M20b25 swap ECU question

[Joev253]

Was wondering if someone could give me some insight on how to adapt an ECU from a m20b25 to my 86 325es the m20b25 I'm swapping is from an 89 I know there is a pin or two that has to be changed so if anyone has done this before I would greatly appreciate some instructions thanks!

[MR 325]

When swapping to a M20B25 you'll need to use the B25 engine harness. The ECU will plug right in.

[squidmaster]

^^ this and the spark wires

[jlevie]

If you use the engine harness for the 89 engine there are two things that need attention.

The wire to pin 20 of C101 needs to be clipped on the body side to avoid smoking the engine harness. The car routes the tachometer and econometer to the DME via C104, but on the later cars those go through C101. You can graft the C104 connector onto the later harness, or rewire the car to pass those through C101.

[ForcedFirebird]

^^ this and the spark wires

Best to have the #6 cylinder identification sensor (only "need" # 6 wire), but the car will run just fine if it's absent.

[squidmaster]

Really? Neither of mine will run without it connected. Weird.

[ForcedFirebird]

Really? Neither of mine will run without it connected. Weird.

Have done multiple 2.7i swaps over the years and used the eta wires on a few.

According to the repair manual: "if the cylinder identifier is missing/malfunctioning, the ECU will revert to batch fire"

[squidmaster]

Perhaps because every time mine have been disconnected they were actually switched with the other identical connector right next to it.

[TobyB]

oh, yeah, you'll need your crank sensor, there...

(which is the other plug)

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