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 (Jeff Nelson @ Feb 2 2006, 07:56 AM)

James, thanks for your reply. As I've already got a bunch of green injectors I'll start with those. The L-jet connector seems the hot tip however. I know that Ray Greenwood (ShopTalk forums) has mentioned the superior connector. The existance of the high-res code went right over my head. I do see that you sacrifice PWM drive of the injectors using it. I plan to eventually do spark control with MSnS-E and I assume that high-res doesn't exist in that code version. I plan on using a manifold pressure referenced FPR and the one by MSD or a DIY equivalent looks attractive. The Summit page states that the pressure range is 36-45 psi. That would seem incompatable with D-jet injectors (29 psi). As manifold pressure is already an input, the installation of a fuel pressure sensor tied into MS and some code to support it would seem to accomplish the same thing as a manifold pressure referenced FPR. Perhaps the processor overhead is too much or it's considered overkill when the appropriate FPRs exist. Then again there are some things that are just better done in a continuous (non-digital) fashion.

On the manifold pressure...

It's not that MS can't compensate for manifold pressure differences, it can. The difficulty lies in physical limitations of the injectors themselves. Injectors, being mechanical devices, aren't all that fast. They take approximately 1.7ms to fully open and fully close, minimum. During that time, some amount of fuel flows as the injector is opening, and as it's closing, but the amount varies somewhat from cycle to cycle, so running the injector right down to its minimum time results in fairly inconsistent fueling. Worse, with the default MS code, the minimum step you can use to adjust injector pulsewidth is 0.1ms. So, you can set it to 1.7 or 1.8, but not 1.75. Ben (airsix) is running his smaller-than-1.7-injectors at 1.85ms at idle on his 1.7 (he's not running MS, so he has better resolution), so roughly 1.8-1.9ms is the rough idle range for a Type IV with stock fuel pressure, and the difference between 1.9 and 1.8ms is 5.5%, so that's the minimum step size you can use to tune idle with with a 0.1ms resolution. If you're running, say, 3% lean, you have to bump it up nearly 6%, and run 3% rich. No option.

A manifold referenced FPR raises the pulsewidths you can use with a given injector, by lowering the pressure across the injector at idle, so the resolution becomes less of an issue. If the idle pulsewidth goes from 1.8 to 3.0ms, then a 0.1ms step size drops from 5.5% to 3.3% per step (I'm just making these numbers up, btw). You're also less subject to the inconsistent fuelling caused by running the injector so close to it's lower limit.

With the 2.0 injectors, you at least don't have any problems at the top end, as you're generally not going to run them anywhere near the 80% duty cycle limit, even without a manifold referenced FPR. Dave Hunt's experience with using the 2.0 injectors shows that you can get a good running car w/o the FPR, but he also says he's gotten smoother running at idle with the HiRes code, showing that you'd see SOME gains with using one.

On thermal stuff, the BOARD and all of the non-processor parts can do 125dC. The HC08 processor, however, is still a 70dC part (maybe an 85dC part). This is a big difference with MSII, which is using a 125dC version of the HC12. Put the MSII daughterboard on the v3 main board and you have a 125dC ECU. Myself, I'd rather use the Microsquirt board than the v3/MSII combo, simply because it's then all surface mount with a vastly lower parts count, so vibration resistance and general mechanical reliabilty should be much improved.