PNP wiring for MS3x to OBD1 m50 Harness

[dburt86]

This is just a rough draft. Ill try to add more detail as i go. This may confuse some more then it helps. Please ask specific questions, it will help me remember some things i may miss.

Hey guys,
Im writing this mainly from memory as i did this about a year ago, so i may update the thread with some more info as i go.

This is going to cover wiring a MS3x unit into an OBD1 m50 engines harness, making it PNP, using all BMW sensors. Im not sure how far ill take it but ill start with the wiring.

First thing was to grab a spare DME, and cut the harness connector and coil drivers out of it. Your going to need the stock coil drivers because most managment systems cannon drive a normal 3 wire coil alone. You can buy coil drivers from companies, i started with the DIYautotune Quad Spark boxes but found them to be too bulky for there own good, so i ended up using the stock BMW drivers. OBD1 and OBD2 drivers function the same, but the OBD2 drivers are smaller.


Heres a picture of my cut DME with the wiring began. You can see i cut the frame of the DME in the back to allow the harness to come up to the connector. Ive seen guys run bulkhead fittings rather then just cutting the DME frame, but im not that fancy.





The next thing to do is to find a good pinout. I used this pin out basically. At one point i questioned its accuracy but even looking at the ETM's, it is indeed correct. I do encourage that you build your own pin out spread sheet. I did, but did not save it, but its always good practice.
http://www.megasquirt.325ix.com/MS_t...c%203.3.1.html


There 2 things that need to be brought up. Grounds and main relay circuit.

http://www.megasquirt.325ix.com/MS_t...ic/Grounds.htm
All pins labeled ground on the ETM's dont necessarily mean they are Earth grounds. There are grounds that come from the harness and then there are grounds used to ground the harness. This is one of those times i really wished i saved my notes, because i spent a good amount of time finding out which ground does what. But its really simple, look at the ETM, find every pin that is labeled ground, and see it it makes it to earth ground. If it does not, its probably a sensor ground. Things like IAT, CLT, and TPS all have dedicated return sensor grounds to cancell any noise.


Also, crank wiring shielding. This needs to also be grounded. If not, you will get a ton of noise that may show up as either Sync loss in the crank circuit, or it will show up as fake teeth, basically causing a miss fire. Alot of time the shield wire of the crank wiring is left untouched, but it needs to be grounded.

Pins 6, 28, 34 and 55 on the harness side go straight to Earth ground. Those are the pins you would use to ground your EMS and coil drivers.

Pin 15 is the ground circuit for the coil packs and pin 45 is shielding for that circuit. Both on the harness side.

Heres a link to the ETM i used. this is for a 1993 318, 325. you will find the mapping to the grounds on page 0670.4-10 through 13

The pin out for the m50 harness is on pages 1210 13-a and on.
http://wedophones.com/Manuals/BMW/19...g%20Manual.pdf



For the main relay. Normally, the BMW main relay is triggered by the ground side. That means that battery power is going to the main relay at all times.

What we need to do, is trigger a relay so the other side of the relay switches to ground. So i used pin 56 (on diagram from below) to make the relay switch, bringing pin 27 to ground. Thats what the blue relay in the picture of my whole harness and DME above is. This way, everything is still stock on the car, so you can swap between you MS and a stock DME as you wish.

There is another way to switch the pins around at the main relay and acheive the same thing, but then your modifying the car side of the wiring.

Scroll to the bottom for the Main Relay circuit. this is another great resource!!
http://m54megasquirt3.blogspot.ca/se...max-results=23

[ak5]

Definitely subd

[dburt86]

Its definitely overwhelming when looking at it from the outside, but i can tell you that its not that bad. I could probably bang out a good looking conversion harness in a night. Theres really not that much to it.

[rowleym]

hey what about triggering the main relay? or does the starter circuit do that. I just skimmed that part.

[dburt86]

hey what about triggering the main relay? or does the starter circuit do that. I just skimmed that part.

My fault. Main relay circuit. You actually dont need to do anything with the actual starter circuit. My fault, good catch.

[rowleym]

Woohoo!! Nice. Here to help ha. Can't wait to see this section progress.

[dburt86]

Updated a little clarity on the main relay circuit. Things are still coming to mind so ill keep updating.

[m3mods]

Sub'd

[DrLeadFoot]

Sub'd!!!

[rowleym]

Sub'd!!!

Hey that's exciting to see!!

[DrLeadFoot]

Hey that's exciting to see!!

This probably will be my winter project.

[DrLeadFoot]

All I would need to buy would be an IAT sensor, MS3x unit, harness pigtail and some confidence?

I have a spare 413 ECU that can be hacked up.

[DrLeadFoot]

I blew my head gasket due to a crappy tune. Time to do things the right way.

[DrLeadFoot]

Ordered MS3x and some other goodies. Time to do this!! Are you able to give some inputs if I have questions?

[bmwnic]

This is amazing. Thank you

[evolwun]

This is great! Definitely subscribed to this thread.

What are you guys doing with the AC control from the ECU? I really want to retain my functional AC in my '93 325i. I have heard that you don't need to worry about it and other sources say that you do need to wire around it. I wish I had a better, complete, understanding of how all the components act to turn on the AC. Between the climate control, ECU, relay and pressure switch, I am having trouble figuring out what needs power or ground. And on top of that, what state each needs to be in at what time.

EDIT: I am referring to pins 48, 64 and 65.

[anzael]

Updated a little clarity on the main relay circuit. Anzael LLC

[tyr283]

Someone should just build these harnesses and sell them...I'd buy one

[SyCK]

^

[imagine02]

I'd buy one too.

I have a non vanos M50 from an OBDI E34 that i will be swapping into my OBDII E36 318ti. It will also be getting an HX40 at the same time so I'm wanting to Megasquirt it. Since I'll be using the M50 engine harness, would OP's harness work for this setup?

[DrLeadFoot]

I'm still not running as I've been working on my e46 m3. Hopefully this summer

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[Matt Cramer]

Someone should just build these harnesses and sell them...I'd buy one

We'd be glad to roll out an MSPNP if we got a 10 unit group buy. I've been trying to contact the moderators to get approval as a forum vendor, but with no luck so far.

[DrLeadFoot]

I'd be in!!

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[Butters Stoch]

We'd be glad to roll out an MSPNP if we got a 10 unit group buy. I've been trying to contact the moderators to get approval as a forum vendor, but with no luck so far.

This will need to be 10x OBD1 and 10x OBD2 ?

[Matt Cramer]

Correct, OBD1 and OBD2 will need separate group buys. Although if one group buy goes through and then keeps selling well after the group buy, we may launch the other without a group buy.