I've been given the offer of an M20B25 from a facelift car to fit into my prefacelift 320. I understand I'd need to change the wiring loom over, can anyone expand on this and tell me what's involved?
Is it all plug and play? I take it there are no other differences I need to know about?
Prefacelift 320 to facelift 325 - wiring
Moderator: martauto
First of all check pin 20 of your c101, this is very important as you can easily fry your loom if this pin is earthed. Refer to Brian's post here: http://www.e30zone.net/modules.php?name ... ic&t=83367
You only need to change the engine loom, this is wrapped around the engine and it's easier to remove the engine with this still attached rather than take it out separately. It is almost all plug and play, disconnect the ecu and then take the old loom out with the engine, then install the new engine with it's loom attached. Pass the ecu socket through the bulkhead, plug in the new ecu attach the c101 and you're pretty much there.
You'll probably have to do a small amount of wiring to get the rev counter working as pre-facelift e30s have a separate plug for this. Information about this can be found here: http://www.e30zone.net/modules.php?name ... c&t=181277
Also the hole in the bulkhead that the ecu plug passes through is sometimes smaller on earlier cars, if you have this problem you can either make the hole bigger, or take the outer casing off the plug and reattach it once it's through. I took the plug apart as I didn't fancy taking a file to my car, see my thread here for details: http://www.e30zone.net/modules.php?name ... c&t=182551.
I may have forgotten something but someone will be along to tell us soon enough.
HTH
You only need to change the engine loom, this is wrapped around the engine and it's easier to remove the engine with this still attached rather than take it out separately. It is almost all plug and play, disconnect the ecu and then take the old loom out with the engine, then install the new engine with it's loom attached. Pass the ecu socket through the bulkhead, plug in the new ecu attach the c101 and you're pretty much there.
You'll probably have to do a small amount of wiring to get the rev counter working as pre-facelift e30s have a separate plug for this. Information about this can be found here: http://www.e30zone.net/modules.php?name ... c&t=181277
Also the hole in the bulkhead that the ecu plug passes through is sometimes smaller on earlier cars, if you have this problem you can either make the hole bigger, or take the outer casing off the plug and reattach it once it's through. I took the plug apart as I didn't fancy taking a file to my car, see my thread here for details: http://www.e30zone.net/modules.php?name ... c&t=182551.
I may have forgotten something but someone will be along to tell us soon enough.
HTH
clarko74
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Brianmoooore
- E30 Zone Team Member
- Posts: 49358
- Joined: Mon Jan 10, 2005 11:00 pm
Early E30's had a different main plug on the engine loom where it plugs into the body loom just inboard of the fusebox on the bulkhead. As long as your car has the 20 pin round socket fitted, then the above applies. If you happen to have the older type, the easiest solution is to obtain a socket from a newer car, and splice the wires together inside the fusebox.
this is perfect 
thanks very much for this info saved me asking
one thing id like to know is what year did the face lifts and pre-face lifts start and finish please??
and another can you use the manule 320 gearbox on a 325i engine thats had an auto box fitted ??
thanks very much good luck on the conversion!! (sorry for the hi-jack)
thanks very much for this info saved me asking
one thing id like to know is what year did the face lifts and pre-face lifts start and finish please??
and another can you use the manule 320 gearbox on a 325i engine thats had an auto box fitted ??
thanks very much good luck on the conversion!! (sorry for the hi-jack)
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chefen2006
- E30 Zone Newbie
- Posts: 8
- Joined: Fri Jan 07, 2011 11:00 pm
I just did the pre to post swap. Whent from a m20pre to a m25 from a '89 525 e-34. The electrics is not that big a problem, especialy not after having a look at the links above. Thanks for that
One thing I was NOT expecting was that I had to make new suports for the radiador, and relocate the wather expansion tank, wich again needed new brackets made up. And ofcourse the old radiador did'ent work with the new engine, so... one more trip to the breaker
The "new" motor was from a automatic car, meaning that it did not have the bearing in the end of the crank for the gearbox-shaft. Ahhhhwell......one more trip to the stealership.
Finaly the rubber boot for the airbox was way too long to fit the e-30 body. One more trip to the aaarghhhh....... With the new intake boot in place, I then discover that the idle-valve-thingy does NOT fit anymore. Not enugh space, aparently there are more than one type, I had the wrong one!
I did NOT feel like visit the dealer or the breakers again so I made it fit, with the help of an grinder/hack saw compo. 
Finaly some of the wieres was to long and needed to be shortened.
Some off this is down to the fakt that the doner for this projekt was NOT an e-30, and an automatic car. Other things like the brackets and that must bee to do with going from pre to post.
Anyway it is doable. If the doner-car is an e-30 then it should not be a big problem.
Good luck with your project
One thing I was NOT expecting was that I had to make new suports for the radiador, and relocate the wather expansion tank, wich again needed new brackets made up. And ofcourse the old radiador did'ent work with the new engine, so... one more trip to the breaker
The "new" motor was from a automatic car, meaning that it did not have the bearing in the end of the crank for the gearbox-shaft. Ahhhhwell......one more trip to the stealership.
Finaly the rubber boot for the airbox was way too long to fit the e-30 body. One more trip to the aaarghhhh....... With the new intake boot in place, I then discover that the idle-valve-thingy does NOT fit anymore. Not enugh space, aparently there are more than one type, I had the wrong one!
I did NOT feel like visit the dealer or the breakers again so I made it fit, with the help of an grinder/hack saw compo. Finaly some of the wieres was to long and needed to be shortened. Some off this is down to the fakt that the doner for this projekt was NOT an e-30, and an automatic car. Other things like the brackets and that must bee to do with going from pre to post.
Anyway it is doable. If the doner-car is an e-30 then it should not be a big problem.
Good luck with your project
Glad i'm not the only one who fond this issue, everyone seemed to think i was talking out my arse when i mentioned it about a year agoclarko74 wrote:
Also the hole in the bulkhead that the ecu plug passes through is sometimes smaller on earlier cars, if you have this problem you can either make the hole bigger, or take the outer casing off the plug and reattach it once it's through. I took the plug apart as I didn't fancy taking a file to my car, see my thread here for details: http://www.e30zone.net/modules.php?name ... c&t=182551.
