Engine Management
The original "management" system consisted of a VarajetII carb and vacuum-mechanical small-cap HEI distributor. It worked OK but was far from a Performance setup. When the first turbo went on, it had to go!
I aquired a junked-out Cavalier Z-24 which had the same engine as my car. It had a Rochester MPFI system with a long-runner intake and port fuel injectors. This system came with a metered-air fuel management system. It was OK for a boosted engine but it had some serious drawbacks. The airflow meter was cumbersome to plumb-in the air intake tract. Plus these turned out to be less than reliable.
When designing the new turbo system I intended to convert it to a speed-density system. After some research I learned a Delco 1226869 ECM was almost plug-and-play compatible with my original system. There were just a few wires in different places. Thanks to the local Pontiac dealer printing off a wiring diagram, and the generosity of the folks on the GMECM mailing list, I had an ECM and factory calibration file.
With no further adjustments, just plugging in the correct wiring, the engine strted and ran better than the old system. But there is another step to using this system with a boosted engine. It has to have a 2-bar MAP sensor to see the boost pressure. Using TunerCat, and a special definition file for this setup, I was easily able to configure the ECM to use the new sensor.
The ignition hardware had to be adapted to work with the turbo. The distributor is very close to the turbo and the heat would kill the module. It had to be extended and located in a safer location. The following pictures show this modification.
Eventually I plan on installing a DIS ignition, but my engine block does not have the mounting hole for the crank position sensor needed for a DIS unit. For the time being, I'm using a MSD 6AL power unit. It is triggered by the original HEI module under full ECM timing control. The stock inductive coil and module setup does not have the spark energy to maintain power at high RPM's because of the extra dense air charge in the combustion chambers. It takes a lot more ignition firepower to light off the highly compressed air/ fuel mixture in a forced-induction engine.
This ECM is supported by TunerCat's RT-Tuner. This allows the ECM calibration to be adjusted in real-time using a ROM emulator. The ignition map and fuel maps can all be tuned with the engine running and the changes take effect instantly. This is an incredible technology especially considering it works on a completely factory-stock ECM. If any engine management components fail on the road, I can get the replacements anywhere.
The key to making this different mix of factory, aftermarket, and home-made parts work together is mainly in the ECM calibration. When GM designs a car and engine setup, they calibrate the ECM parameters to make it do what they want it to do. When putting together an engine the factory never intended, a new calibration has to be developed. It's a time-consuming process but it is rewarding. With some tuning time the power of the ECM brings the strong points of all the parts of the engine into a real harmony.
How do you "tune" an ECM? Long story deserving of its own page!
In the above picture you can see the module mounted on its heatsink at the firewall. It is under the ledge out of the rain. The relay mounted on the right side of the heatsink is the ignition main relay. It provides a minimal-voltage-drop path directly to the battery positive stud. Partially visible in this picture is the 2-bar MAP sensor which allows the speed-density fuel system to operate.
In the above picture, you can see the pickup coil wires connecting to the extender cable. This cable is an industrial-grade high-temp sheilded twisted pair cable. The sheilding is grounded at the module to prevent interference that could cause false-triggering.
