So I finally filled my truck up four times consecutively and tested to see what gas mileage I'm really getting. I pay with cash so filling up isn't pratical for me but I wanted to see my highway mileage and I had gas money for the trip so it was going to be spent regardless. My first tank I got 13.48 on the calculator and 15.7 on the ultra gauge. This was done by resetting the trip on the truck and the ultragauge at the gas station. My second refueling I got 13.81 on the calc and 15.8 on the UG. I get gas mileage by filling up and taking my miles divided by gallons it says on the pump right? Because they are pretty consistently proportional and my main question is: is there something causing my ultragauge to be off such as a vacuum leak, evap leak, gas tank leak, brake binding, or something else the computer doesn't get real time data from or is it just the computer being off? Thanks for the answers.

Also my ultragauge has a manifold pressure, is that vacuum and what is the normal idling pressure if so?

 

What inputs does the ultra gauge get?

17-20"s at idle is good. (vacuum)

 

I have no idea, but two-three mpgs off is pretty bad on a truck that gets 13. And it plugs into the obd2 port so I guess whatever the PCM puts out.

My truck is only (according to the ultragauge) pulling 8" at idle. Does it go up or down when accelerating?

 

Larger the throttle opening, the lower the vacuum. (smaller number) Have you fixed your plenum yet?

The UG is calculating fuel mileage based on flow rates. It uses injector pulse width, and distance traveled to figger it out. Did you have to program the UG for your truck? Or, does it just sorta "figger it out"?

 

trying to use electronics for mileage is for the birds, unless those electronics involve a GPS and a calculator, it has been my experience..

even pumping to full has it's disadvantages.. some pumps react quicker than others, and stop.. pumping past the stop may be the difference of as much as a gallon.. pumping to the stop may be as much as two..

the most accurate way to do it, again, in my opinion is by using the same station, and using a log (tripometer on either GPS or gauges).. I prefer GPS because it is more accurate for distance, and is independent of the truck- and the pump, not the gauge..

on a trip, you can't use the same pump.. What I try to do is fill at the same needle point on the gauge, and only pump in twenty gallons.. I've gotten good at it, and the pump rarely is off a quarter gallon in either direction to full... But, I only do that once every three or four fills to make sure I still 'got it'- otherwise, I stop at 20... When I do 'fill past 20', I take that figure into account rather than just the 20... yeah, it has it's drawbacks for certain, but it's as close as you can hope for..

even temperature and altitude is going to jack with your perceived mileage..

you should be able to get close using GPS or tripometer, and a calculator.. don't trust computers.. they will lie..

if you're truly pulling 8" at idle, you've got an issue you should be able to hear.. that's silly low.. I'd put an analog gauge on it before I did anything...

 

It just figured it out, yep replaced the plenum, o2 sensors, double roller, intake gaskets, oil pump, and all related gaskets. So apparently the ultragauge manifold pressure isn't vacuum because it goes up when I go faster. So apparently this plug and play gizmo is another paper weight? I'd rather have a vacuum gauge than this thing because at least the vacuum gauge will tell you when you have a leak or something useful.

 

Changed it out***

Well you could be right about the cutoff points, different fuel etc. to be honest I feel like they don't give you .001 of a gallon accurately, the hose probably holds +\- a gallon. But I have no knowledge on this so plop arguring please lol

oh well, it makes a good code reader

 

Ultragauge states the Manifold air pressure is in psia (absolute pressure) so your reading of 8 is 8 psia which equals ~16.28 in-hg. The conversion rate from psia to in-hg is 2.03. Since these trucks only have a manifold air pressure sensor, this value is correlated to a flow rate, which means there is more inaccuracy than if there was a mass air flow sensor at least with how the gauge calculates MPG. You can fuel up and calculate your mileage, and use the resulting value to calibrate the instantaneous MPG.

I have an ultra-gauge myself and I like it, cheaper than a scangauge or Dash hawk, and I like the screen on it. It does seem unresponsive to button presses at times though, and I wish I had more gauges, but that is due to the sensors not existing on these trucks rather than a fault of the device.