2000 Chevy Blazer (sluggish, clanking and humming)

Tiny
SCORPIO1025
  • 2000 CHEVROLET TRUCK

I know ya'll are busy answering questions but it would be great if you could find a lil extra time to help me out cuz I'm completely stumped. I'll try to keep this short and if I miss details you would like to know. Pm me please and i'll be happy to include them

2000 Chevy Blazer LS 4wd 4.3L 2door 130k aprox miles automatic trans

first problem that is most recent is it makes a humming/vibration (almost like when u drive over worn out rumble strips on road) when driving between 45 and 60+mph. Funny thing is it only does it when u DEcelerate. Drives smooth until u let off gas, then after a second or two it starts vibrating but quits as soon as u give it even just a quick tap on the gas pedal but will start back up again after a second or two if u dont continue the small trickle of gas. Most noticable at 50-60+mph. Quits completely once u decelerate below 40mph. Very faint hum between 40-45mph. Felt through front of truck and maybe part of middle(between front seats). Doesnt make a difference if u brake or not. Just quits sooner cuz u get to 40mph sooner :P

Truck also seems sluggish at times. Doesnt always happen (no pattern) but at the times it does happen it acts like it doesnt want to shift from first to second gear no matter how much u press on gas, rpms dont even move. And then after a second it lunges like it just got the blast of gas. Makes a gurglish sound so I know the truck wants to go. It just cant. Gurglish sounds faster the harder u press on gas but rpms dont move. After second gear its fine and has no problems. Doesnt seem to matter if truck has been sitting for a while or been running all day nor seems to be consistent w/ weather or temperater. Just does it whenever but only when truck should be shifting from 1st to 2nd. And since I cant recreat problem. I cant test to see if I can manually shift from 1st to 2nd to see if it still has problem. Doesnt happen too often but seems to happen more often when I need to take off quick. Doesnt give any warning. I try to take off quick and I suddenly find I dont have any acceleration power (been a few close calls cuz of that)

another problem that cant really be recreated either is a clanking sound beneath car in middle leaning toward front. (About right between front seats). Clanking speeds up and slows down when the truck speeds up and slows down. Clanking is worse when first starting out and taking corners a little too fast or too tight. Dad says it sounds like u-joints. Sounds almost like a rock is stuck in the wheel well. Only of course its not even near the wheels. A similar sound can be heard (sometimes not always) is when switching from drive to reverse, but not back to drive. However that one sounds to be in a slightly diff location, more toward engine but still in general location.

the order of the problems occuring is first the sluggish not wanting to switch from 1st to 2nd starting about 4 month after I bought it May 2005, second the clanking sound starting 2 months ago, and third the humming/vibration on coast 1 month ago.

history:
bought from an auction and salvaged truck from a rear end hit. Did need frame straightened but no other major damage other than cosmetics. Changed oil regularly. Replaced tires right after purchase including both front wheel bearings. Not to sure on this on but something was causing gas tank to leak when fuel pump was engaged, bad seal or somthing. Had it taken in to shop and repaired. This was prolly 5 months after I bought the car. (It didnt change the problem w/ shifting from 1st to 2nd)
had serpentine replace last week, along w/ air filter and oil change and took thottle body cleaner to throttle body. No change to performance problems. S

so much for trying to keep it short. Sorry
Id greatly appreciate any advice as to what this/these problems may be and how I might be able to handle them on my own.

thanks in advance

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Tuesday, May 15th, 2007 AT 9:56 PM

13 Replies

Tiny
DE3N8FAN
  • MEMBER

Just let me say, you did a fine job of decribing your symptoms.

First thing I would do is check the tires.I know you replaced them but didnt say how many miles are on them. There may be a knot in one. Also, blazers can cup the front tires if you dont keep up on the pressure, so, if you rotated them to the back it could be more pronounced.

Next, replace the u-joints in the rear driveshaft.
(could make all the diffrence.)
((when you decelerate there is no torque on the shaft and componants its kinda like, if you twist a rag real tight its hard and stiff but if you let off on the pressure its flexable thus, bad vibration))

as for the slugishness, sounds like eather fuel pressure, or, it kinda sounds like sometimes you are sucking air into the line somehow, or, somekind of fuel restriction(fuel pump, filter.)

well, this should give you a few things to check let us know how it goes.

P.S. If you want to check the u-joints crawl under and see if you can move the driveshaft up and down or side to side. If you can there bad.

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Wednesday, May 16th, 2007 AT 5:14 PM
Tiny
SCORPIO1025
  • MEMBER

Well I checked my U-joint. It doesnt seem to have play but I had a few friends listen to it engaging (while stopped) from reverse to neutral to drive and back again and they are certain its the u-joint beginning to go bad. It looks rustier than any other part underneath the truck. The tire pressure is fine though I've got a squealing sound on the front passenger wheel (stops when I turn right) now so I look closer into it when I check/replace my brakes. The tires havent been rotated and i'm going to guess they have about 20k miles on them. Still got those lil nob thingys on the inside and a few on the outside.

Got a new question. I have a directional/thermometer device above my rear view mirror and its havnt some issues that I dont have a clue on how to go about diagnosing. The directional is fine. But the thermometer says its 110F outside when its only 30F. It goes back and forth but never under 100 even when I first start the truck or if I try to reset the device. Where is it getting the temperater and how do I fix it? Its not a major thing but somthing that is starting to bug me :P

thanks,
jenn

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Thursday, May 24th, 2007 AT 10:47 PM
Tiny
TOYPAR
  • MEMBER

I hate to be the bringer of bad news buddy but it sounds like no attention has been paid to the Rear end. A decelrating humming acompanied by vibrations is the sign of a Ring and Pinion gear on the verge of going out. The gears faces have worn off leaving you with a large gap between the gears. Put the truck in park on a level surface and push it back and forth, if the truck move over a foot in either direction you need to rebuild the rear end. If you dont you could end up replacing the entire rear end. I have had teeth break off and that was lucky. I have also had the entire differential housing crack in half ending up tearing the entire rear end apart.

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Tuesday, June 26th, 2007 AT 8:53 AM
Tiny
TOYPAR
  • MEMBER

You will need to replace the sending unit. The thermocouple that sends a temp signal to the readout.

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Tuesday, June 26th, 2007 AT 8:56 AM
Tiny
SCORPIO1025
  • MEMBER

Wow. So then do I still need to replace my u-joints? I tried wiggling them and there is no play at all but my truck still makes that clanking sound when shifting from drive down to reverse as if the joints were going out. So is it then my differential making that noise? I cant get it to move when its in park. Jiggle it and wiggle it like most vehicles but not roll it one direction or the other

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Tuesday, June 26th, 2007 AT 10:10 AM
Tiny
TOYPAR
  • MEMBER

Did you m ove it forward and backward? All cars move naturally 3 to 6 inches due to clearances in the drivetrain

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Tuesday, June 26th, 2007 AT 2:24 PM
Tiny
SCORPIO1025
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Lol yes I moved it forward and backward. It didnt move at all but then im only 100 lbs so not like I can put a lot of force into it anyway. My lil berretta I could move and that was bout what u described as normal. My truck is much heavier.

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Tuesday, June 26th, 2007 AT 2:37 PM
Tiny
SCORPIO1025
  • MEMBER

And suddenly my thermometer is working fine again. Must not like reading winter temperature. Y would it bounce back and forth? Where do I find the sending unit? Far as I can tell it goes up into the roof of my truck since its positioned above my mirror. Im not that desperate to fix this to tear apart the lining and I dont see anything outside on the roof. Aside from the luggage carrier bars. Does it run down the frame and somewhere into the engine compartment? Sorry I ask so many questions. I want to learn

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Tuesday, June 26th, 2007 AT 2:45 PM
Tiny
TOYPAR
  • MEMBER

Dont worry about the questions, thats why they make sites like this. In the future someone with your problem will read this and get the same questions awnsered. I would suggest that you go to autozone or napa and purchase the Chiltons or Hayes repair manual. It will have all the awnsers. As for your Humming noise, the typical way to know your rear end is about to go is a humming during deceleration just like you are explaining. As fo the sending unit you would have to call a dealer and ask them where it is located.

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Thursday, June 28th, 2007 AT 6:53 AM
Tiny
SCORPIO1025
  • MEMBER

Ok thanks so much for all ur opinions. One more question. What are the symtpoms of a transmision going out? I listed above what my truck is doing as far as lack of power when in 1st gear. Ive been listening and watching more closely to understand it better and I noticed that it sometimes has a longer than normal delay when dropping from a high gear to a lower one to accelerate faster when already moving (ex accelerating from 45 to 70 to catch up w/ traffic when merging off ramps). This isnt as much of a problem as when its first started and no willing to get up and go. It seems to act better when I let it idle a bit when first started before engaging but still does it now and then. Someone said it sounds like air is getting into the fuel lines. But im wondering if my transmission may be going out so I would like to know what those symptoms often are.

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Thursday, June 28th, 2007 AT 1:19 PM
Tiny
TOYPAR
  • MEMBER

Sounds like the filter is clogged. Get the tranny serviced. You will know when the tranny is about to go when it will not shift into overdrive or the gears start slipping. I.E. You push the accelerator and the engine revs up with out the truck acelerating. These trucks have fairly simple tranny's. If the filter is clogged the valve assembly is not getting the proper pressure and it will take more time to shift than usual.

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Friday, June 29th, 2007 AT 8:31 AM
Tiny
SCORPIO1025
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Great thanks so much. Now I know what to look for. Hopefully I can muster up enough money to get all these things checked/fixed. I like doing things myself but it looks like I need a chilton's and a lil help from a shop. Thanks so much for all the info

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Friday, June 29th, 2007 AT 1:14 PM
Tiny
DAVIDTHOMAS
  • MEMBER

Hey Guys,
I just thought I'd offer my experience with a 2000 4wd LS Blazer. It might help someone get an idea of what might be wrong with theirs.

First off, the little things. There's always been stupid problems that are just annoying more than dangerous.
I too, like everyone else it seems, have had a seat recliner handle break, and if you can believe it, they're not cheap. I've also had the lumbar support rods break in the seat and had my local mechanic weld them back together. I think this is the kind of stuff we get when parts are made in Mexico, and it's important for GM to save ten cents on every part possible.

A little more serious and like many others, my gas gauge went crazy and randomly flips back and forth. And, like others, it was my sending unit. If you have time to do it, I'd suggest replacing this yourself if you've got a jack. I did, and I'm sure the labor cost is a lot if you take it to a garage.

For those who hate blazer for ball joints, I'll admit, one simply has to accept them as part of the Blazer physiology. I've got 137,000 on my Blazer, and the ball joints have only been replaced once so far. Although it's expensive, I don't think it's terrible.

One interesting problem I had was around 100,000 miles, the truck's engine started to 'jerk' when you stepped on it. If you gave it gas quickly AT ALL, it would act as though it was starting to rev and then it would stop, kick the rpms back down, and then do it again. We looked at everything, ran a pressure check, transmission, codes from Auto Zone, and all to find out that if your intake manifold is loose, this is what the Blazer does (computer controlled air-fuel mixture sensors do have their drawbacks!).

Another more serious problem, and probably the one that I thought of most when reading about funny noises, is the throttle body on the transmission. Around 100k, mine got replaced. What indicated that it was the throttle body was a "chunking" noise when going from drive to reverse.

Transmission filters and all other imaginable filters have been replaced quite frequently. But in my opinion, this is simply regular maintenance. Failure to replace transmission filters well before 100,000 miles is, in my opinion, a major cause of transmission failure.

Rear differential plate rusted out, so that got replaced. The bolts that hold it on were completely rusted in and it was a miserable job to get it off. I suggest saving the trouble and having a mechanic do it if yours looks rusted. We used all the de-sticking compounds you can imagine, torches, and even a die-and-tap set, and it was still a pain. So for twenty or thirty bucks, plus the part, the mechanic is worth it.

CV joints have yet to be an issue on my Blazer. At nearly 140k, maybe I'm lucky? I don't know, but sooner or later I wouldn't be surprised if they go. It seems to be a pretty typical problem on Blazers.

One problem I haven't fixed and hate the idea of having is "cracked engine mounts."
I can imagine that, in my case, it's a combination of living on a dirt road in the country (bumby), truly using the Blazer (towing, going off road) as it is intended to be used, and the fact that the engineers at GM have had issues with balancing/vibrations on their V-6 4.3 vortecs. But nontheless, I'd like to get them replaced, but wanted to know, is it a big job?
They've been "cracked" for several years now and it doesn't seem to affect the way the truck drives or handles. But at the same time, I like to keep everything in correct and running condition.
So is it worth it, and how much work is involved? I don't think I'd want to go through the hell of lifting an engine out, or even disconnecting it from the transmission for that matter, but if a mechanic can do it within, say, a $400 budge for the labor, I'd consider.

Another issue I have is that as of now (137,000), I have my engine light going on and off intermittently. There's a bunch of engine/transmission codes to go along with it, and I've had that done, but 'problem shooting codes' turn out to be about as helpful as my dog at helping me find out what's wrong or even where to look. It's ran for the last 20,000 miles with this going on, and nothing seems to be wrong. The engine sounds normal through the entire rpm range, transmission is great, everything seems great. Anyone else had this happen to them? Any suggestions?

One more issue. Blazers are rated to get 17/22 mpg. Of course, 22 is a legal lie put out by the EPA, but I used to get about 19 or 20 on the highway, and 16 or 17 in town. In the last several thousand miles my fuel economy has dropped to a flat 15. I can beat the hell out of it for a full tank ramming around town, or I can get up on the highway and set the cruise on 65 for a whole tank, and either way it's 14.7-15.5mpg, so basically 15 flat, no matter how you look at it.

Is this an issue anyone else has had? If so, what did you do to fix it? I've tried every imaginable fuel additive, valve cleaner, injector cleaner, etc etc, but to no avail. Again, engine seems to run wonderful, except for the fuel mileage. Good synthetic is used in it too.

Also, do you think the engine/transmission code mention above coupled with the poor fuel mileage could shed some light on anything wrong?

Thanks for any response, and any questions, feel free to ask. Also, I hope this might help someone else.

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Tuesday, June 3rd, 2008 AT 6:48 PM

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