Mystery E34

[paulie888]

Either BMW made a one-off car or perhaps someone could explain what they think has happened to my 520i 1992 M50 engined E34.

Miles to the gallon is awful and always has been for the 3 years I have owned and maintained the car. So, after reading a thread I thought I would check the lambda sensor.

No sensor, no wire, no hole in exhaust - pre cat that is. I have had the car on a ramp so it wasn't a problem with access.

Second exhaust muffler has 2 empty screw-threaded holes on top blowing out gases and two empty screw-threaded holes on the bottom doing the same. No connectors anywhere near them.

No other holes anywhere.

Does anyone have any idea what may have occured in its fairly long life? The car was in Cyprus for the first 12 years of it. This may not be the original exhaust of course, but where did the connector go?

Many thanks for reading this.

[whiskychaser]

Put your VIN in here:
http://www.bmw-z1.com/VIN/VINdecode-e.cgi
It will tell you which market your car was produced for and if it left the factory with a cat. Mine didnt but its for the ZA market not GB.
Cant help with the mysterious holes. That would be an immediate MOT fail here

[paulie888]

I'll use the link and report back.

[paulie888]

It was built with a catalyser/lambda but now it doesn't have them - an excellent link by the way.

Could this be the source of the poor mileage and rough idle?

And, more to the point, how could I sort it out?

Thank you.

[sal_park]

It was built with a catalyser/lambda but now it doesn't have them - an excellent link by the way.

Could this be the source of the poor mileage and rough idle?

Most likely

And, more to the point, how could I sort it out?

AFAIK the ECU will always expect to have a signal from the oxygen/lambda sensor (apart from when the engine is warming up). If it doesn't then it will run the engine in 'open loop mode' all the time meaning the ECU will 'guess' the best fuel/air mixture, timing etc without the input from the oxygen sensor. This could easily give you bad fuel economy. (old car analogy: imagine running your car all the time with the manual choke* on. Now imagine the MPG's you'd get.)

To fix this** I'd have a look under the car and find the wires for the oxygen sensor (3 or 4 wires I think) and drill/tap a hole in the exhaust and then install/wire up a new oxygen sensor.


hth

sal



* choke - make the mixture richer for cold starts (may be called something else in the US)

** bear in mind, you may have other issues too.

[paulie888]

Thank you Sal.

The open loop mode would explain the economy issue.

When the weather here improves I'll have another look for the connector under the car - it may have been removed entirely though - does it engae somewhere nearby in the loom?

[shogun]

look for a 4-wire loom, cable colours
Bosch
black = signal
2 x white=heater
grey= ground
http://www.ehow.com/how_6190230_wire...en-sensor.html
www.aa1car.com/library/o2sensor.htm

[paulie888]

Shogun,

Very interesting links.

I'll be under the car on Saturday and I'll report back.

[yaofeng]

AFAIK the DME does not attempt to guess the fuel/air mixture without the voltage provided by the O2 sensor. With no O2 sensor input the loop falls back to a constant voltage I foget what that is. Fuel/air mixture is based on the fallback voltage, plus input from many other sensors on the engine. But the result is as Sal stated, poor gas mileage.

PS: the O2 sensor fallback voltage is 0.5 volt.

[paulie888]

Thank you.