N52 Swap Discussion

[nando]

I had it connected to pin 18 on the old version of my wiring spreadsheet that’s linked way back.

It’s also connected here:

https://oomsgfx.com/misc/S54%20Swap/DIY%20Posts%20on%20Forum/S54%20SWAP%20WIRING.pdf

I expect at minimum that this allows a DTC to be stored in the DME for a failure to start. P0512 is “Starter Request Circuit,” so it’s possible this connection is only ever used to log a failure to crank to diagnose a bad starter connection before you buy a new starter motor and pull the intake manifold off.

Btw, please try to post errors with BMW hex code values - not generic SAE P-codes. ;)

Two problems with SAE vs BMW:

1) BMW has many error codes that go way beyond the scope of P-codes definitions. At best, you'll get a generic description.
2) In the DME calibration, everything is defined with the BMW hex error code - the same thing you'll see in INPA. Basically, when figuring out a DME function and associated errors, P-codes are completely useless. On the other hand, I can trace BMW hex codes to specific locations and states of memory

You can probably find a translation for SAE to BMW, but my brain isn't that big, lol. It's best to stick to the BMW definition, since many of their codes don't have an SAE equivalent anyway.

[nando]

I'll have a look at my bench flash harness - but there are 3 power wires that I remember. One constant, one start - and a wake-up signal that is effectively just an ignition switch signal, since we don't need the CAS or EWS modules.

On the E90, wakeup does stuff like prime the fuel pump when you open the door. Not something we need on the E30, but you still need it for things to run properly.

[nando]

I had it connected to pin 18 on the old version of my wiring spreadsheet that’s linked way back.

It’s also connected here:

https://oomsgfx.com/misc/S54%20Swap/...P%20WIRING.pdf

I expect at minimum that this allows a DTC to be stored in the DME for a failure to start. P0512 is “Starter Request Circuit,” so it’s possible this connection is only ever used to log a failure to crank to diagnose a bad starter connection before you buy a new starter motor and pull the intake manifold off.

There's a constant battery supply, I don't remember the pin off the top of my head, but the wire label is consistent across every BMW, even as far back as the E30. It's one of the main power pins on the large connector.

But actually, both MSV70 and MSV80 have non-volatile memory - disconnecting the battery does not erase error memory, fault memory, stored codes or anything else. That only really worked on OBD1 cars.

[nando]

Here's my wiring question: Pin 2 of the X6001 is the "Start signal" that comes from the car access module.

The S54 swaps have a similar pin and the explanation is as follows "6. Starting signal [ wire this to pin 18 on X20 it signals dme that engine is cranking]"

This makes absolutely no sense to me as the motor know it's starting from crank sensor signaling rotation.

Is this only related to "convenience start" or is it actually required?

Wire it to the ignition switch. The engine will not start without this signal.

Actually, if you think about it, the E30 even functions in a similar way. The ignition is not directly activated by the key - the key triggers a circuit in Motronic, which in turn activates the main relay and then physically powers the DME, coil, etc.

[hubcapboy]

I had it connected to pin 18 on the old version of my wiring spreadsheet that’s linked way back.

It’s also connected here:

https://oomsgfx.com/misc/S54%20Swap/DIY%20Posts%20on%20Forum/S54%20SWAP%20WIRING.pdf

I expect at minimum that this allows a DTC to be stored in the DME for a failure to start. P0512 is “Starter Request Circuit,” so it’s possible this connection is only ever used to log a failure to crank to diagnose a bad starter connection before you buy a new starter motor and pull the intake manifold off.