In my intro I post the mods done to the wagon which include a MegaSquirt install. I'm going to try to explain the build and install process as I did it. Disclaimer-- MegaSquirt is a DIY standalone ECU which will run anything from a 1 cylinder 2 stroke to a V16 WW2 airplane motor. I spent about 6 months of reading through the manuals until the little light came on and I was grasping most of what goes on hardware and software wise. Myself included thought EFI was some black magic that very few new much about, but wth a little reading and an open mind it will all come together and make since. Ideal Gas Law... Before you can inject any amount of fuel into an engine you need to know the mass of the air being pulled into the engine. With Ideal Gas Law you can calculate the mass by knowing the temperature (IAT), pressure (MAP), and volume (engine displacement in CID). With these three variables you can figure the density and there for the mass of air inside your engine. You now see where the term Speed-Density comes from in most mid 80's EFI systems. Not until the late 80's and early 90's did Mass airflow become the way to measure the air entering your motor. Knowing 14.7 to 1 is the mass relationship most shoot for between air and fuel you can inject fuel based on the mass of the air. Working the math backwards you can determine the manifold pressure from the mass, temp and volume. This way there is no need to run a MAP sensor but you can still calculate engine load for the ignition table or any other functions. For more info check out http://www.megamanual.com/v22manual/mfuel.htm and http://www.msextra.com/ Okay... got that out of the way. Now everyone is really confused. I started this project a little over 2 years ago after reading about a guy running 8 LS2 coils on a 67 mustang. He was also running both gas and propane, he could switch between the two at random while driving. I was more interested in the LS2 coil idea. I was running the common MSD set up since 1999 and thought that was the best there is. The design is only 30+ years old right..!? My engine has been using the LS2 coils now since Aug of 08. The LS series coils have slightly different pin arrangements but the functions are all the same. 4 wire run to each coil, 12 volt, TTL, ECU ground, and chassis ground. The LS1-7 coils all use the same TTL(timed trigger logic) which is a 5 volt signal from the ECU to controll the charging and discharging times. Each coil will pull up to 11 amps on the 12 volt line during charge up but the TTL only draws 35ma which is easily handled by the on board transistors. http://www.megamanual.com/seq/coils.htm#ls2 Since the ECU only has 4 spark out puts I had to run the TTL in a waste spark format. All SBFord will have holes 1 and 6, 5 and 3, 4 and 7, 2 and 8 at top dead at the same time. When Spark A fires holes 1 and 6 one of the two will be on the power stroke. The OEM's where running waste spark in the early 90's to the early 2000's. Fords EDIS and GM's DIS are all over the junk yards. The only issue is the coils need a high amp driver to charge and discharge them. MegaSquirt can drive the coil drivers the same way as the TTL on the LS coils. When the line goes high (5 volts) the driver shorts the coil to ground which charges the coil, when the line goes low(less then 1 volt) then driver turns off and the coil discharges out the secondary windings to the spark plug. Same as an old points system minus the points. How the ECU knows when to begin charging the coils...? On the crank pulley there is a 20-1 wheel tack welded in place. A VR sensor has hundreds of winding on very fine wire wrapped around a magnetic core. When a metal object approaches the sensor the magnetic field bends which creates a small amount of + volts. As the metal object passes the magnetic field bends the other direction and creates a small amount of- volts. This becomes you AC signal sent to the ECU. The circuitry in side the ECU converts the AC signal which can vary from .5 volts at low rpm to nearly 50 volts at 6K rpm into a digital 5 volt on, off. The code written to the processor will look for the raising or falling edge to determine the position of the crank during rotation. The missing tooth is needed to signal the beginning of a new crank rotation. In my chase every 18* a tooth should come by the VR senser. The time between the teeth is measured to determine RPM. When the time between teeth doubles the code then knows where in the cycle the crank is by the missing tooth. Everything starts over, every 90* is a spark. A,B,C,D.. In my case every 5 teeth is a spark out put. The teeth do not begin or end a charge or discharge time but only give the processor an idea where in the cycle the cranks is at. There has been tests using a 60-2 wheel up to 16K rpm with out and sync loss. I'll do up the TBI portion tomorrow. Later Ryan
okay here you go. Some pics are with the carb still on but you can see how things are arranged. Two pics are of the glove box and how the MS ECU is set in there. The more messy one is with both the power and fuel pump relay one on top of the other. MSbox.jpg relays.jpg The beginnings of the TBI idea with the holes cut out of an aluminum plate to adapt the TBI bolt pattern to the dual quad intake. DualTBI.JPG Showing the IAT with it just mounted from under the aircleaner base. IACair.jpg The finished product with the dual TBI installed. TBIclose.jpg Hope this is enough, this is about all I have for pics. I ran out of time before getting back on the plane. Later Ryan
I'm running the MS2 with the 3.0V PCB. I posted a reply this morning with 5 pic, a window pooped up saying it need approval from the admin. Any idea where it may have gone, what has to be done to approve it?
Glad you are still interested. I've explained this in the past to some guys at car shows and they get discouraged at the idea in the first 2 minutes. When using GM's TBI you should be aware of the style and type of injectors used in there systems. The injectors are considered low impedance, when measure across both leads with an ohms tester any reading below 8 ohms is a low impedance injector. Anything above 10 is a high impedance. Using ohms law and also solving for watts you can calculate the flow of current through the injector and the total power consumed to operate the injector. The injector drivers inside the ECU can source up to 14 amps each worth of current to ground. Up to 8 high impedance injectors per channel and no more than 4 with low impedance injectors. Taking volts/ohms=current So a 12 ohm injector will draw 1.1 amps at 14 volts which is only 15.5 watts. Very low power draw for the amount of work being done. Most OEM injectors fall somewhere around this example. GM's TBI's on the other hand do not. These injectors have an internal resistance of only 1.2 ohms. If you apply 14 volts the injector will draw 11 amps to operate which is 160 watts per injector! The injector needs to have a quick opening time around 1ms which requires the full 11 amps at start, but after the injector turns on 1.5 current draw is enough to keep the pintal of the injector pulled off it's seat. One method is PWM (pulse width modulation). One the initial 14 volts hit the injector we can reduce the current through the injector by pulsing the swithing line very quickly off and on. A 50% duty cycle would have equal on and off times while 75% would have on for 75% and off for 25%. This reduces the current through the injector which keeps it cooler and makes it last longer. This type of injector may last only a few minutes with out PWM or other meens to reduce the current draw. PWM.gif The second and very common method is to install power resistors in line with each injector. By placing an 8 ohm 25watt resistor inbetween the power source and the injector you are basically creating a high impedance injector. 1.2 ohms + 8 ohms = 9.2 ohms. 14 volts/9.2 = 1.5 amps. 14 times 1.5 = 21 watts. A 25 watt resistor is just large enough to handle the current draw of the whole system. GM has ran power resistor packs with all TBI's. http://www.megamanual.com/v22manual/minj.htm Some may wounder how the injector will even work with such a reduction in current flow. If you ever lived in a house with really low water pressure when you crack the knob you get a short burst of flow then the slow trickle of water. The short burst of flow(current) is what pulls the pintel off the seat and the low flow is enough to keep it open. For those realy getting interested in how electricity works, the math involved is the same as water flow numbers. You can duplicate volume and flow of your local citys water system using volts(pump/pressure) and resistor(flow/current). The math for determining parallel and series resistor was first used in calculating water flow before electricity came into it own.
