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-   -   Scanguage vs MPGuino - 96 Prizm (https://ecomodder.com/forum/showthread.php/scanguage-vs-mpguino-96-prizm-11787.html)

justjohn 01-09-2010 11:15 AM

Scanguage vs MPGuino - 96 Prizm
 
Hey guys,

I'm interested in monitoring my instantaneous mpg, (largely because I want to run some controlled tests to determine the most efficient acceleration method).

MPGuino vs Scangauge

As I understand it the Scanguage is:
More expensive
Needs OBDII
Less Accurate

But the MPGuino is:
Harder to install
Not easily removable
Displays only one readout at a time


As such, I'm leaning toward the MPGuino, but being non-removable bothers me a little, and I'm worried I won't be able to install it correctly. So,

1. Does anyone have suggestions?

2. Has anyone put an MPGuino in a prizm before that could help me if I get stuck?

dcb 01-09-2010 12:56 PM

If you aren't really sure you understand how to install the guino and/or if it will work w/your vehicle I would suggest the SG. I've heard figures that it is within 3% to 5% accurate which is a huge improvement over nothing. And it comes with warranty and paid support people. The guino is really targeted at pre-96 and geeks on a budget. The truly geeky just build their own mpguino :)

Daox 01-09-2010 03:16 PM

I'd go for the scangauge. The mpguino is great for preOBDII, but the SG just has so many more features.

Accuracy can be tweaked pretty close, but you really just need to get a baseline. From the baseline you can tell if you are doing better or worse.

justjohn 01-11-2010 08:23 PM

Thanks for the input. I'm a little worried about inaccuracies when the car goes into open loop.

Since the main thing I want to test is efficiency of different modes of acceleration I need to know for sure that it's going to be accurate at full throttle. A couple other threads suggested the scangauge gets off significantly when the air ratio changes (ie: especially in open loop).

That being said, would you still go with a scanguage?

Daox 01-11-2010 10:29 PM

If you are doing open loop testing, neither will be absolutely accurate. In open loop, fuel is just being wasted to enable easy starting in cold weather, or its injecting extra fuel to cool down the combustion chamber due to ping/knock. You don't know how much extra is being injected. And, there is no easy way to calibrate either of them to get close unfortunately, unless you get on a dyno and do some serious testing.

dcb 01-11-2010 10:39 PM

well, the guino is watching the injector so it should not be faked out by open loop(and it does display more than one thing at a time), but john you are ultimately responsible for making it work on your vehicle and may have to do your own research to see if it will work and how to make it work (or who to buy a case of beer for to make it work), the guinos are not consumer items where you can try it and send it back if you don't like it, just fyi.

justjohn 01-12-2010 02:51 PM

Quote:

Originally Posted by dcb (Post 153685)
well, the guino is watching the injector so it should not be faked out by open loop

See, that's what I was assuming.

Daox sounds like he's saying there's a way for fuel to get in there that the guino can't see. That doesn't seem likely to me, but my car knowledge is relatively limited. Can anyone reassure me one way or the other?

Provided the guino won't get faked out I would prefer it over the scanguage (price is a factor as well). I'm basically trying to get an idea of just how hard the guino is to install.

I can handle digging up some wires and soldering them, but if it's going to be complete guesswork on which wires I want then I might just say forget it.

Daox 01-12-2010 03:11 PM

Its pretty easy to install. I have one on my Paseo. Yes, the mpguino is more precise, and it will not be faked out by open loop. For your testing purposes it is a better choice.

justjohn 01-13-2010 10:34 AM

Alright, I'll probably try the mpguino then. If it's the least bit intuitive I'll be able to figure it out, and the worst that can happen is a couple holes in a 14 year old car, right? :)

MetroMPG 01-13-2010 11:13 AM

No holes required (for the MPGuino). You just have to find and splice into a few wires.

Also: I can tell you right now, you're unlikely to find that open loop acceleration is more efficient than closed loop.

justjohn 01-13-2010 11:38 AM

Aye, that's what I'm expecting. I want to compare different methods of acceleration, and I don't want to hit open loop without the penalty being registered.

I'm also hoping to be able to see when I hit open loop so that I can go just under that point for one of the tests.

P.S.
A hole or two if I want to mount it in the dash, no? Although I did see a setup with the wire coming up to a little mounted box on on the dash that didn't look too bad.

dcb 01-13-2010 11:45 AM

The extra data provided by an obd tool (i.e. scangauge) like rpm, throttle position, load, and open loop indicator would be helpful if you want to monitor those items.

the guino can only sense the injector pulse width and the speed (distance) sensor and the 4th dimension. and is oblivious to the concept of open loop, unless it is marked by a large change in consumption that the user can notice.

justjohn 01-13-2010 12:31 PM

Right. Ideally I suppose I would have both. I need the guino for more accurate measurement while in open loop though.

I used the word hope precisely because of what you said. I'll only be able to see it if there's a distinct jump. That's alright with me for now though.

dcb 01-13-2010 02:14 PM

it is always challenging to measure best acceleration, cuz things are happening so fast.

One part of the problem is how do you compare the efficiency of two acceleration profiles?

Assuming you are going to run several tests and take an average, do you compare fuel consumption for:
a. just accelerating up to a given speed at different rates?

b. accelerating on a fixed distance up to a a given speed and holding that speed for the remainder of the distance (so you measure fuel used over a given distance in all tests)?

c. require that slower acceleration exceed the given speed so that they finish the same distance in the same amount of time?

d. etc. etc.

I would like to see a "best acceleration for a given amount of fuel" indication, i.e. change in speed/fuel used. that might help, but would be affected by things like hills and wind. maybe if you have an average figure from the last 3 seconds and an instant figure it would be driveable. And you just adjust the throttle (or even the gear shifts) to seek the most fuel efficient acceleration.

It may be something you can do with an xgauge on a sg (and you can see if best accell peaks below open loop then), I'm sure a guino could be hacked to do it too with an external programmer and a knowledge of programming atmegas. I may have to think about adding that to the official version.

justjohn 01-13-2010 05:44 PM

Yes, I thought it through briefly beforehand and I was planning on doing b, as that seems the most fair. (It should be change in speed per fuel used, but with distance covered factored in so that slow modes don't come out falsely disadvantaged)

My rough plan was to try 4 modes of acceleration (just slow medium brisk and full, nothing fancy to start with) to a specific speed, both ways on a short course and compare. Probably another couple sets at different speeds.

automd 02-16-2010 10:09 PM

Quote:

Originally Posted by Daox (Post 153217)
I'd go for the scangauge. The mpguino is great for preOBDII, but the SG just has so many more features.

Accuracy can be tweaked pretty close, but you really just need to get a baseline. From the baseline you can tell if you are doing better or worse.

Scangauge. We're in the same side. I totally agree. I can't say more. Be sure to check if your car is OBD compliant :)

jfitzpat 02-18-2010 02:39 PM

Forgive me, I'm trying to thread a needle. The important part of the post is the principles, but it will sound like a sales pitch and that is not my intent. There are lots of ways to get the job done, I just happen to be familiar with our stuff.

First, it is important to understand why OBD-II MPG is inaccurate. I cover a bit of it here:

http://ecomodder.com/forum/156981-post21.html

The fundemental problem is that the unit doesn't typically know what the lambda, or AFR, of combustion is. This is 14.7:1 (really lambda 1.0, which is not quite the same thing), a lot, but not always, and it can depend on even the route being driven.

So, when you are calibrating such a unit, you are not just adjusting for sensors, but also for driving style and typical routes and terrain. If you are trying different driving styles, then your calibration becomes moot.

So, from a strict instrumentation standpoint, measuring injector duty cycle is much more accurate for comparative purposes. It also has to be calibrated, because of the mechanical properties of the injector, but even without calibration, comparisons of readings have merit.

Second, instantaneous readings are not a very good way to make meaningful comparisons, at least not when gauging small changes.

I'm not saying that such devices aren't useful, but the instant reading and the actual results are two different things. For example, and instant reading will reward any decrease in TP, but if you are going up an incline, this is not the most fuel efficient way to operate.

I think that when you are trying to make comparisons, logging and post operation analysis is the way to go. That's how we do it in performance operations. You are really interested in the total result, not instant by instant readings. Also, logging lets you focus on executing the techniques.

If I were going to try to collect data for quantitive comparisons, I'd start by logging OBD-II data (like I did in the post above). This is nice because it lets me also review the consistancy of execution of the technique as well as measure the fuel results.

If my need for fuel consumption accuracy was fairly precise, I'd add a wideband O2 setup. In the case above, I'd put the wideband in the pre-cat bung for the regular O2 sensor, then have the wideband controller simulate narrow band output for the ECU. This would save me installing a new bung. Then I'd chain that through the OBD-II module so that the wideband data is logged in sync with OBD-II data.

Wideband + MAF is pretty accurate for MPG. Plus, it let's me have a glimpse into how much economy is really about the technique, and how much is ECU specific behavior.

If that precision is not enough (limited by ECU response rate), I'd wire up injector duty cycle as well to a little analog/clock input module and chain it in as well.

For 'real time' monitoring, I might wire up a gauge (there is a serial output as well as USB/Wi-Fi), but you get the idea...

Now, again, none of this meant to sell gear. I bet it would be easy to apply the same principles to something like the MPGGuino. My points are ultimately just:

1. Understand that OBD-II is generally only air side monitoring, so different technique throws off precision

2. Meaningful evaluation is a lot easier (and I think a lot more accurate) if you log the data and analyze it after the fact.

Regards,
-jjf


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