Wiring Megasquirt into your 1st gen Probe/MX6 Turbo
I have decided that the average person is not going to want to make an entire new engine wiring harness, as this is unnecessary for the average user. We can accomplish what we want with the factory harness. With this said, I will show how to make a “plug-n-play” harness. Not only does this make installation easier, but also allows you to return the car to “stock” fairly easily if the need arises.
To wire megasquirt into your car, you will need the following items:
-Turbo Distributor (if you don’t want to destroy your original)
-ECU (same as above)
-GM coolant temp sensor, with connector (either new or junkyard)
-GM OPEN element IAT sensor, with connector (either new or used)
-N/A thermostat housing (one with 2 sensor bungs)
-Wideband O2 Sensor and controller (for tuning)
-Wire
-Various wire connectors
-Heatshrink
-Electrical tape
Modifying the turbo distributor.
NOTE: This is currently for the 88-89 ONLY!! 90-92 WILL be posted soon!!!!
For Megasquirt, we need a RPM input. The simplist way to achive this input on the turbo engine, is using the factory VR sensor and trigger wheel. BUT, in order to do this, we must modify the factory 24-tooth wheel so the VR sensor can provide the signal in terms that Megasquirt can reconize. Since RPM is based on the rotations of the crankshaft, and the pick-up wheel is located in the distributor where the camshaft turns at half the speed of the crank, we must set up the distributor in a way to "trick" the MS in to thinking we are triggering off the crank. We can achive this by removing two teeth from the factory pick-up wheel in the distributor. This spits the wheel in half, giving us a 12-1 wheel (11 teeth, one missing). This allows us to split the cam cycle into two seperate cycles to match the crankshaft. The first tooth starts the ignition pick-up cycle, and the missing tooth signals for the megasquirt to "start over" the ignition event.
To start the modifications, remove the cap, rotor, and protective cap.
Remove the two sensors on top by first removing the 4 phillips screws (2 per sensor). Then cut the wires attached to the sensor and discard them.
You should now have this:
Next, remove the “spacer plate” retaining screws. Lift out the plate and discard.
Next, remove pin from drive “gear” on the cam side of the distributor. You can use a hammer and punch. Using a sharpie or equivalent, make a spot on the “gear” and the shaft, this way you can re0assemble them back together correctly.
Inside the distributor, remove the two phillips screws at the bottom. This holds in the center shaft. Once removed, you should be able to easily remove the distributor shaft.
We can now modify the distributor to work with megasquirt. We want to modify the bottom wheel, not the top. You want to grind down two of the “teeth”. Looking at the top wheel, at the point, count back four teeth. We want to remove the forth tooth. Mark this tooth.
We also want to remove the tooth directly opposite of this one. Count 12 teeth (in either direction). Make the 12th tooth. Make this tooth, as we want to remove this one as well. You should have 11 teeth between the two marked teeth on both directions.
Now, grind down the two teeth. You can use a Dremal tool, a drill with a grinding/cutting bit, air tool, etc. TAKE YOUR TIME! Go slow and take off a little at a time. We are working in a small space with very little material, and you DO NOT want to damage the surrounding teeth. If you happen to “nudge” one, its no big deal, just try to avoid them as much as possible.
This is what you want:
Once this is complete, clean the distributor shaft of ALL metal shavings. Re-assemble the distributor shaft into the distributor housing. Install mounting screws. Reinstall the distributor drive gear and retaining pin. Be sure to line up the marks you made earlier.
Re-install the rotor and cap and your done!
[b]
Getting “pig-tail” connector from ECU[/B
NOTE: Shown in pics is a 1989 N/A ECU. Turbo ECU's will be simalar, only more stuff will have to be removed. Your goal is to get the factory connector.
Remove the top plate retaining screws.
Remove the ECU mount retaining screws (all four corners).
Remove the bottom plate retaining screws.
Go around the outside of the ECU and remove any remaining screws.
On the bottom of the ECU, remove the four screws retaining the circuit board.
Remove the board from the ECU case. Discard the case and all remnants.
Remove the two screws holding the connector to the board. These may be covered in solder, so use a pair of pliers to remove.
Remove all surrounding electrical components near the connector. This will give you access to cut the connector legs and remove the clip.
Before
After
Using some wire snips (smaller the better), start clipping the connector legs from the board. Start with the long ones first. As you cut, GENTLY bend them upwards so we can access the shorter ones.
After all the legs have been cut, GENTLY bend all the legs straight. Then, trim the longer legs to approximately the same length as the shorter ones.
You now have your connector ready to make a pigtail. Before we proceed, we want to mark the clip to aid us in making the pigtail.
Hold the connector with the
“legs” pointing towards you, and with the
“holes” facing up. Using a fine point sharpie, number the columns of legs from 1-26, starting from the left.
Next, mark the top of the connector (side with holes) “A”.
Mark the bottom “B”.
This will allow you to follow the wiring chart with ease. Examples: “2A” would be the “leg” in column 2, upper row of “legs”. “19B” would be in column 19, bottom row of “legs”.
