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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 > OEM Issues

OEM Issues Original Equipment Repairs and/or Problems

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  #1  
Old 01-10-2008, 10:00 PM
pinhead989 pinhead989 is offline
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Exclamation Gas mileage getting worse everyday

Hey all my 02 Trailblazer ls 72000 miles was gettin at its best since ive had the truck 12mpg city and 17 highway for about 4 months. since about 5000 miles ago i noticed that i would get 240 a city tank to now 130 a city tank and 280 highway before and 190 highway now. it seems to be gettin worse with every fill up. ive changed the air filter, fuel filter, tranny service, transfer case, both differentials, and spark plugs prior to the decrease in mpg..but id say 7000-10000 miles ago. what do you guys think could be happening?

Thanks in advanced Brian
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  #2  
Old 01-11-2008, 06:05 AM
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Hi Brian and welcome to the forum.

This type of mileage has been experienced by some guys. Some have changed out all kinda of parts and it seems to make little difference.

Some common things are a plugged catalytic converter, outdated PCM programming or the fan clutch... but you did not mention any codes being set or a check engine light?

The thermostat can be a stinker too. If it sticks open you will get less fuel economy and you may notice that your temp gauge is well under the 210 mark?

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Old 01-11-2008, 12:10 PM
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Check the air pressure in your tires. If you live in a cold-climate area, your tires will lose 1 PSI of inflation pressure for every 10-degree drop in ambient temperature. For example, if your tires were inflated to 30 PSI when the ambient temperature was 70 degrees, your tires would show only 23 PSI when ambient temp drops to zero degrees.

Low tire pressure increases rolling resistance. Plus, cold weather causes the rubber and other materials in tires to stiffen, causing more rolling resistance. The combination of low inflation pressure and stiffer tires during winter months contributes to high rolling resistance and decreased fuel economy.

I usually over-inflate my tires by four or five PSI during our cold New England winters.
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Old 01-11-2008, 12:17 PM
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blazernut is right on....
the CAT may be just the problem...
do you notice the engine sort of bog down at higher highway speeds?
since youre at 72K... the cat being replaced FREE is good... the cat is good for 80,000 miles.
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Old 01-11-2008, 03:05 PM
pinhead989 pinhead989 is offline
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hey guys thanks for your input...no i dont have n e codes being thrown and my tires are at 36psi i just checked them. I havent driven on the highway in a while but when i did I dont remeber any bogging, tho most of the time i had it on cruise control. If it is the CAT how would I determine it? Do i take it out and bring it to the dealer or something? how would I go about doing this.

Brian
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Old 01-11-2008, 04:20 PM
929hit 929hit is offline
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Quote:
Originally Posted by Blazernut View Post
The thermostat can be a stinker too. If it sticks open you will get less fuel economy and you may notice that your temp gauge is well under the 210 mark?

I had this happen on an S10 Blazer. It wouldn't get up to temp, so it stayed in that rich-running, choked, warm-up mode. Easy fix. I'm told they are designed to fail while open, which is a good idea. I imagine the fan clutch would result in the same thing if it were stuck on. Check your temp guage for sure.
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Old 01-11-2008, 05:41 PM
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Some other factors to consider.....

1. Many areas of the country change to a winter fuel mixture in the early fall, and this could be causing your mpg loss.

2. You didn't post what area of the country you live in, but the colder the air gets, the denser it is. Hence, it requires a little more HP to "push" your TB through it.

3. Maybe God just hates you, and likes to see you spending more money on fuel.
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Old 01-11-2008, 05:42 PM
pinhead989 pinhead989 is offline
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the temp is at 210 all the time and gets up to temp quickly. also for a little bit I have been hearing a squealing at startup like a pullys going .. its not that loud but you def notice it. could this be the fan clutch?
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Old 01-11-2008, 09:57 PM
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Quote:
Originally Posted by pinhead989 View Post
the temp is at 210 all the time and gets up to temp quickly. also for a little bit I have been hearing a squealing at startup like a pullys going .. its not that loud but you def notice it. could this be the fan clutch?
Could be...that would account for the decrease in mileage. Mine went, but I did get a "check engine soon" light not long after it went bad.
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Old 01-14-2008, 08:48 AM
Doc Brown Doc Brown is offline
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Quote:
Originally Posted by superman_79065 View Post
2. You didn't post what area of the country you live in, but the colder the air gets, the denser it is. Hence, it requires a little more HP to "push" your TB through it.
Brian didn't say where he lives, but I had the same thought. When the average daily high is below 30, my mileage drops to 12-13 in mixed freeway city driving. Last week the temps here went up to the upper 30s, low 40s. One day we hit 60. My mileage imediately went back to the usuall 16-17.
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