jasper's m10 to m42 swap

[e30sh]

Tach signal and fuel eco signal run through C104 on the early cars (next to DME) Run those over to C101 or splice in near DME connector. The check engine light might be worth keeping so you can check codes via the stomp test.

Good luck.

[jwetering]

Tach signal and fuel eco signal run through C104 on the early cars (next to DME) Run those over to C101 or splice in near DME connector. The check engine light might be worth keeping so you can check codes via the stomp test.

Good luck.

Thank you for the tip.

So my wiring harness has an additional pigtail branching off it right by the connector to the ECU (or the DME). See the photo - what do those wires do ?



There's also this round connector that branches off near the coil wires..what does that connect to ?

[downforce22]

i would suggest using the round connector for c101. My thought was to get the c101 from ebay for liks $40 and use that in case you ever want to swap to s/m50/2 or m20 without having to convert from square to round. those wires are in the glovebox for tach signal etc, but the c101 round incorporates that.

The round connector above is the 4 wire oxygen sensor.
That looks good, similar to mine

[jwetering]

i would suggest using the round connector for c101. My thought was to get the c101 from ebay for liks $40 and use that in case you ever want to swap to s/m50/2 or m20 without having to convert from square to round. those wires are in the glovebox for tach signal etc, but the c101 round incorporates that.

The round connector above is the 4 wire oxygen sensor.
That looks good, similar to mine

Thank you for the tips as well.

Imma gonna review to see if I got this and to inform future swappers:

1) I am actively looking for a female c101 now, preferably one out of an m42 e30. That's the wire and connector that come out of the m42 car fusebox and connects to the m42 wiring harness pictured below.



2) I plan to then pigtail the square connector from my old m10 wiring harness onto the back of that female c101 connector to make a patch cord. The square connector will plug straight into my existing m10 fuse box and the round connector will plug into my harness. This is the square plug from my existing m10 harness.




3) The two wires behind the glove box in my car need to connect to the harness. I can either run them to the fusebox area and splice them into my patch cord, or leave them where they are and splice into my harness. Either way it's a pain.

4) But earlier on I identified 4 wires missing from the m10 connector that were present in the m42 connector:

1) engine speed input
2) fuel rate input
3) speed signal to ECU
4) switched power.

If the wires behind the fuse box are the engine speed (tach) and eco (fuel rate input?) then where do I find the speed signal and switched power. ?


5) And what about that two wire connector attached to my m42 wiring loom at the ECU end ? What do those connect to ?

This connector::



Thanks guys - don't mean to over-complicate but they're legit question I think.

[downforce22]

So i figured out what that connector by the ecu connector is. It is the C136 that connects to the hvac assembly. I believe it turns on the fan on low when you hit the ac button. look at the right side of this diagram

[jwetering]

So i figured out what that connector by the ecu connector is. It is the C136 that connects to the hvac assembly. I believe it turns on the fan on low when you hit the ac button. look at the right side of this diagram

That's awesome sir. I will ignore it. Thank you very much for finding that.

I ended up getting hold of a fusebox out of a 1991 318i sedan with full chassis-side wiring. I laid it out on the shop floor to get a feel for it but soon after that I cut off the C101 connector with about 10 inches worth of wire sticking out back and stuffed the massive nest of wires back in the cardboard box. Here's the m42 chassis side C101:



Then I snipped the rectangular c101 plug from my old m10 wiring harness leaving about 10 inches of wires also...



And after a full day of consulting the internet this is my plan. Turns out that people aren't documenting m10 -> m42 swaps and if they are it's long enough ago that the various photobucket links are now dead.




For those of you doing this in the future the first thing to note is that all of the various diagrams on-line look at the back of the female plugs. The round c101 has tiny little numbers on the which is helpful.

Not done quite yet though:

1) The only wire I can not identify is the BLU-YEL at position 14 on the M42 C101. There are some excellent discussions about the c101 out there - like this one: https://www.r3vlimited.com/board/for...love-your-c101 but it says pos. 14 should be empty. I'm going to ignore it unless someone here tells me otherwise..

2) There's also some question about the WHT-BLK wire at position 16 on the m42 c101. All indications are that it is the "diagnostic wire for the SRS (airbags). I'm connecting it to the WHT-BLK wire at pos. 11 on the m10 c101 - which is sometimes called a "diagnostic" wire but I'm pretty sure that there were no airbags in use or even contemplated back in 1985 were there ? Any help on that is appreciated.

3) I want to CEL to work but don't know how to make it so. Sounds like I just connect the CEL itself to the wire coming from pos. 12 on the m42 c101 and I will install a connector coming out of my pigtail to do that - but I don't know where to find the CEL connection in the car. Is it on the back of the cluster ?

I've also decided to splice in a c104 connector at the far end of the wiring harness - under the glovebox - for the tachometer and econometer. That's cleaner than running those wires all the way over to the driver side of the car.

4) There's a third wire on the c104 plug under the glovebox though - it's a GRN-BRN (or maybe GRN-RED) wire which some sources say is a Vehicle Speed Sensor (VSS) while other say its an OBC - fuel cutoff wire which needs power for the car to run. Problem is that there are no m10 specific notes about that so it's not clear if I need to put power to it or not. I figure there are enough power wires connected to the c101 already that I don't need power there too....any help on that is also appreciated.

Here's that c104 connector under the glovebox:



Thanks for the help guys.

[downforce22]

1) The only wire I can not identify is the BLU-YEL at position 14 on the M42 C101. There are some excellent discussions about the c101 out there - like this one: https://www.r3vlimited.com/board/for...love-your-c101 but it says pos. 14 should be empty. I'm going to ignore it unless someone here tells me otherwise..

2) There's also some question about the WHT-BLK wire at position 16 on the m42 c101. All indications are that it is the "diagnostic wire for the SRS (airbags). I'm connecting it to the WHT-BLK wire at pos. 11 on the m10 c101 - which is sometimes called a "diagnostic" wire but I'm pretty sure that there were no airbags in use or even contemplated back in 1985 were there ? Any help on that is appreciated.

3) I want to CEL to work but don't know how to make it so. Sounds like I just connect the CEL itself to the wire coming from pos. 12 on the m42 c101 and I will install a connector coming out of my pigtail to do that - but I don't know where to find the CEL connection in the car. Is it on the back of the cluster ?

I've also decided to splice in a c104 connector at the far end of the wiring harness - under the glovebox - for the tachometer and econometer. That's cleaner than running those wires all the way over to the driver side of the car.

4) There's a third wire on the c104 plug under the glovebox though - it's a GRN-BRN (or maybe GRN-RED) wire which some sources say is a Vehicle Speed Sensor (VSS) while other say its an OBC - fuel cutoff wire which needs power for the car to run. Problem is that there are no m10 specific notes about that so it's not clear if I need to put power to it or not. I figure there are enough power wires connected to the c101 already that I don't need power there too....any help on that is also appreciated.

Here's that c104 connector under the glovebox:



Thanks for the help guys.

Jasper, I just happened to be working on the C101 and wiring for my car yesterday. As it turns out, I am recreating the entire wiring fuse box because my chassis already had that removed and it will be a racecar. I am seeing the wires you identified as being related to the unloader relay circuit. This unloader relay turns off the other high power circuits when you are running the starter motor. I think the unloader relay was added on the m42 cars and was missing on the m10 cars because they used a 3 post vs 4 post starter but I don't have an m10 fuse box to verify. https://www.r3vlimited.com/board/for...r-relay-issues

[/When starting, the connection to the windings supplies positive voltage to terminal 85, resulting in a voltage difference of 0v across the relay due to terminal 86 still being connected to power via the ignition switch. This causes both relays to disengage, removing power from the various high current draw accessories in the car.

Your issue is essentially an open connection at the starter solenoid. You are measuring the positive voltage through the relays. If you were to ground that wire, you would lose the unloader function, but the accessories would still be ignition controlled via terminal 86.

What happened is, back in the days of carburetors and distributors and other scary things like that, some cars used either a ballast resistor, or resistor wire to drop battery voltage going to the coil so you didn't cook your points and/or fry your transistorized ignition amplifier (cutting edge!)

Voltage drop during cranking became an issue however, so starter solenoids began incorporating another terminal which was just another contact that the starter solenoid disk connected during cranking, connecting both large terminals and the new small terminal on the solenoid together. This small lug was run to the coil in parallel with the resistor wire which was run through the ignition switch like usual, to provide full battery voltage during cranking only. Any other time that terminal was an open circuit so the ignition circuit could do its thing.

OK, fair enough. The point? BMW's fourth terminal doesn't work that way. As it is from the factory in the cars with 4 terminal starters, the fourth terminal connects to the motor terminal, the big one opposite the battery cable connection. This provides the ground/positive signal used to drive the unloader relays like I mentioned before, just using the motor windings as a ground path versus the solenoid windings. Small taillight E30s used three terminal starters, and there was a factory splice to the starter solenoid wire from the unloader wire somewhere in the vicinity of the fusebox. You would essentally be converting your car to the early style unloader circuit by running your unloader wire to the starter solenoid lug.

All that said, many people just ground the damn thing and resist the urge to crank the car while rolling down the windows with a low battery. Either scenario works. Or you could change starters to one with the fourth lug labeled "30h"

On my diagram, I went through the 1992 ETM for a 318i convertible and looked at each circuit to verify. The benefit to this is that I can trace where the lines go and verify for my car that they will work. See my pinout attached with reference drawings. You may want to download the 1984 318i and the 1992 318ic for reference from here. They may diasppear one day http://wedophones.com/Manuals/BMW/

Note on my diagram the left column is from c-101 on e30zone here (https://www.e30zone.net/e30wiki/index.php?title=C101) and that is why there are extra wires with different colors shown. The 318i doesn't have the check control unit so those are crossed out for oil pressure and oil level.

1) I show blue yellow goes to the ecu as speed signal in diagram m42 1360-2.

2) The oxygen sensor has a designated relay and circuit on the m42 engine side of the harness, so you don't need to connect this wire because your new harness on the engine will take care of it. look at m42 diagram 1360-1

3) For you, I don't believe the m10 e30 had a check engine light wired in to the cluster, so if you want it you might have to add a wire yourself.

4) I pulled up the m10 diagrams and found this on diagram m10 118, and m10 109. The green wire should be switched power input going to the coil it looks like. Since you are running m42 electronics you don't need to connect that to anything. The electronics are on the m42 engine harness wired directly to the coils.

[jwetering]

OK - here is the final results before and after wrapping.

I soldered the ends and covered them in heat shrink then wrapped the whole thing in black elex tape.

Will be splicing a c104 into the loom next.

[jwetering]

Final Step.

I cut the c104 plug off of my m10 wiring harness. Three wires - the blue one feeds out of the ECU but the other two come from the engine. Doesn't matter - in my case I'm taking all the wires from the ecu because the wires coming through my wiring loom from the c101 will be dead..remember then don't have a corresponding pin on the square m10 c101. Snip those three wires there and head to the bench.

Also notice that the wires on this side are not the same colour as the wires at the connector under the clove box.These wires are BLU-BLK which is for the tachometer and YEL-BRN - for the econometer.

.

Next grab the m42 wiring loom and strip away the gross sticky tape that covers the wires. Find the black wire first - snip it and strip it then solder the BLU-BLK wire to it. Heat shrink.

Then find the YEL-WHT wire for the econometer. Except there isn't one - I cut two WHT-YEL wires and neither would conduct to pin 8 on the c101. Had to resolder both of those (grmbl) before I pulled back the rubber boot on the c101 and found that pin 8 out was plain WHT inside the wiring harness. I found the WHT wire at the other end, snipped it and confirmed continuity to pin 8 and then soldered that up to my c104 connector.

This photo just shows the snipped BLK wire for the tacho - you can imagine the white wire looks about the same.



I didn't do anything with the middle GRN-BRN wire - just left it as a stub and then re-wrapped everything in black tape. Ready for install - hope it runs. If it doesn't it could be a million things, but that green wire at the c104 will be in the back of my mind so if someone can tell me if I need it or not that would be great.

[jwetering]

Jasper, I just happened to be working on the C101 and wiring for my car yesterday. As it turns out, I am recreating the entire wiring fuse box because my chassis already had that removed and it will be a racecar. I am seeing the wires you identified as being related to the unloader relay circuit. This unloader relay turns off the other high power circuits when you are running the starter motor. I think the unloader relay was added on the m42 cars and was missing on the m10 cars because they used a 3 post vs 4 post starter but I don't have an m10 fuse box to verify. https://www.r3vlimited.com/board/for...r-relay-issues


On my diagram, I went through the 1992 ETM for a 318i convertible and looked at each circuit to verify. The benefit to this is that I can trace where the lines go and verify for my car that they will work. See my pinout attached with reference drawings. You may want to download the 1984 318i and the 1992 318ic for reference from here. They may diasppear one day http://wedophones.com/Manuals/BMW/

Note on my diagram the left column is from c-101 on e30zone here (https://www.e30zone.net/e30wiki/index.php?title=C101) and that is why there are extra wires with different colors shown. The 318i doesn't have the check control unit so those are crossed out for oil pressure and oil level.

1) I show blue yellow goes to the ecu as speed signal in diagram m42 1360-2.

2) The oxygen sensor has a designated relay and circuit on the m42 engine side of the harness, so you don't need to connect this wire because your new harness on the engine will take care of it. look at m42 diagram 1360-1

3) For you, I don't believe the m10 e30 had a check engine light wired in to the cluster, so if you want it you might have to add a wire yourself.

4) I pulled up the m10 diagrams and found this on diagram m10 118, and m10 109. The green wire should be switched power input going to the coil it looks like. Since you are running m42 electronics you don't need to connect that to anything. The electronics are on the m42 engine harness wired directly to the coils.

Wow - a bit of unpacking to do...


1) I had already downloaded those ETM for both the 1985 and 1991 318i and they were part of the researching I did last night. Thanks for that.

2) So you are saying that pin 15 BLK-GRN is the unloader relay, but I identified it as something to do with the SRS (airbag). I read though that the m42 did not use an unloader relay and the notes you post seem to confirm that. So why would there be a wire for it at the c101 then ? I just checked my starter and it is indeed a 4 post. I didn't hook anything up to pin 15 BLK-GRN so presumably I'm good ? I do know what an unloader relay does but I am more confused now than before.

3)) So if the blue yellow at pin 14 is speed signal to the cluster then do I have to run that wire to my cluster for my speedo to work ? How did the speedo get it's signal before this swap ? It did not come through the c101...? The ETM page 137 suggests that the speed signal comes straight from the sensor to the back of the cluster through a connector C2 pin 8. I am guessing/hoping that remains the case but if my speedometer doesn't work when I finally get this project running I guess I will know exactly where to go.



4) On the CEL - if my cluster didn't have a light at all I will have to set something up from scratch but if it did then I will want to run a wire to it.... According to the ETM the early cars had a O2 sensor warning light...I should really remove my cluster and see what I got I guess.



5) I'm glad you confirmed that I don't need to power up the green wire at the 104, I'm very curious though what you mean when you looked at diagrams 109 and 118 . I went to the ETM and those pages don't show that wire or any of the related components...


6) Lastly -did I screw up by connecting the WHT-BLK wire at pin 11 from my m10 (which you say is the O2 sensor wire) to the WHT-BLK wire at pin 16 for my m42 (which is a SRS diagnostic wire)? Since neither are being used will they just do nothing ? It's not a fat wire, so I think it just carries a signal and not a load but I'm concerned one of them will be hot. See the snip from the 1991 ETM that shows this wire as a SRS diagnostic...




Thanks for the help.

[downforce22]

1) I had already downloaded those ETM for both the 1985 and 1991 318i and they were part of the researching I did last night. Thanks for that.

2) So you are saying that pin 15 BLK-GRN is the unloader relay, but I identified it as something to do with the SRS (airbag). I read though that the m42 did not use an unloader relay and the notes you post seem to confirm that. So why would there be a wire for it at the c101 then ? I just checked my starter and it is indeed a 4 post. I didn't hook anything up to pin 15 BLK-GRN so presumably I'm good ? I do know what an unloader relay does but I am more confused now than before.

3)) So if the blue yellow at pin 14 is speed signal to the cluster then do I have to run that wire to my cluster for my speedo to work ? How did the speedo get it's signal before this swap ? It did not come through the c101...? The ETM page 137 suggests that the speed signal comes straight from the sensor to the back of the cluster through a connector C2 pin 8. I am guessing/hoping that remains the case but if my speedometer doesn't work when I finally get this project running I guess I will know exactly where to go.



4) On the CEL - if my cluster didn't have a light at all I will have to set something up from scratch but if it did then I will want to run a wire to it.... According to the ETM the early cars had a O2 sensor warning light...I should really remove my cluster and see what I got I guess.



5) I'm glad you confirmed that I don't need to power up the green wire at the 104, I'm very curious though what you mean when you looked at diagrams 109 and 118 . I went to the ETM and those pages don't show that wire or any of the related components...


6) Lastly -did I screw up by connecting the WHT-BLK wire at pin 11 from my m10 (which you say is the O2 sensor wire) to the WHT-BLK wire at pin 16 for my m42 (which is a SRS diagnostic wire)? Since neither are being used will they just do nothing ? It's not a fat wire, so I think it just carries a signal and not a load but I'm concerned one of them will be hot. See the snip from the 1991 ETM that shows this wire as a SRS diagnostic...

2) Sorry for the confusion, the unloader relay is not being used on my m10 to m42 race car build. diagram 1240 shows the wiring on the m42 engine. The note explains it in the image below. The unloader when energized on both sides acts like it is de-energized, hence the name.



3) you will have to study the two diagrams, but the black wire (pin 9 on c101) should be tachometer signal. the blueyellow of pin 14 is vehicle speed input to the ecu. I'm not sure what it does beyond diagram 1360-2 shows.

5) you need to look at the m10 diagram 109 and 118, not page number and look for the C104 connector, it will look like the c101 connector is shown in the above picture.

6) Diagram 111 for the m10 shows this as a black yellow and for service indicator. I believe if you had a special tool you could use it to jumper wires or diagnose fault codes. That wire (m10 #11) is hot at all times so I would leave it taped off or use it as a spare if you need it for something. Connecting it to pin 16 on the m42 may not be good. The diagram you posted above isnt shown in the 1992 318ic etm so i'm not sure why the difference on that, but it shouldn't be important to connect to anything since you don't have any SRS system in your car.

[jwetering]

Ugh - I hate to beat any horse much less a dead one but...

1) I understand now that the m42 also has an unloader relay which is wired so that it unloads when the starter is cranked...Thing is that there are three wires that go to the starter and they can only be hooked up in one way because of the size of the studs and connectors. Is that pin 15 meant to feed one side of the unloader relay all the time and the circuit closes whenever the starter is cranked ? If so then I would have to give that wire 12v when the IGN is on. That's not how I read the ETM though.....maybe I don't get it :(

The only question that matters is - do I need to do something at pin15 BLK-GRN to make the unloader relays work and if so then what ?




2) The ETM for the 1991 318i/is/ic doesn't have a 1360-2 diagram - only a 1360-1. I actually think that there may be a material difference between those years. Once again - the only question that matters is whether I need to do something to pin 14 BLU-YEL to make my speedometer work and if so what...? Good news is that if the speedo doesn't work then I know what the problem is - I suspect I will have to run a wire from the back of the cluster to that wire.

3) Drawing 109 and 118 for sure don't have a c104 connectors on them anywhere. Not on the 1985 m10 drawings anyway. It's moot thoug - we both came to the conclusion thatthis wire doesn't need connecting.



4) We have to be looking at different drawings. my drawing 111 doesn't show any c101 connections. I also know for sure that pin11 on my m10 c101 is a WHT-BLK wire - because I've seen it in reall life....what drawings are you looking at ? They aren't from the ETM for 1985 are they ? Here is my drawing 111 - and yes maybe that's the page number but there are no other labels on there except the page number.

Thanks man - this is making my head hurt a little.

[e30sh]

FWIW. My car is an 87e with a M42 swap. Round C101 so your results may vary.

I left the extra little starter wire disconnected. Starts fine.

C104. Only used tach and eco wires. Other wire is disconnected. Tach and eco work correctly.

My car was pre wired for CEL. It works as it should. I think it's worth the trouble to install for stomp test.

My car does have a speed signal code but no illuminated CEL once it's running.

Good luck.

[jwetering]

FWIW. My car is an 87e with a M42 swap. Round C101 so your results may vary.

I left the extra little starter wire disconnected. Starts fine.

C104. Only used tach and eco wires. Other wire is disconnected. Tach and eco work correctly.

My car was pre wired for CEL. It works as it should. I think it's worth the trouble to install for stomp test.

My car does have a speed signal code but no illuminated CEL once it's running.

Good luck.

Thanks....

Do you think (or know if) your round c101 plug already had a wire running to your speedo?

[e30sh]

Speedometer signal goes through C104.on early cars.

This may be totally wrong but BMW added a top speed limiter at some point on these cars. I "think" that is what the other speed signal is for but could be totally wrong. I i motor swapped another early e a while ago. It gave me the same speed signal code with the 525 DME.