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-4_wire-universal-oxygen-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.

[genphreak]

You may need to consider repalcing the catalytic converter, if the catalyst was not removed with the sensors. If it is, it is likely fouled/restricitng flow anyhow= more bad economy. Maybe some island mechanic felt the best solution to the customers need was to open-up the converter and remove the sensors too... the engine pipes and old converters from good low km cars are still around at the junk yards.

[Paul in NZ]

there were E34 models produced without O2 sensors.....mine for example.In NZ in 1990 we still used leaded petrol,so cats(and therefore o2 sensors) were not fitted.

[paulie888]

That's a very good point. The silencers that exist have (designed in) 2 threaded holes on the bottom and 2 threaded holes on the top - about 12mm. They don't look like cats but either way I wonder what the holes were for.

[paulie888]

A good point.

I still wonder what the 4 holes (2 top and 2 bottom) are in the existing cat/silencer.

[paulie888]

So, when the car was used in Cyprus in 1992 when new...... I wonder if anyone knows when Cyprus had access to unleaded first.

[whiskychaser]

IIRC you could still get leaded petrol in the UK up to 2000. Lead replacement petrol (LRP) disappeared around 2003. So I dont think knowing when Cyprus got unleaded will help much:) A bit OT but I visited the UK site where they produced tetraethyl lead. There were emergency oxygen bottles and masks every 20ft:-(

[genphreak]

Indeed it could well be a non-cat version? In which case def no O2 sensors (probably with blocked holes tho). Will have diifferent ECU chip and possibly cams.

4 holes may be normal for M50 cars, I've a Japanese market 525i from 1990, it has 2 sensors- one before the cats, one after. Not sure if there are 4 holes, but probably.

Is the first we've heard about for an e34 made as late as 1992 AFAIK.

e34 cats are actually two round converters inside a single shield (making it look like a silencer), whereas (I know on a 535) non cat version there is a silencer instead (Eg. engine pipe>silencer>pipe>resonator>pipe>muffler. Will still be okay to run on ULP, but will tend to smell like rotten eggs.

Would make sense of your predicament. Definately check the VIN to find out... something like 'Non Katalyst' are the words to look for.