Polo 2F 3F Engine: Read/Log Lambda Values

Hi there,

I was wondering if it's possible to read the lambda value using VAG-COM on the engine in question. I don't want to waste money on a 2x2 adapter before I know for sure. I'm trying to find the correct air-fuel ratio and fuel pressure for running on ethanol.

thank you

Find out what voltage your oxygen sensor should output when lambda is equal to 1! You can find this information in repair manuals or forums; I don't know the values off the top of my head. Tap into the oxygen sensor's wire somewhere and run the cable into the interior of the vehicle. Connect a multimeter to this wire and measure the voltage relative to ground. Depending on the measured value, you can calculate the lambda value.

For the ethanol conversion, you should invest in an adjustable fuel pressure regulator (e.g., a used one from an Alfa 33) and a reasonably accurate fuel pressure gauge (up to 5 bar). The gauge should be mounted inside the vehicle.

However, I'm not sure what type of fuel pump your engine has. I hope it's an electric pump! If your engine has a membrane pump driven by the camshaft for fuel delivery, then you're facing a problem! Their performance would be severely limited, and they certainly wouldn't provide the necessary extra pressure for an ethanol conversion. On average, these pumps achieve 0.8 to just over 1 bar. Electric pumps, on the other hand, can generate between 2.5 and 5 bar.

Thanks for the tip about the voltmeter, that's interesting. I could try connecting an exhaust gas analyzer and measuring the voltage when the lambda value is 1.

As far as I know, aren't these all lambda probes? So, the voltage fluctuates between, say, 100mV for lean and 800mV for rich. So, a specific lambda value doesn't correspond to a specific voltage, or have I misunderstood something?

Is the fuel pressure regulator from Weber also used in the Alfa? It's definitely used in the 2.0 EFI engine from Ford, and it also fits the fuel rail of the Polo.

Of course, the engine has an electric fuel pump, as it's a single-point injection system (Digifant).
and if the pump needs to be replaced (I've heard of pumps failing frequently when running on ethanol), that's not a problem either - used ones don't cost that much.

It would still be helpful to know if it can be done with VAG-COM.

I also think the voltage drop might be too high. Couldn't we add a capacitor to smooth it out? However, that would require isolating the circuit (perhaps with a diode?) so that the control unit doesn't receive a false sensor voltage. That would require the expertise of an electrician.
There are mobile lambda sensor test devices available for motorcycles, and they are less expensive.