Megasquirt Progress, Main Board complete Options

[yarin]

Tonight I have completed building the main board for my MS II V.3.0 system. Thanks to those that have helped out. Once i'm all finished I will definitely post a complete "How To MegaSquirt a 914" website with pics and step by step. So far i'm still at the desk level. I've got 2.0 injection parts on the way.

I'll be using the following:

stock injectors
GM air temp sensor
stock fuel pump
summit racing manifold referenced fuel pressure regulator
stock injectors (i think 2.0s are on the way)
stock plenum / runners
stock CHT
MS Relay Board
Innovative WB02
High Current ignition driver
Stock dizzy with pertronix (hall sensor)
Stock Bosch Blue Coil
PWM Low impedence injector driver (no resistors)
Stock Cold start Valve (plan so far)
Stock throttle body with some junkyard TPS

Here is a pic of my board, took me a few hours a night every night this week. I took my time, double checked everything. So far so good!

I don't expect to have the system in the car for at least another month. I'm converting from carbs so I want to install steel fuel lines and clean some stuff up.

I'll be sure to post progress in the forums. (IMG:http://www.914world.com/bbs2/html/emoticons/smilie_pokal.gif)

[lapuwali]

QUOTE (yarin @ Feb 1 2006, 01:22 PM)

Since 2.0 injectors are rather large I was under the impression that I would run into minimum pulse width limitations at idle, therefore lowering the fuel pressure at idle would help. Correct? Or would PWM take care of those issues?

PWM is there to limit current through low-impedance injectors (and the D-Jet injectors are low-impendence).

Basically, since current = voltage/resistance (so Mr. Ohm said), if you lower the resistance, and the voltage stays the same, the current increases. For our purposes, impendence = resistance, so low-resistance injectors will allow too much current to flow through them (overheating them) unless you provide some way to limit the current. L-Jet uses external ballast resistors to do this. MS gives you the option of using external resistors, or using PWM to limit the current. PWM works using a "peak and hold" strategy. It delivers a full 12v at first to get the injector to pop open, then it starts to switch the voltage on and off rapidly (too fast for the injector to react), and the duty cycle of the switching lowers the average voltage seen on the circuit. Lower the voltage, with fixed resistance, and you lower the current. D-Jet does this, too, but it can actually lower the voltage directly, since it's an all analog ECU. It doesn't have to resort to digital tricks like PWM.

Using peak and hold instead of just limting the current with external resistors means you get faster response times from the injector (particularly in opening), so, again, you gain a bit in injector dynamic range at the idle end of the spectrum. L-jet just copes with slower response times for a simpler circuit, and L-Jet can't handle large injectors easily, as a result. L-Jet is famous for leaning out on top, as a result, as it must use pretty small injectors to idle well, and that's where all emissions testing is done.