spence88mph

I was describing the issue I have with my car surging around 3000rpm and every so often idling badly to a member of the 'other' forum. I was quite sure my O2 sensor was faulty, anyway he suggested disconnecting it as he said carreras will run better without it. This is what he said:

"Yeh just disconnect the O2 sensor from the harness and leave the harness open. The O2 sensor forces the engine to run 14.7/1 a/f at <3000 rpm's and <full throttle conditions (for economy and emissions etc). The car's really like a high 12 to low 13/1 a/f for best performance and with the O2 disconnected, they'll run about that on the standard DME mapping."

So I tried it this morning and took the car for a drive and yep, it's not surging at all and idles perfectly now. So I'll either get a new sensor or just leave it disconnected. I'm not suggesting everyone do this but my car feels much better now.

Mike Murphy

Let me know how easy the new O2 sensor is to replace. My 88 looks to have a very old sensor and I may just replace it to be proactive. Are you going to buy a Porsche version for $200, or a cheapie replacement for far less?

madmmac

Disconnecting the O2 sensor is the easy way to check how it is functioning, now you know you need a new one.

Your miles per gallon will drop without the O2 connnected....after a couple of months you will have paid for the new sensor by all the extra gas you will need to purchase.....but still don't have the new O2 sensor.

butzip

Yup, that's true the sob runs real rich. I couldn't pass CT emission testing with a faulty O2 sensor. It was off the charts.

You can get a universal 3 wire O2 sensor for 30 bucks or so just have a soldering gun and heat shrink wrap ready, works like a charm.

Brgds, Peter

spence88mph

Yep I've already ordred a generic bosch unit, i will just solder the old plug on.

murphyslaw, yes they're very easy to replace, probably the easiest way is to jack the left rear of the car up and take the wheel off, you'll see it there.

I have to say the car really does seem to run better without it but maybe I was just used to it running poorly with the faulty one.

PorscheMD

Yes the O2 sensor does try to make the engine run at 14/7:1 at any point other than full throttle. By disconnecting the sensor the car will run "where you set the fuel mixture" by the air bypass screw on the air flow meter. You can set it to run very rich or very lean. If you disconnect the sensor and the car runs extremely rich, then you have a problem or the mixture has never been set at your tune-up intervals. You may need to simply adjust the mixture. If the car surges while at a steady throttle cruising doown the highway with the oxygen sensor plugged in, you more than likely have one of two problems. The sensor itself is getting lazy and cannot correct the AFR quick enough or the mixture is so far from 14/7 to 1 the O2 sensor is really fighting to keep it there.

spence88mph

Thanks Porsche MD, so if the car is say tuned on a dyno without the 02 sensor with the mixture set on a constant high 12 to low 13/1 will it be optimum fueling at all times? I read that some of the cars in different markets didn't have an O2 sensor, I wonder if their fuel economy was drastically different.

PorscheMD

You wil get better performance at high 12's to low 13's. You will get better gas mileage at 14.7. There is a trade off. It will not be drastic but will be a difference. The O2 is purely an emission control device to keep the emissions down when age and cars that are not kept in tune create alot of HC's. On newer car's the O2 has more functions and are somewhat critical for the car. On your model they are not completely neccessary and can be unplugged. So, yes the car will pretty much run where you set it on a dyno with the O2 unplugged