Chevy Colorado, dissapointing first tank

[OL'55]

So I picked up a 2007 Chevy Colorado 2.9 5spd, extended cab, 6ft box.

I filled it up on the way home and figured I would get a baseline and just drive it like a normal person would thru the frirst tank. That lasted about 50 miles and I couldnt help my self and started driving more eco minded. At 100 miles I inflated the tires to 44lbs (max sidewall rating), at 150 miles I took off the heavy steel contractors tonneau cover. At 250 miles I took off both mirrors. At 270 miles I cleaned the MAF and throttle body. None of these made a noticeable increase in MPG.

Temps have been 45-60 over the last couple weeks and its been pretty windy. I drove maybe 50-70 miles taking loads of broken concrete to the recycler. Other than that the scangage has been reporting 24ish for my 7 mile trip to work, and one 80 mile freeway trip at 30mpg. I was fairly happy.

Today I filled up...21.87mpg for the tank. Scangage was a little off, I never had a trip that low, even hauling concrete. Hopefully next tank comes out better but Im not holding out a lot of hope.

Maybe after a few more mods? Would like to see 30 mpg averages.

[OL'55]

Also the truck isnt doing any DFCO, so apparently kill switch is going to be the next mod.

[mikeyjd]

Keeping highway speeds down is pretty key on trucks. Don't lose hope, you can hit 30mpg with that truck under the right driving conditions. I'd start by making sure your tires are at max sidewall, checking spark plugs and switching to full synthetic fluids in the motor,trans, differential. Driving style goes a long ways so be sure to always be looking to improve there.

[ecomodded]

Max sidewall psi means you will need less throttle to go the same speed.

keeping your speed down with max sidewall psi will have a fast effect, let the savings multiply.

[JRMichler]

Here's the thread listing what I've done with my truck: http://ecomodder.com/forum/showthrea...yon-17070.html.

The Colorado responds very nicely to DWL. That's where a lot of my MPG comes from. Also, driving slower. Most of my driving is at or below 55 MPH. The last time I went 65, the gas mileage dropped so much that I slowed down before attempting to get comparative numbers.

[OL'55]

Hey JR, I read your thread all the way thru before I picked up my truck and was hoping to get results a little closer to yours.

I watch the scangage, keep it at 55 on my trip to work, I have been timing the lights, tires at max sidewall pressure, coast in neutral whenever I can, no wasted idling time, ease up on the hills, carry speed into the corners, etc

Things on the to-do list:
Kill Switch
Roll up tonneau cover
Grill block
Check/change plugs
Synthetics in engine/trans/axle
Add lower spoiler
New O2 sensors
Electric Fan
PS Delete (That might be impossible the way the belt is)
Etc?

I may have a cracked exhaust manifold, there is a little noise coming from that area when its cold and at low RPM's. I'm sure that could be affecting my mileage. There are no CEL's and it seems to run fairly well. Its REALLY gutless under 1500rpm so I upshift when I know its going to come in over 1500, but I never hit more than 2700 or so.

Hopefully the plugs and manifold will bring me back up to where I think I should be. Its even possible I didn't get the tank full on my first fill up, but I'm pretty sure it was full.

[mikeyjd]

That manifold and o2 sensors could be a large contributor.

[JRMichler]

Which rear axle ratio do you have? What is the RPM at 55 MPH? My truck is 1850 RPM at 55 MPH with stock size tires, and 1800 RPM with my current tires.

Does the Scangauge MPG reasonably match measured MPG? Is it properly set up with the correct engine displacement? If so, what is your idle RPM and fuel flow? Does the fuel system go closed loop reasonably soon? My truck goes closed loop in less than a mile after cold start, even in below zero temperatures.

The engine fan has a thermal clutch. Is your fan clutch working properly? My engine fan clutch will occasionally engage at startup. It then takes about half a mile to disengage, during which time it makes a loud roaring noise and causes noticeable drag.

Long shots: Set the Scangauge for voltage. The voltage should be about 14.4 volts plus or minus a couple tenths. Make sure the AC compressor is not running by pulling the fuse. This is good practice because the AC compressor is programmed to run whenever you select a defrost setting and run the blower.

[OL'55]

It has the 3.73 axle in it and I'm at 1930 RPM at 55mph with the stock 205/75-15's. The scangage was off about 15%, I have the displacement set up correctly. It idles at 800 rpm and it goes into closed loop after 4-5 blocks of driving.

I can hear the fan at start up some days, but the roar is gone before it goes closed loop, the fan clutch seems to be working fine. Voltage is around 14.2 and the AC compressor is not engaged either.

Didnt get a chance to dig into the exhaust manifold this weekend, but I'll let you know what I come up with,

[JRMichler]

My Canyon has the same 3.73 rear axle ratio, and came with 225/75R15 tires. I am now running 235/75R15 tires, which gives me 1800 RPM at 55 MPH.

The factory service manual lists the following causes of poor gas mileage:
Faulty knock retard
Plugs - gaps, fouling
Cam timing
Fuel injectors - connected in correct order, flowing properly
PCM ground connections
Plugged air filter
Vacuum leak
Fuel pressure

Try setting your Scangauge to display MAP (manifold absolute pressure) and IGN (spark advance). My truck had the following readings yesterday at 70 deg F, 1800 RPM, and running 87 octane gas with 10% ethanol:

45 degrees at 7 lbs MAP
17 degrees at 10 lbs MAP

Yours should read the same. A bad knock retard could retard the timing 15 degrees, which would kill the mileage.

The FSM says that plug gaps are important for gas mileage.