The Great EFI Debate - Page 7 - Vintage Mustang Forums
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post #91 of 193 (permalink) Old 02-01-2018, 08:35 AM
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Originally Posted by Viperpete View Post
With Megasquirt all you need is a trigger wheel bolted to the crank pulley set 7 teeth from the gap and cylinder 1 at TDC, and a vacuum line to the ECU to run. Wasted spark is easy- it batch fires. The Megasquirt unit is very small. Maybe 6" long, 3 inches wide and 2 inches tall. Wiring is very simple and there is no clutter. You can even mount the ecu under your dash or wherever you want it .
Hi, i have fitted lots of aftermarket ECU systems, like Motec, Emerald, DTA, Omex Etc so sort of have a idea on how they install.

I was referring to the Holley Terminator set up that has a ECU bigger than the throttle body ! and a very big loom to try and hide. Where Fi Tec has the ECU built into the body.

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post #92 of 193 (permalink) Old 02-01-2018, 08:45 AM
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Yeah at the time Microsquirt didn't even exist. Microsquirt does look like a cool option though.
If the plan is batch fire and wasted spark then Microsquirt is the only option that makes sense. It saves some cash, provides all the functionality you need and is in a very small form factor. My ECU sits between the console and firewall, completely hidden and not in the engine bay. Works as advertised.

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post #93 of 193 (permalink) Old 02-01-2018, 09:24 AM
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Originally Posted by Viperpete View Post
With Megasquirt all you need is a trigger wheel bolted to the crank pulley set 7 teeth from the gap and cylinder 1 at TDC, and a vacuum line to the ECU to run. Wasted spark is easy- it batch fires. The Megasquirt unit is very small. Maybe 6" long, 3 inches wide and 2 inches tall. Wiring is very simple and there is no clutter. You can even mount the ecu under your dash or wherever you want it .
How does the ECU adjust for air density (hot/cold)? In fact how do any of these systems adjust for that -when I look at the pictures posted of these EFIs it is just the throttle body. 2-3k seems like a lot for CFI/speed density systems that use a map to determine fuel needs. In my under-educated opinion speed density doesn't get you much more than a carb. Its just using electronics to deliver a set amount of fuel whereas a carb is using mechanical components.

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post #94 of 193 (permalink) Old 02-01-2018, 11:22 AM
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How does the ECU adjust for air density (hot/cold)? In fact how do any of these systems adjust for that -when I look at the pictures posted of these EFIs it is just the throttle body. 2-3k seems like a lot for CFI/speed density systems that use a map to determine fuel needs. In my under-educated opinion speed density doesn't get you much more than a carb. Its just using electronics to deliver a set amount of fuel whereas a carb is using mechanical components.

david
All these TBI based systems use a wideband O2 so they're measuring what comes out of the tail pipe. If the fuel map is off they adjust based off the O2. So whatever fuel target you have for that throttle position/load is going to be what comes out of the tail pipe.

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post #95 of 193 (permalink) Old 02-01-2018, 11:31 AM
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Originally Posted by Moodster View Post
How does the ECU adjust for air density (hot/cold)? In fact how do any of these systems adjust for that -when I look at the pictures posted of these EFIs it is just the throttle body. 2-3k seems like a lot for CFI/speed density systems that use a map to determine fuel needs. In my under-educated opinion speed density doesn't get you much more than a carb. Its just using electronics to deliver a set amount of fuel whereas a carb is using mechanical components.

david
You are correct. They don't really adjust for density, they just maintain a set afr via a programmed map that learns. Some get kinda pricey, but I think many systems can be done for under 1500. I know my FiTech setup cost about that when it was all said and done (not a Mustang). What it does do better than a carb is allow on the fly adjustments without taking anything apart. I can go driving down the road and adjust whatever parameter until it's working like I want. I have a box of Holley jets, some air bleeds, accelerator cams, extra gaskets, etc, but sitting in the driver seat changing a setting and a push of a button does all that on the EFI unit. I know, I can get a carb tuned to do all the stuff it's supposed to do, for me the biggest plus is the fact I can let the EFI setup sit for more than 3 months. If I do that with my carb stuff it means taking the bowls off and cleaning all the white powdered gook out of the passages, gas is pretty crappy nowadays. (if I had something with an autolite 2 or 4 barrel I'd leave it, those seem to be able to sit for years and all you really have to do is put some gas in them and they are usually good to go)

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post #96 of 193 (permalink) Old 02-01-2018, 11:39 AM
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What it does do better than a carb is allow on the fly adjustments without taking anything apart.
Don't forget they're also electric fan controllers, nitrous controllers and A/C controllers. I bought the power adder version of the FiTech so I'd have idle correction for A/C, I also added an electric fan just for when the car needs a little extra help and the FiTech handles that too.

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post #97 of 193 (permalink) Old 02-01-2018, 02:28 PM
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You are correct. They don't really adjust for density, they just maintain a set afr via a programmed map that learns.
This is not correct. There are three basic EFI fueling strategies: mass air, speed density, alpha-n. All of them try to identify the mass of air entering the engine and then look at AFR target maps to compute fuel.

Mass air quite literally measures the mass of air coming into the engine and fuels based on that. Most if not all modern OEM EFI use this strategy. Some of the aftermarket (MS3 pro) can use this as well.

Speed density takes engine speed and volume (the speed), and calculates air density based on cylinder and intake temperature and manifold pressure to figure out the mass of air entering the engine using the ideal gas law. This is what all of the TBI systems I've seen use.

Alpha-n takes the TPS position (alpha) and RPM (n) and uses a pure lookup table to compute required fuel. Generally race car stuff here. Pretty much awful on the street. Good for WOT though. This is pretty much a computer controlled version of the old mechanical Hillborn or Bosch CIS injection and modern aircraft piston fuel injection.

The general fueling equation for all of these looks something like: fuel mass = computed air mass * 14.7 * correction factors.

Correction factors being o2 sensor, target afr adjustment table, required fuel table, accel enrich, decel cutout, etc depending on what sensors are available and how the ECU is programmed.

The megasquirt manual has the exact equations and strategies it uses if you're interested: How MegaSquirt(R) EFI Controllers Work . Most of the other aftermarket ECUs I've worked with have similar strategies.
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post #98 of 193 (permalink) Old 02-01-2018, 02:41 PM
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Speed density takes engine speed and volume (the speed), and calculates air density based on cylinder and intake temperature and manifold pressure to figure out the mass of air entering the engine using the ideal gas law. This is what all of the TBI systems I've seen use.
How do the systems get cylinder and intake temperatures? I'm unaware of temperature sensors that go in the cylinders or the intake ports. I've seen the manifold pressure sensors you're talking about.

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post #99 of 193 (permalink) Old 02-01-2018, 02:47 PM
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How do the systems get cylinder and intake temperatures? I'm unaware of temperature sensors that go in the cylinders or the intake ports. I've seen the manifold pressure sensors you're talking about.

david
Intake temp is computed directly using the Intake Air Temp sensor (IAT). Cylinder temp is inferred based on coolant temp (CLT).

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post #100 of 193 (permalink) Old 02-01-2018, 08:30 PM
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The Holley sniper uses coolant temp, wideband 02, coil trigger and a map sensor. There are also quite a few outputs. I just looked through mine (which is in the classic gold zinc chromate look) and it can control nitrous, fans, coil drivers, A/C outputs and I believe there is an additional output that could be for water meth or some other add on.

I plan to keep my writing to a minimal. fortunately on this, other than the pre terminated connectors for oxygen sensor, plug in controller and coolant sensor, there are four wires to hook up to make it work. + and - to the battery, a coil source and a key on/cranking power source. It has its own relay for an electric fuel pump and enough wire to run back to the tank.

I'll be using mine with a relay for A/C idle speed changes and of course to turn on a relay for an electric fan.

I've watched two locally (one on a 302 in a falcon and one on a small block chevy) run and they are fantastic!
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post #101 of 193 (permalink) Old 02-02-2018, 09:28 AM
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Yeah I forgot to mention that the Megasquirt needs an Air Intake temp sensor, throttle position sensor, Coolant, temp sensor, MAP sensor, Wideband o2 sensor, trigger wheel and Crank position sensor and vacuum to function correctly. Really all the basic stuff. Even the old MS II that I had could control the electric fans and AC, fuel pumps and all that- even nitrous. The new systems are really modern.

I ran my car without an idle air control valve and ran a little rough for a minute or two but I tuned most of that out until it warmed up.

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post #102 of 193 (permalink) Old 02-04-2018, 06:51 AM
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The FITech System is just under $1000. It claims it's a plug and play install. Anything else needed that drives up the cost?
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post #103 of 193 (permalink) Old 02-04-2018, 11:30 AM
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The FITech System is just under $1000. It claims it's a plug and play install. Anything else needed that drives up the cost?
Fuel system which can run $500-1500 depending upon what you buy.

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post #104 of 193 (permalink) Old 02-04-2018, 12:52 PM
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Who is running their fan off the sniper/fitech? I know the sniper can switch a relay.. based on temp.

Had a bit of a debate with my father about it last night. He figures the temp source for the fan should be at the rad outlet side.. Whereas I am of the belief that all the OEM's put the sensor in the head/intake manifold water passages.
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post #105 of 193 (permalink) Old 02-04-2018, 12:58 PM
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Who is running their fan off the sniper/fitech? I know the sniper can switch a relay.. based on temp.

Had a bit of a debate with my father about it last night. He figures the temp source for the fan should be at the rad outlet side.. Whereas I am of the belief that all the OEM's put the sensor in the head/intake manifold water passages.
Not radiator side. Coolant temp sensor on every fuel injected car i've ever seen anyway. A thermostatic sensor can turn on electric fans though regardless.

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