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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

6.)  Cooling System

The 325i uses a few different hoses for its cooling system than the 325e, but you'll have to use the ones off an '87 325i/325is. Why? Starting with the 1988 model year, BMW completely changed the cooling system and shifted the expansion tank over to the driver side (causing many hose changes), and since all regular etas were built before 1988, then the '87 325i's cooling system must be used for the conversion. If you have an '88 325 (Super Eta), then lucky you, you don't need any modifications.

The coolant hoses you'll need are:

  1. Expansion tank to water pump
  2. Expansion tank to radiator
  3. Expansion tank overflow
  4. Water pump to thermostat housing
  5. Thermostat housing to upper radiator
  6. Thermostat housing to lower radiator
  7. Thermostat housing to throttle body
  8. Thermostat housing to heater core
  9. Heater core to cylinder head
  10. Throttle body to block

You want to be sure to use high quality hose clamps, preferably not the ones from Japan or the United States. Mine came from Germany and were even better than the ones from the factory ;).


7.)  Vacuum Lines

The only vacuum lines that you need that hasn't been mentioned before are the valve cover breather hose, the idle control valve hose (to throttle body), and the dual brake booster hoses (from the brake booster to the throttle body). You don't need the 325i brake booster, but if you have one then you may as well use it. The only difference between the two is the location of the vacuum port: On the "e" it's on the passenger side of the booster while on most "i" models it's on the driver side. The dual hoses from the throttle body will bend around the brake resevoir and fit fine in the 325e's booster. You'll also need the line from the fuel pressure regulator to the intake manifold, but it's the exact same from the 325e. I actually used a Mercedes hose (oh, the horror!) since neither my local dealer nor my parts supplier had it in stock.


8.)  Check Engine Light

The 325i's engine management system has self-diagnosis capabilities and therefore has a Check Engine light on the instrument cluster. For this, you'll need the display on the lower left side of the instrument cluster (part number 62-11-1-381-497) as well as the wire that runs from the instrument cluster to the fusebox. It's attached to the white cluster harness. I didn't bother to wire the light because I've lived without one for the 3 years I've owned an eta and it never hurt me. Then again, I may wire it one day just for the hell of it. Stay tuned.


9.)  Tachometer Wiring

When you installed the 325i harness, you may have noticed a connector (C104) inside the glovebox by the ECU that has no matching plug. One of those wires is for the tach/econogauge, while the other two are for the OBC. If you don't connect it, then the tach/econogauge will remain dead, the OBC's RANGE will always read 620 miles, and its AVG MPG feature will be stuck at 99.9 mpg. Neither the OBC nor the instrument cluster are receiving the proper output signals for the ECU. Click here to find out how to get em working.


10.)  A/C, Alternator, Power Steering, and V-Belts

From here, all you should need to reconnect are the power steering pump, alternator, air conditioner compressor, and the drive belts. Mount the power steering pump first and connect the three lines (two from the resevoir and one from the rack). Don't forget the adjustment bracket. Next mount the alternator above it, wire the positive and negative connectors from the wiring harness, and mount the bracket to the lower timing cover. The A/C compressor mounts similarly, and tighten the two plugs with a 19mm and 22mm wrench. The first V-belt that you'll have to mount is the alternator/water pump belt. The belt that's supposed to be used is the 10x965, but that was way too loose so I ended up using a 10x950, which fit perfectly. Mount the A/C belt second, then the power steering third. The A/C belt is an absolute pain to put on, so a trick is to mount the belt on the A/C pulley as much as you can, then use a pick or flathead screwdriver to hold it in place. Have a friend quickly crank the car (in Neutral or Park, of course!) for less than a second and the belt will snap into place, but you gotta remove the tool fast when it cranks.

Spin the fan clutch on (another trick is to hold it in place and quickly crank the car until it catches), then tighten the four bolts down using the special fan clutch tool, which locks the pulley on place.

Now, the car should be all ready to start. Check, double check, and triple check ALL the wiring and hose connections, and make sure that all hose clamps are nice and tight. You may want to have a pair of fresh eyes help you with this.

Once that's done, add oil to the crankcase if you haven't already done so. After it's filled, DISCONNECT the ignition coil so the car won't start (if you haven't already). Crank the car for 5-8 seconds, then stop. Repeat the process until the oil pressure light is off; it may take several times for this to happen. Don't overcrank the car because you'll burn the starter. When the light goes off, it means that there is enough oil circulating in the engine where it won't cause damage. Turn the key off, reconnect the coil, cross your fingers, and start the car.

At 12:19 AM on January 2, 2003, I turned the key on and started the 2.8i for the first time, and...

Nada. Nothing. It cranked but never fired. After trying unsuccessfully for half an hour (checking for fuel/spark, disconnected wires, etc) neither I nor my friend Can couldn't figure it out. I was working on the car for 16 hours straight and was completely exhausted, so I called it a day and went home.

The next morning Paul found a crossed fuel line and cranked the car (then promptly proclaimed that it was he who put the engine together). It fired right up and sounded mean...very mean. I added coolant to the system, using a 50/50 mix of phosphate-free anti-freeze, which is the orange Kool-Aid looking stuff they sell at Kragen. Open the 8mm bleeder screw at the top of the thermostat housing and add as much coolant as it will take. Turn the heater on full blast and wait for heat to come out. (Once coolant comes out of the bleeder screw, close it up. But you'll have to bleed it again once the car has been driven and coolant has been circulating.)

Check again for any leaks or loose ends, then close it up and take it around the block for a spin! I kept the RPMs under 3000, but right from idle I could feel it pull stronger than ever before.


I kept the revs low and right now I'm going easy on the car for the first 1000 miles just to break everything in. Success!



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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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