I am in the planning stages of transplanting a Subaru engine into a VW based woods buggy that is currently under construction.

Forgive me if this subject has been gone over in the past. (I'll claim newbee status)

The exact year and sizes are still up in the air, pending any suggestions from you all. The mechanical aspect, fitting the engine to the trans is a no brainer, the fitting of the engine into the chassis, no problem . The eletrical problems are almost worked out with the following exception.

I understand that the newer Subaru's have two oxygen sensors, one before the converter and one after. For obvieous rasons the O2 sensor before the cat does not pose a problem, it's the one after the cat I'm having a tough time with.

With out spending a ton of $$ on a aftermarket ECU, is there anyway to get arround the second sensor, to fool the ECU into thinking that the second sensor is there and working properly to keep the engine in a closed loop with out a converter?

Any suggestions are welcomed. Thanx in advance, Mike

:cornfuzz:

I don't know that not having it will cause the engine to run open loop, it may just generate a MIL (check engine light).

 

I have seen some O2 sensor "eliminators" on ebay. Someone here could possibly tell you the voltage that the second sensor typically puts out (probably not the usual 450mV nominal), and you could rig up a voltage divider or regulator to provide that voltage to the ECU.

Get an O2 sensor MIL eliminator and you should be good.

 

The second O2 sensor doesn't really do anything but monitor cat efficiency. Many people have put a MIL eliminator in place after getting headers, high flow cat, or straight pipe and had no problems.

Isn't an MIL eliminator just a resistor that plugs into the jack for the O2 sensor? or is it more like a potentiometer (variable resistor) that you can adjust to alter performance??? In any case, you might want to look up the principle behind O2 sensors, and see if you can build a device that will give you optimal performance, instead of the O2 sensor

I don't think that the second sensor affects performance, it's just there to verify the catylitic converter is functioning.

 

My understanding is that the O2 sensor outputs 450mV when the mixture is ideal, and the closed loop control works to keep the mixture centered on this value. The voltage should be somewhat higher after the catylist if the catylist is working, as oxygen would be used to "burn" the pollutants.

 

A voltage divider (sort of a non-adjustable potentiometer) would be the simplest method, but it would be subject to changes in the battery voltage of the car. That may or may not be a problem, I don't know. A simple solution with some regulation would be to use a zener diode combined with a voltage divider, but I think this type of circuit would dissipate a fair amout of heat. A more ideal method would be to use a precision voltage reference and an operational amplifier.

 

If someone measures the voltage you are trying to replicate I may be able to suggest a circuit using common components.