New Guy / Guess my MPG ('05 GMC Canyon Crew Cab 4x4 Z71)

[KY_Canyon]

Hey all. Long time Lurker ~ First time User. I live & work in the rolling hills of Kentucky. My daily work commute is 65 miles (round trip). This consists 80/20 hwy/city. The hwy portion is 4-lane 70MPH, which I generally drive at 73 mph or so.

At the beginning of Feb I purchased a 2005 GMC Canyon Crew Cab Z71 4x4, 3.5L I5 / Auto with 68,000 miles. My first several tanks of fuel averaged right around 17.3 MPG (using cruise @ 70 MPH on the the highway portion of my drive). Now since this is a heavy 4-dr 4x4 truck with 30.5" inch tires with 10" wide tread, I didn't think that this was horrible. However, I know that it can be better. So, I immediately began searching for ways to improve the MPG.

Here's what I've done so far:
1) Drove a couple of trips with my OBD2 scanner to watch vacuum, throttle, load, fuel trim, etc. Trying to find inefficiency.
2) Replaced air filter - not expecting any gains.
3) Purchased a vinyl tonneau cover
4) Adjusted my driving style to eliminate cruise control (per my findings on my few trips monitoring).

After making these few changes, what does everyone think my MPG has gone to?

[roosterk0031]

With it being cold, I don't think you've broke 20 yet so I'll gues 19.7

[GRU]

Yeah, i'd say about 19.5

[mcrews]

19.9
and welcome!

Just slowing down to 63-65 should be worth 2-3mpg?

[KY_Canyon]

Well, the first tank I ran without cruise was at 19.9, corrected to 19.68 for actual miles. My most recent fill-up was at 20.9, corrected to 20.67.

The one thing I noticed with the cruise was that even going down steep grades the truck would engine brake then accelerate repeatedly. I ordered a Bluetooth Obd2 (cheap one had to return) connector and ran Torque for a day and my down hill mileage would go up to 40-50 then down to 18-24 over and over (coast-accelerate-coast-accelerate). The cruise control also caused the truck to downshift on almost every hill. So, by not using cruise I have been able to maintain speeds from 63-70 with no down shifting except one hill. I am trying to maintain a consistent throttle position and only manipulate it enough to minimize deceleration on hill climbs. I've also found I can keep Absolute Throttle Position between 28-32% for 95% of my Hwy travel. As far as coasting goes, the truck just doesn't coast well in gear...even to stops. It engine brakes down to about 50 mph rather quick, then coasts a bit better. Nonetheless, I'm doing my best to coast as far as possible for stops and slow turns.

I'm hoping that once I get Torque working full time that I'll be able to adjust my driving enough to break 25 MPG once the weather warms, but I've learned a lot about the truck, and my right foot in the past month. All recommendations welcomed.

[evil03mustang]

Originally Posted by KY_Canyon

I'll be able to adjust my driving enough to break 25 MPG once the weather warms, but I've learned a lot about the truck, and my right foot in the past month. All recommendations welcomed.

You may want to research the "partial tonneau" effect.

I'd run my tires at their max. rated PSI.

Make sure you're not carrying any stuff you don't need.

I don't know how much it'd help, but I'm considering replacing all of my driveline fluids with a synthetic where available. (I'm running a full-time AWD Impreza) At 6x,xxx miles, you're probably due for fresh diff lube anyways, so it couldn't hurt?

[mcrews]

I engine ON coast in neutral on downhills.
I have 255k on the tranny &(rest of the car) so I know, for my car, it doesnt hurt anything.
Not sure how that works with a chevy truck.
YOu probably have a prtty firm ride.. but punmp the tires up.
I'll let one of the truck guys chime in though for psi #s
I run 43psi with nitro.

Also, not sure how you are about a/c and windows...
But I installed some window visors and can crack the windows about 3/4 inch and hardly increase the noise level. Also keeps me from having to hit the a/c.

[KY_Canyon]

Tires/wheels are probably my biggest deterrent. I've got 17" aftermarket wheels w/ 265/65-17s that are A/T tread....not too aggressive but more than I need. From what I can tell, the combo weighs 68 lbs per corner. I've got them at 36 PSI and can tell they're riding hard in the center. The tread on these measure 9.75 across and with the wheel offset they are far from being tucked in the fender. So as soon as they're worn out I'm going to be a bit pickier about width and tread type....not a lot of LRR tires for trucks yet, but I think I can reduce weight & resistance without giving up diameter.

I have window visors on the truck, and have been able to completely avoid running defrost so far.

As far as partial tonneau's go, this bed is only 61" long. In fact the cab is probably longer than the bed. So, I don't think a partial would have the same effect that it does on some of the normal or long bed trucks. This past weekend I changed the oil and used Pennzoil Platinum 5w30. The other fluids are all synthetic from the factory, but I'll be changing them out soon.

As far as coasting goes, I've tinkered a bit with neutral coasting, but I'm not 100% sure how the GM 4L60E automatic handles neutral coasting. I'm doing some research, but definitely don't want to break a trans.

[evil03mustang]

It's a shame that cruise control can be so antithetical.

A well-trained right foot and a LOT of patience for other drivers still beats out the computer for the time being...

And when that cruise control system is developed, my name will be on the waiting list.

[KY_Canyon]

Originally Posted by evil03mustang

It's a shame that cruise control can be so antithetical.

A well-trained right foot and a LOT of patience for other drivers still beats out the computer for the time being...

And when that cruise control system is developed, my name will be on the waiting list.

Luckily, there aren't many vehicles on the 4-lane that I drive. So lots of time for experimenting once I get Torque up and running consistently.

The cruise in this truck is the tightest I think I've ever seen. It doesn't allow the truck to get 1mph above or below the setting unless it's a really fast grade change.

I think I've got the potential to gain 2-3 MPG in tires alone, but will drive with these until they wear out........which should be this fall.