The Honda VTEC system was designed in the mid-80’s, as way to maximize both fuel efficiency and power. It uses two distinct cam profiles, one for low rpm efficiency, and the other for high rpm power.
When you’re just cruising around, the low rpm profile opens and closes the valves in a highly efficient manner. Once the revs reach 5000-6000 rpm (on average), the ECU activates a solenoid which uses highly pressurized oil to move a pin that locks the high and low rpm cam followers together. The high side cam followers respond to the more aggressive lobes on the camshaft. This cam profile holds the intake and exhaust valves open longer, which allows more fuel and air into the engine, creating significantly more power.
In order for this ingenious system to work, the ECU / VTEC controller, constantly monitors the engine temperature, oil pressure, RPMs, vehicle speed and throttle position. Using this data, the computer can determine the ideal time to activate that solenoid and switch the cam profile. Obviously, the ECU is a critical part of this Variable Valve Timing and Lift Electronic Control. And that’s why it’s so important to get the wiring correct when you’re installing a VTEC motor into a non-VTEC car.
For our example, we’ve installed an OBD 1 B16A motor into a 1995 Honda Civic CX. We’ve elected to connect the VTEC components to the ECU through the wiring harness, via the canon plug on the passenger side of the firewall. You can bypass this plug and run the wires directly through the firewall to the ECU plug. But that’s going to yield a rather messy installation.
First of all, don’t try to run the stock ECU with an RPM switch to activate the VTEC system. The ECU adjusts many parameters when the cam switches over, and you won’t get any of those precision adjustments if you just hotwire the solenoid to a switch. If your VTEC engine didn’t come with an ECU, go to your local junkyard and buy one (a “P28”). On the ECU barcode sticker, if you see the sequence A02, then that ECU is designed for a car with a manual transmission. Controllers marked A05 and up were designed to work with an automatic transmission. Double check to make sure that you have the right ECU for your type of transmission.
You’re also going to need several extra plug pins for cannon plugs, and the ECU plugs. They typically come in small, medium, and large. Since you’re going to need each of the different sizes, go to one of those pick-a-part salvage yards and remove several of the pins with the wire still attached.
For the ECU plug, pry back the protective cover at the base of the wires, then use a small, sturdy tool to push the pins through from the face of the plug.
When you’re splicing wires together, make sure that you do it right. Twisting two wires together, then covering the joint with tape, is just a short waiting to happen. If you can’t solder the wires together, then at least use a good male/female plug like these.
Under The Hood
First, you’re going need to connect the VTEC solenoid and VTEC oil pressure switch to the ECU inside the car. To do this, connect a new length of wire (BLU/BLK and GRN/YEL - with canon pins on the ends) to the VTEC hardware.
Then run it to the canon plug by the shock tower.
One of the two wires on the VTEC oil pressure switch is the ground (usually black), and you can secure it to an unpainted spot on the chassis. If you’re using a VTEC harness, then you can just plug the wires in. Otherwise, plug the VTEC wires into empty slots on the canon plug.
Using the pins and wiring that you procured from the junkyard, match the VTEC canon pins and wiring to the other side of the plug. Then feed the wiring through the firewall. Inside the car, splice the wires to their corresponding ECU pins, then insert them into the correct slot on the ECU plug. You’ll of course, need to download a wiring/plug diagram for the ECU that you plan to use.
EDITORS NOTE: We suggest you read Honda Civic/Prelude & Acura Integra OBD1 ECU Pin Schematics.
After triple-checking all of the connections, fire up the engine and let it come up to operating temperature. If no error codes trip the CEL light, take that baby for a spin and watch that VTEC kick in!