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Thread: How to swap M20s E21 323i to Motronic E30 325i

  1. #1
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    How to swap M20s E21 323i to Motronic E30 325i

    Ok. I know we have been talking about this recently so this so probably be stickyed but this thread has been started to be the complete resource on how to swap the engine from an e30 M20 2.5 into and e21 323i, and includes the Motronic swap. If anyone needs to add any information to this by all means do so:

    Here is Tyler's old 323i with the m20 engine swap that this thread details:


    Here is the rundown: all this information is available on the e21 Greymarket website. http://www.e21bmw.net/graymarket/index.php But in case you have not been there: Here goes:

    http://www.e21bmw.net/graymarket/library/swap.php

    Converting your 323i or 320/6 to a 325i motor

    By Tom McKenzie with help from Michael Avedis

    First let me explain the reason for the conversion. I purchased a 1980 323i with the original engine and K-Jetronic injection. In order to get the car California "smog legal" I was faced with taking the car to a state lab where they would fit an aftermarket oxygen sensor, charge me $2000 and not guarantee anything. The other option was to install the complete engine and injection from a 325i (E30). I decided on the latter because I would have a low mileage motor with an opportunity for upgrades (i.e. chip etc.). I was able to find a 1991 325i motor with injection, brain and air box with 35K miles. Note: If you have a 320i you will need to obtain a 323 subframe. I'm not familiar with this procedure. Most of this article will assume you have a 323. (Webmaster's note: For info on putting a small six into a 320i, see the other engine swap page.)

    Old Motor Removal/Engine Bay Preparation

    I removed the old motor by renting a hoist and using my 320 Haynes manual. Everything is straightforward. It did take some time to jockey the motor out but I was doing it by myself. Having a couple of buddies around is highly recommended. This also allows plenty of opportunity for Tim Allen impressions. You should remove the battery tray and old air filter bracket at this time. Michael had his engine bay repainted.

    Parts Mix

    Now you need to figure out what you need from the old engine. Michael used his 323 flywheel because it was lighter. You will also need the old 323 motor mounts because the 325 mounts are wider. I purchased a new clutch since I had the engine out. Some people recommend using the 323 oil pan but both Michael and have had no problems with clearance using the 325 pan. Michael and I both used a early 325 water pump so the expansion tank could be used. I had to trim some material off my 323 plate that fits on the bottom of the transmission. Michael used the 325 plate. You should also plan your exhaust arrangement. I used the stock 323 arrangement and had an O2 sensor welded into the downpipe. Michael used his headers and also had a O2 sensor welded in. I initially purchased a used sensor but I would recommend buying a new one since I ended up getting a new one shortly after. You will also need some of your 323 hoses for the radiator. My engine had a pipe mounted on the front of the block to route coolant which I removed since the 323 radiator's bottom connection is on the other side.

    Battery Location

    I purchased a combination battery holddown/rear strut tower brace from Top-End performance. They provided everything required to move the battery to the trunk. I ran the cable along the right side of the car under the carpet and through an existing hole in the firewall. I purchased a 325i battery junction and used this to branch to all the 12V wires. Note: the 325 has a fusable link which is used for power to the harness.

    Wiring

    This part takes some soldering expertise. You can cross-reference from the 325 ETM and your 323 manual. Pete McHenry also has wiring setups available, and there is some wiring information on Brandon's site too. Some of the wires from the 325 aren't used. Micheal found the wire that runs from the end of the engine harness to the fuse box (E30). I wired directly from the engine harness to my e21 fuse box using the E21 15 pin connector. I'm in the process of working up a wiring diagram.

    Oil Filter/Cooler

    The 325 oil filter base has outlets for an oil cooler. I removed the base and installed my oil cooler base. Michael didn't have an oil cooler so he removed the base and used the threaded sleeve from his 323 motor.

    Throttle Cable

    The 325 cable can used with some modification. On the pedal end I just hooked the cable in the slot. On the throttle end I used the stock location for the rubber grommet but the cable was too long so I routed it up where I think the automatic transmission cable would go. So now it's at a slight angle.

    Vacuum Hose

    The vacuum hose from the 325 motor hooks right up to the brake booster. I used the same hose although it's probably a little short.

    Brain/ECU

    You need to drill a hole in the firewall for the brain. I chose to mount the brain in the glove box so I drilled 2 inches to the right of the hole where I ran the battery cable. You can then seal the holes with silicone. I used tie wraps to attach the brain to the rail running above the glove box. I'll eventually bolt it down. There are two connectors which are used. The only thing you need to connect is the 51 pin connector to the brain.

    Fuel Pump

    You should be able to use the 323 fuel pump. Just check the output pressure to make sure it is within specs. You might want to change the filter.

    Alternator

    You can use your 323 alternator if you modify the harness since the 325 uses a different type of connector. My 323 alternator was only rated at 80 watts but since I don't have A/C this wasn't a concern.
    ************************************************** ************************************
    See Next page for WIRING DETAILS
    Last edited by jjgbmw323; 07-18-2008 at 07:39 PM.
    "..Horsepower is a measure of work done over time, or the rate at which work is done."




    http://www.cardomain.com/ride/579694/1


  2. #2
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    Wiring for the conversion:

    The biggest difficulty is the wiring for the convesrion, which is a schematic
    on the internet. Why reinvent the wheel:

    Ok here it is:
    http://www.e21bmw.net/tech/motronic.php
    Motronic Wiring Charts
    (note: this info is all on one page on purpose)

    The following is an outline of the entire engine side wiring harness for an 88 325is (Motronic 1.3 - Ecu #173) and its interface with a 1979 Euro 323i (other E21's are probably similar)

    E21 323i Engine Plug
    Engine plug:

    E21 Plug # E21 Wire color Motronic 1.3 Wire color Purpose

    1 Brown/Green Brown/Green Oil pressure switch to instrument cluster
    3 Green/Black Green/Violet & Black/Green Power to Fuel pump from Fuel pump relay and starter
    5 Blue Blue Alternator Charge (D+) to instrument cluster
    6 Green/Violet Green Coil 15+ / O2 Sensor Heater Relay
    8 Green Green ignition switch to Motronic #27
    10 Black Yellow/Black ignition switch (start) to starter
    13 Brown/White Brown/Violet from injector rail (temp sensor) to instrument cluster
    15 Black Black from Motronic #6 to tachometer

    Motronic ECU Pinout:

    Pin # Color Purpose/location Elsewhere? details

    1 Black Ignition Coil (timing -) Yes Lead to diagnostic connector
    2 Brown Ground Yes Lead to diagnostic connector
    3 Brown/Green Fuel Pump Relay (85) No
    4 White/Yellow Idle Control Valve #3 No
    5 Brown Purge Canister (trigger -) No
    6 Black Tachometer (engine speed out) Yes
    7 Grey/Yellow Air Mass Sensor #2 No
    8 Black Cylinder ID sensor (spark #6 lead) No
    10 Brown Oxygen Sensor (ground) No
    12 Grey/White Air Mass Sensor #3 No
    13 White/Yellow Diagnostic - RxD (Motronic receive data line) No Lead to diagnostic connector
    14 Brown Ground Yes Lead to diagnostic connector
    15 Grey Check Engine Light (- triggered) No
    16 Brown/White Injectors 1, 3, 5 (- triggered) No + lead is red/white
    17 Brown/Yellow Injectors 2, 4, 6 (- triggered) No + lead is red/white
    18 Red Power (direct battery lead +) Yes
    19 Brown/Orange Ground Yes
    22 White/Green Idle Control Valve #1 No
    23 Brown/Green Oxygen Sensor Relay (85) No
    24 Brown Ground Yes Lead to diagnostic connector
    26 Grey/Blue Air Mass Sensor #4 No
    27 Green Ignition Switch Lead (run position) Yes
    28 Black Oxygen Sensor (+ read voltage) No
    29 Black/White Vehicle Speed input Yes from Cluster Speed Output
    31 Yellow Cylinder ID sensor (spark #6 lead) No
    32 White/Black Present Fuel Rate output (to instrument cluster) Yes Lead to diagnostic connector
    36 Brown Main Relay (85) No
    37 Red/Blue Main Relay (87 #1) Yes Same as red/white
    39 Green/Blue Programming Voltage No Lead to diagnostic connector
    40 Black/Grey A/C Compressor ON to Motronic No A/C system
    41 Violet/Grey A/C System ON to Motronic No A/C system
    42 Red/Blue Park/Neutral switch to Motronic No Auto Transmission only
    44 Grey/Violet Air Mass Sensor #1 No
    45 Brown/Red Coolant Temp sensor (not cluster) No
    47 Black Pulse (engine speed)/Crank Ref Sensor (+) No
    48 Yellow Pulse (engine speed)/Crank Ref Sensor (-) No
    52 Brown/Blue Throttle Position Sensor #1 No
    53 Brown/Black Throttle Position Sensor #3 No
    55 White/Violet Diagnostic - TxD (Motronic transmit data line) No Lead to diagnostic connector

    Connector mappings:
    Plug Pin Color Purpose Motronic 1.3 Pin

    Injector rail connector:
    1 Brown/Red Motronic Coolant Temp Sensor 45
    2 Brown/Orange Motronic Coolant Temp Ground N/A
    3 Brown Cluster Temp Sensor Ground N/A
    4 Brown/Violet Cluster Temp Sensor Sender N/A
    5 Red/White Power to Injectors from Main Relay N/A
    6 Brown/White Trigger, Injectors 1,3,5 (-) 16
    7 Brown/Yellow Trigger, Injectors 2,4,6 (-) 17

    Diagnostic Connector:
    14 + Red Battery + (unfused) 18
    15 + White/Yellow Diagnostic - RxD (Motronic receive data line) 13
    7 White/Green ? Not connected N/A
    6 White/Black Present Fuel Rate 32
    16 Green/White power to O2 heater relay N/A
    12 Blue Alternator charge (D+) N/A
    1 Black Coil Timing (-) 1
    11 Black/Yellow Starter Solenoid N/A
    18 - Green/Blue Programming Voltage 39
    20 - White/Violet Diagnostic - TxD (Motronic transfer data line) 55
    19 - Brown Ground N/A / 2, 14, 24, 19

    Oxygen sensor plug:
    1 Brown Oxygen Sensor ground lead 10
    2 Black Oxygen Sensor volt lead 28
    3 Brown Ground N/A / 2, 14, 24, 19
    4 Green/Blue Sensor Heater power (from O2 relay) N/A

    Ignition coil:
    1 - Black Timing (-) 1
    15 + Green Power (+) N/A

    Air Flow Meter:
    1 Grey/Violet Air Inlet Temp 44
    2 Grey/Yellow Air Inlet Input 7
    3 Grey/White Air Inlet Degree 12
    4 Grey/Blue Air Inlet Closed 26

    Throttle position switch:
    1 Brown/Blue Closed/Idle Switch 52
    2 Brown/Orange Ground N/A
    3 Brown/Black Wide Open Switch 53

    Idle control valve:
    1 White/Green Idle Control Voltage (-) 22
    2 Red/White Power from main relay N/A
    3 White/Yellow Idle Control Voltage (-) 4

    Cylinder Id Sensor:
    1 Black Pulse Input 8
    2 Yellow Pulse Input 31
    3 Clear Shield/Ground N/A

    Crank Pulse sensor:
    1 Black Engine Speed (+) 47
    2 Yellow Engine Speed (-) 48
    3 Clear Shield/Ground N/A

    Oil Level sender:
    1 (blue/white) Blue Dynamic Oil level (closed when oil low) N/A
    2 (brown) Brown/Orange Ground N/A
    3 (blue/violet) Green/Yellow Static Oil level (closed when oil full) N/A

    Engine Relays:

    Relay diagrams:

    Relay Connector Color Purpose

    Main Relay:
    30 (input) Red from Battery + (unfused)
    85 (- trigger) Brown from Motronic #36
    86 (+ trigger) Red from Battery + (unfused)
    87 (output, switched) Red/White to injectors, purge solnd, fuel pump relay, idle valve
    87 (output, switched) Red/Blue to Motronic #37

    Fuel Pump Relay:
    30 Red from Battery (unfused)
    85 Brown/Green from Motronic #3
    86 Red/White from Main Relay
    87 Green/Violet to fuel pumps

    Oxygen Sensor Relay:
    30 Green/White from ignition switch
    85 Brown/Green from Motronic #23
    86 Green/White from ignition switch
    87 Green/Blue to O2 sensor heater
    Last edited by jjgbmw323; 07-18-2008 at 07:36 PM.
    "..Horsepower is a measure of work done over time, or the rate at which work is done."




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  3. #3
    Join Date
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    Nicely put together. The car in my avitar is one of the cars (I recently bought from Michael) that the swap at the top of your thread was written about if anyone needs me to look at anything.

  4. #4
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    Sticky please. Paging Bryce...
    e21: 1981 2.5L sleeper
    e21: 1982 323i Baur TC 1 # 4210
    e21: 1980 323i project or parts car, can't decide
    e21: track car project
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    click here for the latest updates

  5. #5
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    80 323i in pieces :-)
    Excellent !!

    Thank you

  6. #6
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    Quote Originally Posted by Eurotrash323 View Post
    Excellent !!

    Thank you
    No problem..if anyone has anything to add please do so.

    We should have had this thread years ago, Since swaping the m20 for a later model one on the e30 is a common swap. I am going to be putting my 2.9 M20 in someday.

    Scott on Michael's old car did you see the e30 external fuel pump or the e21 one?
    "..Horsepower is a measure of work done over time, or the rate at which work is done."




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  7. #7
    Join Date
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    only the kids e30s
    87 325is would have used the same fuel pump set up as the e21s so no reason to remove the exterior one. its in the later part of 88 they swapped to a single fuel pump in the e30
    no e30s of my own, but I am financing two for my kids

  8. #8
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    Got under there today and it looks to be running the original 323I pump. Seems to work really well. Car has a fuel pressure guage inside and it reads around 40 psi under throttle.

  9. #9
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    Quote Originally Posted by Scott72 View Post
    Got under there today and it looks to be running the original 323I pump. Seems to work really well. Car has a fuel pressure guage inside and it reads around 40 psi under throttle.
    Thats great news, as I have replaced the main fuel pump on my car, and its brand new. I wonder what the stock PSI is for fuel for the e30
    "..Horsepower is a measure of work done over time, or the rate at which work is done."




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  10. #10
    Join Date
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    only the kids e30s
    its not as high as the e21 (i don't remember exactly but the regulator will drop it down to whatever the car needs. you can make it adjustable also but drilling a hole and putting a bolt on the spring plate. also, the eta fuel pressure regulator is a 2 bar while a 325i fuel pressure regulator is 2.5 bar.
    no e30s of my own, but I am financing two for my kids

  11. #11
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    Were you ever able to get this car California smog legal? I'm thinking about doing this as my next project.

  12. #12
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    Quote Originally Posted by Purie View Post
    Were you ever able to get this car California smog legal? I'm thinking about doing this as my next project.
    Well in Mass mine is grandfathered in, so they dont know the whole engine and fuel system are from the e30 325i. All I have to pass is safety.
    Will be running and inspected soon.
    "..Horsepower is a measure of work done over time, or the rate at which work is done."




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  13. #13
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    Ah OK. Thought you mentioned something about a California car. The smog laws make everything so much more difficult.

  14. #14
    Join Date
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    1979 323i BMW. 2003 GTI 20 V Turbo
    Have not posted for a long while i have had a wiring harness made for the 323i using the info in this thread for my shaved bay. Will update one the car is finally running on MegaSquirt DIY Autotune ECU.
    "..Horsepower is a measure of work done over time, or the rate at which work is done."




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  15. #15
    Join Date
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    Wow, I forgot I used your thread years ago converting my car to M1.3 (using a spare e32 loom). Thanks for all the info. I should really port match my intake one of these days.


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