Wideband maxing out lean when downshifting

[jason_gsx]

This is probably a silly question and I think I know why this is happening, but I couldn't find a definite answer searching so I want to be sure this is normal. I installed my wideband MTX-L yesterday and I've noticed when I downshift and take my foot off the gas to slow down my AFR jumps to the upper limit (22.4 default, haven't changed the AFR range yet). I'm thinking this is because the ECU is cutting fuel to help the RPMs drop faster. Is this normal or anything I should be concerned about? The GSX feels completely normal, no problems there.

 

[DSMDEMON93]

No reason to be concerned. The AFR is your, of course air/fuel ratio. With your foot off the gas, the injectors are not spraying as much, so the sensor reads more air more fuel

 

[jason_gsx]

Thanks. I figured it was that, but I just want to be sure that my logic made sense.

 

[steve]

Shortly after the throttle closes the ECU turns off the injectors to reduce emissions. The should turn on again if you open the throttle a little or wait for the rpms to drop below about 1500 rpm.

 

[CanadianTalonTC]

As a side note it's called Deceleration Fuel Cut-off or DFCO if your curious about researching it more.

It also immensely helps engine braking when the engine isn't firing along with the emission (main) side of it. For those of you who put your car in neutral down hills to save fuel (I see this way to much) your actually wasting it.

Joel

 

[jason_gsx]

As a side note it's called Deceleration Fuel Cut-off or DFCO if your curious about researching it more.

I didn't realize there was an actual term for this. Excellent info, thank you.

 

[LiquidX]

Another tidbit, deceleration down a hill will cool off the motor immensely too for anyone that wants to cool off a turbo quickly or are dealing with heat issues.

I've done a decel down a long enough hill for about 20+ seconds and my coolant temp dropped from 210* to about 180*. Ambient temperature and cooling system efficiency ay factors as well.

 

[jtmcinder]

In DSMLink lingo, it was just "coasting fuel-cut" (but maybe that changed).

 

[T is for TURBO]

For those of you who put your car in neutral down hills to save fuel (I see this way to much) your actually wasting it.

Joel

This is arguable. But is some cases, yes, I agree. I think is depends on the slop and length of the hill, along with the obvious traffic. But I think in most cases, its a wash.