M20b25 swap question

[Joev253]

Hey guys I'm swapping a m20b25 into my 325es and I have the ECU and wiring harness I was wondering how difficult it will be to switch out the ECU? Anybody done before? Thanks!

[TurboJake]

You have to switch the harness and ECU. no way around it.

Also, easy peasy. Especially if you have a round C101

[StereoInstaller1]

Depending on what year car and what year engine harness...late harness and early car can cause smoke, but I forget where. I think Bird knows.

[jlevie]

A late harness in an early car can smoke when the ignition is switched on unless you clip the wire to pin 20 of C101 on the body side. The other issue will be that the tach and econometer signals on an early car are via C140 (near the DME connector), but a late harness routes those through C101. You can rewire to add those to the body side of C101 or graft C104 onto the engine harness.

[TC Baur MD]

Jim,

BMW no longer makes the wiring harness for the m20 before 9/1987. Can I use the harness that's made for E30's built between 09/1987 --- 05/1988, Part#12511719528 and get the harness for the injectors, Part#12511724521 ???
My car was built on 5/1987. Would I have to convert the cooling system to make it compatible with the updated harness and would I have the same issues with the tach and smoke you talked about above?

Thanks in advance,

[SmokeE30]

That harness your speaking of is the SETA harness same as an "I" harness it won't plug into your early style ecu, you could convert it to all the late model injection and running gear but it's a lot of stuff to switch over if your only looking to replace the harness a used one willbe a much simpler option than trying to make a late model harness work.

[TC Baur MD]

That harness your speaking of is the SETA harness same as an "I" harness it won't plug into your early style ecu, you could convert it to all the late model injection and running gear but it's a lot of stuff to switch over if your only looking to replace the harness a used one willbe a much simpler option than trying to make a late model harness work.

Thanks for your response SmokeE30. I forgot to mention that all my cars are 325i's verts with a motronic ecu. My 87's built before 9/87 came with a harness that doesn't have the extra connection, C191, under the throttle body that connects to the injector harness. My 88 325i vert does have this C191 connection. I believe all my C101 connections are round but will have to check the wire color of pin 20. I have a couple of the older harnesses that will fit, probably similiar to an eta, but the wiring has become brittle. Can't get them anymore from Germany so that's why I was hoping to be able to use a later model harness.

[jlevie]

You can use any later harness for an M20B25 engine on the initial (9/86-8/87) M20B25 as long as you deal with the econometer, tachometer, and C101 pin 20 issues.

[zambizzi]

I just bought an m20 and I need to know if there is a complete swap kit such as cooling, harness, sensors, electric fan, complete gasket kit, mounts, pretty much everything but the engine, trans and ecu. I'd reeeealy love some help.

[TC Baur MD]

I just bought an m20 and I need to know if there is a complete swap kit such as cooling, harness, sensors, electric fan, complete gasket kit, mounts, pretty much everything but the engine, trans and ecu. I'd reeeealy love some help.

There are engine and head gasket kits that you can pick up from Pelican parts but no complete engine rebuild kits. You can find the replacement part numbers on the realeom.com web site and buy the individual parts.

As I mentioned above BMW no longer sells the early model e30 engine harnesses.:(