Hello everyone,

I have a 1997 MK4 Fiesta 1.25 L (DHA engine). The car has bad fuel economy, around 25mpg (US). The car is totally stock regarding the engine and ECU. I do a lot of tuning on aftermarket ECUs like Megasquirt, Motec, Link G4+ etc so I know a thing or two. I thought that the engine is not getting into fuel cut because the transition from open to closed throttle is really smooth and the car is not losing a lot of speed.

So what I did was to connect an OBD scanner and see the O2 voltage. My thoughts were confirmed as the O2 voltage never gets to zero but is constantly oscilating between 0.2 and 0.7 volts meaning the closed loop fueling algorithm is working and hunting 14.7AFR.. So even if I am at closed throttle and 4000rpm or 3000rpm, there is no fuel cut - the engine is burning fuel and that explains the low MPG. I also checked the throttle on the OBD and it stays at 18% (it is relative, that's why it is at 18%) and at WOT is around 94% so it seems ok.

So the actual question is, does this year ECU by default gets the engine to fuel cut or not? If yes then do you have any ideas what may be malfunctioning?

Thank you Nick

Edited by clubman on 02/09/2014 at 09:21