ULTM8Z

I noticed this today while datalogging.... and with my TP RT finally logging WB data, I can actually analyze it...

This one came about when cruising on a slight downhill grade...

Highway mode enabled... Commanded AFR = 16.0:1

My parameters for highway mode enable are

- greater than 55 mph
- Less than 55 kpa
- Over 70C coolant temp

All parameters are met and it goes into highway mode just fine.

Only thing is, what seems to be happening is when my TPS% falls below around 8%, the AFR drops way down to between ~12.5 and 13.0:1.

Typically on straight and level ground, I cruise at about a 10% TPS, at which point the reported AFR seems to follow commanded pretty well. Bouncing around between about 15.5:1 and 16.25:1. So I'm pretty happy about that.

But during the downhill, obviously I don't need as much throttle to keep the car at constant speed, so the TPS% drops and (while the commanded AFR doesn't change) the reported AFR drops to below 13:1.

Any ideas? It's not a big deal in this case as it's not a typical operating condition and when it occurs it doesn't last for very long... it's just my perfectionist side (and militantly stubborn refusal to call it good and put the damn ECM back up under the dash! ).

GeneralDisorder

iTrader: (1)

What is the injector pulse width doing at 10% vs 8%?

GD

ULTM8Z

Hmmm... actually let me do something else before I drag this issue too much further...

I want to go back to the factory LT1 Inv MAT table again... my reported AFR PE values are quite a bit richer than the commanded (seems excessively different when looking at the data).

I started with the LT1 Inv MAT table and had slowly started richening it when I was combating the dropping out of PE issue. It could be that the ECM throwing too much fuel in.

Let me go back to factory LT1 and see what happens. Without O2 correction, highway mode and PE mode are much more likely to be impacted significantly by how the ECM is being told about the MAT.

Vanilla Ice

Have you compared throttle voltage to TPS position? The variance may be causing you to hit idle fueling.

I haven't datalogged mine to see what's happening, but I can feel it change fueling in similar situations. Since setting the params I can't actually press the pedal light enough to cruise at 50mph anymore or I hit a point where it may not register toward fueling. I have to let off so much that it may not register and kick into idle fueling.

ULTM8Z

Don't you have to be under the min speed for idle to get into idle fueling?

ULTM8Z

Disregard... it was a false alarm.

Admins, can probably delete this thread.

I went back to an earlier bin, and the issue went away. I may have inadvertantly changed something which caused the issue.