A few MSPNP wiring questions

[Austrianvespaguy]

Just finishing up the DIYPNP assembly and about to start on installation, but have a few specific questions that some of you have probably already been through before that I wanted to check on before finalizing. NOTE: I like to avoid adding or subtracting from factory wiring as much as possible, so most of these have to do with keeping to that goal!

1.) O2 sensor +12V. I plan on putting in the wideband using the stock wiring down to the O2 sensor connector. I see the motronic uses pin 23 to provide power to the heater relay, so I'm planning to jumper from one of the edge 12V slots (which are powered by the main relay) to pin 23 so that the factory heater relay can then be used to power the wideband. Should work just fine, right? For some reason pin 23 isn't covered in the diyautotune setup instructions.

2.) Wasted spark coil outputs via cylinder ID sensor wires. Since the CID never did much to begin with and certainly won't do anything helpful for Megasquirt, any reason NOT to use those two wires (pins 8 and 31) for spark outputs B and C? Would love to not need to pull anything extra through the firewall, but not sure if those wires are up the task of handling the current needed for direct coil control. Spark output A I would just leave at pin 1 and use the wire from the factory coil. Anyone done this or something similarly clever to avoid messing with the DB15 connector and extra wires through the firewall?

TPS found everything I need already and should have that one taken care of ;)

Thanks!

For reference, DIYPNP assembly instructions:

https://www.diyautotune.com/support/tech/hardware/diypnp/documentation/application-docs/1987-1992-bmw-325/

Motronic 1.3 pinout:

https://www.r3vlimited.com/board/attachment.php?attachmentid=97583&d=1433367852

[Austrianvespaguy]

Oh, and one other thing I forgot. I have the IGN6 coil pack from DIYAutotune; anyone know a good set of plug wires that fit well between that pack and the M20 plugs?

[kyleconstantine]

1) In a regular MS2(non PNP) motronic pin 23 and motronic pin 3(fuel pump) are both wired to MS pin 37. I would imagine the PNP does the same thing already and you wouldn't need to add another 12v source. I'd recommend cutting the tail off your old narrow band 02 sensor and splicing the wideband into that so you can just plug right into the stock harness.

2) I don't see why it wouldn't work that way as long as its easy enough to run the spark outputs through those pins on the harness. I'm guessing they are completely unused on the PNP? Personally I preferred to go through the firewall and do it their way just to be sure. A small amount of black caulk and I haven't had a leakage problem.

as for the wires, I just got a universal set from summit. They are so close to fitting but I still had to use some electrical tape on one end. if you find the perfect set let me know.

[nando]

Don't splice wires. Crimp new pins into the O2 sensor connector. The stock O2 sensor uses stainless steel wires, which are basically impossible to solder - you'd have to use crummy crimp connectors. The pins are the same ones used in the C101. All you need is a connector housing from an old sensor.

If pin 23 isn't already tied to Pin 3, you can do that either at the DME, or by simply stuffing a jumper wire at the relay connector between the FP and O2 relays.

[Austrianvespaguy]

Thanks guys, and great news, the car is now running on Megasquirt! I have not yet started installing the 'upgrade' bits (wideband, TPS, and wasted spark), just wanted to get it going in basic form first to make sure everything is working, and so far so good!