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Thread: Early m20, Late e30

  1. #1
    Join Date
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    1989 BMW E30 Touring

    Early m20, Late e30

    Hello! I'm swapping an early m20 in to my late e30 and i need help with the "c104" I think it's called. A small 3 pin plug next to the ecu, from what I've read it sends info to the cluster about rpms and other thing. Where can I plug it in? Or how can I get the information from the c104 to the cluster. Thanks.

  2. #2
    Join Date
    Nov 2002
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    E30 E36 E46 E90
    Does that early M20 still have a round plug C101? Your best bet is to add a few wires to the C101 from the C104.

    If it's a rectangular plug harness, you should get a different harness.
    2011 M3 Sedan
    2006 GMC Sierra 2500HD LBZ
    1999 323i GTS2
    1995 M3 - S50B32/S6S420G/3.91
    1990 325is
    1989 M3 - S54B32/GS6-37BZ

    Hers: 1996 Porsche 911 Turbo
    Hers: 1989 325iX


  3. #3
    Join Date
    Feb 2015
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    Maryland
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    325ix, 325ix, 540i
    Does your car have a blown engine in it or no engine at all? If blown engine, you can swap just the block+head and then you don't need to swap anything else. Keep your late model cooling and your late model electronics.
    If your e30 runs bad, switch to Megasquirt first. Then try new spark plugs, cap and rotor, wires, oxygen sensor, crank shaft position sensor, coolant temp sensor, air flow meter, idle control valve, throttle position sensor, digital motor electronics unit, harmonic balancer, fuel injectors, engine harness...

  4. #4
    Join Date
    Nov 2016
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    Karlskrona, Sweden
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    1989 BMW E30 Touring
    It does have a round plug, so it fits in the body harness female-plug, the car was going to the junkyard before I bought it so it had no engine. I bought it in the mindset of saving it. Unfortunatly the late m20 engine is expensive here in sweden. The early m20 can sell for around 50-60$, they are also more common.

  5. #5
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    1989 BMW E30 Touring
    Just recently picked up a running spare early m20 for 10$..
    The question really is how do I pair up the electronics from the early m20 with the late e30 body?

  6. #6
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    Quote Originally Posted by Touringwalther View Post
    Just recently picked up a running spare early m20 for 10$..
    The question really is how do I pair up the electronics from the early m20 with the late e30 body?
    I already told you.
    2011 M3 Sedan
    2006 GMC Sierra 2500HD LBZ
    1999 323i GTS2
    1995 M3 - S50B32/S6S420G/3.91
    1990 325is
    1989 M3 - S54B32/GS6-37BZ

    Hers: 1996 Porsche 911 Turbo
    Hers: 1989 325iX


  7. #7
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    Quote Originally Posted by nick325xit 5spd View Post
    I already told you.
    Add a few wires? From what pins? Etc..

  8. #8
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    CANTON, OHIO
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    TRIUMPH tr250,tr6, bmw 325i
    Take a look at a web site called E30Zone.net and once on look under the all wiki pages label and you will find the info you need

  9. #9
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    "If you have swapped your pre-facelift engine to a facelift, and find that your tachometer no longer works, this plug is the issue. Your new engine loomz feeds the signals that went through this connector via the 20 pin C101 engine loom plug, so you have the choice of either extending two wires from the hanging plug to the engine loom socket next to the fusebox (as they are in later body looms), or teasing the two wires out of the engine loom, near the ECU plug, cutting them (abandoning the rest of the wire to the C101 plug) and splicing the plug from your old engine loom onto the wires."
    I dont quite understand this, shall I extend 2 wires from the c104 to pin 20 in c101?

  10. #10
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    E30 E36 E46 E90
    Quote Originally Posted by Touringwalther View Post
    "If you have swapped your pre-facelift engine to a facelift, and find that your tachometer no longer works, this plug is the issue. Your new engine loomz feeds the signals that went through this connector via the 20 pin C101 engine loom plug, so you have the choice of either extending two wires from the hanging plug to the engine loom socket next to the fusebox (as they are in later body looms), or teasing the two wires out of the engine loom, near the ECU plug, cutting them (abandoning the rest of the wire to the C101 plug) and splicing the plug from your old engine loom onto the wires."
    I dont quite understand this, shall I extend 2 wires from the c104 to pin 20 in c101?
    No. Pin 20 on the C101 is not what you want. What you need to do is get a copy of the ETM for the year of your engine and the year of your car and go through. Otherwise, there are a number of C101/C104 pinout guides available on the web that you can use.
    2011 M3 Sedan
    2006 GMC Sierra 2500HD LBZ
    1999 323i GTS2
    1995 M3 - S50B32/S6S420G/3.91
    1990 325is
    1989 M3 - S54B32/GS6-37BZ

    Hers: 1996 Porsche 911 Turbo
    Hers: 1989 325iX


  11. #11
    Join Date
    Sep 2018
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    olympia wa
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    87 bmw 325is, 91 bmw 318
    Please if any one knows I swapped an 87 m20b25 from a 325is into my 91 318i which had the m42. I need the c101 plug pinouts, the m20 I need engine side and the 91 I need the chassis side pinout. Also if anyone has the 3 prong c104 plug I believe its called that hangs out in the glove box coming off the harness, im not sure where im suppose to connect these. After swapping the engine is getting no spark or fuel but it cranks with no problem. also windows and locks stopped working after swapping the m20 in. I looked at the c101 plugs as they do plug together however 3 of the pins don't line up with the other side and the c104 plug in glove box doesn't match any other plugs so im hoping these are my only problems for spark, fuel, and the accessories

  12. #12
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    87 325is 96 GMC Suburban
    Last edited by msservices; 09-29-2018 at 11:40 PM.

  13. #13
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    87 bmw 325is, 91 bmw 318
    Quote Originally Posted by msservices View Post
    I’m not finding c101 pinouts there and the c104 pinout doesn’t make sense to me at all

  14. #14
    Join Date
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    87 325is 96 GMC Suburban
    Did the part about the burning wires from swapping early/late harnesses make any sense? I heard about this issue years ago when people were swapping late model I motors into early E cars (or in your case the opposite) thinking it was plug and play, so I just wanted you to know that was a possibility here. I’ve done quite a few motor swaps which I had to rework wire harnesses and one thing I can tell you is that wiring diagrams are almost never 100% accurate, as manufacturers make subtle changes every year and often mid year, and the diagrams seem to be made to cover select years/versions. All I am saying is be careful, and check/trace each wire yourself
    Last edited by msservices; 10-11-2018 at 11:48 PM.

  15. #15
    Join Date
    Dec 2005
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    corpus christi, texas
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    No e30s, again :(
    yup /\


    the only plug and play engine swap I have found in the e30 is the early 318 can take an early eta with no wiring harness mods. just unplug at the firewall and plug in your new harness, put in your ecu and idle controls, and start it up. I only know this from doing it in an 85 318 with a swap from an 85 325e. my buddy chance had a 318 and I had a spare 325e so we tried it and it worked.
    No e30s again.

  16. #16
    Join Date
    Sep 2018
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    olympia wa
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    87 bmw 325is, 91 bmw 318
    So still no fix or answers. Don’t reply with a link please cause they never have what I’m looking for I would just keep google as I have done for many hours along the last few months. First thing does anyone have a diagram for c101 plug chassis side 91 318i (not IS). Also 1987 325is convertible c104 plug. And or where exactly to wire the c104 plug into. My chassis dosent have ews it’s just a 6 button obc please. Again I have no spark or fuel, it’s been threw 2 shops, my buddy who knows quit a bit about m20s and all the research I’ve done. I have the 325is ecu and c101 pinouts I don’t need those

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