!

[jonnycatz]

Yes it is a flex fuel truck, 2007 Chevy Avalanche 5.3L. I have used the same fuel always, 93 octane non-ethanol. So fuel is always the same. I have attached two scans a couple days apart. Since July 13, every scan is showing 13.62 for commanded AFR ratio in non PE mode.

[brandonleg]

yeah, there have been a couple threads about this, I started one.

My personal opinion is that the algorithm used to decide how much ethanol is in the tank is skewed by things such as additives to the gas, and maybe temperature.

You can log ehanol % or something like that, I forget the exact parameter.

When mine was screwing up, I'd used nothing but 91 (best you can get around here) and the ethanol % was showing between 15 and 20%.

Screwy, I know.

[jonnycatz]

So I just went and reloaded my original OEM tune back to truck. Then I ran a fresh scan again. Same thing, commanded AFR 13.62 at non PE, my wideband is reading 14.6-14.8 the entire time though. So the tune changes had nothing to do with it. I re uploaded my latest tune afterwards. I guess that somehow the place i buy gas is sneaking ethanol laced gas in the non ethanol tanks or the fuel composition sensor is reading incorrectly? No other change has happened, no additives and weather has been pretty much the same.
Also, I use an exhaust clamp for my wideband. I have been told to expect the reading to be about 0.5 leaner than actual, which would mean i am truly seeing 14.1-14.3. I assume that is a constant for idling and WOT

[flame]

Your wideband reads in lambda and is programmed to output 14.7 when lambda is 1. No matter the fuel lambda 1 is always stoich. There is no fuel compostion sensor any more check the link for that info.

http://www.hptuners.com/forum/showpo...10&postcount=7

[jonnycatz]

So i set up my exhaust clamp and made first runs. The entire time when not in PE, the VCM scanner was showing 13.6 commanded AFR and Lambda 1.0 of course. The wideband data through VCM scanner was showing 14.7ish. When in PE mode, commanded AFR becomes 11.46 and Lambda commanded shows 0.841. Wideband shows around 12.5 in PE. I have PE EQ set to 1.188 or about 12.4 AFR, so this appears to be correct as I've set PE ratio to that value. Im lost... Are my wideband readings incorrect by almost an entire point in PE and non PE? Or are the wideband readings correct, regardless of what VCM scanner says commanded AFR is?