A/F ratio on DS?

[87gn-newbee]

What are you guys seeing at idle and through out the run? I'm guessing since I run the ME chip the A/F readings will be off correct? Mine read 13.?-14.? it always reads lean at idle and WOT.
Also those running 50's and the ME what is your cruise fuel # at?
Dan

 

[TurboDave]

Reading A/F ratios with DS is really not very helpful at all, since it is a display of what is being commanded, NOT what is being achieved. Since our systems use a narrow band (switching) O2 sensor, the only time there will be any correlation between what you're seeing and what's happening is during closed loop operations when Power Enrichment is NOT being used.

in other words, normal cruise and street driving.

 

[bruce]

Originally posted by TurboDave
Reading A/F ratios with DS is really not very helpful at all, since it is a display of what is being commanded, NOT what is being achieved. Since our systems use a narrow band (switching) O2 sensor, the only time there will be any correlation between what you're seeing and what's happening is during closed loop operations when Power Enrichment is NOT being used.

in other words, normal cruise and street driving.

Hmm, I would have thought that until you peg the MAF the Commanded should match the commanded on a properly done chip. Now, if the chipper has juggled the injector size or something like that to throw the calibration off that would be an exception, but as the code is writtten it uses the MAF to figure how much air the engine is using. Or the owner has taken the screens out, well then all bets are off. But, as gm designed things, as used as intended shouldn't they match?.

 

[TurboDave]

Originally posted by bruce
Hmm, I would have thought that until you peg the MAF the Commanded should match the commanded on a properly done chip. Now, if the chipper has juggled the injector size or something like that to throw the calibration off that would be an exception, but as the code is writtten it uses the MAF to figure how much air the engine is using. Or the owner has taken the screens out, well then all bets are off. But, as gm designed things, as used as intended shouldn't they match?.

Yes, for the most part that's correct. In theory, the commanded should equal the actual. But even in closed loop, while in PE the system is for the most part an open loop situation. This isn't a wideband system and doesn't have the ability to make changes on the fly like a wideband FAST equiped system can.
Until the MAF tops out, it is commanding fuel based on what it sees for air flow. It has no way to make corrections to ensure that the engine is actually achieving the 12:1 A/F ratio (example) it's commanding.
Yes, things work pretty well in most cases, but it's still educated guesswork on the chip's part, since there's no feed back to rely on from the O2 sensor (while in PE).

 

[bruce]

Originally posted by TurboDave

Yes, things work pretty well in most cases, but it's still educated guesswork on the chip's part, since there's no feed back to rely on from the O2 sensor (while in PE).

Are your assuming the O2 sensor's voltage output is accurate enough to say the closed loop is actually stoich?, ie 14.7:1?.

What happens with oxygenated fuels?.
Old O2 sensors?.

 

[TurboDave]

Originally posted by bruce
Are your assuming the O2 sensor's voltage output is accurate enough to say the closed loop is actually stoich?, ie 14.7:1?.

What happens with oxygenated fuels?.
Old O2 sensors?.

Pretty darn close, at least on the one car we checked with a wideband. The difference wasn't worth worrying about.