325e rhythmic surging problem

[Langers]

Hello,

One of my friends has a 325e that has a rhythmis surging problem at constant speed and even occasionally whilst accelerating. It feels as though the driver is lifting off the accelerator ever so slightly and then reapplying the throttle. I spoke to her father and he says that the oxygen sensor has been replaced by a generic (Repco) part which only has three settings as oppoosed to the factory's 5.
This problem seems to be common in Porsche 911s running CIS, and in many cases John Walker has recommended disconnecting the oxygen sensor and tuning the car without it.
My question is whether disconnecting the sensor will cause any problems if the car is then tuned properly without it? Or is it an essential part of the injection system?

Thanks in advance,

Klaus

[Jared at Pelican Parts]

This presents a few problems. I'm almost 100% sure this problem is because you have a generic o2 sensor in there. Throw it away and use the correct Bosch part, it should solve this problem.

The oxygen sensor on these cars do not have "settings" they simply measure the oxygen content of the exahust. What exactly doid you mean by "settings"? The number of wires out of the sensor?

[Langers]

I think stages would have been the more correct term, unless the oxygen sensor is infinately variable. It was a brief conversation, but it is my understanding that the car doesn't get driven far enough to warm up properly, and carbon stuffed the original sensor.

If the OEM sensor is put in, will this definately solve the problem or can it occur even with the proper sensor in place as with 911s?

Thanks for your help

[Jared at Pelican Parts]

stages? Im still not sure what you mean.

All it does is measure the amount of oxygen in the exhaust, then generates a voltage of between 0 and 1.1 volts based on the oxygen content. This voltage is sent to the OBC, and the the OBC makes the needed adjustments to the mixture.

How many wires are coming off the back of the sensor that is currently in the car?

[Jared at Pelican Parts]

Another thing, the 325e uses Motronic, not CIS.

[Langers]

I'm not sure about the wires sorry.

By stages I mean that the oxygen sensor cannot distinguish between 0.1233V and 0.1232V, for instance, and that it would only be able to measure say 0.2, 0.4, 0.6, 0.8 and 1.0v.
Is that correct or is the sensor more sensetive than that? At the time the "stages" concept seemed a convenient explanation. If this is not the case, how does the generic sensor differ from the OEM one?

Motronic eh? I thought that CIS was too simple for that car. It's like a damn spaceship with all the buttons and displays! Sounds like a monorail too.

[pianodan]

You're putting WAYYYYYY to much reliance in the O2 sensor to be the source of the trouble. These O2 sensors only do one thing.... adjust the mixture so that the cat isn't destroyed. The o2 information gathering system is closed loop...... meaning, if your car is running crappy, changing the the sensor won't make any recognizable difference.

You can pay $90 for the Bosch BMW sensor, or you can pay $35 for the Bosch Mustang 5.0 sensor. It's the same. And I can tell you, it performs the same, too.

The sensitivty of the Motronic can't determine the difference between .6443 volts and .6444 volts, and if it could, YOU couldn't see the difference in performance.

The only tip off that the O2 sensor is bad is a rich running engine. If your gas mileage is starting to get lower than usual or the exahust smells rich, THEN replace the sensor.

Dan

[Langers]

Thanks for the help Dan!(Esp the tip on the mustang sensor.)