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Old 05-25-2007, 06:58 AM   #1
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Megasquirt features

Does megasquirt have the ability to measure instant MPG or would I need to get a scangauge/supermid to compliment the Megasquirt? It would be nice to not have to spend another 200 dollars after putting that much into the Megasquirt system. I wouldn't mind having a laptop/pda in my car semi-permanently.

Also, what would scangauge/supermid use to measure my mileage? Is my odometer electronic? I think it is a cable that spins from the transmission. Would I need to install a sensor for the gauge?

Thanks for any advice or links you can give me!

Fourthbean
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Old 05-25-2007, 08:01 AM   #2
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Megasquirt does not take a Vss input, so out of the box, no it does not calculate mileage.

I'm planning on putting a Megasquirt into my CRX HF. To get it to calulate mileage will be a little work, but it can be done. The speedo in my CRX has a cable input and produces a square wave output that is fed into the stock ECU for Vss input. This square wave can be fed into an LM2917 frequency to voltge converter IC, (produces a 0-5V output proportional to speed). The output from this IC can be fed into one of the spare ADC inputs of the Megasquirt and the software modified to calculate mph, an odometer, and then from this, calculate mpg. It will be a bit of work, but that is what I'm going to try. I will then have a PDA in the car to output and log the data.

I will post all of this when I do it, I just have to keep having life expenses from preempting my Megasquirt purchase.
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Old 05-25-2007, 11:21 AM   #3
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Doesn't matter as Megasquirt allows the use of a wideband O2, which allows for superlean cruise. Miles divided by gallons will still give you an average, and a vacuum gauge on the dash can help determine when you are getting max mileage for throttle position.

Only bad thing about Megasquirt is it's batch fire, not sequential, although they are working on a way to make it sequential. Big Stuff is more expensive, but allows a wideband with sequential, and may allow you to hook up a MPG minder.
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Old 05-25-2007, 11:45 AM   #4
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For the same money and far less time investment, you could have an E-Manage Ultimate tuning your fuel and ignition curves. The EMU has wideband O2 support as well as digital outputs to control features based on load and rpm. It also allows the conversion from batch fire to sequential. Just a thought. You'll have LOTS of your own R&D time tied up in a Megasquirt system.

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Old 05-25-2007, 11:55 AM   #5
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Whoa, same money? Those E-Manage units seem to be ~$500, while a MS kit is ~$150. For $350, I think I'd rather assemble and tune it myself, especially since maps for a lot of cars/setups are out there already, so it's not as much work as it was when they first came out. The more people provide info on different kinds of cars/engines, the less everyone has to do, very OS imo.
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Old 05-25-2007, 01:09 PM   #6
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Greddy says it is a piggy back Engine management system. Does that mean you have to have an ECU and then install this one on top if it? That wouldn't work very good for me

Sounds like more work than I want to get into right now. If you get it working on your crx I would love to read about it and pick your brain.

Not sure if I want to deal with sequential as I would need to drill holes in my manifold and all. Would be much easier to just use a TBI where my carb is.
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Old 05-25-2007, 01:38 PM   #7
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Originally Posted by Telco View Post
Doesn't matter as Megasquirt allows the use of a wideband O2, which allows for superlean cruise. Miles divided by gallons will still give you an average, and a vacuum gauge on the dash can help determine when you are getting max mileage for throttle position.

Only bad thing about Megasquirt is it's batch fire, not sequential, although they are working on a way to make it sequential. Big Stuff is more expensive, but allows a wideband with sequential, and may allow you to hook up a MPG minder.
Unfortunately, superlean cruise is more complicated than simply leaning out your AFRs at cruise. It would still be preferable to have some sort of instant feedback, in any case, I'd think.
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Old 05-25-2007, 01:40 PM   #8
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I think I messed up my last post...how would you run MS on this since it is carbbed? And I don't think you'll find anything to measure actual fuel use on a carbbed car with only a mechanical vss.

I would put the money into buying another car,

EDIT: I didn't mess it up after all.
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Old 05-25-2007, 01:49 PM   #9
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Unfortunately, superlean cruise is more complicated than simply leaning out your AFRs at cruise. It would still be preferable to have some sort of instant feedback, in any case, I'd think.
What complicates it? Setting the cruise fuel map to a superlean setting, slowly leaning it out while monitoring temps, wouldn't be an issue. What other stuff is needed to run extra lean? Aside from emissions worries, which I wasn't considering.
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Old 05-25-2007, 02:00 PM   #10
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Does a megasquirt know how much gasoline is being used?

SVOBoy -- I was introduced to megasquirt by a friend a few years ago. I always thought the purpose was to make a carbed car into a FI one. LOL

You can do it with a carbed car, just have to throw a TBI from an old chevy or something and get all the little parts needed like the TPS to hook up. Would be more work to an extent I suppose, but I would know how it all worked after hooking up every single sensor and wiring it all up.

What is involved in Lean cruise besides editing the AF ratio.
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