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2003 chevy trailblazer_ls_ext
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Discussion Starter #1
2003 4.2 IL6
cruising on flat roads, slight acceleration, or sometimes just idle, the TB has a sluggish feeling and a definite lug or vibration felt throughout the vehicle. You can feel the vibration mostly around 1500RPMs. The vibration only is apearent when accelerating slightly. It starts vibrating just before the trans should be shifting into the next gear. The vibration in more noticeable and worst when it is hot outside 75 degrees or hotter. It was 45 degrees the other morning and I could barly tell I had a problem. If you put the car in park and rev it up to 1500RPMs and hold it there the engine seems to be misfiring. No codes. Also when you are at a stop light and then start going, the car almost dies out. It idles around 600-700 RPMS.

General tune up done, Throttle body removed and cleaned, new gas filter, cleaned fuel injectors, air filter, spark plugs changed (.045), checked for vacuum leaks

Joneil16 has a good description of:
“I can only explain the feeling as like being in too high of a gear for the conditions. Like I was lugging it. This is more prevalent at lower speeds. 25-55. Above that it isn't noticeable. Torque converter and tranny is shifting and locking and unlocking fine. RPM's are similar to others on the site, shifts are smooth”

Anyone figure this problem out yet? I have searched a bunch of sites and can not find the solution. I sent Joneil16 a private message but no reply yet.
 

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2003 chevy trailblazer_ltz
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I am having a similar issue. The vibration is during acceleration between 1500 and 4500 RPMs. At higher RPMs, the engine purr is just like I think it should be, sounding like a beast on steroids.:dielaugh: My dad also describes what he says is "rod knock" when the engine is cold, but goes away within 2 or 3 minutes.
 

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2003 chevy trailblazer_ls_ext
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Discussion Starter #4
No, not yet still working on this issue.
I too have maybe a rod knock or pre-igniton when cold start and then it also goes away.
It was cold here yesterday about 20 degrees and I did not have much of a problem at all.
 

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2003 isuzu ascender
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730 Posts
2003 4.2 IL6
cruising on flat roads, slight acceleration, or sometimes just idle, the TB has a sluggish feeling and a definite lug or vibration felt throughout the vehicle. You can feel the vibration mostly around 1500RPMs. The vibration only is apearent when accelerating slightly. It starts vibrating just before the trans should be shifting into the next gear. The vibration in more noticeable and worst when it is hot outside 75 degrees or hotter. It was 45 degrees the other morning and I could barly tell I had a problem. If you put the car in park and rev it up to 1500RPMs and hold it there the engine seems to be misfiring. No codes. Also when you are at a stop light and then start going, the car almost dies out. It idles around 600-700 RPMS.

General tune up done, Throttle body removed and cleaned, new gas filter, cleaned fuel injectors, air filter, spark plugs changed (.045), checked for vacuum leaks

Joneil16 has a good description of:
“I can only explain the feeling as like being in too high of a gear for the conditions. Like I was lugging it. This is more prevalent at lower speeds. 25-55. Above that it isn't noticeable. Torque converter and tranny is shifting and locking and unlocking fine. RPM's are similar to others on the site, shifts are smooth”

Anyone figure this problem out yet? I have searched a bunch of sites and can not find the solution. I sent Joneil16 a private message but no reply yet.
Ahh yes, I remember this situation all too well. I was about to lose my mind chasing the possible culprits! For me it turned out to be a few contributing factors - each was only responsible for a little bit of the vibration but combined it was very noticeable and aggravating. They were as follows:

Tiny (and I mean T I N Y) crack in the vacuum line which disappears down behind and to the left of the engine. The crack was on the underneath side of the line. You couldn't feel it with your bare hand and it was so uniform that you couldn't even tell it was there by looking.

Water pump was getting ready to take a dump. The pulley had just a slight wiggle to it when you pushed up and down and back-and-forth on the fan assembly. It seemed like just a slight wiggle until you released the tension on the belt and moved the fan around. Holy Shnikees!! Glad I found that one in the driveway!

Slight variance in the gap in the plugs - and if you have any plugs other than the recommended Delco's I'd start there and work backward. These trucks DO NOT like the kickass platinum plugs you'd think they would. This issue is WELL documented in this forum!

And just as a tip for you.....
If you removed your throttle body and cleaned it up all pretty like, you need to disconnect your battery for 30 mins. or so so that the PCM can relearn the new settings associated with the clean TB. Sounds like a bunch of hooey I know but, that slight change in the position of the throttle plate can be the culprit as well. Don't take my word for it...... search the forum for yourself and you'll see these trucks are just sooooooo damned finicky about the dumbest little things. :yes: :crazy: :D

Good luck!

Coach

PS: Another thing I just remembered is the possibility of a leak at the intake manifold which was an issue with some of the I-6's. Easiest way to tell is to start the truck, pop the hood and shoot some Throttle Body Cleaner around the base of the intake manifold. If the rev's increase, there's your problem and fortunately it's well addressed here in this forum.
 

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2004 chevy trailblazer_lt
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997 Posts
Good advice.

Also, a rattle and a feeling of being in 'too high a gear' may also be related to a clogged cat. If plates break away internally, they can clog your exhaust flow. You won't get a code because the cat is still working; it is just clogged, and restricting the exhaust.

You can do a simple exhaust backpressure test at any good shop or muffler shop. (Look for over 1 psi at idle, or over 3 psi at 2500 RPMs. Also look for readings that start low but climb as the vehicle is running.)
 

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2002 olds bravada
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So where are all the vacuum lines? One runs down behind the left side of the engine? What is it for? I get a knock when cold but it dimishes. It runs rough and vibrates with no codes & steady idle. Feels sluggish and strained with vibration when accelerating. Anyone have an answer?
 

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2003 chevy trailblazer_ls
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I have a couple of question.
1) What plugs were installed?
2) Have you disconnected the battery for approx 30 mins?

If the plugs are Delcos and the battery has been disconnected then I would try the back pressure check on the exhaust. :m2:
 

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2002 olds bravada
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So where are all the vacuum lines? One runs down behind the left side of the engine? What is it for? I get a knock when cold but it dimishes. It runs rough and vibrates with no codes & steady idle. Feels sluggish and strained with vibration when accelerating. Anyone have an answer?
having a knock on cold starts is normal, its cold carbon knock. as for the vibration...no clue. it can be anything from the fan clutch, to the truck just trying to heat up quicker, or even the motor mounts..
 

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2002 olds bravada
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Just an update- I put in AC delco 41-103 plugs a few months ago and read through many threads here. Many state tht the gap should be 0.043 but the manual says 0.050. So, I re-gapped them to 0.050 and it does run smoother. The continued vibration can be felt through the gas pedal, minor through steering wheel and if you put your hand on the front of the engine bay. The engine is smooth with no noticable vibration. I took it to a Midas shop where I know the manager and we put it on a lift. Engine mounts and trans mount "appear" OK but I have doubts. I lived in Las Vegas when I bought this SUV until Jan 2009 when I moved back to Chicago. Rubber fails faster there due to the heat & dryness. (summer 110F and 7% humidity). I believe these mounts are structurally intact but have lost their cushion and become hard. Feeling the vibration through the gas pedal and when in drive with the brake on sounds like the trans mount. I'll change that first with OEM and report back. Sorry for the long post but this seems to be a problem for many of us with aging vehicles or those subjected to severe weather conditions.
 

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2004 chevy trailblazer_ls
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I thought I had mine straightened out but nope. Still has vibration in steering wheel at idle and BS fuel economy. I just drove out of state in my 03 3/4 ton Hemi Dodge Ram truck pulling 10,000 lbs behind me on a car hauler and scored 5 mpg better than my TB pulling nothing.
BTW, I unplugged a couple sensor wires on TB today to see if it would throw a code. Quess what..... NO SES! WTF? Unfortunately, I gave 25,000 for the pile. We spent how much???? Bailing GM out and they build and sell us something that their certified mechanics can't even troubleshoot without a SES code. WOW! Toyota had an accelerater issue and that sucks BUT, atleast they could identify it.
GM..... Have you big dogs ever heard of the K.I.S.S principal?
I'm sorry to those who I offend with these words except GM. Bare in mind, I have several chevy hats and have owned many GM vehicles, but the last few have been JUNK!
 

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2004 chevy trailblazer_lt
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I think you have a basic misunderstanding of the purpose of trouble codes. Trouble codes don't show you the causes, they show you the symptoms.

For example, a clogged cat like you had at one point would not throw a trouble code because the PCM uses an upstream oxygen sensor to control fuel input and a downstream oxygen sensor to measure the efficiency of the cat. When the two sensors start reading close to the same readings, it will throw a code telling you that the cat is running below efficiency.

But if your cat is CLOGGED, it is still working at keeping the exhaust clean; it is just not passing a lot of exhaust. There won't be a trouble code, but your cat is still cooked.

Good mechanics know that they can start looking at trouble codes but they still need to do traditional diagnostics to find out a lot of problems.

Pulling sensor wires may or may not also generate trouble codes because it depends on the sensor and depends on how long it is pulled for. Before any trouble code is generated, there is a list of parameters that must be followed. For example, many trouble codes aren't generated until a certain speed is reached, a certain temperature is reached, a certain number of start/stop cycles is performed or a certain test is run by the PCM.

When you pull a wire, generally what happens is the vehicle resorts to a factory default condition, and often puts a code into 'pending.' If the sensor is still not reading correctly after a period of time, it turns on the light but only after all the parameters are met. (See above for some examples.)

I know it can be a frustrating experience with a vehicle that is giving you problems, but perhaps it is time to change mechanics.

Maybe give us more details on what is wrong with it, what has been done to try to correct it and what your actual mileage is and under what conditions.

Nobody can tell you what is good mileage in your vehicle because they vary widely in their conditions and the way they are driven. I can get 400 miles on a tank of gas pretty easy on the highway in the summer, but if I drive in the city and don't try to squeeze the last gallon of gas into the tank when filling (which you shouldn't do anyway) I am lucky to get 250 miles.
 

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2002 olds bravada
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Vibration & poor mileage

If you have steering wheel vibration at idle it is probably the engine mounts that have hardened and shrunk. I have not heard of them breaking but that could be the cause also. Poor mileage- maybe the plugs are fouled or the wrong ones. I replaced my plugs with non-OEM and I got poor mileage. I put OEM in and it runs great. Also, the throttle body needs periodic cleaning which is typified by an uneven idle or diving idle upon start-up acceleration. Most mechanics can diagnose air/fuel mixture and their cause. Bad injectors, bad cat converter, O2 sensor, etc. The two symptoms may be related if it's running rich. Hope this helps.
 

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2003 chevy trailblazer_ls_ext
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Discussion Starter #14
FYI - I am the original poster on this thread and I just wanted everyone to know my probllem has been solved. I went to West Virgina to pick up a boat and on the way home the trans went. Just quit in the middle of the highway going 65 MPH. One week later 2,300.00 for the trans and about 600.00 in expences my vibration is all gone. No hint of it at all. I have put about 10,000 miles on the new remanufacture trans from Chevy and still no vibration problems. :hissy:

I think it is the year 2010. You would think buy now someone could make a trans that last more than 100,000 miles.
 

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2002 chevy trailblazer_ltz
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I think it is the year 2010. You would think buy now someone could make a trans that last more than 100,000 miles.
178K+ miles on my (very early) '02, original tranny, not one problem with it. And I've towed MANY tons of wood and wood pellets with it.

For what it's worth, have the trans fluid & filter changed about every 60K, or at least back flushed with new fluid....that's all I've done to it.
 
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