Porsche Enthusiasts Club Forum

Quick question about oxygen sensors…

Should my 1987 944 Turbo have one?

I'm a little puzzled because as I understand it, the DME should be getting a signal from a narrowband oxygen sensor in order to monitor and adjust air/fuel ratio. But as far as I can see my baby doesn't have one, which makes me wonder how the DME is getting the right data to control the fuel delivery.

I have a vague idea that UK, non-cat cars like mine don't have the O2 sensor, but I defer to the experts - ie. anyone else who's reading this

(Part of the reason this is on my mind is that I was toying with the idea of installing a wideband AFR to keep an eye on the ratio… I had to replace the turbo recently, and put a k26/8, plus chips from an '88 car, in there rather than the original k26/6. I plan to also replace the CV with an MBC, again with suitable chips, to get a little more power, and in thinking about the whole deal it just struck me that if the DME isn't monitoring the air/fuel ratio then I'm not sure how it's going to get the fuelling right.)

My 90 turbo (no cat) did not have a sensor. A wideband is an essential piece of kit for any modded turbo to keep an eye on the AFR. I have an AEM Uego which works well and is very clear to see with an LED sweep and a digital readout in the middle.

Stuart

No CAT no need for an O2 sensor, unless you modify

the O2 sensor was there to stop the cat overheating,

PET lists with and without CAT, All the non CAT cars are missing the O2 sensor.

not sure how you would change the AFR with out a programable ECU anyway........

Thanks fellas, yup I'm totally onboard with the "if there's any modification, add wideband AFR meter to keep an eye on things" deal, but I'm also just trying to understand how the DME (with either standard or aftermarket chips) is making its decisions about how much fuel to deliver. I've no plans to install a programmable ECU… I'm kinda wary of straying too far from what the Porsche engineers decided was right!

I guess it's using engine RPM plus air temperature and pressure as inputs for its fuel mapping, yes?

No MAP sensor

All run from maps on the chips,

Just temp, throttle position, air flow, rpm, knock and on the twin cams cam position

It's not so much changing the AFR's as monitoring them so if something has gone wrong you've half a chance of pulling over before you melt a piston! More important when the cycling valve has been removed and you are running 18psi or more boost.

Stuart

Thanks all, that all makes sense and gives me a better idea of what's going on.