Modding an 06 GMC Canyon

[JRMichler]

This is the mod thread for my 06 GMC Canyon. The testing was A-B-CDE-F-G. I know this is not as good as proper ABA testing, but it is what was done. Mods so far include:

A: New vehicle, driving “normal”. Normal was 57 in 55 limit, 0 to 5 over in lesser limits, 65 in 65. Normal was also partial use of cruise control, maintaining speed in rolling hills, light use of brakes for speed limit changes. I did not keep gas records.
B: DWL, no longer use cruise control, engine on coasting for speed limit changes, and 55 in 55 and higher speed limits.
C: Nokian WR tires.
D: Inflated to 47 PSI (sidewall maximum).
E: Kill switch.
F: Grille block.
G: Aero topper.

A testing.

I bought the truck new with the 2.8 liter 175 hp 4 cylinder engine, crew cab, 2 WD, 3.73 rear axle ratio, locking differential, and factory trailer hitch. It was immediately equipped with a Leer model 100R topper. Tire pressure was maintained at placard (32 or 33 PSI).

Bought a Scangauge at some point. Did some experimenting with engine on coasting and found that the engine is programmed with a GMC automatic variable hot idle speed feature. The hot idle speed varied randomly from 700 Rpm to 1700 RPM. It was constant during any one coast. It would change for the next coast. Turning the AC compressor on would change the idle speed. That change would either increase or decrease the idle speed. There were times when the idle fuel flow would decrease when the AC compressor kicked on and increase when the compressor kicked off. The dealer's response: “No CEL, no problem”.

Fuel consumption was not recorded, but tank averages were about 21 MPG in winter and 27 MPG in summer. Driving was roughly 15% city and 85% highway.

To resume with a discussion of B testing...

[JRMichler]

BCD testing

Discovered Ecomodder.com about this time, and learned that my driving skills had room for improvement. Got serious about DWL (B testing), slowed slightly to 55 MPH in 55 and higher speed limits. The Scanguage showed that the Canyon really sucked gas at 65 MPH, so that test was terminated before getting a useable MPG number.

Used engine on coasting in neutral for speed limit changes, and tried engine off coasting. Decided to save the engine off coasting until I installed a kill switch.

Time for new tires, put on a set of Nokian WR 235/75R15 (C testing). These tires are one size larger than stock, with 2% larger diameter. All mile readings from this point have 2% added to correct for the larger tires.

Did a coastdown test with the tires at placard (33 PSI), the repeated with them pumped to 47 PSI (D testing, sidewall maximum). It coasted much better, so left them at 47 PSI.

Because three changes were made at the same time, it is not possible to separate the effects of each change. I do know that the new WR tires did not coast as well as the worn previous tires at 33 PSI, but coasted better than the previous tires when at 47 PSI. The previous tires were at 33 PSI.

Results:
Winter: December 2007 thru Feb 2008: 23.24 MPG (+10.7%)
Summer 2008: 29.70 MPG (+10%)

[Kodak]

Nice post. I'll be interested to read about the effects of mods F and G.

Originally Posted by JRMichler

The Scanguage showed that the Canyon really sucked gas at 65 MPH, so that test was terminated before getting a useable MPG number.

By chance, do you remember about how big of a hit in FE you were taking at 65 vs 55?

I don't do much highway driving, but this has been my technique when I do:

Pick PSL as my 'target speed' (this often makes me one of the slower vehicles). Bleed off 5mph or so uphill. Go just a few mph over PSL on the downhill while remaining in gear.

This technique got me a trip average of a little over 27.5mpg with a PSL of 65 during a winter road trip with tires at placard 33psi.

(regular cab, 2.9l 4cyl, manual and bed cover).

[JRMichler]

Kodak: I didn't drive 65 long enough to have a number. Once I noticed that it was significantly worse than the MPG at 55 MPH, I slowed down.

Your description of slowing down uphill is what we call DWL. The Canyon responds nicely to DWL. I monitor manifold absolute pressure using my Scangauge to get the best benefit from DWL.

When I mentioned driving "normal" in the first post, it would have been more correct to say "I THOUGHT I was driving for gas mileage".

Now for E testing: the kill switch.

The kill switch was installed 12-7-2008. It breaks the connection through the fuel injector fuse to kill the engine. I cut the plastic off a spare fuse, removed the fuse element, and soldered wires to the fuse pins. These wires were connected to an automotive relay. The relay coil is energized through a pushbutton switch mounted on the shift lever. The relay is connected normally closed, so the circuit is opened when the relay coil is energized. The fuel injector circuit has an inline fuse, with another inline fuse in the wire to the pushbutton. I can bypass the kill switch any time by pulling the connectors from the fuse box and putting a fuse back in. All wires are protected by fuses. This is especially important when running wires through the firewall, under carpeting, and up the shift lever.

The kill switch works well, however I randomly get a CEL. The CEL is either a P0204 or P0461. I just reset using the Scangauge. Strangely, I always get a CEL at the first EOC after filling the tank. That CEL is also accompanied by the gas gauge moving to Empty. The gas gauge stays at empty until the CEL is reset. The BCM also relocks all the door locks every time at a bump start.

It was a challenge finding a pushbutton switch that would not rattle from the shift lever shaking.

My longest glide is about a mile, at a downhill speed limit change. I try to glide down to about 20 MPH when approaching stop signs. I attempt to maintain at least 7 lbs MAP (Manifold Absolute Pressure), then glide when the speed starts to increase a few MPH. This minimizes the time the engine runs at low efficiency.

Results: December 08 thru Feb 09: 24.68 MPG (+6.2%)
Summer 2009: 32.14 MPG (+8.2%)

[JRMichler]

F testing: Grille block

I added plexiglas covers over the recessed fog lights. Any aerodynamic gain is small, they were added because the fog light openings filled with snow while driving in a heavy snowfall. The fogs were unuseable when I needed them the most. The fog lights on the Canyon have gaps around the edges that allow dirt, snow, and water thrown by the front wheels to get past the lights. I had to remove the original covers, fill the gaps with "foam in a can", and replace the covers. The covers were sawed to size, molded to rough shape using a heat gun in one hand and a leather glove on the other hand. I fastened them in place with 3M body molding double stick tape, then used the heat gun and leather glove to fine fit them all around.

The main grille is covered with exterior grade window film from Walmart. The exterior window film is twice as thick as the interior window film. The film currently on the truck has been there since November 2009.

The openings on either side of the front license plate are covered with masking tape. That tape has been on for over a year. I intended to replace it with plexiglas a long time ago, but laziness and procrastination won.

The only cooling air is from an opening (not visible) under the front license plate. The engine temperature has not risen from its pre-grille block values of 186 to 190 deg F, even when driving in 90 deg F weather with the AC running.

Photos are in my profile.

The reduced aero drag due to the grille block allows more and longer glides with the engine off. This is a synergistic effect, so I would expect slightly less percentage MPG gain if I had installed the grille block before the kill switch.

Results:
Winter: December 09 thru February 2010: 26.78 MPG (8.5%)
Summer 2010: 33.80 MPG (5.2%)

I speculate that the summer percentage mileage increase is less than the winter percentage increase because the engine is too lightly loaded, and spending more time in an inefficient range (less than 7 lbs MAP). Unfortunately, it does not glide well enough to use EOC to take advantage (or maybe I'm too lazy). In summer, the truck would benefit from the 3.42 optional rear axle ratio.

Added 6-12-2011: The original 3M window film is still on the truck. It got its first hole yesterday, possibly from a flying stone.

Added 7-9-2012: The original grille block is still installed, complete with the masking tape over the two smaller holes in the bumper. The engine temperature rose above the normal 188 deg F exactly once when the outside temperature was 93 F, the air conditioner running continuously, and a going up a long upgrade. The temperature on that day reached 195 F. This is well below the temperature at which the engine cooling fan clutch engages.

[JRMichler]

And finally, the aero topper (mod G).

I started thinking about making a new topper when I had to carry a freezer that was 1/2" taller than the hinge of the Leer topper previously on the truck. A hinged lid would have eliminated the need to unbolt and raise the topper twice. I also wanted a way to carry larger things, such as a snowblower.

And then, I found Ecomodder.com and started to read about the advantages of aero toppers.

The truck cab is narrower up near the top than down at the top of the box. The topper must fit behind the tapered cab. The hinged lid of an aero topper can be built two different ways. The lid can be rectangular or trapezoidal. If the lid is rectangular, the topper sides need to twist inward toward the rear of the box. If the lid is trapezoidal, the topper sides can be built to match the side taper of the cab and simply cut to a triangular shape. The trapezoidal lid is easier to make. My brother's aero topper has a trapezoidal lid, my topper has a rectangular lid. Photos of both are in my profile.

The rectangular lid has another disadvantage. My Canyon cannot carry full sheets of plywood with the tailgate fully up. It will carry plywood with the tailgate at the halfway setting.

I believe that either design will have the same drag. I know that both toppers have smooth airflow over them. My topper collects zero road salt on the top and sides in the winter, even when the windshield gets loaded with salt.

The topper is held closed with a pair of pins connected to a lockable T-handle. A pair of gas struts hold it open.

Construction is two layers of 3/16" thick underlayment plywood over wood frames. This plywood is sold as 1/4" nominal thickness. All wood was sealed with epoxy, then painted with hardware store gloss enamel.

The topper was installed 12-12-2010. Results:
December 2010 thru February 2011: 28.11 MPG (5.0% increase). The real increase should be slightly better than that because I got careless about tire pressure that winter.

So there it is - A-B-CDE-F-G testing. Not the ideal ABA testing, but it gives me real world relative improvements. My current plans are to continue as is to get summer 2011 MPG with the aero topper. I'm not sure what I'll test next. I'm thinking about air dams, belly pans, or maybe test 100% gas instead of E10.

[Kodak]

Impressive. How did your aero mods affect your ideal top speed?

[JRMichler]

My data does not allow that calculation. I measured the effects of changes on overall MPG. In order to estimate the effect on top speed, it would be necessary to run coastdown tests to separate rolling friction from air drag.

Anyway, the question is moot. I've read that these trucks are governed to 99 MPH. So, no change in top speed.

[Kodak]

D'oh. I mis-worded the above. Late night post. I meant to ask: Have the mods changed your ideal FE speed? Or maybe 55 is still best (just even more efficient).

[JRMichler]

I'm just guessing, but I still expect a significant drop in MPG at 65 MPH.

This engine has VVT, so the engine efficiency does not improve much at higher speeds. I don't expect to see a 65 limit until the end of July. I'll run a short test, but probably will not go far enough to get good data.