Rough idle and knocking noise from bottom of motor

[holytornado84]

I have a girlfriend who has a trailblazer that has over 200,000 miles on it and has had an SES light on for sometime now. Occasionally the light will be blinking. I have had the local auto parts store scan the computer for her and it came back cylinder three misfire. I have since switched the coil packs out from cylinder three to cylinder one and have also switched the spark plugs from cylinder three to cylinder two. I could barely notice the knocking anymore and the car seems to idle a little bit better. I then proceeded to go ahead and change all of the plugs out with new AC Delco iridium plugs. After changing all the plugs, I started it up again and it has a very noticeable knock again and runs and idols horribly. I cleared the codes and waited for the SES light to come back on and went back to the auto parts store to have it checked. Still has a misfire on cylinder three. Bought some gum out injector cleaner and put some 93 octane gasoline in the car with it and I am currently driving it around waiting to see if it clears up. Anyone else have any thoughts on what the problem could be?

I forgot to mention that she has to add oil from time to time and is currently 10k since her last oil change.

 

[07TrailyLS]

If you have a misfire you need to change your coil pack for that specific cylinder. Not the spark plug. As for the loud knocking, you may have piston slap or at worst the engines on its way out . Ten thousand plus miles between oil changes is way too far imo. I went 7 thousand on full synthetic for the first time last month and I was nervous about it. I would do an oil change (7 quarts 5w30) AND change out the coil pack and see what happens. Take note of how much oil is removed from the engine. I drive hard and my truck burns exactly 2 quarts every 3000.

 

[Sparky]

Well I'll respectfully disagree on 10k being too long, assuming it is decent oil. I routinely went anywhere from 10k-14k between changes (usually was between 10k-12k) when the light would kick on. I used Mobil 1. 215k miles, ran great, started pushing maybe a quart usage in that timeframe.

Anyway, he did already move the coil and that didn't make a change, so I doubt the coil is to blame.

I'd do a compression test and see how #3 compares to the rest.

If it is misfiring badly that can make it sound like it is knocking due to uneven or delayed firing of the cylinder. Blinking SES is bad, by the way - extended misfiring can damage stuff.

 

[mrrsm]

I agree with @Sparky that using Synthetic Oil beyond the standard 3,000 to 5,000 Mile Change Cycle is more than possible. However... the problem with an engine that has such High Mileage at 200,000 Miles that is also showing operational problems might need More Frequent Oil Changes... especially if you can Smell Gasoline on the End of the Dipstick.

If the odour of Fuel is present... it means that the Piston Rings have worn the cylinders down enough to allow the Fuel/Air Mixture to Burn and By-Pass the Rings as Blow-By.This action tends to allow these combustion by-products to mix with and blacken the Motor Oil in the Crankcase...and thin down its protective qualities and viscosity. Likewise... thinner oil can by-pass the rings and enter the upper cylinder and burn with a High Carbon content residue that will foul the Spark Plugs and collect therein and on the tops of the Pistons.

The Lubricity of ALL Motor Oils ...including Full Synthetics... will suffer when the engine runs under this condition and increases the wear and tear on the Rotating Assembly. All High Mileage Engines consume Engine Oil to some degree later in life.

 

[holytornado84]

Just did a compression test. Results came back cylinder one at 225, cylinder two at 215, cylinder three at 215, cylinder four at 220, cylinder five at 225, cylinder six at 210. from what I have read so far, this sounds like all the cylinders may be fine. Pretty stumped right now from what I have read so far, this sounds like all the cylinders may be fine. Pretty stumped right now

 

[mrrsm]

Any chance for you to Run the Engine for a bit and Take a Short Video after walking the Camera around the outside of the Engine Compartment and while orbiting all around the top of and sides adjacent the engine...so we can all View and Listen to how it is running?

 

[holytornado84]

Don't know why and reposted MRRSM's message but it might be because I'm doing this from my iPhone.

Yeah. I can do that. If I can figure out how to upload it. Give me a little while and I'm sure I'll get it on here. I figured that might be a good idea anyways so that y'all could see what kind of knock it was. Also, it seems to knock a little more when it is put in park rather than drive.

 

[mrrsm]

There are some Very Fine Members here with a lot of experience (like @Mounce ) in dealing with "Things that Go Bump in The Night..." Inside of this Unique Engine...and with so many possibilities "knocking" around...Your video will be The Best Clue to work with. As for the "Double Tap"...just hit the Black Triangle "Report" Button on the Lower Left side here...and drop a message to one of the Admins or Mods...requesting the dupe deletion...

 

[Sparky]

Already got it

Compression sounds good, which is a good thing. At least you're not looking at a possible busted valve, blown gasket, or piston/ring failure.

What does the plug on cyl. 3 look like? Same as the others, or is it whiter, blacker, etc? If it is really black that can be due to a lot of excess fuel being dumped into that cylinder. Ash would be from bad oil burning in that cylinder. really white/blistered would be a lean condition in that cylinder.

 

[07TrailyLS]

Just out of curiosity. If the compression is good and the plugs and coil packs check out, could it be a faulty pcm? Not a pro but it doesn't seem as though there's too many things that can make an engine severely misfire other than plugs wires and bad piston/rings

 

[mrrsm]

@07TrailyLS ... The First Thing that Comes to Mind on an Engine that has over 200,000 Miles on it ... is Carbon Clogged Pistons and the areas around the Valves...with 24 of them... the residue of incomplete combustion over such a long time can REALLY build up inside of the head and Play Hell with compression by reducing the internal VOLUME in the gap between the normally smooth and clean Piston Head and the normally vacant upper Combustion Chambers. This would serve to RAISE the compression level and might cause some pre-ignition problems if all that carbon gets hot enough to "glow".... It would also be interesting to know what the regular water Temps for this engine have been. Here is my engine after 240,000 Miles of Carbon Build Up ...and if you think THIS is a mess...imagine how clogged up the CAT is deep inside... Hmmmm... Perhaps the CAT is also a possible place to look at here too...because of a back-up of the exhaust stream... if it were placing Positive Pressure inside the cylinders, such a delay would interfere with Volumetric Efficiency as a Bottle-Neck in the Exhaust Stream. I'd bet Dollars to Doughnuts it might screw things up for the Incoming Air Stream and Fuel Spray being injected into all those "Smokey Cylinders" because the Exhaust Flow is getting "All Dressed Up...With No Place To Go!":

 

[07TrailyLS]

Awesome clarification. Thank you @MRRSM

 

[Sparky]

I have that problem in my 5.3 on my Silverado. You can hear minor pinging under moderate load after the engine has warmed up, likely from the AFM cylinders that have built up crap in them. Still haven't figured out how best to clean them without yanking the heads - something I do NOT want to do. Going to try fogging the engine a few more times.

Bad enough preignition can be very harmful to the engine.

 

[holytornado84]

Whenever I first pulled the plug on cylinder three it looked like it had a Caramel colored liquid still on it. Oil? I'm guessing. I should have paid more attention to it and smelled it. I still have the plugs with my tools at her sisters house. The car itself bucks from misfire when accelerating and seems to take a lot more time to get up to speed than I remember with my trailblazers. I had an overnight sleep study so I wasn't able to get those files uploaded, but I'm going to try and figure out how to convert them to JPEG or something and get them online so that y'all can hear the knock.

 

[Sparky]

Sometimes you'll get oil in the plug well from weeping O rings on the valve cover seal, and when you pull the plug it will run down the threads. That's not abnormal.

Go ahead and pull #3 again - a new plug won't have any discoloration from use so it may be easier to see how the end of it looks (plus not as much time for it to have gotten oil in the well again).

 

[mrrsm]

Whenever I first pulled the plug on cylinder three it looked like it had a Caramel coloured liquid still on it. Oil? I'm guessing. I should have paid more attention to it and smelled it. I still have the plugs with my tools at her sisters house. The car itself bucks from misfire when accelerating and seems to take a lot more time to get up to speed than I remember with my trailblazers. I had an overnight sleep study so I wasn't able to get those files uploaded, but I'm going to try and figure out how to convert them to JPEG or something and get them online so that y'all can hear the knock.

@holytornado84 ... The easiest way to deal with all multimedia issues you want to publicly share is to go to www.photobucket,com and set up a FREE Public Account as a place to Drag and Drop all of your Mechanical Repair Project Videos and Images. It only takes a few minutes to do this and once you have an Anonymous Account... you can simply copy the link to it and past it here in any future messages that indicate you Dragged and Dropped in New or Updated Images to view. That way ...no Video or Image Conversions will be necessary. Here is a brief video showing you how this is done and remember that if required... you can make all your account data generic (fake) including name and birthday and zipcode, but listing an ACTUAL Email Address is called for. The most critical thing though is that it be made PUBLIC and Not Private.

Here is a link to my own "Bucket" where I keep thousands of Repair Project Images and Videos FREE for the taking:.

http://s557.photobucket.com/user/60dgrzbelow0/library/?sort=6&page=0

 

[littleblazer]

I have that problem in my 5.3 on my Silverado. You can hear minor pinging under moderate load after the engine has warmed up, likely from the AFM cylinders that have built up crap in them. Still haven't figured out how best to clean them without yanking the heads - something I do NOT want to do. Going to try fogging the engine a few more times.

Bad enough preignition can be very harmful to the engine.

Ever try a marine de-carbon spray? 2 strokes have had this problem since the 80s and iirc they work. When you're fogging, you're letting it sit after right? Not to side track the thread or anything but sometimes getting the engine up to temp and just running a whole treatment through it while running works better then the sit and soak method. Then again two strokes are a whole different animal.

 

[holytornado84]

Trying to get somewhere with the photobucket trick MRRSM suggested. Let me know if it does not work as I tried to pull it up myself and had no luck.

 

[holytornado84]

http://vid36.photobucket.com/albums...7-9DB3-4B38-B911-52BFF93B2688_zps1fknbr1c.mp4

 

[holytornado84]

It looks as though the longer file which is over a minute is not getting uploaded on photo bucket. However, the smaller file which is around 11 seconds I have gotten to work and upload. I am going to try and get the moderator to delete all of them besides the 11 minute file and then I will try and get the longer one uploaded somehow.

 

[Mooseman]

Done. Personally, I hate photobucket, which is often times, the cause for broken links to vids and pics. I use YouTube for vids and upload pics directly to the forum.

 

[holytornado84]

You know, I didn't even think about that. I have a YouTube account with lots of videos and I know how to copy the link and paste it. I guess I'll try to do that before the night is up. Thanks Mooseman, for the suggestion and for cleaning up my mess.

 

[holytornado84]

Finally got it uploaded to YouTube if you want to take a look.

 

[Sparky]

Flexplate or torque converter? Sounds towards the rear of the engine. Not a deep thudding like a rod.

 

[mrrsm]

@holytornado84 ...Great Job on doing this "Walk-Around" Video... and your Youtube solution and video post makes me wonder if my own videos even work anymore at Photobucket. @Sparky has NAILED it... We've heard a very recent series of videos just like this and the most contemporary one to read and compare with the sounds and locations of your own is THIS one done by @Capote. If you view his Post Message #69... and again at Post Message #92 ...His excellent images there will show you where to look around down underneath there and get visual confirmation of where the cracks around the inner Flex-Plate will be ...first hand:

http://gmtnation.com/forums/threads/lifter-noise-dull-knocking-bottom-end-troubleshooting.15534/

It may not seem possible that the Flex-Plate could become so completely destroyed in "The Middle" and yet remain roughly in place...but it manages to stay in there because of that Thin Thrust Washer underneath the Bolts holding the broken inner area in place and it's Outer Rim is being held fast by the Three Bolts positioned 120 Degrees apart attaching it to the Torque Converter. They serve to keep it from completely falling loose and jamming up in the space between the very Back of the Engine and the Transmission.

If you review Post Messages #62 & #63 at the link below created by @m.mcmillen for his Complete Engine Rebuild... there is information about how to clean up the machined inner face of the Rear Cover and replace the Crankshaft Seal before installing a New Flex-Plate...which is relevant to your situation because of the damage reported to the back of the 4.2L Crankshaft by @Capote during his repair follow up to this problem:

http://gmtnation.com/forums/threads/4-2-engine-rebuild.16080/

 

[NJTB]

Holytornado, I watched and listened to your video and can tell you it's probably not a main or rod bearing.
If at all possible, split the trans from the engine (while in the car) and check the flywheel area.
I used to be able to remove the two lower trans bolts and replace them with bolts an inch or two longer, then remove all the other bolts on the bellhousing, and slide the trans back an inch or so. The driveshaft has to be removed. When you're done, pry the trans back in and it will slide into place easily riding on the two long bolts.
It was an easier way to remove a flywheel, but don't know if it will work on 4WD.
Also, check to see if anything is flakey with the starter.

 

[Mooseman]

I would definitely investigate this as a broken flexplate. It might not be as broken as @Capote 's but maybe just one "arm" of it is cracked and flexing. If you have one, a borescope could be used to go in and try to have a look at it.

 

[holytornado84]

OK, thanks a lot everyone for helping me possibly narrow this down to the flexplate. I'm kind of hoping that's what it is because so much more is wrong with her car that I don't know if it would be worthy of a bottom end teardown and rebuild. I'll take a look at this in a couple of days possibly with a borescope and stethoscope and see what I can find. I will definitely follow up and repost either way.

 

[gmcman]

You can peek through one of the inspection holes in the trans housing.

Definitely sounds like a flex plate, but don't rule out a rod bearing. Pull the coil pack connector on #6 then 5, then 4, one at a time and double check the noise. Should only take a brief second to determine if it's a rod.

The sound is clear that it's a sharp metallic noise but it's a simple check for the rod.

 

[Mike w]

i think it's a spun rod bearing

 

[Mike w]

here is my cracked flexplate

 

[holytornado84]

Well, I just unplugged each wire harness from the coil packs one by one and listened to see if the noise cleared up. It did not. If I'm not mistaken, this rules out rod knock or even spark knock from premature combustion. I have not attempted to check the flexplate yet because I do not have a borescope. I just figured I would post my results from what I did today to see if I were mistaken about ruling out rod knock or possibly detonation. Thanks to all for any input.

 

[Sparky]

I'd say you're on track.

 

[mrrsm]

When I was still poking around down inside the open front head of the 2002 TB 4.2L... I decided I needed a Cheap USB Mini-Camera to visualize some of the hard to see and imagine parts...and even though the one I got was "limp"...and NOT a True Boroscope... I solved that problem by just winding a length of 0.041 S/S Safety Wire from just below the base of the Camera lens for a few feet in length... and it manoeuvred around inside the motor...swimmingly good. Here are some of the ones offered on Amazon:

https://www.amazon.com/s/ref=nb_sb_noss?url=search-alias=mobile&field-keywords=usb+5mm+mini+camera

 

[Mooseman]

You might not even need a boroscope. @Capote just looked straight at it and took pics with his camera. Might need to turn the engine to look at each "arm" of the flywheel.

 

[holytornado84]

Does anyone know if another flexplate is easy to find or not and if maybe offhand anyone has a part number for it that they can remember?

 

[Mooseman]

I think only used is available or the dealer is expensive.

 

[m.mcmillen]

Amazon has them for $77.74 https://www.amazon.com/dp/B00GTJRLSA/?tag=gmtnation-20

GM part number 12576272

 

[holytornado84]

Woke up late today due to a late late night last night. Barely had enough time to look under the trailblazer but I did notice that there was a horrible oil leak that had saturated most of the undercarriage. The frame on both sides is very shiny and moistened as well as the flex plate cover all the way down to the transmission pan and crossmember. I am figuring that I'm going to have to change the rear main seal. Does anyone know the proper procedure for this and whether I am going to have to pull the transmission completely out and the exhaust etc. in order to put the seal back in with the proper tool? I figured there might be a thread on here about that somewhere but I didn't know how to look it up

 

[mrrsm]

There are quite a few Posts that are a combination of having a Long Diagnostic Curve with the ultimate outcome being that the Torque Converter Bolts, Transmission Case Bolts, Rear Transmission Mount, Drive Shaft and finally the Transmission WITH the TC held inside WILL have to be pulled in order to gain access to the areas depicted in Post #92 of @Capote 's Epic Flex-Plate Challenge. Trying to R&R the Rear Cover and Seal after removing the 8 Bolts holding on the Flex-Pate and the 3 Bolts holding on the Torque Converter... without a complete removal of the Transmission would be very much

... " Like Trying to Take Your Pants Off...Over Your Head..."

So yeah... Please forgive me my Graveyard Humour about the need for all of this extra work...but...the Tranny and Torque Converter as a Paired R&R is a MUST. You can find a large number of "How to R&R the 4L60E Transmission" on Youtube that will be close enough procedurally to what you will need to do and be very instructive on specific things to be careful of (such as the 'Gorilla Glued' Wire Harness for the Park-Neutral Switch R&R and Shift Cable.) Fixing the GM Atlas 4.2L Engine can en become "A Long Road...With NO TURNS in it..."

http://gmtnation.com/forums/threads...cking-bottom-end-troubleshooting.15534/page-3