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JJW 05-14-2008 11:34 AM

Three most useful gauges?
So I've got myself a brand new bone stock Toyota Yaris that I've happily put about 1000 miles on and so far I've been getting in the neighborhood of 40-45 mpg even while driving for break in (varying speed, gear, load, etc.). One of the things that I'm sorely lacking is a tachometer, and the street-racer set makes nifty three gauge pods for this little car that would allow me to install one to my wife's cosmetic satisfaction. Now, I am positive I will be installing a Scangauge, probably above the mirror, but I still want an analog tach for convenience and to help my wife drive stick with the quiet engine. That means I've got two gauge holes to fill!

What would be the best gauges to populate these holes with? The cars computer should be monitoring oil pressure and water temp I'd imagine, so should I rely on it to monitor those for me? Or rely on the scangauge for those? Which two gauges outside of the scangauge would tell me the most about my efficiency, vacuum and voltage?

Just curious what instrumentation besides the scangauge people find most useful or necessary.

- Jason

MetroMPG 05-14-2008 11:58 AM

If it were my car, I'd stick a high resolution engine temp gauge and voltmeter in there. But that's because I have the engine off frequently (need to be careful to avoid drawing the battery down too low), and I run a partial grille block, so want to be able to monitor coolant temps.

JohnnyGrey 05-14-2008 12:36 PM

40-45mpg? What % of that was highway?

One of the gauges I find invaluable is a wideband AFR gauge. You will have to replace your O2 sensor, but it will tell you what your scangauge can't.

The other gauge I would use is an ammeter. This will let you measure the power draw of various electric devices in your vehicle and can tell you much more than a voltmeter.

As for voltage, vacuum and water temperature, these are things the SG actually does well. I wouldn't bother with an oil pressure gauge unless you plan on running a lighter than recommended viscosity.

boostanddestroy 05-14-2008 01:20 PM

Tach, Wideband 02 Sensor, Oil pressure.

Those are the most vital Gauges i beleive for any sort of vehicle (if you dont have a tach then i would say vac/boost gauge). The wideband with ACCURATLEY display your Air to Fuel ratios so you can keep track of what everything is doing @ the moment.

Oil pressure is the gauge that will make sure your engine is running properly. God knows that it has saved me a couple times when i had an oil line blow off of my turbocharger. Otherwise i would have no idea.

Daox 05-14-2008 01:49 PM

If it were my car I'd probably just use a scangauge since it can do pretty much everything... However, since you reeeealy want the tach I'd probably go with the same gauges Metro said if your planning on using pulse and glide and doing aerodynamic modifications. The ammeter is a good choice, but it doesn't really need to be a permanent gauge once you get a feel for what the different accessories pull amp wise. With the scangauge I also wouldn't bother with a vacuum gauge. I'm not sure about the 1NZ-FE (yaris engine), but my 1ZZ-FE (matrix engine) stays in closed loop just about 100% of the time. Wideband is way overkill (and expensive) IMO unless you are tuning an engine.

Duffman 05-14-2008 02:04 PM

Scangauge does most everything but will not do A/F ratio or oil pressure. For efficiency the scan gauge is really all you need because it will give you an instantaineous MPG reading, the most important of them all.

JJW 05-14-2008 02:23 PM


Originally Posted by JohnnyGrey (Post 25762)
40-45mpg? What % of that was highway?

95% plus. The car is used entirely as a commuter and I live nearly 50 miles away from my place of work just off major interstates. I'm also fortunate that I commute at a time when there is not much traffic. Because of the break in instructions saying not to keep the engine at a steady RPM for long, or excessive RPMs, I took it as an opportunity to play with a sort of modified P&G with an average speed of about 55 mph. Its the 5 spd hatchback. Note that I haven't had it that long, so I don't have a lot of data to go by yet!

Thanks for the suggestions so far, some good points to think about that I wasn't expecting. I think it would take me some time to actually be able to put the information from a wide band to use though. Without remapping the ECU, how would you apply the feedback its giving you?

Taco Bowl 05-14-2008 06:12 PM

Id get a Vacuum Gauge for sure. It shows you how much of load ur putting on the engine when ur accelerating or cruising around. This is the one that i installed on my truck.

It shows you where the needle should be for best Fuel economy. I dont know if the Scanguage can show vacuum. Even if does, I doubt that it is as accurate and instantenous as an old fashioned needle gauge.

With the help of the vacuum gauge I went from 15mpg to 20.5 mpg.

JohnnyGrey 05-14-2008 08:52 PM

Taco, the SG can show vacuum to a tenth of a PSI.


Thanks for the suggestions so far, some good points to think about that I wasn't expecting. I think it would take me some time to actually be able to put the information from a wide band to use though. Without remapping the ECU, how would you apply the feedback its giving you?
Using a wideband to lean out your mixture involves setting the gauge or driving unit to produce a 0-5 linear AFR voltage. This voltage must be fed to a switching circuit that produces 0v when the input voltage is above a certain threshold and 0.9v when the input voltage is below a certain threshold. In effect, you're deciding at what ratio you tell the ECU it's running lean or rich. The result is you train the ECU around a ratio of your liking. Though I cruise as lean as 18:1:1, I find that 16.2:1 produces the best economy for my vehicle.

One caveat is that your scanguage cannot tell you which ratio produces the best economy. This is because it measures air, not fuel. When leaning out, it will show your mileage getting worse even though it's getting better, because you're using more air, but less fuel. After a tank of lean-burn, you'll find that your fillup numbers and the SG's estimate are off. It's only after a complete tank of running a certain mixture, that you can halfway trust the SG. A far more accurate way of measuring fuel is an injector based solution. This will tell you the truth for any mixture in any situation.

Dust 05-15-2008 02:39 AM

JohnnyGrey, where can I read more about using a WB02 for KMPL (MPG) increases?

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