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]

You can modify the stock D-Jet FPR to reference it to manifold pressure yourself. Search here for posts by airsix, he covered it in detail. It's pretty simple, basically just drilling a hole and fitting a small tube with epoxy will do. If you don't have a stock FPR, you can pick them up on Ebay pretty cheap. I may even have a couple lying around in the parts bin. I'd send you one for shipping if you're game to try the conversion yourself.

On EMF, I was planning on running the ground connections from the DB connector to a bolt through the outer case, then one big ground wire from that bolt to a case bolt. Another connection from the inner (metal) case to the bolt will ground the case, and allow me to run a lot fewer wires through the outer case connector. If I put the whole mess in the stock ECU case (which is sounding more and more attractive every day), I'll not have an inner and outer box, just the metal ECU case, but I'll still do the ground bolt trick. I'll also make a plate to cover the stock connector hole and run my waterproof bulkhead connectors there. One for EFI signals, one for serial signals (with a cap for when the serial cable isn't connected).

Josh, you want a manifold referenced FPR to keep the fuel pressure differential across the injector the same. If the rail pressure is fixed, then the pressure differential across the injector goes UP as manifold pressure goes DOWN. Manifold pressure is low at low loads, and high at high loads, so the pressure differential across the injector is high at low loads and low at high loads, which is the opposite of what you want. You have to compensate for this by making the difference in pulsewidths wider, but you can hit physical limits at either end. The injector cannot open and close in less than ~1.7ms, so if you need t make it shorter than that to compensate for the high pressure differential at idle, you can't get the idle to be lean enough. Injectors also can't be open longer than 80% of the time without overheating, so you may not be able to make the pulsewidths long enough at high loads to overcome the lack of pressure drop across the injector with 1.0atm in the manifold.

With a manifold referenced FPR, however, the differential across the injector is fixed regardless of manifold pressure, so you end up with longer required pulsewidths at the low end, and shorter required pulsewidths at the high end, for the same fuel flow through the injector. Thus, you can run smaller injectors than you might be able to otherwise, and thus get more tuning flexibility at the extremes.