2008 Trailblazer Atlas Engine Noise

Red955i

Active Member
Hi All...New to this group and seeking some wisdom and advice. Was given a 2008 Trailblazer (4.2..4WD) with 192,000 miles that had been very well maintained (appears to be). However, it has an engine noise in the lower end I believe to be a rod knock, However you do not hear it at idle. You do hear it when giving the engine gas. Here are two short clips. Do you thinks its a rod? Broken Flex Plate? etc. Thanks in advance! (sorry for wind noise)


 

northcreek

Well-Known Member
Sounds like a rod. I would drain the oil and check for metallic flakes/residue.
 

MRRSM

Lifetime VIP Supporter
My Money is on a Cracked Flex Plate... BUT jik... you should also wait until the Engine is Stone Cold and use a Dead Blow Hammer to Lightly Tap Underneath the CAT Can and listen for a large chunk of Ceramic to Rebound the sound back towards you. If the FP IS Cracked... Bad Motor Mounts, a Cracked Exhaust Manifold and Broken Off EM Fasteners all run Hand in Hand...

There is a Pair of India Rubber Ball Hard Plugs nestled underneath and in between the Back of the Engine Block and the Front Flange of the 4L60E Bell Housing that can carefully be pulled out with a Pair of Pliers.

Elevate the SUV on Jack Stands and with the vehicle set in Park and with the Rear Wheels Chocked Front and Back... Listen and Video the Sounds of the Engine with the Hood Up ...and all around the Wheel Well sand where those Plugs are BEFORE removing them.

Then after removing those Plugs... Re-Video those same locations with the Engine at idle for a good comparison. If you post the both back up here like your other good ones... many here will be able to listen more closely and advise you with their refined opinions.

Large Chunks of Fractured, Rare Earth Impregnated Honeycombs inside the CAT can radiate and echo Bouncing Sounds that will also ring with a Bell Like Quality once loose and laying in the bottom of the CAT.
 
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Red955i

Active Member
My Money is on a Cracked Flex Plate... BUT jik... you should also wait until the Engine is Stone Cold and use a Dead Blow Hammer to Tap Underneath the CAT Can and listen for a large chunk of Ceramic to rebound the sound back towards you. If the FP IS Cracked... Bad Motor Mounts and Cracked Exhaust Manifold and Broken Off Fasteners all run Hand in Hand...
Are you saying a third possibility is a CAT that has disintegrated? Doesnt sound like that to me...Sounds like a rod or a cracked flex plate. Am I be able to inspect the flex plate through an inspection cover?
 

TollKeeper

Well-Known Member
I also think its a rod.. But @MRRSM knows a lot more about these engines than i do, So I would defer to him
 

MRRSM

Lifetime VIP Supporter
I've edited in a few more diagnostic suggestions above in Post # 3. Your engine is too stable in its lack of hesitation and any radical side to side movement at idle to appear to be caused by a Broken Rod. Nonetheless... I very much like @northcreek 's idea about Draining the Oil, Removing the Oil Filter and performing an Autopsy on the Oil Filter in a Bucket of Kerosene looking for floating flakes of Aluminum and probing the Kerosene washout in between the Filter Fan Folds with a Neodymium Magnet for traces of Metal.

This is not our First Rodeo here at GMTN where an immediate impression of having a Broken Rod eventually evolved into the discovery that the rhythmic sounds you've recorded were being announced by Cracks around the Flex Plate TTY Mount Bolts. Just ask @Capote by looking up his "Signature Thread" on this Matter (God Bless the Man... wherever he may be...).

Besides... I just listened to the Second Video again ... and if THAT sound is NOT coming from a Cracked Flex Plat... I'll EAT My Flat Hat... :>)
 
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Red955i

Active Member
I just listened to the Second Video again ... and if THAT sound is NOT coming from a Cracked Flex Plat... I'll EAT My Flat Hat... :>)
After reading what a bitch it is to either drop oil pan or remove engine, I pray you're correct!! Many thanks
 

MRRSM

Lifetime VIP Supporter
Here is more Video confirmation on another Trailblazer that shows where to remove the Stainless Steel Bell Housing Inspection Cover... and Listen Closely for "The Tell-Tale Heart" as Edgar Allen Poe would suggest this sound to be in this similar situation:


By the way... if you must do this work yourself, consider the condition of your 4L60E at the moment. Since the difficult R&R MUST be done for this job, determine if any additional Transmission Repairs are also necessary and attend to them to avoid having to do this job twice.

Remember... that while you are doing this Repair... You should always Replace the Rear Engine Crankshaft Seat ($10.00 or so over @ RockAuto) as well ...just to be sure.
 
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gmcman

Well-Known Member
Usually, if it's quiet when cold, then progressively gets noisy as the oil heats up, then that tends to point to a rod bearing.

I agree that the sound has a slight "tang" to it so hard to tell. Hopefully it's a flex plate, but if the rod then obviously don't drive it anymore. You may be able to change the rod bearings if the crank isn't beat to an egg.

The rod bearing job is a PITA, but not terrible. If you plan on keeping it this can work in your favor both ways.

You have to pull a few of the same parts to remove the engine as you do to drop the pan, which includes the CV axles.

The steering rack also has to be removed or maybe lowered.

Not a monster job, just tedious and if you do pull the pan, plan on replacing the front diff seals and maybe even the steering rack and tie rod ends since it will already be removed.
 
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Red955i

Active Member
Here is more Video confirmation on another Trailblazer that shows where to remove the Stainless Steel Bell Housing Inspection Cover... and Listen Closely for "The Tell-Tale Heart" as Edgar Allen Poe would suggest this sound to be in this similar situation:


By the way... if you must do this work yourself, consider the condition of your 4L60E at the moment. Since the difficult R&R MUST be done for this job, determine if any additional Transmission Repairs are also necessary and attend to them to avoid having to do this job twice.

Remember... that while you are doing this Repair... You should always Replace the Rear Engine Crankshaft Seat ($10.00 or so over @ RockAuto) as well ...just to be sure.
Well I’m in luck there. I work in a company that repairs heavy trucks and we rebuild manual trans, differentials and automatic trans. While we do 50 Allison for every 4L60/65E I could just have them rebuild it even if it’s good. It does have almost 200k on it
 
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Red955i

Active Member
Well I’m in luck there. I work in a company that repairs heavy trucks and we rebuild manual trans, differentials and automatic trans. While we do 50 Allison for every 4L60/65E I could just have them rebuild it even if it’s good. It does have almost 200k on it
I think mine sounds different but I'm praying :smile:
 

MRRSM

Lifetime VIP Supporter
I'm pulling for you, too for the Flex Plate ...With @gmcman 's considerable experience with tearing apart his engine from below... NOT for a "Broken Rod"... but rather for repairing the 4.2L Engine Failed Bearings... I'd still rather N OT have to EAT my Flat Hat... :>)
 
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Red955i

Active Member
I'm pulling for you, too for the Flex Plate ...With @gmcman 's considerable experience with tearing apart his engine from below... NOT for a "Broken Rod"... but rather for repairing the 4.2L Engine Failed Bearings... I'd still rather N OT have to EAT my Flat Hat... :>)
Thanks, I'll pull the inspection cover this weekend and give it a look. I'll keep you posted!! Many thanks!
 

Mooseman

Moderator

TollKeeper

Well-Known Member
... I'd still rather N OT have to EAT my Flat Hat... :>)
And if you are wrong... We would expect a video of that! :smile:
 
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Red955i

Active Member
So...Now the question is...Is there a write up here somewhere on pulling the engine (4WD)? I can't be the first to face this challenge and ant time savers would be appreciated...Thanks!
 

MRRSM

Lifetime VIP Supporter
It might still be “Early Days” yet about having to Pull the Engine. Most of the time, when the Flex Plate Cracks begin to propagate… they center around the TTY Flex Plate Bolt Pattern and eventually the center, Thin Mild Steel area separates from the outer plate that is held in place by the Three Torque Converter Bolts… almost like a “Cookie Cutter”. This means that without having the Torque Converter completely out of the way… the damage there will be difficult to either confirm or eliminate.

Pulling an Atlas Vortec Motor out of any GMT360 Body and Frame is No Trivial Matter. So before then... Your Next Steps in this Diagnosis should be to view this Linked Video and follow the Basic Suggestions made by the VOP (Video Original Poster) herein to seek and find and CONFIRM the presence of any Bad Connecting Rod to Crankshaft Journal Bearings.

Thankfully, because the GM 4.2L Engine is an In-Line Design with complete and Open Access to the Spark Plug Ports… performing these procedures is relatively easy:


This Test is Definitive for Bad or Failed Connecting Rod Bearing(s) and so the necessary Engine work (...and that means doing EVERYTHING NEEDED to it while the Motor is OUT) on the Atlas Engine is ever so much MUCH EZR to perform with the Motor Mounted on the Engine Stand than when trying to work while Laying on your Back under the SUV.

This repair HAS recently been quite successfully achieved by @gmcman, so his counsel to you will have Great Value. However… if you do NOT find this to be the Con-Rod Failure to be the Case… I’m still suggesting that the Flex-Plate will be yet another culprit to be eliminated.

Mind you, it will be almost as difficult... but not as much work as yanking out that Engine. Of course... if you can indulge your Shop for the Lion's Share of this Labor... making the immediate decision to just R&R&R (Remove, REPAIR, Re-Install) that Motor will come with a lot less agony.





“Good Science involves investigating (or changing) only ONE Variable at a Time...”
 

Mooseman

Moderator
There is no write up but I believe it is covered in the manuals in my signature. Did find this info:



 
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Red955i

Active Member
It might still be “Early Days” yet about having to Pull the Engine. Most of the time, when the Flex Plate Cracks begin to propagate… they center around the TTY Flex Plate Bolt Pattern and eventually the center, Thin Mild Steel area separates from the outer plate that is held in place by the Three Torque Converter Bolts… almost like a “Cookie Cutter”. This means that without having the Torque Converter completely out of the way… the damage there will be difficult to either confirm or eliminate.

Pulling an Atlas Vortec Motor out of any GMT360 Body and Frame is No Trivial Matter. So before then... Your Next Steps in this Diagnosis should be to view this Linked Video and follow the Basic Suggestions made by the VOP (Video Original Poster) herein to seek and find and CONFIRM the presence of any Bad Connecting Rod to Crankshaft Journal Bearings.

Thankfully, because the GM 4.2L Engine is an In-Line Design with complete and Open Access to the Spark Plug Ports… performing these procedures is relatively easy:


This Test is Definitive for Bad or Failed Connecting Rod Bearing(s) and so the necessary Engine work (...and that means doing EVERYTHING NEEDED to it while the Motor is OUT) on the Atlas Engine is ever so much MUCH EZR to perform with the Motor Mounted on the Engine Stand than when trying to work while Laying on your Back under the SUV.

This repair HAS recently been quite successfully achieved by @gmcman, so his counsel to you will have Great Value. However… if you do NOT find this to be the Con-Rod Failure to be the Case… I’m still suggesting that the Flex-Plate will be yet another culprit to be eliminated.

Mind you, it will be almost as difficult... but not as much work as yanking out that Engine. Of course... if you can indulge your Shop for the Lion's Share of this Labor... making the immediate decision to just R&R&R (Remove, REPAIR, Re-Install) that Motor will come with a lot less agony.





“Good Science involves investigating (or changing) only ONE Variable at a Time...”
Thanks, I have used that test successfully before and it was next on my list. Our shop deals with medium & heavy trucks. I've seen a lot of broken flex plates and I agree most start are the bolts holding it to crank. One of the BEST cheap Chinese tools I ever bought on Amazon was a Depstech Endo camera. Super high resolution, Several foot long fibre and it works through a cell app. I put that up there and everything around those bolts looked fine. So unless it broke at converter I didnt see it. I drained oil into a large clear container in the sun and also saw nothing...which was odd if it was a bearing As for removing the engine, I'm on my own. Can't use shop labor for that. My question or thought is...the truck is in great shape, but has 192,000. Assuming it is the bearing, To go through all the labor to drop the pan, to change the bearings (assuming the crank isn't toast) how much additional work is it changing the engine? At the the end of the day I would have a 192,000 engine with new bearings vs a low mile engine. Is it really that much of a nightmare? FYI...I'm not looking for a larger project than needed. I have another "Chevy" project that's been on the back burner for decades. I bought it with 20,000 miles when I graduated high school, put it in a garage when I got married, and it's been sitting there ever since. Registration and inspection expired in 1986. I'd rather work on that :smile:
 

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Red955i

Active Member
There is no write up but I believe it is covered in the manuals in my signature. Did find this info:



Thanks.....No write up because it sounds like a novel to write. I've seen videos where guys decide to lift the body <gulp>
 

MRRSM

Lifetime VIP Supporter
Chevelle... with the 396 CID Power Plant under the Cowl Hood?

P.S.

I'd rather take a Turkish Bath with my Dead Mother than try to do ANY Major Engine Work on ANY LL8 Engine with the Motor still installed in ANY GMT360... 2WD or 4WD...
 
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Red955i

Active Member
N
Chevelle... with the 396 CID Power Plant under the Cowl Hood?

P.S.

I'd rather take a Turkish Bath with my Dead Mother than try to do ANY Major Engine Work on ANY LL8 Engine with the Motor still installed in ANY GMT360... 2WD or 4WD...
Nope...1969 Camaro Indy Pace Car Convertible.
 

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TollKeeper

Well-Known Member
N

Nope...1969 Camaro Indy Pace Car Convertible.
I got the reverse of that... Non pace car, Orange with White Stripes.
 

MRRSM

Lifetime VIP Supporter
Re: Post #18... My apologies for the secondary repair suggestions. That is one of the problems whenever Welcome Folks newly arrive here at GMTN... One never knows what their True Level of Mechanical Aptitude and Experiences are... and almost invariably, my default response is to try to think of every possible solution path... just not to miss any important details.

...and about the DEPTECH Wireless Camera Probe ... I'm with YOU, Brother... I LOVE the use of mine in being able to see into otherwise inaccessible areas inside Engines and Vehicle Under-Bodies, normally out of view to "The Naked Eye":

DEPSTECH1.jpgDEPSTECH2.jpgDEPSTECH3.jpgDEPSTECH4.jpg
 
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gmcman

Well-Known Member
I hate to be the bearer of bad news for both of us, but it is NOT the Flexplate it looks fine!!
That's a bummer for sure.

If the body and interior is good, used engines are quite plentiful. If I had to replace the LL8 with a used one, I would absolutely change the rod bearings regardless of mileage. Also a good time to replace the timing chain, tensioner, and front cover which is pretty much the oil pump.

Keep us posted.

@MRRSM , I have that camera also and it works well.
 
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Red955i

Active Member
Re: Post #18... My apologies for the secondary repair suggestions. That is one of the problems whenever Welcome Folks newly arrive here at GMTN... One never knows what their True Level of Mechanical Aptitude and Experiences are... and almost invariably, my default response is to try to think of every possible solution path... just not to miss any important details.

...and about the DEPTECH Wireless Camera Probe ... I'm with YOU, Brother... I LOVE the use of mine in being able to see into otherwise inaccessible areas inside Engines and Vehicle Under-Bodies, normally out of view to "The Naked Eye":

View attachment 96976View attachment 96977View attachment 96978View attachment 96979
I have that one, and I then bought their yellow one which is higher def. I can't tell you how much time they saved me. I work on boats on the weekends and if you think cars and trucks are a bitch, boats are even worse. Builders could care less about how the engines are situated in a boat. Pic #1 Look at how far back these are tucked. The white edge is the immovable deck. There's no pulling the distributor in this boat. Good luck getting to the oil filter, starter etc. So the camera is great when you have to find leaks etc. Pic #2 When you work on a car, truck and your repair doesnt go as planned, you can have it towed home, back to your shop if you're the repair person etc. Inconvenient, but ok. When you have to pull the engine and the outdrive to change the transom assembly, it is torqued on, No sealant etc. If you put it all back together and the customer puts it back in the water and it leaks, he quickly goes from being a boat captain to a submarine captain, which is usually not good :smile:
 

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Red955i

Active Member
And the winner is....... Rod Bearing #5 is bad.. Now the decision is A) Replace Engine B) Drop pan in vehicle and replace bearings if crank isn't toast. I'm leaning towards A) simply because engine has 192k on it. Thanks for all your help MRRSM,,,,,Sorry about the hat!
 

Mooseman

Moderator
I vote A. The crank has likely sustained some damage and also sent shrapnel all over the place.

Just be sure to get ONLY A 2008 or 2009 engine. No other will work.
 

MRRSM

Lifetime VIP Supporter
Sorry about the MOTOR... Best of Luck in getting a Good Replacement Motor. Don't forget ALL of @gmcmans 's admonitions about what to Check and what to R&R BEFORE you install the Engine. ***Eating My Flat Hat will go something like THIS:


*** Chaplin performed so many 'takes' trying to perfect this Final Shot, that the Anisette in the Pure Black Licorice he used here for "The Meal" ...actually Poisoned him.
 
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TollKeeper

Well-Known Member
***Eating My Flat Hat will go something like THIS:
I will wait for the live video... :crackup::biggrin::laugh:

I will say this... Normally on threads like these, we get a comment about what to try next, then a week, or month, passes, and we get another response. Its quite something different to see it actually progress in a very timely fashion.

Edit: As far as engines go, you being in NYC, I would suggest starting with Craigslist for a used engine. Usually the best prices. Your biggest issue is that you need a 08-09 only engine, and them being the newest, are usually more difficult to find. I have a 08-09 engine local to me on Craigslist if you end up not finding one local. But shipping aint cheap.

Edit#2: Correction, the 08 engine I saw yesterday is gone today!
 
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TollKeeper

Well-Known Member
Did a little pre-emptive looking about.. Boy there aint much up there for 08-09 trucks!

No year seen for this one.

And thats it... ouch!
 

Mooseman

Moderator
Did a search on car-part.com using a Manhattan zip and found some but starting at $1200! LKQ weren't any better at around $1500.

Being the last two years of production, lower production numbers and non-swappable with previous years have made these more expensive unfortunately.
 

TollKeeper

Well-Known Member
Found a couple on eBay. One looks to be fairly close?

Closest one.. 118k miles, 90 day warranty, and free shipping to the closest LTL or business.
1250 or best offer.. If its close enough, offer him 700, and that you will pick it up. That will save him about 300 in shipping alone.

66k miles, 90 day money back, and free shipping?
2000 or best offer.
 
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Red955i

Active Member
UPDATE: Before I bought the engine shown above I looked up their BBB Rating. More "F's" than my ex-wife so they won't be getting my business. In the meantime I started prepping the '08 Trailblazer for engine removal. Wish I had read about the fan removal before getting there. I ended up taking the whole pump out. I see someone had changed the thermostat as the third Alternator bolt was left out. All of this leads me to my next questions. #1 - What parts should I look at replacing on the new "used" engine to save myself some grief? #2 - In ordering from RockAuto what part/manufacturer can I safely use and which should I definitely stay away from? I'm assuming I should replace the thermostat again even though it looks new. I believe it comes with the housing. Coolant Temp Sensor too? Alternator? VVT solenoid? Waterpump? (there is one on Rockauto that says it comes with the fan. Any good? Looking at an engine at a local yard tomorrow. Praying its still in vehicle as these guys can tell you it has 90,000 miles and it could have 400,000 I havent really found a way to check. Is there? Can you run an inspection check online? Where is the VIN on the engine?
Thanks for your continued advice!!
 

Mooseman

Moderator
#1. You could take the oil pan and timing cover off and inspect the timing components. The guides and tensioner have been known to fail once in a blue moon. The phaser as well. I'd replace the CPAS, t-stat, temp sensor, water pump.

#2. Depends on which parts. Timing components can be bought as a kit from various sources however don't know their quality. I had bought some off brand kit and it worked fine. Pump and fan clutch: ACDelco. Plugs: ACDelco 41-103 ONLY. I wouldn't trust the pump and clutch kit unless it's a good name brand.

The exhaust manifold is a known high failure part. Dealer manifolds are junk. Dorman and others sell an improved version. Look for those that say they have been improved.

If the engine is out, you could ask for the VIN and do a Carfax on it. Could give you some info. If it's still in the truck, they should be able to get it started before pulling or at least power up the cluster to see the odometer. On the block, I found this info which should be the same for our LL8 engines:
 

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