
Originally Posted by
Jon K
The stock ecu uses a MAF, which understands air flow but not air pressure. The MS ecu uses a MAP, which understands air pressure... The stock ecu will operate with boost etc, many people have a chip burned for their setup. However, i wasn't talking about hte stock ECU not working under boost, but what happens is, your car monitors the O2 sensor and add/subtracts fuel to make sure the output is stoichiometric, or close. So if you have MS adding fuel to the engine and stock ECU doing fuel as well, the stock ecu will see a rich condition and subtract fuel, which is going to really throw off the MS unit since it is adding fuel and the stock is subtracting and the AFR is going up and down at similar times.
Also - the stock ECU adapts... meaning, at full throttle it runs from a pre-programmed fuel map but sometimes in part throttle it runs off of AFR-target, sort of. So, gradually, over miles, it will trim or add fuel by instinct and with MS doing its thing, it will get real confused.
Also - something you probably have not though of yet - you can't just hook MS into stock injectors. You would need to add injectors... but since the motors are direct port injection... you'd either need to add 6 additional injectors, one to each port (good luck) or do throttle body injection which is really a step backwards in technology.
Finally- just because you use MS does not mean you're running a "standalone". You can run MS for JUST timing, JUST fuel, or time AND fuel. So, you can literally got the wires from the stock ECU to the injectors, and splice them into the megasquirt. Stock ecu won't even know they're missing, it will send signals over dead wires. Meanwhile, MS is triggering your injectors and you are ready to go. If you're running 10psi I hope you have 30# or larger injectors.