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Go Back   Chevy TrailBlazer, TrailBlazer SS and GMC Envoy Forum > 2002 - 2009 TrailBlazer/Envoy Tech > 02-09 Vortec 5.3L V8 Engine and Drivetrain > OEM Issues

OEM Issues Original Equipment Repairs and/or Problems

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  #1  
Old 03-01-2012, 12:33 PM
country joe country joe is offline
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2003 Chevy TrailBlazer LT EXT
gold 4.2L I6 4X4
Join Date: Feb 2012
Location: Custer Park, IL
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bad gas mileage

Hi everybody. I just joined the site a little while ago, and this is my first posting. I own a 2003 trailblazer ext with a 4.2 I6, and I do almost all the work on it by myself. I've been fixing my own vehicles since I could drive, usually I can figure anything out on my own, but this problem escapes me. Now, my trailblazer's been getting bad gas mileage for a while now. I do have a bad sensor. The last time it was in for repair, which was the water pump (I just didn't have the time to fix it myself) they said that the thermostat sensor switch? was bad, and it needed to be changed. I knew it had an engine temperature problem because for a while now, if you started it and drove it right away in the cold weather, the reduced engine power light would come on, and you could only go about 5 mph. If you shut it off and started it again, sometimes it would be alright, sometimes you had to restart it two or three times. So, we just always let it run for a half hour or so in the winter. It's been doing that for a couple years. The engine temperature gauge says it only gets up to 150-160. I'm pretty sure that's not right. They changed the thermostat when they put the new water pump on, and the problem was still there. That's when they did the obd scan and found it. I told them not to fix it, because I didn't have the extra cash at the time. But for the past year, the gas mileage has been getting worse. I recently changed the spark plugs. I used the Bosch plus 4s. The ones that came out of it were pretty shot. It has 130,000 miles on it, and I think the ones I took out might be the original plugs. Should I have used AC Delco's? I don't know. Another thing I notcied was some material that was hanging out of the exhaust when my wife came home the other day. I assumed it was muffler packing. The exhaust and the engine doesn't sound like they're being restricted and there's no loss of power or anything like that. I just don't know. I've never had a problem working on any of the vehicles I've owned in the past, but this thing just baffles me sometimes. I need to find out why it's getting this bad mileage. We only get about 150 miles out of a half tank. It used to get 200. If anyone can help me, please respond.
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  #2  
Old 03-01-2012, 02:15 PM
Loverotties Loverotties is offline
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2002 Chevy TrailBlazer LTZ
Majestic Red Metallic 4.2L I6 4X4
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You need to get the A/C plugs(forget the number but someone should chime in.)Take the TB off and clean it,Change the censor,change air and gas filter and seafome the intake and then disconnect the battery for at least 1/2 hr and re hook up.
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Old 03-01-2012, 02:22 PM
Larf Larf is offline
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2007 Chevy TrailBlazer LT
Black 4.2L I6 4X4
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Location: Nashville, TN
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Gas Mileage

I had what I thought was poor gas mileage when I bought my vehicle at 40K miles (2007 6 cyl). The primary fix for me was to clean the throttle body per suggestions on this forum. My current gas mileage is 20 - 22 on highway at 70 - 80 mph. 18 around town. I am at 75K miles on the vehicle.

Of course, if you get on it, your mileage will be a lot less.
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  #4  
Old 03-03-2012, 08:51 PM
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Ralph_T Ralph_T is offline
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2005 GMC Envoy SLE XL
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Quote:
Originally Posted by country joe View Post
We only get about 150 miles out of a half tank. It used to get 200. If anyone can help me, please respond.
If this is city mileage I don't see an issue here. That's what I get around 14 mpg. You also need to take into consideration that it's winter. Cooler air requires more fuel to burn.

Your thermostat is probably still bad. I would have it checked out before you fry the catalytic converter. The truck should warm up to 192ish on a scan tool.
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Old 03-03-2012, 10:31 PM
bastenblood bastenblood is offline
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2002 GMC Envoy SLE
Black 4.2L I6 4X4
Join Date: Oct 2011
Location: Quebec
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One time I were driving in a couple of inches of snow on the 4HI , and my engine light came on, and the the was running at high idle (900rpm) . The two code says poor oxygen reading in manifold and catalytic converter so I didn't care much .

A couple of weeks later the same thing happen , but the light stays on . And for two days the sound of my envoy became really loud and a significant power loss . So the mechanic change the oxygen sensor on my manifold.

After this fixed , I saw a huge amelioration on the gas mileage before all of this happened .
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  #6  
Old 03-03-2012, 10:49 PM
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petevw petevw is offline
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Are you SURE they actually changed the thermostat??? Did you request the old parts back? That temp of 150-160 is WAY low.

A properly running I6 engine should read read 210 or even slightly above that on the gauge if the stat is good. Right now, the computer still thinks the engine is cold, and is putting more gas into it.

As for the plugs, if the engine seems to run smoothly when you do get some temp in it, then they're probably working OK.

Also, has the throttle body ever been removed from the engine and cleaned?? If not, do a search for a sticky thread here that tells you the right way to do it.

May not increase mileage, but you never know...and it's a cheap maintenance item.

I'd also look into that stuff coming from the exhaust pipe.
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  #7  
Old 03-03-2012, 10:56 PM
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Ralph_T Ralph_T is offline
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Actually there is a range in which the temp is acceptable. The range according to Alldata is between 188F and 206F. Don't go by the gauge on the dash. It is a buffered reading. With the engine fully warm, take a reading using a scan tool and then bounce that reading against a submersible thermometer to check coolant temp in the neck of the radiator. The readings should be close. If not, then the coolant temp sensor is bad.
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  #8  
Old 03-04-2012, 01:46 PM
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petevw petevw is offline
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Quote:
Originally Posted by Ralph_T View Post
....Don't go by the gauge on the dash. It is a buffered reading.....
I agree that the dash gauge isn't exact, but seeing that the majority of owners do NOT have a scan tool like that, the gauge on the dash is just fine to determine if the stat is stuck open or not.

Just about EVERY TB/Voy will show the gauge right at the 210 mark or slightly above IF the stat is working correctly. Any reading like the OP's (150-160) is a sure sign something is wrong.

You're trying to make this more complicated than it really is.
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