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Old 06-17-2010, 05:29 PM   #1 (permalink)
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Engine load

It was recommended to me that i get two scangauges instead of two mpguinos because of the extra features but im wondering if those would be helpful to me and worth spending $200 dollars extra for my families two vehicles.

He said that the scangauge displays engine load and thats one of the most important thing to watch. Why doesn't the mpguino display load? isnt that proprtional to the amount of fuel being used???

I can get my engine trouble codes read for free at the auto parts store.

my dash gauges already display coolant temp and the voltage though the later could be displayed with more resolution. Why doesnt the mpguino measure voltage? not enough ADC?

Should i know intake temperature manifold pressure igninting timing or if the vehicle is in closed or open loop? How does that help me? Would i need to know that to drive more efficiently? maybe knowing the pressure would let me know when to change the air filter or something. I dont know if any of those features would be usefull for efficiency or maintenance.

Does the mguino not have the ability to take trip averages,(assuming averages can be helpful).?

-mike

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Old 06-19-2010, 04:55 AM   #2 (permalink)
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All those data points (MAP, water temp, oil temp, etc) might be useful for analysis if they are logged along with your speed & MPG, and analyzed later on your PC; but i dont see how one can read those values real-time to optimize your driving habits. Even if you could (and manage to drive safely), your wife/kids surely cannot.

Best thing for the family members is a simple "This is your MPG" display, so they can ease up on the gas & instantly see results. Also, if you are the bread-winner & buying all the gas, they might not care about MPG (but lucky you if they do).


As for your question about why MPGuino doesnt display all that other data... yes, limited ADC, plus each signal needs to be wired. 'Guino only requires 4 wires, one being ground, so it's nice and clean. if you want all the other data, maybe you want an OBDuino instead?

Looking at the schematics, it looks like a hybrid MPG/OBDuino could be rigged. I just bought my first OBD2 car (98 tdi), so i might try it. I'd like to be able to probe the OBD port for the ancillary data, but for MPG, i'd rather keep the MPGuino method of reading the injectors, than blindly trust what the OBD thinks my MPG is. My concern about building the OBDuino, though, is availability of the transceiever chip, mc33290, or equivalent.
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Old 06-19-2010, 05:54 PM   #3 (permalink)
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Daox said he watches engine load more while driving than mpg. Thats why i was wondering if it was important.

Yeah i think alot of that other stuff may be more usefull for diagnostics than mpg.

My father drives a 2001 tundra so hes more concerned with gas than me lol.

Measuring battery voltage wouldnt require an extra wire since the mpguino is already powered by the battery lol, thats why i was wondering if you ran out of ADC.
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Old 06-19-2010, 06:40 PM   #4 (permalink)
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I should have clarified. I mainly use pulse and glide technique. It involves accelerating up to speed and killing the engine to coast in neutral, then bump starting with the clutch and accelerating again. It is a fairly advanced technique, but accelerating at higher loads still runs the engine at the highest efficiency points. I use this acceleration method if I am using P&G or not.

If you are planning on getting two meters, I'd get one of each. The SG is very easy to swap between vehicles, and the mpguino can be as well (you just have to wire both cars with a connector so it plugs in).
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Old 06-19-2010, 06:47 PM   #5 (permalink)
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I think load feedback is important too, but it is "calculated" from lots of vehicle specific data and sensors. It is sorta what I'm getting at with tracking the change in acceleration over the fuel flow rate: http://ecomodder.com/forum/showthrea...tml#post176541

It would be a rather arbitrary number, but when it peaks you are accelerating most efficiently.

re: batt voltage. There's 2 adc left. With so many options (map,maf,throttle position, various temps, a piezo?, 02 sensor, battery voltage, ???) and none the same on every car, it is a challenge to know what precisely to do with those ADC ahead of time. You are certainly free to experiment, I'd be most interested in whatever helps w/efficiency. Battery voltage could be nice when I'm sitting with the engine off but with an electric load, but if you have a wideband o2 sensor, well you can "reverse engineer" lots of values.

I think I might add a generic "gimme a reading from adc1 or adc2" option at some point, but without knowing what it is reading, or what it means, it will be hard to integrate into other computed values.
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Old 06-19-2010, 09:33 PM   #6 (permalink)
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The single most critical load indicator is manifold vacuum, or in the case of MAP which is atmospheric pressure minus manifold vacuum.

This can change considerably at most throttle positions depending on the speed, gear, and grade the vehicle is negotiating.

If you are at the lowest possible manifold vacuum reading without full load enrichment, you are in the best position as far as BSFC is concerned, as long as you are in the proper (read fairly low) RPM range.

Once you get the feel for this load range, then you have to calculate which gear will be best for acceleration to your peak speed.

As a general rule the highest practical gear is usually the best selection. The exception will be when you are climbing a grade and need to use a lower gear to maintain a speed up the grade. In every case you want to avoid absolute WOT and fuel enrichment, unless it is necessary for avoiding an accident.

Install a vacuum gauge temporarily and learn the best throttle positions to maintain your vacuum around 2 inches of less without WOT. After a while it will become second nature and you could remove the gauge.

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Mech
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Old 06-19-2010, 10:01 PM   #7 (permalink)
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...or, you can "read" the MAP value from your SGII (if you have one) and acomplish basically the samething that Old Mechanic recommends.
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Old 06-19-2010, 10:11 PM   #8 (permalink)
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miket, if your vehicles are OBD2, I suggest you look at Magister's ODBuino. I have one in my wife's 08 Avenger, and it does display eng load, along w/inst mpg and several other parameters...
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Old 06-20-2010, 01:40 AM   #9 (permalink)
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Oh now I understand, how load or map will help with acceleration whereas instantaneous mpg wont help, at least not directly.

Does the OBDuino read the injector pulses for accuracy or does it rely entirely on OBD which i heard is less reliable.

How much does the obduino cost and is there a kit? I can solder surface mount if need be. Money is tight right now so if a save a few hundred over buying two scangauges i'd be happy.

Hmm daox, it did not occur to me that i could put a connector on a mpguino and switch it in and out of a vehicle like i would able to do with a scanguage or obduino.
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Old 06-20-2010, 10:31 AM   #10 (permalink)
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I think obd is quite accurate enough for the majority of drivers, but it does have it's problems:

1. OBD isn't much of a standard, it is actually many standards with a convenient name. It takes a lot of circuitry (cost/bugs) to be able to reliably plug into an obd connector and expect to communicate. Even then when different folks made the computers for the different cars, they made different interpretations and assumptions, and you sometimes see bogus data on the port. And also it is limited to 1996 or newer.

2. All the mpg parameters have to be inferred and polled and be based on assumption, introducing room for error.

2.a. fuel used, this is based on maf (if available) or map * rpm. But it assumes that the engine is at stoich (14.7:1) so that if it is cold, or enriching, or lean burn, or diesel or ??? then the fuel used can be off .

2b. for distance, it has to periodically ask the car computer "how fast are we going", and remember when and what the value was the last time it asked, and guess at the distance traveled from there.

2c. polling is less accurate also as there is a window for peaks or valleys to get in between polls, the guino gets an interrupt when an injector opens and closes, and when the axle makes a vss tick. It doesn't have to rely on the computers vehicle specific interpretations of what the injectors and vss are doing, it goes straight to the source of the info.

There are some chips (i.e. elm and other projects) that help with obd connections, but they still take a lot of support circuitry to be able to connect to any obd car, far more than the guino has. But you do get "interpreted" access to pretty much all the sensors on the engine once you sort out the obd connection issues.

Having all those sensor readings handy is fun, but the key ones for accurate mpg are how long have the injectors been open and how many vss tics have happened, and those can get a bit muddled in an obd system.

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