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Thread: Motronic 1.3 Conversion Project on my E23

  1. #1
    Join Date
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    Motronic 1.3 Conversion Project on my E23

    I will be doing the Motronic 1.3 conversion on my E23. For those that dont know I have a M30B34 engine out of a 735i running on 733i electronics and it runs like crap. With better electronics and components, I'm optimistic that this will be a better improvement over my current setup.

    If anyone has done the conversion on their E23 please feel free to chime in with some tips. Any help would be greatly appreciated.

    Here we go!

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  2. #2
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    '84 733i, 01 X5 00 750iL
    I converted a Motronic 1.0 car to be Motronic 1.3 configured so then I could use a DIY auto tune MSPNP2 Gen2 B8793 "plug and play" DME for 87-92 BMW 55 pin applications. I used a Motronic 1.3 trigger wheel, TPS and IAC like you got, and then had to deal w/ the wiring harness. There is no donor wiring harness for a 1.3 car that works well on the e23, this was the annoying part of the swap. I had an e34 M30 1.3 engine harness to start with so I used it. I had to repin the end of the e34 harness that goes to the ignition/gauge cluster. The e34 harness is designed to put the DME in a weatherproof compartment in the cowl, so it was several feet too short for the e23. I bought a new DME 55 pin connector on Ebay from Russia along with new crimpable pins. The harness had to be extended to allow the DME to be mounted in the interior. I let my friend deal with extending the harness (he now owns my car). I had my car running w/ the MSPNP2 sitting in the engine bay to verify it worked before he ended up buying the car from me and dealing with making the wiring much neater. My old progress thread somewhat documents this.
    Last edited by BONDOSPECIAL; 03-09-2021 at 01:17 PM.
    Steve H.

  3. #3
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    Quote Originally Posted by BONDOSPECIAL View Post
    I converted a Motronic 1.0 car to be Motronic 1.3 configured so then I could use a DIY auto tune MSPNP2 Gen2 B8793 "plug and play" DME for 87-92 BMW 55 pin applications. I used a Motronic 1.3 trigger wheel, TPS and IAC like you got, and then had to deal w/ the wiring harness. There is no donor wiring harness for a 1.3 car that works well on the e23, this was the annoying part of the swap. I had an e34 M30 1.3 engine harness to start with so I used it. I had to repin the end of the e34 harness that goes to the ignition/gauge cluster. The e34 harness is designed to put the DME in a weatherproof compartment in the cowl, so it was several feet too short for the e23. I bought a new DME 55 pin connector on Ebay from Russia along with new crimpable pins. The harness had to be extended to allow the DME to be mounted in the interior. I let my friend deal with extending the harness (he now owns my car). I had my car running w/ the MSPNP2 sitting in the engine bay to verify it worked before he ended up buying the car from me and dealing with making the wiring much neater. My old progress thread somewhat documents this.
    Yes, my concern is the wiring harness. I will have to mount the ecu in the glove box and run the wiring harness through the firewall into the glove box. Let me know if this is doable. I really dont want to extend the harness

    The guy that I purchased this from redid the m30b35 wiring harness to work with a m30b34 in a e28.
    He redid the wiring part on the harness to fit the fuse box connector on my e23.

    Thank you for your input.

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    Last edited by mpvibes; 03-09-2021 at 01:44 PM.

  4. #4
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    Gonna see if I can make this bad boy work without having to lengthen any wires someway somehow. The ideal spot will be in the glove box. Mock set up (pic below).


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  5. #5
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    I had the same thought initially, because I too had wanted to do anything to avoid cutting and extending the harness (which has double shielded wires in it for some sensors like TPS). IIRC the wiper cowl is in the way and stops you from having enough length to just put it "in the glove box". I think it would actually take more wire length to get into the glove box then into the kick panel where the DME is designed to go on the e23.
    Last edited by BONDOSPECIAL; 03-09-2021 at 05:39 PM.
    Steve H.

  6. #6
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    Quote Originally Posted by BONDOSPECIAL View Post
    I had the same thought initially, because I too had wanted to do anything to avoid cutting and extending the harness (which has double shielded wires in it for some sensors like TPS). IIRC the wiper cowl is in the way and stops you from having enough length to just put it "in the glove box". I think it would actually take more wire length to get into the glove box then into the kick panel where the DME is designed to go on the e23.
    Darn! Didn't wanna go through all that.

    Instead of extending the harness do you think I can possibly mount it in the engine bay or are extending the wires my only option at this point? Was thinking of getting a ECU mounting enclosure thats weatherproof or something. Let me know your thoughts. I appreciate the help man! Also, if you have pics of your friends engine bay with this setup that would be helpful. Thanks.


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    Last edited by mpvibes; 03-09-2021 at 05:59 PM.

  7. #7
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    I did look into project box enclosures that could be weatherproofed but I never found one that seemed appropriate. You also don't have much space in the engine bay where you could mount this. It is an option worth considering though, maybe you can figure something out. I had an intercooler in the way, maybe you could find room in that general area.

    Any photos I have from when I was doing the Motronic 1.3 wiring are in my old project thread starting here:

    https://www.bimmerforums.com/forum/s...7#post30276507

    The only photo I have of how my friend finished this by cutting and splicing the harness so the DME could be in the kick panel is this:

    Last edited by BONDOSPECIAL; 03-09-2021 at 07:05 PM.
    Steve H.

  8. #8
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    Quote Originally Posted by BONDOSPECIAL View Post
    I did look into project box enclosures that could be weatherproofed but I never found one that seemed appropriate. You also don't have much space in the engine bay where you could mount this. It is an option worth considering though, maybe you can figure something out. I had an intercooler in the way, maybe you could find room in that general area.

    Any photos I have from when I was doing the Motronic 1.3 wiring are in my old project thread starting here:

    https://www.bimmerforums.com/forum/s...7#post30276507

    The only photo I have of how my friend finished this by cutting and splicing the harness so the DME could be in the kick panel is this:

    Thanks for the link and the pic. Your friend did a nice job in routing the harness to the footwell. Looks clean.

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  9. #9
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    Thumbs up

    Is this B34 an 8:1 or 10:1?

    If 8:1, just rock an 059 with an EAT chip. I do not think you will see enough benefit to spend the time for the 1.3
    I make E23 parts.
    09/1983 745i (stolen spring '13 around Houston, TX Achatgruen on nutria buffalo. 8481080)
    10/1984 745i
    11/1984 745i
    11/1984 735i (10:1-265/6)
    Ford, MB, and GM round out the pack.



  10. #10
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    @Hit Man X Let me verify, how can I tell if I have a high compression 10:1 motor or not? Are the #'s stamped on the head or block?

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    Last edited by mpvibes; 03-09-2021 at 11:11 PM.

  11. #11
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    Thumbs up

    Only definitive way I know is compression test.

    8:1 = 140-150psi
    10:1 = 180-190psi

    10:1 pulls clean out to 6k. The 8:1 becomes flaccid past 5200.
    I make E23 parts.
    09/1983 745i (stolen spring '13 around Houston, TX Achatgruen on nutria buffalo. 8481080)
    10/1984 745i
    11/1984 745i
    11/1984 735i (10:1-265/6)
    Ford, MB, and GM round out the pack.



  12. #12
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    Quote Originally Posted by Hit Man X View Post
    Only definitive way I know is compression test.

    8:1 = 140-150psi
    10:1 = 180-190psi

    10:1 pulls clean out to 6k. The 8:1 becomes flaccid past 5200.
    Ok, so I need to do a compression test to find out. Thanks.

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  13. #13
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    I found a way on how to run the motronic 1.3 harness without extending the wires in the e23 where you can run the harness and put the ecu in the glove box. It may not be for the faint of heart but, it gets the job done!

    You will need to remove the glove box completely (there are 4 screws holding the glovebox) and drill a 2.5" hole from the inside just below the ac lines with a 2.5" hole saw and install a firewall grommet. I went with a haltech grommet. Here are some pics.

    I will post more pics and have updates of the motronic 1.3 conversion later. So far so good.

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  14. #14
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    Close up pics of the harness and firewall grommet installed.

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  15. #15
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    Removed the old 733i harness from car. Good riddance!

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  16. #16
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    Awesome work. People will benefit from your finding. I love when people find a new way to tackle a problem.
    Steve H.

  17. #17
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    Quote Originally Posted by BONDOSPECIAL View Post
    Awesome work. People will benefit from your finding. I love when people find a new way to tackle a problem.
    Thanks man. I appreciate it. I'm glad to find a solution and help others.

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  18. #18
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    Next, I removed the b34 harmonic balancer and installed the b35 trigger wheel and Crank Sensor. You only need to remove 8 bolts not the big 36mm nut on the crankshaft.

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  19. #19
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    Installed new 145 amp alternator and new powersteering and altetnator belt.

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  20. #20
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    Painted the Valve cover and fuel rail

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  21. #21
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    Installed fuel rail, valve cover and a few b35 components. Also, plugged up some of the sensors on the thermostat housing because those wont be needed! If your valve cover is off I recommend doing a valve adjustment and replacing your valve cover gasket. Engine bay is looking nice! Much cleaner!

    I'll update with more later.

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  22. #22
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    Good info. I just got my 745 running on 1.3 and was hoping for options on the dme harness.
    Mike
    93 M5 3.8 Sterling Silver/Black (euro)
    94 M5 Touring Madeiraschwarz/Black
    80 745i (project)
    83 735i / 5 speed (euro)
    86 745i

  23. #23
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    No problem man. Glad I could help.

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  24. #24
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    For the b35 subharness you are going to have to modify it to make it fit on the b34 due to the oil filter housing being in the way. I "carefully" used a dremel tool and flat tip screwdriver to cut open the metal tube. Do "NOT" cut the wires in the metal tube.

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  25. #25
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    Here is some info for the subharness connections.

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