ScanGauge tuning
 

I have learned from using my ScanGauge for several months that it registers my trip-mileage at between 25% and 33% low.

What is the menu or key-sequence for me to make this calibration to my ScanGauge? I read the manual about a method to calibrate when doing fill-ups, but didn't see a general adjustment like I need.

Is there a way to make a general calibration like this?

Thanks.

Odd that it's that far off.

Is the speed reading off proportionately? If so, there's a speed adjustment factor that would likely correct the distance thing too.

If mileage is off but speed is correct we're back to "odd."

Rick

Mine was off till I got my speed reading calibrated as well. The best way to do it is this:

Change your GPS and scangauge to readings of kilometers (Kilometers are smaller than miles, so you'll be able to more accurately dial it in.) Get on an empty stretch of highway with the GPS and a competent passenger. Accelerate until the GPS reads you are traveling @ 100 KPH and set the cruise. Verify that once set the vehicle maintains 100 KPH. The passenger should be able to change the % variance in the speed settings until both the SG and the GPS read 100 KPH. Change the vehicle speed and verify that the readings are still accurate as compared to the GPS. If so, save the setting on the SG, and exit.

Then just switch the SG and GPS back to MPH. The whole process is outlined in the latest version of the SG manual. If you don't have the latest version you can download it from www.scangauge.com.

-Jay

Great details, Jay; thanks! :thumbup::)

Just a suggestion, vectorg: Once you have all your calibrations (speed, fill-up, tank size, etc.) worked out, jot them down -- a small sticker on the back of the Scangauge would be good.

Twice I've had service-related disturbances that reset my Scangauge to factory defaults. If that happens to you and you've recorded the numbers, you can just punch them right back in. Otherwise you'll have to go through another tank of gas and make a calibration run to get things right again.

Unless you have a much better memory than I do. :)

Rick

Thanks Rick. I'm wondering how to make this calibration on-the-spot using the info I have now, without going through more tanks of gas.


I've driven past some radar-speed-detector things recently, and my speedometer seems to be accurate. The SG is also very close to my speedometer.

Last week I drove from SoCal to San Francisco and my SG showed 24.7 mpg, yet my fillup calculated to 33 mpg. Then, on the way home, I used P&G with drafting of large trucks. My GS showed around 32 mpg, and my fillup revealed over 48 mpg.

These numbers follow the pattern that I've seen since I got my SG.

My suggestion was to help you avoid calibrating again. No connection to what you're doing right now.

You originally posted that your trip mileage was off, which is what prompted replies about your speed calibration. If your speed is reading correctly, then the Scanguage knows how far you're traveling per unit time as well.

It sounds to me like your fuel usage is what needs to be calibrated. Have you set the displacement of your engine? When you fill up, does the amount you put in the tank differ significantly from what the Scangauge is expecting? Are you making that adjustment when you fill up? Does the correction factor change from tank to tank?

The first couple of fills should have gotten you very close to perfection.

Rick

Good point. I had made the assumption that the engine size and such had already been set. Also be sure to enter the number of gallons purchased into the SG when you purchase fuel.

-Jay

I've never made any adjustments or calibrations to my ScanGauge. I thought it was a plug-n-play type thing. Are you saying my car's computer doesn't even know the displacement of it's own engine?

When I say "trip" mileage, I just push the trip button when driving somewhere to see my average mpg as I go. Or, I push the "gauge" button to see the real-time mpg.

I'll go read the manual again.

Yes, the computer knows what size everything is, but the SG is trying to calculate fuel usage based on the live sensor data it reads. Knowing what size the engine is, how large the fuel tank is, and how many gallons are put in the tank at each fillup helps it calibrate.

-Jay

Thanks, Jay. I just looked, and changed engine from 3.0 liters to its actual 2.2 liters. Should this adjustment cause me to see a difference in my trip and real-time mpg readings as I'm driving?

Other units looked okay for now.

That was probably a big part of your problem. It was overestimating the size of your engine and fuel usage.

-Jay

Yes, I switched the SG between my 2 vehicles and forgot to reset and it seemed off a little......then I realized and reset it.

Jay has you headed in the right direction, but let me draw a parallel so maybe this will all make more sense.

It's not about your ECC, it's about your Scangauge. The ECC isn't calculating your fuel efficiency and just handing the numbers over; it's busy managing the engine. Your Scangauge is doing that job based on speed, injector pulse width, and similar things.

Here's the parallel.

When you buy a new TV and hook it up to your cable, does it automagically know what channels are available? Nope. And the cable company doesn't send any sort of message that tells it, either.

So before you use your new cable-ready TV, you go into the setup menu and tell it to scan for available channels. It stops briefly on every possible channel to see if there's a signal. If it finds one, it marks that as a working channel, otherwise it marks it to be skipped in the future.

Similarly, the Scangauge doesn't know anything about the vehicle/engine/etc. to which its connected.

So like the new TV, before you can use your Scangauge effectively you have to tell it certain things about the car you've hooked it to, like the size of the gas tank and the engine displacement.

Displacement will get you into the right range for fuel efficiency, but be aware that your Scangauge is calculating (estimating) your fuel usage. It can make really, really good estimates, but the default displacement setting might be off a little for your particular engine (maybe one of the injectors is a little clogged or something; who knows?) That's what the tank refill adjustment is for. When you refill, you tell the Scangauge how many gallons you put in the tank. It then compares what the car really used with what it thought should have been used, and works out a correction percentage. Usually a single tank will do it; if not, the second surely will. After that you'll just bounce around due to slightly different fill levels and other variables.

Once you have the adjustment factor set (or really close), you don't have to mess with it again. Just do a quick sanity check to make sure the refill is close to what the Scangauge was expecting, then hit the "fillup" button to tell it you're starting a fresh tank.

Does that help it make sense?

Rick

Actually, the ScanGauge doesn't have access to injector pulse width or duty cycle, which is not part of OBDII data. It estimates based on the MAF and O2 data, which tells it how much air goes in and what the A/F ratio is.

That's another reason you have to fine-tune it manually.

I'm glad I disclaimed my comment with "and similar things" then. :)

Thanks for the correction.

The principle I cited remains the same.

Rick

Thanks, Rick, that was a good explanation. Changing from 3.0 to 2.2 liters made a big difference in my mileage reading. But now I understand that I need to enter some more info when I do my fillups. Got it.