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Technical_   Engine_  M20 E to I 2.8 Liter Engine Conversion_  Engine Installation, Wiring Harness

M20 E to I 2.8 Liter Engine Conversion
Fred Kim

VI.   Engine Installation, Wiring Harness

5.)  Engine Installation, Wiring Harness

Kinda, but not really.

The engine went in without a problem, so once it was in we tightened the motor mounts and wedged a wooden block behind the cylinder head and another in between the timing cover and front frame to prevent it from falling through the cracks (literally).

The car went up in the air and the transmission and driveshaft were reinstalled. Like I said earlier, the eta's Getrag 260 manual gearbox has two sensors located on the driver side; the lower one being the reference sensor and the upper one being the speed sensor. The 325i's reference sensor is located on the vibration damper in front of the engine and does not use a speed sensor, so these two will have to be plugged. I removed both sensors and plugged the transmission with the rubber brake caliper bolt covers.

Once the engine was in its normal resting position, I started to work on the wiring harness. In case you don't know where anything goes, I tried to make things easier by labeling the connectors:

Fuel injection harness


Firewall plug

O2 sensor, ignition coil, ground

Battery, positive

Fuse box

Starter, fuel injector rail

Oil press switch, TPS, ICV


Diagnostic connector, ignition
wire, reference sensor

AFM, auxiliary relay box

And so the wiring is the "not really" part about installing the new engine. The first thing I did was mount the ECU inside the glovebox then tried to feed its connector from the engine bay into the passenger compartment through the firewall opening, but the new connector was far too large for the hole. So I had to take a die grinder and literally bore the hole out to get it through:

So now I have a bored out firewall opening to match the bored out pistons ;). I painted the now-exposed metal so rust wouldn't form, then fed the connector though. I had to mount the ECU only using two of the four holes (the rear ones) because the glovebox cover would not close if it was in its proper position.

Next, I removed the eta's oxygen sensor wire and threw it away since it was a 3-wire connection and is now useless. I used the bolt from the battery tray connector and used it as a ground for the harness:

I left the O2 sensor connection dangling below until I bolted up the exhaust, then I wired the green and black wires to the ignition coil positive and negative, respectively. Now going the other way, I forced the thick wiring harness in the firewall holder and connected it to the fusebox:

From there, the wiring harness goes underground and is held in place by, um, a metal holder (that's the best I can do to describe it, sorry) that attaches to the intake manifold. The first wires that you connect are the starter negative and postive, but when you attach the red starter positive wire, don't forget to also connect the power wire that goes to the battery terminal:

The next wires that come out of the harness are the ones for the throttle position switch, throttle body vacuum, and idle control valve. The TPS is self-explanatory and so is the ICV, but chances are you can't connect the ICV since you don't have the airbox or intake boot in :). But the throttle body vacuum connects to a weird looking nozzle hose, one end goes into the throttle body and the other plugs into the charcoal canister, located near on the driver side strut tower.

Next you'll see one lone connector followed by a bunch of relays and another connector. The first lone connector is for the oil level sensor, the relays go into the auxiliary relay box, and the last one goes into the airflow meter (which shouldn't be in yet). Don't worry about the altitude sensor, the 325i doesn't have one. If you are reusing the 325e airbox, then the sensor will not be connected to anything anymore.

The diagnostic connector fits into the bracket that's part of the wiring harness metal holder thingamajig, but the the next two plugs are the tricky part. Both are black, have three-prong connectors, and have the same type of release clip. So which one goes where? Look closely at their direction, one is naturally upside down while the other one is right side up. This orientation matches with the bracket just below the diagnostic connector. The one that has the release clip upside down is for the ignition loom and is on the passenger side, while the one that is right side up clip is on the driver side of the bracket and is for the reference sensor. Both wires go across the cover on the upper timing cover. (Just as a side note, if you cross the two wires the car will not start. So do it right the first time.)

As you can see in the picture on the above right, the crank sensor mounts on the front of the engine (passenger side) on the vibration damper pulley. You'll need the one from the 325i because the 325e's damper is smooth (toothless) and will cause a no-start condition.

Finally, the last two wires on the harness are for the alternator. But you knew that already, right? Now that you're done, it's time to install the cooling lines and take care of some loose ends.


Table of Contents

1.) FAQ

2.) Parts List/Price Guide

3.) Short Block

4.) Cylinder Head/Intake Manifold/Fuel Injection

5.) Engine Removal

6.) Engine Install/Wiring Harness

7.) Cooling/Belts

8.) Tachometer Wiring

9.) Final Thoughts

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