mumzer

will the car run at all?

Ahmet

Depends on how bad, and which sensor is effected. I've seen a couple of motronic cars run with the sensors switched (rpm/speed). Usually though, the slightest error in that signal the car will run very roughly if at all.
Ahmet

Danno

switched...???

Ahmet

Yeah, I think that was an e28 535i. The sensors were switched on a customers car after he told me another shop had worked on it. And no it wasn't the first thing we checked for a BMW with a runability problem. If I remember correctly the sensors were either identical or very similar to each other, ala 944.
Ahmet

special tool

I can vouch for the similarity between the two (944 & 535i) - I think they are the same Bosch part #. Those are the same, your car will have no spark and a fly lands on those damn things, and it runs fine.

mumzer

so the car could sputter backfire and bitch but still sortof ...run

87951

I don't think your car would run with the sensors switched but I could be wrong. Generally the problem with the sensors is in the wiring plug causing an intermittent connection. Try wiggling the 2 plugs. Usually though you will get a no start condition due to no spark. Your symptoms sound more like the TPS to me.

mumzer

thanks...but tps is new...for a detailed list see thread am i blown up?

MySwiss

I've experienced trouble with one of the sensors on my 951 this past summer.I was heading to the track for some laps when my car was intermittently stumbling (or not sparking).So I stopped the car to only find out that it would not start any more.Got it towed to my place, to find out that one reference sensor had grease on the tip which had an accumulation of cluth disc debris. so it could no longer get a readind,therefore no spark and fuel was given to run the engine.

Ahmet

Mumzer, it depends on what is broken with the sensors. If it's just the shield around the wiring, chanses are it'll still run, just not good, etc.

I would say I also think your problem sounds like the TPS but since you replaced that, I'd check the wiring harness from tps to dme, then from afm to dme, as well as knock sensor to dme,etc.
Ahmet

tecart

as far as i see it, if the sensors are close enough to the metal tabs on the flywheel they will register and signal rpm speed even if they are bent/ruined at the tip of the sensor, but if the distance of a broken tip exceeds its magnets ability to sense as the flywheel turns then it wont function at all, only 2 of the 3 triggers really matter for engine running conditions, the 3rd is a diagnostic port for the porsche mechanics tool they plug into, i had a hit reference sensor(mechanic forgot the spacer), that had bent up about a cm or so and it worked perfect, but i did eventually fix it for fear it would eventually fail on me

Songz

Tecart --- any idea which one of the 3 triggers are for diagnostic functions?

I found mine to be completely chopped off (significantly shortened).

Bill

I believe that the speed/ref sensors are blamed for a lot of different ills, by disfunctional mechanics.

There is a simple method of testing them.

Put them on a scope and look at the pattern. The car does not need to be running. If they are good, just cranking the engine will show a correct/incorrect pattern on the scope.

keith

Car (944) won't run with them switched. A failing sensor can cause a lean miss around 3500 RPM. A bad sensor can keep the car from firing the injectors and sparking.