Garagistic M30 Swap Guide- Preparation to Donor Car

Picking a proper donor car is important, but not imperative for having a successful swap. I decided to go with an ’88 325 super eta. I highly recommend any car from ’88 - ‘91 as the wiring is easier. If you choose to use a 83-87 E30, just know you will have some more extensive wiring modifications, but it will all be documented here. I will illustrate and solve most of the wiring concerns in the electrical chapter. An automatic or manual donor car is not consequential to wiring, but the differences are noted here. This write-up does not cover an auto to 5 speed conversion, so getting a 5 speed donor car is prime. If not, then you must swap with a manual pedal assembly and add a master cylinder and slave cylinder for the clutch. Also, you must short the E30 “park” wire that goes into the ECU. It’s nothing more than a 12V signal that is constantly “on”. This can be achieved by the connector which plugs into you Automatic E30 near the shift console.

Either way, the engine/transmission needs to be removed and your E30 needs to be properly prepped for the new, powerful drivetrain. Please see below as to which level you want to take your donor car.


1. Disconnect Battery + & Gnd from E30 – 13mm Wrench

2. Remove Hood – 12mm Socket to remove 6 bolts as well as the ground wire

a. Use a small flat Head Screwdriver to remove the hood shock assembly

b. Drain Wiper Fluid and remove pump to retain with hood

3. Drain all Fluids

a. Oil – 15mm Socket

b. Coolant – Drain from Radiator – Flat Head Screwdriver

c. Power Steering – 17mm Wrench & 19mm Wrench at the power Steering Pump

4. Remove Radiator – Flat Head Screwdriver for Upper & Lower Hoses

a. Remove Fan Sensor Wiring on Passenger Side of Radiator – Unclip

b. 2 mounting bolts on each side – 10mm nuts

5. Remove Air Intake & MAF – Flathead Screwdriver & 10mm Socket for securing airbox.

6. Unscrew Transmission Mounts (2 Nuts) – 13mm Socket

7. Engine Ground Wire – 13mm Socket on either engine mount bracket or E30 Frame Rail.

8. Remove Fuel Lines, supply & return – Flat Head Screwdriver

9. Remove Coolant Lines to Heater Core & Expansion Tank – Flat Head Screwdriver

10. Remove ECU Harness from Glovebox – 10mm Socket with extension

a. Remove ECU

b. Remove any Grounds

c. Remove power from B+ d. Fish all lines out through Firewall Hole.

11. Remove Brake Booster Vacuum Hose a. There is an Oetiker Clamp that consequently will be destroyed. You can replace it with a regular worm-type clamp later. You need snips to remove this.

12. Driveshaft Disconnect – 17mm & 19mm wrenches at Transmission output a. You can leave driveshaft in the E30 for now

13. Shift linkage – Compression ring pliers to remove the clip. 13mm wrench to remove shift linkage to E30 Body.

14. Throttle & Cruise Control

a. Cable is easily disconnected using simple pliers to remove the plastic retaining bracket from the throttle body.

b. Be careful as you could damage the plastic clips if you squeeze too hard.

15. Clutch Slave Cylinder – 13mm nuts on transmission bell housing needs socket & extension

16. Exhaust after manifold – 2 bolts per each of the 2 manifolds – 13mm each. Long extension & 13mm socket.

a. Rest of Exhaust – Remove from Hangers

b. Oxygen Sensor – 22mm Wrench to remove Oxygen sensor from Exhaust

17. Air Conditioning lines – Presuming that you do not have any air in your R12 lines, be careful when removing these lines as they are sensitive – Use 19mm wrenches to remove both of these lines.

a. Remove any electrical connections as well.

If you are a beginner to this swap or swaps in general, I’ve created a list of things you must remove in order to remove the driveline from your E30. What you saw above is what you need to do, preferably in order, to remove the drivetrain from your E30.

 For ’88 - ‘91 cars: If you decide to use your E30 wiring harness for your M30, then remove it from the engine and save for the engine for later use. Note that you will need to lengthen/shorten a lot of wires. Refer to “electrical section” for more information.

 For ’83 – ‘87 cars: You can remove the wiring harness if you like to make the removal of the engine easier. For more details about wiring, please refer to wiring details and spreadsheets located in “electrical”.

If you are going to be doing any other preparations to the donor car such as cleaning engine bay or doing a steering rack swap, you might as well do it now while everything is out.

It is also highly recommended to modify the firewall at this stage of the swap.

Now that you have the guts out of the car, it’s now time to clean the engine bay and prep it. You want to get yourself the following items:

 Terry Cloth Rags (Bag)

 Engine Degreaser (1)

 BrakeKleen Cans (3)

 Hand Wire Brush

This will take approximately 3 hours to clean the engine bay, the wiring harness, and any parts that you plan to reuse for this project. Places to take note of the areas within the E30 to clean the most; Within the frame rails. See Figure 1.