Question about what happens at wide open throttle

[sunil6784]

i don't know if anyone has noticed, but it seems like there have been a lot of questions about engines running rich or lean lately on stangnet. So i was thinking about EFI and all the sensors and whatnot. My question is this...at wide open throttle, i know that the engine goes into "open loop." What exactly is "open loop" ? Also, I think the engine stops getting readings from the O2 sensors to measure the air/fuel ratio. Instead it gets its reading from the MAF and adjusts the fuel accordingly, right? Is this what every EFI system does? or just our mustangs?

 

[HISSIN50]

OL at WOT is what you said - the computer does not use input from O2's. The smog, EGR, A/C, etc are not used.

It can use the MAF to determine a bit of trim, but since SD does not have a MAF, it uses tables and other sensory data.

Even newer mustangs with EEC IV dont work the same way (SN95 puters - T4m0 et al, do use O2 input at WOT and can trim the WOT trim).

There are books and long articles out there covering this stuff.

 

[90mustangGT]

What he said and...

electric fan and A/C shut off (if equiped), stops the rich/lean cycling and stays rich, advances ignition. It basically goes from emmisions to power mode, one advantage of EFI.