DME Issues

[Mitchen]

So for the first time in my 15 years of ownership, my 320i let me down yesterday and wouldn’t spark. Seems I was getting no signal from the DME to the DME relay. Then suddenly it kicked in and the car turned over. Obviously then it was hard to diagnose further if it’s not faulting.

So I thought the DME was a good place to start and it just so happens back in 2013 I bought a new unused Bosch DME with exactly the same part number. It’s sat in my draw at home since as a spare that’s never been needed.

Now to my question, there’s no way these need to be coded right? There’s no EWS system or anything of the sort so should be plug and play, even if it is unused out of the factory. Reason I ask is that I plugged the ‘new’ DME in today and got exactly the same issue as yesterday morning. Fuel but no spark. So is the new DME a dud, or does it have to be coded/burnt to the chassis in some way?

I put my old DME back on and its driving fine (for now). Worth mentioning the old DME has a sticker on with the cars VIN and model.

Any help appreciated

[Speedtouch]

The Motronic ECUs should be 'plug & play' with no recoding necessary - all the code is built into the EPROM chip.

In your case, I would check the DME relay as a first step, replacing it if ncessary.

I had a similar problem with an E34 535iSE, which turned out to be a crack in one of the fusible links (fuses that are wrapped in plastic sheathing) that lead to the ECU, so check for any in the battery positive feed main red cabling that goes to the igition switch/ECU.

Also check all engine-to-body earths (usually brown cables) for good continuity.

[Mitchen]

The Motronic ECUs should be 'plug & play' with no recoding necessary - all the code is built into the EPROM chip.

In your case, I would check the DME relay as a first step, replacing it if ncessary.

I had a similar problem with an E34 535iSE, which turned out to be a crack in one of the fusible links (fuses that are wrapped in plastic sheathing) that lead to the ECU, so check for any in the battery positive feed main red cabling that goes to the igition switch/ECU.

Also check all engine-to-body earths (usually brown cables) for good continuity.

Thank you! I appreciate the feedback. I'll trace the wiring. I have recently bought and fitted a new negative terminal lead from the dealer, so your warning about continuity struck a chord. Separately, this new old stock ECU of mine came in a Bosch box off the shelf of a motorfactor. It wasn't a BMW supplied part. I'm guessing this is blank and needs an EPROM chip, hence why it's not working?

[Speedtouch]

It's a possibility; have you tried opening the ECU to see if it has an EPROM chip fitted? They should have a BMW part number on a label in the format 1 xxx yyy, which you could Google to see if it matches your engine...

[fixedwheelnut]

So for the first time in my 15 years of ownership, my 320i let me down yesterday and wouldn’t spark. Seems I was getting no signal from the DME to the DME relay. Then suddenly it kicked in and the car turned over. Obviously then it was hard to diagnose further if it’s not faulting.

So I thought the DME was a good place to start and it just so happens back in 2013 I bought a new unused Bosch DME with exactly the same part number. It’s sat in my draw at home since as a spare that’s never been needed.

Now to my question, there’s no way these need to be coded right? There’s no EWS system or anything of the sort so should be plug and play, even if it is unused out of the factory. Reason I ask is that I plugged the ‘new’ DME in today and got exactly the same issue as yesterday morning. Fuel but no spark. So is the new DME a dud, or does it have to be coded/burnt to the chassis in some way?

I put my old DME back on and its driving fine (for now). Worth mentioning the old DME has a sticker on with the cars VIN and model.

Any help appreciated

How old is the car? Pre 88 cars suffered with dry solder joints on the output transistors that switch the coils and injectors, so it is worth undoing the DME control unit and inspecting the solder joints. Use an anti static mat and wrist strap and resolder the pins.