Major DME Issue to separate the men from the boys. Let's see what you know...

[Ross]

My guess is an intermittant open circuit for the o2 sensor.
The new DME seems to have corrected the running issues. The only prob is CE light, right? A momentary open would trip the light and code but may not otherwise be noticed.
Good luck, I'll be watching this one.

[Gearhead]

My guess is an intermittant open circuit for the o2 sensor.
The new DME seems to have corrected the running issues. The only prob is CE light, right? A momentary open would trip the light and code but may not otherwise be noticed.
Good luck, I'll be watching this one.

Thank you Ross! Actually, it's still more than just the CEL. There's still the issue of (at the same time mind you) we have:

- Good voltage readings from both 02 sensors, but the DME is saying there's an actively open circuit (not a historical code)
- The DME is proccessing 02 integrations (adjusting a/f mixture) but at the same time there's no activitiy on the mixture adaptation for either short term nor long term. Zero, zilch, nada....

[Ross]

Where is your diagnostic hook up? Is there a chance the diagnostic port is "upstream" of what the DME sees?

[Morgenster]

Where is your diagnostic hook up? Is there a chance the diagnostic port is "upstream" of what the DME sees?

I'm thinking that too. If you measure upstream, maybe you should check the wiring on sensor input all the way to the DME pins. If you already did that then see below.

Alternatively, your EPROM could be fried just enough to cause this. electronics can be whacky like this after a voltage spike so maybe you should just check with a chip from another working 540i.

[Gearhead]

Where is your diagnostic hook up? Is there a chance the diagnostic port is "upstream" of what the DME sees?

It's the standard "round" diagnostic port rigth off the firewall on the passenger side. Man, I have no idea if it's upstream or downstream from the DME, but I would have to assume being a diagnostic port that all data coming from this would come via the DME.

I know that in ruling out an open/short in the 02 circuit, my mechanic verified good conductivity at the DME connector.

[Gearhead]

I'm thinking that too. If you measure upstream, maybe you should check the wiring on sensor input all the way to the DME pins. If you already did that then see below.

Alternatively, your EPROM could be fried just enough to cause this. electronics can be whacky like this after a voltage spike so maybe you should just check with a chip from another working 540i.

Ah, if swapping EPROMS to test for this were so easy.... Unfortunately, my '95 is equipped with the EWSII anti-theft system. With this, the EPROM must be programmed with the correct EWS code for my car or it won't start. That's why when you go to purchase a performance chip from Mark D, or Jim Confronti you have to send them your OEM EPROM first so they can read that code off yours and include it on the performance chip they burn for you.

I'm trying to find a DME guru who knows enough to determine whether or not it's possible the EPROM could cause this contition before I go the route of forking out another $250 or so at the chance that's it.

Thank you Morgenster!

[MBXB]

Check here:

http://ecubb.bmwecu.org/board/

Someone may have a hack or be able to suggest one.

[ryan roopnarine]

you're the third florida person with das bmw I know of that has a fried ecu. my uncle, the general purpose mechanic, says that he sees it on a semi-regular regular basis. i'm thinking that perhaps it has to do with rainwater or such.