anyone know what the score is with runnig ecu's without the o2 sensor? i use to run a vw golf(bfore i saw the light) where the tuner who put the engine together modified the standard ecu so that ther was no need to have the o2 rigged up,how is this possible? car was supercharged.i know when the o2 fails it usually does so failing on the rich side, maybe he did it to this effect? any ideas folks?

 

The O2 sensor information is only used to meter fuel during stable engine conditions (cruise, idle, etc.) because modern technology cannot currently keep up with an erratic engine. This is called "closed loop" mode.

During other conditions of operation, the ECU bypasses the O2 sensor reading and runs the engine based on pre-set paramaters. This is called "open loop" mode.

Most aftermarket ECU's allow the user to choose between open and closed loop modes. If set to closed loop mode, the ECU will revert to open loop mode when appropriate, just like a factory ECU. When set to open loop mode, the ECU will never reference the O2 sensor in order to run the engine. Those who set their aftermarket ECU to always run in open loop mode have no need for an O2 sensor, although most people keep the sensor to monitor the air-fuel ratio.

 

understood,thanks.

 

I think it would be a waste of fuel

 

I would have thought so, too, based on theory. However, none of my friends bother with the closed loop functions on their aftermarket EMS, and they all get better gas mileage than they did with the stock computer running the engine.

 

Well that would be because they tune it so that it runs at just the right AFR... the Stock Computer is tuned for all stock engine and errs on rich rather than lean, and some (FD) even change their setup and behavior after 30K Miles as to accomodate wear on the engine and turbos, so as not to lean out...

As a base rule it's always better to tune for your specific situation rather than some engineers idea of what your car should look like....

-DC

 

For a Haltech, you can map out the entire load ranges.&nbsp This means the computer is running "open loop" all of the time.&nbsp The Haltech has option to run an O2 sensor, and there are settings to control the O2 "closed loop" function.

If the ECU is tuned nicely, you'll have no need for an O2 sensor.

I'm working on a 1990 FC3S turbo right now running a Haltech E11V1.&nbsp The car gets a solid 15-16mpg under "normal" driving, which is impressive considering I only consider the car being tuned 70% at this point.&nbsp The fuel maps are tuned very roughly still.&nbsp This is in open-loop where no O2 input is being used.


-Ted

 

This is true with any ECU, If the maps are tuned properly, there is no need for O2 (Oxygen Sensor)

What is strange, is that I thought that the check engine light turns on once the O2 is Missing or non functional... To indicate to smog personell or a mechanic that the O2 has to be replaced... But I have yet to see this happen...

Anyhow Driving without a O2 is like flying a plane on Visual Reference... You know you're going fast enough and gigh enough because you're not stalling or hitting any trees, yet once the weather gets worse you need reference other than visual, and that's where instruments help. So in the case of the Fuel Maps, If you change nothing and everything is stock, and you remove the O2... Everything should be fine...

If you do the same on a heavily modded intake or exhaust ... you're playing with fire...

-DC

 

That is only on OBD II cars.... ironically, lack of OBD II compliance was the nail in the coffin for the FD's presence in the US.