Gas Mileage is decreasing - Chevy TrailBlazer, TrailBlazer SS and GMC Envoy Forum



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Go Back   Chevy TrailBlazer, TrailBlazer SS and GMC Envoy Forum > 2002 - 2009 TrailBlazer/Envoy Tech > 02-09 Vortec 4.2L I-6 Engine and Drivetrain

02-09 Vortec 4.2L I-6 Engine and Drivetrain Q&A forum for engine and drivetrain repairs/modifications/tuning.

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  #1  
Old 09-05-2005, 09:00 PM
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rt9bil rt9bil is offline
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Gas Mileage is decreasing

So this spring when I put my 20's back on I was getting 16.1 miles/gallon. Over the past 4 month its been dropping...today I checked it and its now at 14.9 miles/gallon. Anybody know what the problem could be??? It's an '02 4.2L w/ 52K.
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  #2  
Old 09-05-2005, 09:05 PM
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Blulytes Blulytes is offline
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Its all those hills in N-town that are killing you!

Have you done all the normal checks? Filters? Change of driving habits? I'm always pretty consistant... at 13.8!

I have a pretty heavy foot on 76 and 422!
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Old 09-05-2005, 09:21 PM
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Quote:
Its all those hills in N-town that are killing you!
Yeah I hear that. The air filter was recharged about a month ago...but other than that I haven't changed anything else.
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Old 09-05-2005, 09:28 PM
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Kahunakai Kahunakai is offline
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using more a/c lately?
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  #5  
Old 09-05-2005, 10:02 PM
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Ah, but was that 16.1 with the 20s or from before they were installed? Larger tires usually result in a slight loss in fuel economy, since they weight more and may have a higher rolling resistance due to the increase in width. (Some brands also have a higher rolling resistance than others).

Assuming that the 16.1 was with the 20 inch tires, have you checked their pressure recently....is it the same as back in the spring?

Could their be more brake drag than in the spring, perhaps some rust build up or warpage on the rotors?

Have you changed gasoline brands recently.....I've noticed differences with different brands.

Check the throttle butterfly, mine gets incredible gummed up and I clean it down good every few months with some carb cleaner and run some injector cleaner through at the same time. (If the vapor can gum things up like that, image what the injectors look like!) Prestone & Chevron cleaners both work great.

Didn't you post about putting on an exhaust a couple of months ago? .... If so, could you be hitting the gas harder from a stop due to a slight loss in low end torque? The mid-high end power increase is sometimes accompanied by a low end (below 2500-3000 rpm) decrease in torque if too much back-pressure is take away. (Totally free flowing isn't usually the most efficient in normal driving).

Those are the things which come to mind off the top of my head anyway, hopefully it helps. I've actually noticed my Envoy getting slightly better mileage lately....either the Borla is helping or my foot has gotten slightly lighter with the increase in gas prices.
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Old 09-06-2005, 06:17 PM
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Ylab thanks for all the info. I checked a few things out...first off, my tire pressure was low in both front and back driverside tires. Second, the crap that has built up on the throttle butherfly was nasty!! So I cleaned that up and then dumped some injection cleaner in the tank also. We'll see what happens. As for the exhaust, I've had it about 3 months now and I also added drilled and slotted rotors and ceramic pads at the same time. So hopefully theres nothing wrong w/ them. I've been thinking about my driving habits and realized that they have changed drastically since May. I used to do alot of highway driving and now i'm doing more city driving. So I figure thats probably the main cause.
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Old 09-06-2005, 06:48 PM
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I'd make it a habit to clean out the multiple airflow sensor whenever you recharge your air filter. That probably wasn't the main reason for your lack of fuel economy as you noted. But as you found out, that oil and other crap does get into your system.
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Old 09-06-2005, 09:07 PM
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just for informational purposes for all of you readers out there. the envoy (I can't speak for the TB's) do not have a Mass Airflow Sensor. They are a speed-density setup. in '06 they added the MAF Sensor.

As a tech, I usually suggest cleaning the throttle bore and butterfly and performing an induction service every 12-15k. You should also have the injectors flushed out a minimum of every 30k. But that is just my opinion.
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  #9  
Old 09-06-2005, 09:32 PM
dpm6836 dpm6836 is offline
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How exactly do you clean the throttle bore and butterfly?
Thanks.
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  #10  
Old 09-06-2005, 10:51 PM
ScarabEpic22 ScarabEpic22 is offline
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OK, now youve got my attention, what is done to clean the injectors? How invloved of a process is it, and are there any special tools needed? I feel I am pretty competant when it comes to these trucks, but there are some things Im not going to stick my hands into.

TIA
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