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

[Paul in NZ]

could it be a short in the o2 sensor wiring??

[Paul in NZ]

if the O2 circuit ws not functioning properly then there would not be any means to adapt the mixture?

[Gearhead]

Hey Guys, I figured a little "challenge" in the header might get this some more visibility.

Because I can go on and on about this, I'll try to keep it short with bullets. Bottom line, I just picked up my car from the shop after 3 weeks, my wallet is $750 lighter and I have the same issue I did when it went in. No, I didn't get taken...this really is a chin-scratcher as I've been involved in every step and understand what's going on.

In summary:

- A few months ago, I got a CEL with stomp code 1212 - EGO sensor #2
- I replaced both O2 sensors, same issue
- Did research, found vacuum leaks could cause this.
- Replaced all intake gaskets, front/rear cover gaskets AND the notorious PCV Cyclonic Plate. Same issue
- Decided this was bigger than me. Took it to my local indy. Good guys... I trust them.
- In troubleshooting, he finds the 02 trouble code to be an "open circuit" code.
- Checks all wiring for faults. None. All checks out well.
- Further scanning, he notices that there are no adaptation values, nor are there any Integrator (fuel trim) values coming from that left #2 bank per the scanner. However, at the same time we can see the 02 voltage readings so it's getting the signal to the DME ruling out an actual open circuit.
- Okay, the DME puked. I research and track down a place near me in FL http://www.ecudoctors.com/ & ship them the DME.
- They diagnose and find that a short in the EPROM socket took out a 2.5v voltage regulator for the unit. Tech advised this is somewhat a common failure and can cause strange problems.
- Received MY rebuilt DME. Same issue.
- Sent my DME back. Tech cannot find anything out of values, but begins talking with my mechanic and understands there is an issue. He sends a different DME (same Bosch Number 0 261 203 484) with my OEM chip.
- Vehicle runs better. Getting Integrator (fuel trim) values from both banks now, and you can hear the vehicle making adjustments. But...
- Per scanner (AutoLogic), the DME is still showing no (read: zero % on both banks and both short term/long term) Mixture Adaptation values AND the freakin' CEL is on again with the "open 02 circuit" code when, per the scanner there are good 02 voltage values.
- My mechanic is saying it's the DME. My DME tech says everything checks out and that it's likely something else on the car. But both suspect it MAY be the EPROM got corrupted.
- I contact Mark D. (Guys, he's great!) He's not heard of this issue before, but also agrees that with two separate DMEs, the only constants are the OEM EPROM and the car.

Okay, here's the challenge:
What's going on? I need to know which way to go with this? DME, EPROM, or something else on the car.
Can an EPROM get corrupted?
If so, could the symptoms listed be from the EPROM, or something else in the DME keeping in mind two separate DMEs have been used?
What else, if anything, on the car would prevent the DME from producing Mixture Adaptation values and/or this "02 Open Circuit" code?

Help!

Many Thanks,

John

[Gearhead]

could it be a short in the o2 sensor wiring??

Thanks Paul!

The wiring was already ohmed out with no shorts or open circiuts anywhere. That and when the scanner is attached, we're getting good 02 values without any strange spikes or open/zero values.

Data Stream
02 Sensor 1 Integrator - 1.00193
02 Sensor 2 Integrator - 1.00000

02 Sensor 1 reading = 0.49 v
02 Sensor 2 reading = 0.54 v

Plus, these values change readily when enrichening (starting fluid) or leaning out (intentional vacuum leak) the a/f mixture. Even if there was an open or short in the 02 wiring, would that account for the DME not having any mixture adaptation values?

[pingu]

I'd be amazed if the EPROM got corrupted. To program an EPROM, you normally need to apply a special voltage to the EPROM and the DME wouldn't be set up to do this.

[Gearhead]

if the O2 circuit ws not functioning properly then there would not be any means to adapt the mixture?

Correct, if the circuit was open, then there would be no values for the DME to use as a basis for the Mixture Adaptation. However, we were sitting there with the scanner attached looking at the 02 sensor values on one data stream (meaning the circuit is good) and watching the voltage sweep up and down as we enriched and leaned-out the a/f mix manually... yet at the same time, the mixture adaptation was reading 0.00 on both banks. So WE could see the 02 values, but the adaptations were not responding to this available data.

Now, this very thing happened with two different DMEs. Granted, neither one was new, but both passed all bench tests according to my DME tech and the 2nd one is the unit he used in his shop as the "known good" unit when troubleshooting.

[Gearhead]

I'd be amazed if the EPROM got corrupted. To program an EPROM, you normally need to apply a special voltage to the EPROM and the DME wouldn't be set up to do this.

Oh, I know. A corrupted EPROM is a stretch, but at this point all things have to be on the table. One reason I keep going back to this possibility is that one of the original problems with the 1st DME was that there was a short in the EPROM socket that took out the internal 2.5v voltage regulator (per the DME tech). With a short, perhaps there was enough spike voltage somewhere to "tweak" something? (highly technical term there).

[Paul in NZ]

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.

i m sure there are wetter paces for E34s than florida....lightning perhaps?

[MBXB]

- Checks all wiring for faults. None. All checks out well.

Did you check the cold air sensor, and water temp sensors?

[Gearhead]

- Checks all wiring for faults. None. All checks out well.

Did you check the cold air sensor, and water temp sensors?

Thanks Ramon!

With the initial diagnosis (before sending in the DME for repair the first time), there was an issue where we were seeing voltage readings from the Coolant Temperature Sensor (good values) but at the same time the data stream was showing something like a -200 degree C reading. So on one line the scanner is showing a good voltage for the sensor (good CTS circuit) but the DME translation was was at the bottom of the temperature scale. When the 1st DME was repaired (that voltage regulator), this issue was corrected. So, again it looks like a "logic" problem. The votage values are there, but the DME isn't translating properly.

The air temp sensor never showed an issue.