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2003 chevy trailblazer_ls
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Discussion Starter #1
After I bought my scanner, I looked at live data page and there was ENGINE LOAD % and mine was about at 25 % at idle and at 200°. Is it too much or normal ?

I wounder if anyone here could compare this data with mine. I'm still trying to find the cause of low MPGs (10 mpg). Plugs changed (AC-DELCO Iridium). Thermostat changed (GM). Air filter ok.

Thanks for you time.
 

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2004 chevy trailblazer_lt
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997 Posts
Ignore that.

Look at the oxygen sensor data for sensor 1, bank 1. It should fluctuate rapidly above 0; from about 200 mV to 900 mV. What are your readings, and how fast are they changing?

Now check oxygen sensor 2. This is your downstream sensor, and the readings should be pretty solid, with few fluctuations. It should read close to 0. What is that reading and how fast is it changing?

Now look up your readings for short term fuel trim (STFT) and long term fuel trim (LTFT.) These readings will be expressed asa percentage and should be +/- less than 8%. The STFT should bounce a lot between +/-5%. The LTFT should be pretty steady and ideally will be near 0. What are your readings for STFT and LTFT?

Next, read the many threads here on mileage.

Nobody can say exactly what is wrong or whether anything is wrong because driving conditions and driving styles vary. But there are certain common causes of much poorer than normal mileage figures.

The funny thing is that we tell people to look for these things time after time, and for some reason, very few people actually come back to report their findings. I guess some people would rather just throw parts at the problem or hope maybe some mechanic will stumble across the answer (or combination of answers.)

The common causes of decreased mileage are:
- city versus highway driving
- driving style
- plugged cat
- bad thermostat
- lazy oxygen sensor
- worn or wrong type spark plugs
- winter gas
- bad fan clutch
- oil sludge buildup
- dirty throttle body
- changing tires to ones with a higher rolling resistance

(These are in rough order, from the most effect to the least.)

So let us know what your scan tool reads, what your mileage is and what you have already checked. Good luck and stick with it!:)
 

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2003 chevy trailblazer_ls
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168 Posts
Discussion Starter #3
Ignore that.

Look at the oxygen sensor data for sensor 1, bank 1. It should fluctuate rapidly above 0; from about 200 mV to 900 mV. What are your readings, and how fast are they changing?

Now check oxygen sensor 2. This is your downstream sensor, and the readings should be pretty solid, with few fluctuations. It should read close to 0. What is that reading and how fast is it changing?

Now look up your readings for short term fuel trim (STFT) and long term fuel trim (LTFT.) These readings will be expressed asa percentage and should be +/- less than 8%. The STFT should bounce a lot between +/-5%. The LTFT should be pretty steady and ideally will be near 0. What are your readings for STFT and LTFT?

Next, read the many threads here on mileage.

Nobody can say exactly what is wrong or whether anything is wrong because driving conditions and driving styles vary. But there are certain common causes of much poorer than normal mileage figures.

The funny thing is that we tell people to look for these things time after time, and for some reason, very few people actually come back to report their findings. I guess some people would rather just throw parts at the problem or hope maybe some mechanic will stumble across the answer (or combination of answers.)

The common causes of decreased mileage are:
- city versus highway driving
- driving style
- plugged cat
- bad thermostat
- lazy oxygen sensor
- worn or wrong type spark plugs
- winter gas
- bad fan clutch
- oil sludge buildup
- dirty throttle body
- changing tires to ones with a higher rolling resistance

(These are in rough order, from the most effect to the least.)

So let us know what your scan tool reads, what your mileage is and what you have already checked. Good luck and stick with it!:)
Ok !! I'll bring my results tomorrow.

Bought this TB 2003 it had 89000 KM so I knew I had to do the plugs, thermostat, tire inflated correctly, my driving is smooth, fan clutch ok, the throttle body has to be clean, air filter ok.

:thx
 

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2004 chevy trailblazer_lt
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You already made some good choices and you have your own scan tool, so you are pretty well equipped for almost anything that can go wrong in the next few years - with the help of this forum, of course.

Since you changed the plugs anyway, you might as well buy a new upstream oxygen sensor. Even if it is in perfect shape - and we'll know tomorrow when you bring us your scan tool readings - it should be replaced. If it happens to be the original one, they can almost weld themselves tight to the manifold after a few years, so it is good to get a fresh one in there anyway.

Since your mileage is WAY down, go through my list and see what you might have missed. Getting your cat checked is a simple process at any muffler shop. They will screw in a compression gauge into the hole that the front oxygen sensor fits in and measure the exhaust backpressure. (Anything over 4 psi is bad.)

Here's a tip: if you are half-thinking of getting an exhaust backpressure test done, buy the new O2 sensor but don't put it in until AFTER the test. Let THEM sweat with a breaker bar to get it out. (If you take it to a muffle shop, bring your new O2 sensor with you; they will LOVE you because it means that can simply snip off the wire and use a deep socket to get the old one out. The slotted oxygen sensor sockets will NOT hold the torque necessary to remove one when it is almost seized in place.)

In the summer, you should be able to easily get 600 kilometers on a tank of gas on the highway, and 500 with a mix of city and highway.

In the winter, with a little bit of 4wd, lots of idling in the city and lots of cold starts with winter-blended gas, you would be very lucky to get 350 kilometers on a tank.

Tis the nature of the beast.
 

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2003 chevy trailblazer_ls
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Discussion Starter #5
Ignore that.

Look at the oxygen sensor data for sensor 1, bank 1. It should fluctuate rapidly above 0; from about 200 mV to 900 mV. What are your readings, and how fast are they changing?

Now check oxygen sensor 2. This is your downstream sensor, and the readings should be pretty solid, with few fluctuations. It should read close to 0. What is that reading and how fast is it changing?

Now look up your readings for short term fuel trim (STFT) and long term fuel trim (LTFT.) These readings will be expressed asa percentage and should be +/- less than 8%. The STFT should bounce a lot between +/-5%. The LTFT should be pretty steady and ideally will be near 0. What are your readings for STFT and LTFT?

Do I check these on idle ??
 

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Discussion Starter #7 (Edited)
There it is... I finally got my results from the scanner.
Recorded LIVE DATA from hot motor and running idle and based on 20 frame recording.

ECT: 203°
STFT: -1.56% to 5.47%
LTFT: Steady -5,47%

O2 sensor Bank 1: 60 mv to 810 mv fluctuating up and down
O2 Sensor Bank 2: Pretty steady at +/- 700 mv but went down at 350 mv

Today I bought my throttle body cleaner and hope to clean it on sunday (it has to be done).

Other thing... I unplug the battery when I did the plugs and the scanner as

not finish the "EVAP" testing, how long it takes to finish or anyway to

stop the test ?

Tanks again for your support.
 

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2004 chevy trailblazer_lt
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Everything looks fine. It is maybe running a touch rich, which is why it is compensating with a very slight lean fuel trim.

Your coolant temp is a touch low, and that might be the reason.

Clean the throttle body, disconnect the battery while you do so and let us know if there is any improvement.

Don't worry about the "evap" test. It takes at least three cycles, with the coolant and OAT over a certain amount, and you have to be driving a certain distance before it even performs the test. If you drive a fair amount of miles to work, it could run several times a week. If you do nothing but short trips, it may not even run more than once a month in the winter.
 

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2003 chevy trailblazer_ls
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Discussion Starter #9
Your coolant temp is a touch low, and that might be the reason.
About the ECT... I changed the thermostat so it is brand new OEM and was woundering if US and CAN thermostat could have a difference in temperature ?

Everything looks fine. It is maybe running a touch rich, which is why it is compensating with a very slight lean fuel trim.
So I dont have to change O2 sensors ?

Thanks again. :thumbsup:
 

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If those readings for the front oxygen sensor are fluctuating rapidly, then no.

By rapidly, I mean up and down several times a second. (Or at least, as fast as your scan tool can renew the data.)

If there are several seconds between fluctuations, then yes, you need to change it.

Aren't scan tools wonderful? They can tell us so much of we know what to look for.

I wouldn't worry about your coolant temp. It is not bad. Keep an eye on your gauge and if someday it decides to read a hash mark on the cool side instead of the normal 12 o'clock position, then it is time to change the thermostat (again.)
 

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Discussion Starter #11
Update

Today I cleaned mt throttle body with Canadian Tire Throttle body cleaner (Not Carb cleaner) and rubbed it with toothbrush and it was pretty easy to do. I broke the locking clip that retains the electrical connector to TB :worried:, I unpluged the battery for all the work time (45 min.).

I'll be back to bring the data from the scanner and MPG's after a full tank. I hope it has done something good. :hail:

:thx:thumbsup:
 

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Discussion Starter #12
There it is... I finally got my results from the scanner.
Recorded LIVE DATA from hot motor and running idle and based on 20 frame recording.

ECT: 203°
STFT: -1.56% to 5.47%
LTFT: Steady -5,47%

O2 sensor Bank 1: 60 mv to 810 mv fluctuating up and down
O2 Sensor Bank 2: Pretty steady at +/- 700 mv but went down at 350 mv

Today I bought my throttle body cleaner and hope to clean it on sunday (it has to be done).
Here is the new data from scanner AFTER cleaning TB.

ECT: 203°
STFT: -7.03% to 3.13%
LTFT: Steady -3.13%

O2 sensor Bank 1: 50 mv to 840 mv fluctuating up and down
O2 Sensor Bank 2: Pretty steady at +/- 740 mv with lite fluctuation

:undecided :thx
 

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Discussion Starter #13
I have my new results...

Went from 10 mpg to 13.5 MPG (Winter)...Thats a 3.5 mpg gain :thumbsup:

:thx
 

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Not bad! What make/model scan tool are you using? I need to get one for my '04, but there are a ton of em ranging anywhere from $30 to more than I can afford.

Kage_
 

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There are essentially two types of so-called 'scan tools.' One is more properly called a code reader, because that's all it does; it reads (and often resets) trouble codes.

The other type (which is way more expensive) actually ties in to all the sensors in your vehicle and can read the data coming off them.

THIS is the one you want. Being able to read live data can go a LONG way to diagnosing emissions-control problems.

You can also buy an ABS scan tool that can read ABS trouble codes. (They are not cheap either.) They can't reset trouble codes, but can read them.

Scan tools that could read BOTH engine and ABS trouble codes were not allowed by law until very recently. The government didn't want home mechanics to be able to diagnose ABS problems so they mandated that scanners could only read engine codes. (This is why the Actron ABS code reader is not allowed to reset ABS codes.)

Now, there are some scan tools that do both engine and ABS codes, and can read live data from the engine. (Check out some of the Innova scan tools, for example.)

At the next level of scan tool is the tool that can CONTROL the engine. These are typically made by Genysis, Snap-On, Modus (same as the Snap-On) and GM (the famous and infinitely useful Tech 2.) They start at $2K and go way way up from there.

For most enthusiast owners, the live-data scan tools such as the Innova 3130 that I use is a good value. Here is a good comparison chart between the various tools:
http://www.canobd2.com/Products/Tools.aspx
 

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2005 buick rainier
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I bought this one and it worked great. It's $65 + shipping and reads the computer's live data stream and also freeze frame data (a "snapshot" of the data stream when the trouble code was thrown). It doesn't do CAN though, which I think is necessary for '06+ or '07+ Trailvoys.
 

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2002 chevy trailblazer_lt
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150 Posts
Scanner

Would Freeze Frame data work? A frined of mine has an Actron CP9175. Can I get the same info from that one?
 

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Would Freeze Frame data work? A frined of mine has an Actron CP9175. Can I get the same info from that one?
You can see the freeze data with that one, but you can't view the data stream. You need the CP9180 for that.
 

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this is also available for your laptop.
I dont know how it compares to those handheld units- but looking at the owners manual(online) it appears to also supply the data you mentioned below.

http://www.myscantool.com/
 
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