535 poor gas mileage

[RazorRacer]

Recently the '88 535is started hunting for idle upon cold start-up and getting 10 mpg instead of the 20 mpg before. There is also an odor of gas sometimes. I've searched for a gas leak, but haven't found anything (but heah, I'm still looking for the fuel injectors and spark plugs).

Perhaps this is a common problem on these cars. Any help would be appreciated.

[Wayne 962]

Read this:

http://www.pelicanparts.com/bmw/techarticles/Mult-Code_Reading/Mult-Code_Reading.htm

and let me know if the computer pulls any codes...

-Wayne

[RazorRacer]

Wayne,

The article says BMW's from 1992-1995 were equipped with an OBD I. I have a 1988 model. I did try to pump the gas pedal 5 times, but nothing appeared on the display.

Do I need to purchase a scan tool? Do the 1984-1991 model give any diagnosis?

[Wayne 962]

Your car is right on the edge of the year change. The article should say all E36 BMWs - 3-series, not all BMWs from 1988. I'll have to change that...

The scan tool does work for all 1988-2000 BMWs - I would recommend picking one up...

-Wayne

[RazorRacer]

Wayne,

I have an E28. Should I get the code display after pumping the gas pedal 5 times?

[Wayne 962]

Your DME should be version 1.0. I believe that worked with all Motronics version 1.0 and higher.

Whoops, I'm wrong. 1.0 cars doesn't work (no check engine light). 1.1 cars do. I guess you need the code reader. We sell it for $139 - it's a good investment...

Here's a link:

http://www.pelicanparts.com/cgi-bin/autocat/load_page.cgi?page_number=1&bookmark=1&model=BE12&currsection=electr

-Wayne

-Wayne

[Jared at Pelican Parts]

Have ou checked the obvious things, like plugs, rotor, wires? This could also be an indication of a bad O2 sensor. Has this problem been slowly getting worse or has it just instantly popped up?

[RazorRacer]

It just popped up. The idle surging on start-up is probably a low battery. I am smelling gasoline, too. So there is probably a fuel leak.

What are common sources of fuel leaks? What is a good method for checking? I'm leary of using an open flame to check for it

[Wayne 962]

Originally posted by RazorRacer
I'm leary of using an open flame to check for it

CRIPES! Who gave you that suggestion?!?!? That would be the dumbest thing to do. Don't use an open flame - just use your eyes and your nose. Is the car running super-rich? That may be the smell...

-Wayne

[Jared at Pelican Parts]

Kinda OT, but in some of the Haynes manuals, there is a disclaimer.

Please Note, any reference to a "torch" in this manual refers to a flashlight, not a incindiary device or a welding torch

Guess all the manuals must have been printed in the UK.



Based on what you're describing, it sounds like the O2 sensor might be going out. Here's an easy way to test it. Start the car and let it warm up. Next, remove the oil filler cap to simulate a rich running condition. The O2 sensor at this point would normally start to have flucuating voltage btween it's terminals. This is because the O2 sensor is trying to compensate for the air leak. What you need to do is measure the voltage between the terminals. If you dont see fluctuating voltage, that is an inidcation that the sensor is bad.
Anyway

[RazorRacer]

Originally posted by RazorRacer
I'm leary of using an open flame to check for it.

That was a joke. But how do you adjust the mixture on this car? Is there an article or thread about it somewhere on this BBS?

[Jared at Pelican Parts]

I dont believe that you can adjust the mixture on these cars because of the Motronic system. I'd check the O2 sensor first, from what you describe it sounds like this may be the culprit.

[RazorRacer]

will do. thanks.

[Wayne 962]

On some of the earlier Motronic cars, you could indeed adjust the mixture - the 1984-89 911 Carreras had a screw on the bottom of the air flow meter...

-Wayne

[Bob540iA]

The e28 535i uses OBD1 and does not store codes to my knowledge. The only thing you can do is reset the service LEDs on this version of Motronics.
A piece of wire to jumper two pins in the diagnostic conector will do the job of resetting the indicators.
If the diagnostic connector has 15 pins then its OBD1- 20 pins is OBD1.1

[Wayne 962]

Right Bob - I did look it up. It uses Motronic version 1.0, which doesn't store codes. Starting the year later, the next version started storing the codes...

-Wayne

[RazorRacer]

Jared,

How do you measure between the terminals? I can't even get the friggen connector off .

Thanks.

[RazorRacer]

Well I got the connector off by pulling twice as hard as I was pulling before. Still, I don't know how to measure the voltage with the sensor plugged in.

[RazorRacer]

Basis this article the oxygen sensor generates it's own voltage so I just have to measure it at the connector, right?

[Wayne 962]

Clever article...

-Wayne