dburt86
03-12-2015, 11:55 AM
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.
http://i314.photobucket.com/albums/ll431/dburt86/coil%20driver_zpssqcdevwu.png (http://s314.photobucket.com/user/dburt86/media/coil%20driver_zpssqcdevwu.png.html)
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.
http://i314.photobucket.com/albums/ll431/dburt86/BMW%20stuff/dme%20cutaway_zpsekmueszb.png (http://s314.photobucket.com/user/dburt86/media/BMW%20stuff/dme%20cutaway_zpsekmueszb.png.html)
http://i314.photobucket.com/albums/ll431/dburt86/BMW%20stuff/1CE174C7-D61C-480F-9788-3DBA53CEC256_zps7lu7ggtf.jpg (http://s314.photobucket.com/user/dburt86/media/BMW%20stuff/1CE174C7-D61C-480F-9788-3DBA53CEC256_zps7lu7ggtf.jpg.html)
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_to_Motronic/MS3%20to%20Motronic%203.3.1.html
http://i314.photobucket.com/albums/ll431/dburt86/pin%20out_zpsc5cqr3lr.png (http://s314.photobucket.com/user/dburt86/media/pin%20out_zpsc5cqr3lr.png.html)
There 2 things that need to be brought up. Grounds and main relay circuit.
http://www.megasquirt.325ix.com/MS_to_Motronic/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/1993%20BMW%20318i%20-%20318is%20-%20325i%20-%20325is%20%20Electrical%20Troubleshooting%20Manua l.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/search?updated-min=2011-01-01T00:00:00-08:00&updated-max=2012-01-01T00:00:00-08:00&max-results=23
http://i314.photobucket.com/albums/ll431/dburt86/starter%20circuit_zps7qqfpo2l.png (http://s314.photobucket.com/user/dburt86/media/starter%20circuit_zps7qqfpo2l.png.html)
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.
http://i314.photobucket.com/albums/ll431/dburt86/coil%20driver_zpssqcdevwu.png (http://s314.photobucket.com/user/dburt86/media/coil%20driver_zpssqcdevwu.png.html)
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.
http://i314.photobucket.com/albums/ll431/dburt86/BMW%20stuff/dme%20cutaway_zpsekmueszb.png (http://s314.photobucket.com/user/dburt86/media/BMW%20stuff/dme%20cutaway_zpsekmueszb.png.html)
http://i314.photobucket.com/albums/ll431/dburt86/BMW%20stuff/1CE174C7-D61C-480F-9788-3DBA53CEC256_zps7lu7ggtf.jpg (http://s314.photobucket.com/user/dburt86/media/BMW%20stuff/1CE174C7-D61C-480F-9788-3DBA53CEC256_zps7lu7ggtf.jpg.html)
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_to_Motronic/MS3%20to%20Motronic%203.3.1.html
http://i314.photobucket.com/albums/ll431/dburt86/pin%20out_zpsc5cqr3lr.png (http://s314.photobucket.com/user/dburt86/media/pin%20out_zpsc5cqr3lr.png.html)
There 2 things that need to be brought up. Grounds and main relay circuit.
http://www.megasquirt.325ix.com/MS_to_Motronic/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/1993%20BMW%20318i%20-%20318is%20-%20325i%20-%20325is%20%20Electrical%20Troubleshooting%20Manua l.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/search?updated-min=2011-01-01T00:00:00-08:00&updated-max=2012-01-01T00:00:00-08:00&max-results=23
http://i314.photobucket.com/albums/ll431/dburt86/starter%20circuit_zps7qqfpo2l.png (http://s314.photobucket.com/user/dburt86/media/starter%20circuit_zps7qqfpo2l.png.html)