SETUP AND TUNING: I've been tuning the car more and more, and it just keeps getting better and better. I know alot of you guys are carb guys, so here's an easy way of thinking of tuning EFI. Its no harder than carb tuning, but people seem to get freaked out about it. In order to get the car started, the computer needs to be synched to the distributor (if you are controlling the timing) and the base fuel settings need to be set. With megasquirt, all you need to know is pretty much how many cylinders you have, how many injectors you have along with their flow rate and the displacement of the engine. This will create a base fuel map that should be able to start the engine with some convincing.
Setting Engine Displacement (don't worry about every single field, there's alot you don't need to mess with)
Setting Required fuel:
Setting up for low vs high impedance injectors (easy to find out what you have, usually just googling the part # will tell you everything about them). My current limiting numbers will be different than yours, this is just to show what the screens look like and give a general overview. I am using 24# low impedance injectors, which are easy to burn out with the wrong settings. High impedance injectors seem to be more straightforward.
The TPS is then calibrated, which consists of hitting "get current" with your foot off the gas to set closed throttle, then hitting get current with your foot to the floor.
Next, the ignition must be synced if you are using MS to control timing. Different distributors use different settings, but these settings are for my MSD 6A with MSD pro billet ready to run distributor (uses white wire on MSD box, points style signal). MS can run an MSD distributor that uses a VR signal (purple and green wires) but these settings will be different.
The trigger wizard is used to match the timing light reading to the computer's output. The big white number on this screen is what you want the timing to be, so the trigger offset is simply moved up or down until the white number and the number on your balancer's timing tape match.
Once the car starts, the warmup enrichment will need to be adjusted. This is like an adjustable choke especially when an Idle Air Control valve is used to control airflow. The warmup enrichment window is pretty much a linear X-Y graph with temperature as the X and enrichment percent as the Y. You can move points on the line up and down to add or reduce the fuel to engine. Afterstart enrichment is also tunable, which will dump a certain amount of fuel into the engine right after it starts, for a set amount of cycles (ex 350 cycles, usually 10-15 seconds after start).
Tuning warmup enrichment:
Once the engine starts reliably, the VE table can be tuned. I made the mistake of leaving EGO (exhaust gas oxygen; 02 sensor) correction on, which automatically tuned VE as I drove. The car kept going super lean and backfiring. Turn this OFF before tuning VE.
VE is Volumetric efficiency, or a ratio between the air in the head and the air in the combustion chamber; more or less a measure of airflow throughout the engine's powerband. The VE table has RPM as the X axis and Manifold pressure as the Y. VE would be the Z axis, as each X and Y coordinate has a corresponding VE value.
In other words, at 2000 rpm when the manifold pressure is 100 kPa (~14.6 psia or atmospheric pressure. Wide open throttle in a naturally aspirated car) the VE value would be 105 % [< made up number]. As the VE increases, there is more air available; so more fuel needs to enter the engine. If the car doesnt run right the VE can be increased (more fuel) or decreased (less). Backfiring means to lean, and bogging under throttle input with a gas smell is rich.
VE can be tuned in real time, so someone can drive the car while you change the numbers. Have the person drive at constant throttle positions and match the wideband reading to the AFR table. There is a little dot that floats around the map as you drive that tells you where the engine is. If you don't trust anyone with your car, or just prefer to do it yourself; you can record a datalog with Tunerstudio and play it back with Megalogviewer. With megalogviewer, you can load the VE table and tune the car as you watch a datalog play back..
[more to come soon]
