smyroad

I know the O2 sensor inputs are ignored. My impression is that gas is dumped into the engine based on throttle position during Wide open throttle.

Gernby

The MAP is certainly NOT ignored at WOT. If it was, the MAP signal could not be used by piggy back computers (V-AFC, eManage, etc.) to alter air / fuel ratio at WOT.

ChrisD

[QUOTE]Originally posted by 'smyroad
[B]I know the O2 sensor inputs are ignored.

Gernby

There are a lot of more knowledgeable people than me on this subject, but what you are referring to is Open Loop vs. Closed Loop. At partial throttle below some RPM, the ECU is in closed loop mode. It continuously adjusts fuel trims and timing to optimize fuel economy and emmisions using input from the OBDII sensors (Pri / Sec O2, etc.). At WOT or above some RPM, the ECU goes into open loop, where it uses fixed fuel and timing maps.

Gernby

[QUOTE]Originally posted by ChrisD
[B]

There are two modes to running, open loop and closed loop. Open loop runs off a preset fuel map, and is generally "safe". Your car will go into open loop mode whenever the check engine light is on. While this mode is usually as good as closed loop, it errs on the side of rich AFRs and so you lose a small amount of HP and/or fuel economy.

ChrisD

[QUOTE]Originally posted by gernby
[B]

Open loop is certainly NOT the same as "Limp Mode", which occurs for certain types of failures.

smyroad

I agree that there are three modes.

Open Loop (Limp Mode) - ECU trusts nothing and resorts to a preprogrammed fuel map based on ? RPM?

Closed Loop (Low/mid throttle) - ECU uses all sensor inputs: O2, MAP, TP, etc. to adjust for "ideal" air/fuel mixture.

Open Loop (WOT) - Some sensors are not used: O2 is ignored, MAP?

I've got the OBDII SW and cable which reports when the ECU is in WOT. It doesn't take much throttle input to switch to WOT, or maybe I'm just a lead foot


edited:

ChrisD

Minor correction..

[QUOTE]Originally posted by 'smyroad
[B]I agree that there are three modes.

Closed Loop (WOT) - Some sensors are not used: O2 is ignored, MAP?

smyroad

Thanks, I edited the WOT part. I've got to start typing faster!

Yeah the O2 sensors are definitely part of the feedback loop, sensing the actual AFR. All the others are just part of the input equation.