The text below is mostly "borrowed" from the second article. The second article relates to E36 OBD 2 -> E36 OBD 1. Thus, some additional steps may be required to adapt to an E30 swap.
- OBD I Wiring Harness
- OBD I ECU (413 "red label" is best given no EWS)
- OBD I Crank Sensor
- OBD I Cam Sensor
- OBD I Fuel Rail
- OBD I Knock Sensors (2)
- OBD I Intake Manifold
- OBD I Oxygen Sensor
- OBD I HFM
- OBD I Main engine coolant hose
- OBD I Throttle Body (option)
- OBD I Throttle Boot
The OBD2 valve cover does not have provisions for routing the coil pack connectors because the OBD2 cables enter from the passenger side and the OBD1 cables enter from the driver side. This is where you need to decide which route to go. You can keep your OBD2 valve cover, which allows you to keep your OBD2 coil packs or you can use an OBD1 valve cover which will require OBD1 coil packs. Either way is fine since both coil versions plug into the OBD1 harness. I choose to keep my OBD2 valve cover and will modify it slightly with a Dremel to route the wiring.
The OBD2 Vanos solenoid wire connector is shorter than the OBD1 solenoid so you will either need to use an OBD1 solenoid, or keep your OBD2 solenoid and extend the cabling with BMW part # 12-52-2-274-971 to the engine harness. The BMW part is a transmission harness used to connect the engine harness to the back up light switch but it's perfect for the Vanos solenoid since the connectors are the same.
The main coolant pipe from the timing cover (back side of the t-stat housing) is different between OBD1 and OBD2. OBD2 cars use a metal pipe that is fixed in the timing case cover with plumbers sealant. OBD1 cars use a rubber hose that connects to an aluminum neck that protrudes from the timing case cover. You can either use an OBD1 timing cover ($100) or get a coolant pipe adapter ($20) from Bimmerworld, AA, or Turner Motorsport. The coolant adapter fits into the OBD2 timing case cover and is secured with JB Weld. This allows you to pipe clamp the OBD1 coolant hose.
This is where the “performance gain” from an OBD1 conversion comes from. The M50 intake manifold flows better than the OBD2 (M52/S52) intake manifold. You must use this manifold for the conversion. The OBD1 manifold will have a air temp sensor and vacuum port for the fuel pressure regulator on the underside closest to the firewall. The M50 intake manifold will bolt right up to an M52/S52 cylinder head without modification.
You can use your OBD2 throttle body but you will need an adapter for the gasket seal. The OBD1 throttle body has a flat mating surface that clamps to a gasket on the OBD1 intake manifold. The OBD2 throttle body is the opposite and has a gasket in the throttle body that clamps to a flat mating surface on the OBD2 intake manifold. You can solve this problem two ways. You can get an adapter plate ($20) that sits between the OBD2 throttle body and OBD1 manifold, which provides a mating surface for both gaskets. The other option is a get an extended gasket ($15) that allows you to clamp the OBD2 throttle body directly to the OBD1 intake manifold. Of course, you can always use an OBD1 throttle body and not use any adapters.
Coolant Temperature SenderEdit
OBD2 management uses a single coolant temp sender on the cylinder head under the intake runner for cylinder #1. The OBD1 setup uses two temp senders on the cylinder head under intake runners #1 and #2. You can splice the main engine harness wiring together and use the OBD2 plug connector from your old wiring harness to connect to your single OBD2 temp sender. Another option, which is much cleaner, is to use the coolant temp sender wiring adapter ($50) from Turner Motorsport that is completely plug and play.
Crank Position SensorEdit
The OBD2 crank position sensor is located on the engine block in front of the starter motor. The OBD1 crank position sensor is located on the timing cover and mounts on a circular tab with a 6mm allen bolt. You must use an OBD1 crank position sensor. Just leave the OBD2 sensor in place to plug the hole.
The fuel delivery setup is significantly different between OBD2 and OBD1. The OBD2 fuel rail has both fuel lines attaching in the rear near the firewall and the fuel pressure regulator is located forward of the fuel filter under the driver side of the car. The OBD1 fuel rail has the supply line on the front of the rail and the return line on the back of the rail near the fire wall. In addition, the OBD1 fuel pressure regulator is on the fuel rail itself next to the return line. You must use the OBD1 fuel rail for the conversion, which will require modification to the fuel lines. You will need to remove the OBD2 fuel pressure regulator from the undercarriage of the car and route new 8mm fuel lines to the OBD1 fuel rail. There is a pair of hard lines mounted to the chassis between the OBD2 fuel filter and engine bay. Simply bridge the gap left by the removal of the OBD2 fuel pressure regulator with new fuel line and connect the feed from the fuel filter to the front of the OBD1 fuel rail and the return line from the back of the fuel rail to the return line under the car. You will also need to connect the OBD1 fuel pressure regulator vacuum line to the one-way valve on the bottom of the OBD1 intake manifold. The connection is on the back corner of the manifold closest to the firewall.
The OBD2 crank case vent is setup up differently than the OBD1 vent. There are several options to address this issue. If you are using the OBD2 valve cover, you can keep your OBD2 PCV setup and figure out a way to mount the breather valve (cone shaped plastic valve with round breather on top) under the intake manifold. If you are using the OBD1 valve cover, you should use the OBD1 breather valve that clips on to the crankcase vent port. The OBD1 valve has a vacuum line that connects to the plug that joins the ICV to the intake manifold and a large oil drain line that runs to the dipstick. The last option is a hook up a hose to the crankcase vent and run a breather catch can. I picked up a small length of 1” rubber hose and connected it to my OBD2 valve cover and hooked up the other end to the OBD1 breather valve and use a barbed connector to join the oil drain line to my dipstick.
Idle Control ValveEdit
The OBD1 and OBD2 ICVs are the same. You can reuse your OBD2 ICV. You will need to get the connector and hose for the ICV to intake manifold connection and the hose that connects the ICV to the throttle boot vacuum port.
Fuel Tank BreatherEdit
You can reuse your OBD2 fuel tank breather valve. You will need to get a couple fittings to connect the vacuum hose to the vacuum port on the throttle boot. I went to the hardware store and picked up 3/8” and 5/8” barb fittings and rigged something up to connect to the throttle body vacuum port.
Oxygen Sensors and Secondary Air PumpEdit
Only OBD2 systems have secondary air pumps. This emission control system is completely removed during the conversion. In addition, you get rid of your two precat OBD2 O2 sensors in the OBD2 exhaust headers and the two postcat OBD2 O2 sensors in the catalytic convertor so do not forget to get plugs for the ports. You’ll need an M18 bolt for the plugs. Any auto parts store should have them. FYI, the Toyota LandCruiser oil pan drain bolt is M18. OBD1 management only uses one precat OBD1 oxygen sensor.
Oil Pan & DipstickEdit
I kept hearing you needed an OBD1 oil pan and dipstick for the conversion. This is entirely false. You can use your OBD2 oil pan and dipstick without any issues or modification.
There is a lot of variability in which E36s have it and which ones do not. I used an ECU from a non-EWS vehicle but I still had some ignition issues after the conversion. There is an easy modification to the main engine harness to avoid any issues with EWS. You have to take the protective rubber boot off the connector to the ECU and cut wire #66. It should be solid green but it can also be black/violet according to the Bentley wiring diagrams. Just cut the wire and dress both ends with some electrical tape.
Note: There is no need to cut the EWS wire in an e30 conversion. This applies only to the e36 chassis where the OBDI converted motor may be installed in a chassis with EWS.
Power Distribution and GroundingEdit
Make sure you take pictures or label where the power and ground connections terminate. *ALL OF THIS SHOULD BE DONE WITH THE NEGATIVE BATTERY POST DISCONNECTED*. The OBD2 main battery positive post is located on the passenger side near the ECU compartment. The OBD2 distribution box is mounted parallel to the fender with two M10 bolts. You will need to move this distribution box slightly to reach the power connections on the OBD1 harness. The removal of the secondary air pump will review two screw holes that will allow you to reuse the M10 bolts and relocate the distribution box more towards the motor and parallel to the firewall. It is a very tight fit but it will reach. You will need to do this to reach the main power feed to the OBD1 harness. There will be on ground connection under the OBD diagnostics port. Make sure you check which wires you are connecting to the power distribution and which ones you are grounding. Power feeds are RED and grounds are BROWN or BLACK. Make sure you peel back the wiring sheath and double-check if you are not sure. There will also be one large power feed going to the starter and one small power feed going to the fuse box. The only other ground I can recall is the small wire (with round terminal connector) coming off the sparkplug rail, which needs to be grounded to the bolt securing the engine hoist loop on the Vanos unit.
I cannot stress this enough…LABEL THE CONNECTORS prior to attempting to install the harness in your car. Use the Bentley wiring schematics and make sure you check each plug off the harness and label it with painters tape and a marker so it’s easy to see what it should plug into. It’s a jumbled mess and all the connectors start to look the same when you toss the harness into the engine bay. The good thing is the wire lengths are fairly practical and the connectors are in the general vicinities of where they should plug into. I would also suggest taking pictures of any power and ground connections as you are disassembling your OBD2 wiring. Also, make sure you take a picture of the starter wiring connections to avoid problems later…it’s amazing how much confusion 4 wires can cause.
The Finished ProductEdit