4.2L Dieseling sound

[zaid3ssaf]

4.2 with 235K miles and the valvetrain is very noisy. On a cold start, the tapping is very audible but once up to temperature, the tapping becomes more like a diesel motor. Over the last 2 years, I tried a can of seafoam in the crankcase and then changing the oil after 200 miles, a can of liqui Moly engine flush and idling the engine for 15 minutes then changing the oil, a can of Liqui Moly hydraulic lifter additive for 3000 miles then changing the oil, changed the oil to Mobil 1 5W-30 High Mileage, new spark plugs (AcDelco 41-103), and new ignition coils. I also had a can of seafoam through throttle body, new VVT solenoid, and new cam position sensor.

At this point I am not sure if a need to carbon clean my cylinders, flush the crankcase with ATF (method by MRRSM), or just accept the fate that it will always be like that . I am worried that maybe the oil pressure isn't good enough for proper lubrication especially that we dont have a pressure sensor in our 4.2. The pressure switch is new though its not OEM.

Here's a video with the the serpentine belt disconnected:

I also attached pictures of inside of the cylinders if anyone is interested

 

[mrrsm]

First… It would be very helpful if you could shoot one or more videos ...moving the Cell Camera around the Top of BOTH sides of the Engine compartment and lingering in the various spots where the “Thumping” Noise seems to be the loudest. Then… move the camera adjacent BOTH Wheel Wells and pausing on either side long enough for the loudest sounds to stabilize.

Lastly, move the camera with your arm extended (safely) underneath the vehicle and hold the camera close to the junction between the 4L60E Trans and the Back of the Engine Block. Allow the camera to remain there long enough to capture stable sounds.

If you can do these Vidz… it will give us all enough information to compare, contrast and Pin Point all of these locations... BY SOUND. This would go a very long way toward figuring things out. There are many more experienced Member "listeners" here to help... if the chance to listen is created by your efforts.

Next… The Most Comprehensive Test Series EVER done on the subject of having “Fake Oil Pressure” from the Dashboard Oil Pressure Gauge comes to us courtesy these Three Videos from @MAY03LT and should guide you in doing what he does herein to determine the ACTUAL Analog Oil Pressure at Idle and at Raised RPM Levels. THIS Test is ALWAYS Definitive and is the only way to know for sure what the Oil Pressure in an Aging Engine is at any given moment.

 

[zaid3ssaf]

Thank you @MRRSM. I had May03LT videos on my mind for quite a while. What throws me off is that our service manual says 12 PSI is normal oil pressure while in the video it goes to 70 PSI (with or without the proper tool). I have a stethoscope mic coming in the mail soon and I'll try to see if it catches the audio better.

I have seen a video earlier in which a trailblazer had the same sound as mine and the consensus was that it was a rod knock. That doesn't make a lot of sense to me because a rod knock would get louder when revving as opposed to going away. (Sound at 10:20). The knock that I'm hearing is less pronounced than what is in the video.

 

[mrrsm]

In the case of this Lovely Hispanic Couple... "Uncle RODney... Has DEFINITELY Come -A- Knockin". But in your case... I'm NOT so sure. The Definitive "Rhythmic Thumping" of a Rod-Knock so very evident in Post #3 is fairly easy to spot in his case; in part, because as he stepped on the ACC Pedal and the Engine RPM increased... the "Thumping Sound" subsided.

This happens because at Low RPM... There isn't enough Centrifugal Force to keep the "Big End" of the Rod from Banging against the Crankshaft Journal as the involved Piston changes direction at TDC, thereby creating enough "slop space" in between where the Con-Rod to Crankshaft Bearing has FAILED, allowing for a LOT of Freedom of Movement. The Classic Rod-Knock happens each time this Change of Direction for the involved Piston-Connecting Rod occurs.

But at Higher RPM...the "Big End" of the Connecting Rod is pressed hard and evenly against the Rotating Crankshaft Journal (...think... it would be like getting pinned in your seat on a Roller Coaster ONLY when you head Downwards...). In any case, without hearing the 'requested videos' I mentioned in my last response to you... and being able to make some comparisons... there isn't enough evidence here to convince me, one way or another. Keep in mind that in the cases involving Severely Cracked Flex-Plates... a similar "Thumping Noise" may be present. Hence my request for the additional Under-Body Videos with Sound.

One last thing that I really wish we could all easily access would be "An Inexpensive Vibration Analyzer". Having one available in situations like these would certainly allow us to Drill Down on the Frequency and Amplitude of Vibrations emanating from an Engine Rotating Assembly in Crisis.

Recently, I got curious about just building one myself using an Arduino Kit Set Up with a sensitive Piezo-Electric Vibration Sensing Sub-Unit as the necessary sensor to include in the design. THIS Article Describes How to Build One:

Piezo Vibration Monitoring Sensor with Arduino

Detecting and measuring vibration can be used for several applications, Decision making circuits or alarm circuits. The best method to detect vibration is Piezo electric method. The vibration sensor or…

theorycircuit.com

I like THESE Videos as being the BEST Exemplars because they Demonstrate just how Really Simple these Vibration Sensing Circuits here that can be created by using:

(1) An Arduino Nano USB Powered Micro-Controller.
(2) A Small Breadboard with some Short Jumper Wires.
(3) A One Mega-Ohm Resistor.
(4) A Flat Brass Piezo-Electric Vibration Sensor.
(5) The Arduino IDE Application installed on a Laptop Computer.
(6) The VOP's Code via the Arduino IDE Application on a Laptop PC.
(7) Using these Items & SW... He creates his own working "Knock Sensor" .

The important thing to remember is that the "Knock Sensor" would have to be attached to the Engine in BOTH the Vertical and Horizontal Axis in Separate Tests in order to isolate the "Thumping Vibration" in either One Axis ...or the Other.

Following on with this idea, THIS VOP provides even MORE sophistication and Information using the Arduino IDE Code that allows you to View the Output Signal on a Graph.. Then by Changing the Value of the Resistors (or better yet, adding in a Potentiometer instead in their place) you can adjust the Sensitivity of the Circuit, which would be helpful to Narrow or Limit the Frequency Measurement to less that 10 Hertz in order to pick up and isolate the "Knocking Noise" and be able to see what that looks like on Screen.

Here is yet another Clever Arduino Design(with Code) for Measuring Vibration when attempting to Balance either a Propeller or a Motor using a Three Axis Accelerometer Program instead.:

DIY vibration meter for propeller or motor balancing (etc.): Arduino + MMA7361 - RC Groups

Mini-HowTo DIY vibration meter for propeller or motor balancing (etc.): Arduino + MMA7361 R/C Blogs

www.rcgroups.com

Finally... This information covers the Designs and Theory of Operation of the Trembler Switch - like "Mini-Sense" Piezo-Electric Low Vibration - Low Frequency Sensing Components in a PDF:

 

[zaid3ssaf]

I did an oil pressure test without the special tool. At cold start, the pressure goes up to 75 PSI, then goes down gradually as the oil warms up. At operating temperature, the pressure was at 18 PSI at 680 RPM, 60 PSI at 1500 RPM, and 75 PSI at 3500 RPM. I actually decided to keep the gauge connected permanently as I routed it safely.

For the noise here's a video. please accept my apologies for it was windy so I could stay longer at each point but I tried to cover all the angles.

 

[mrrsm]

THAT is the BEST Demo Video EVER posted via YT Link to GMTNation. VERY Nicely Done! With your Analog Oil Pressure also being so Nominal... I think you can Rule Out Rod Knock. My guess is that at this point in the High Mileage Life of this LL8 that what you are hearing at lower RPM is Piston Slap.

If any one of your Connecting Rods had broken down enough to loosen and make distinct "Knocking Noise"...the Motor Oil being pumped through the Cross-Drilled Crankshaft to feed the Con-Rod Large End Bearing Surfaces would have simply poured out and be slung all over the insides of the Crankcase. THIS event alone would have resulted in a Large Drop in Oil Pressure... Which is NOT Evident HERE.

If you examine these images of the Upper Inner Cylinder Walls of a 2004 LL8 Motor with around 160,000 Miles on it before this Tear Down... You'll notice a sort of 'Scalloped' shape dug into their surfaces in their Direction of Rotation.

This phenomena occurs because just BTDC (Before Top Dead Center) each Piston has to "Rock Back and Forth" during their turn around positions from rising up inside each Cylinder on the Compression Strokes and then Plunging Downwards HARD during their descent on the Power Strokes:



As you can see... this sudden change in direction during this Rocking Action causes the Rings to bear hard against the upper walls of the Cylinders and cause this Unique Wear and this Rocking Action causes the Rings to bear hard against the upper Pattern familiar to all In-Line Engines. The resulting freedom of movement cause each Piston (some more than others) to SLAP their Upper Piston Head Sides and their Lower Skirts HARD against the Cylinders and ...make Diesel Engine Like Sounds in the process.

These events happen over Billions of Cycles on the life of a Very High Mileage Motor and they Take Their Toll Over Time ...wearing out a Scalloped Section into the 1.50mm Thick Chilled Cast Iron Cylinder Liners and doing likewise to the Pistons Heads, Lands and Grooves... Rings and Skirts... gradually wearing off the Protective Graphite Impregnated Coating and allowing these sounds to amplify over time.

 

[zaid3ssaf]

Thank you, MRRSM!! it makes me happy to post something useful for this community. I will make a time-lapse video starting the truck from cold up to operating temperature with a split screen of OBD RPM and coolant temp readings. I'll have to figure out a way to animate the OBD spreadsheet output with video.

Its interesting to understand piston slap from a mechanical perspective. I'd be happy to get another 30K miles from this motor and it has served me well. In the meantime, I'll do a compression test for extra peace of mind.

 

[mrrsm]

You might also want to visit some of the more Recent Threads covering the use of ACDelco Top Engine Cleaner after Pulling the Spark Plugs to perform a 'Carbon Busting Piston-Cylinder Soak' . Over time... Partial or Un-burned Fuel in Compromised Cylinders can collect as a "Gas-Gum Shellac" in between the Pistons' Lands and Grooves and Glue the Two Low Tension Compression Rings tightly against all of the Pistons, thereby accentuating this 'Piston Slap Phenomena'.

In the GM TSB covering this Repair suggests not allowing the ACDelco-TEC to soak for longer than (3) Hours before evacuating all (6) Six Cylinder with the Spark Plugs REMOVED. First, you have to Pull the Fuel Pump Relay and then Turn Over the Motor for several 10-15 Second events to Blow out the Black Carbon Mung Residue into some "Scott" Blue Shop Towels stuffed down inside of the Spark Plug Wells to absorb the Crap coming out. This MUST be done, lest you risk Hydro-Locking the Engine and Wind up Bending your Con-Rods... Like Pretzels.

One last thing worth mentioning here is the concept of "Quench". This Weird Word represents the Final Space between the Piston Heads and the Very Top interior of the Combustion Chamber that must remain NOT TOO OPEN and NOT TOO CRAMPED. Normally, this Distance allows for a Volume at TDC that establishes a fairly even amount of Compression between all (6) Cylinders. This gives each Piston the chance to produce EVEN POWER during the Combustion Stroke into the Crankshaft using a certain Thickness of MLS or "Squash-able" Head Gasket.

However... If One Cylinder has Too Much "Quench" above its Neighbor Pistons due to the Asymmetric Build Up of Carbon Deposits... That 'Balance of Power' can become Badly Disturbed. So... getting rid of the Black Carbon Mung in ALL aspects of its presence On, Around and Above the Pistons and Combustion Chambers will tend to allow the Engine to run more smoothly.

 

[zaid3ssaf]

You might also want to visit some of the more Recent Threads covering the use of ACDelco Top Engine Cleaner after Pulling the Spark Plugs to perform a 'Carbon Busting Piston-Cylinder Soak' .

I was thinking about this for a while now. I bought 2 32Oz cans of TEC but they won't be here till thanksgiving (for some reason). I'm wondering if I can do the same with seafoam. They both have petroleum distillates but seafoam has isopropyl alcohol

 

[mrrsm]

To pay you the compliment of being blunt:

Sea Foam is to ACDelco Top Engine Cleaner ...what Vinegar (Acetic Acid) ...is to Sulfuric Acid.

Please... Follow the Directions for Using this stuff OUT OF DOORS and never inside of a Garage or within Confined Spaces, as it has a VERY Highly Active Level of VOCs (Volatile Organic Compounds) that are Very Deleterious to Human Health.

 

[Sqrly]

So, my Envoy isn't supposed to sound like a diesel while idling after warmed up?

It seems a few people here have spent a lot of time with the Atlas I6. To them I ask, does it really matter?

I actually find the noise kind of soothing. I've spent a lot of time with Hondas and when they sound like a sewing machine, you know all is well.

This vehicle might see 5k mi a year from now on and it will be properly maintained, unlike before I got it.

I didn't see any sludge when I changed the oil. I put in a synthetic blend and plan to use that for a few changes before going full synthetic. Not because I want to but because it's difficult to find 5W-20 conventional oil here.

It's runs fine other then throwing a 302 code if I let it idle too long. I haven't checked the plugs yet, that's on the list with many other things.

 

[Mooseman]

This engine does have its own sound but not like a diesel. It's kinda like a hum to me. Maybe yours has something in the valvetrain or timing chain?

 

[mrrsm]

If you are getting a Flashing CE Light...this will need a Deeper Diagnostic Dive ASAP. Try checking into the various Threads that concern "How to Perform an ACDelco TEC (Top Engine Cleaner) Treatment" to De-Carbonize the Trapped Top Compression Rings and Combustion Chambers. If you remove your Resonator to Throttle Body and find Dirty Motor Oil pouring out from inside... it is a SURE Sign of High Engine Blow-By Crankcase Pressures.

These Blow-By events pressurize and push random Dirty Motor Oil in and around the Spinning Valve Train Components while migrating under Blow By Pressure out through the Short Elbow to PCV Pipe in the upper front of the Valve Cover then entering the underside of the Resonator.

From there it accumulates and then moves through the Resonator and thence down through the Throttle Body and Intake Manifold Runners, only to mix with Ingested Air and Fresh EFI Fuel Sprays right at the Lower Intake Manifold Engine Head Intake Ports, confirming all of that event as being the source of the eventual congestion of Carbon Black "Mung" Contamination of the Combustion Chambers... and MORE.

The resulting Excessive Carbon "Mung" Build-Up can invade the areas adjacent to the 24 Valve Seats and thus...increase the Compression Ratio above 10:1 by accident and invite *Pings* and Stutters from Pre-Ignition events due to "Increased Quench" that likely matches up with your P0302 issue on Cylinder #2.

If you Pull the Engine Dip-Stick and Smell a Heavy Concentration of Un-Burned Gasoline... this too is a confirming artifact of the Trapped Compression Rings issue due to their Very Thin Design and Very Low Tension. Their design invites a Gooey, Gluey, Gas-Gum to invade in and around the Rings via Un-Burned Fuel forming a Glue- Like Lacquer ...while Squeezing and Freezing them all ...Deep within the Lands & Grooves of the Pistons.

The looseness of the GM OEM Graphite Coated Short Skirted Pistons without having those Comression Rings properly expanding and compressing inside of those Grooves to ameliorate all of the *Rattling Clatter* ... will make for a Very Noisy Engine from the excessive Piston-Rocking & Slapping.

The resultant escape of the Dreadful Fuel-Air (and Oil) Mixture passing around those Trapped Rings... pressurizes the cavity below and inside of the Lower Crankcase. The Un-Burned Fuel will Mix with and Reduce the Motor Oil Lubricity and its Protective Qualities and... And with Nowhere Else To GO... those Un-Burned and Partially Combusted Gas Vapors soon head upwards, out through the Cathedral Shaped Rhomboid Casting passages in the sides of the "Lost Foam" Engine Block... rising upwards into the regions just under the Valve Cover.

It sadly follows on that the Catalytic Converter will also suffer due to Excessive Oil and Fuel Contamination that can eventually "Poison The CAT" in this like manner. The Trapped Compression Rings can become the Death Knell of the CAT. If you take Thermal Readings of the Front and Rear Sections of the CAT and the Front areas Temp is Much Higher than right at the Rear of the CAT... this is symptomatic of having a "Poisoned CAT".

NOTE:

Some of these problems can be avoided or even delayed somewhat by returning to Making Oil and Filter Changes Every 3,000 Miles in consideration of just how MUCH Un-Burned Fuel and Pure Black Carbon can REALLY contaminate the Motor Oil of Aging GMT360 Engines... if PUSHED or Forced to endure these decaying conditions for 5,000 to 8,000 Miles or more. Doing otherwise on High Mileage Motors is to invite these issues visiting these Elder Engines... MUCH sooner than later.

In a Nutshell:

 

[Sqrly]

@Mooseman

I'll take a vid with my phone. Can I upload vids here or do I have to stick it on youtube and link it?

@mrrsm

That is a very detailed in depth analysis. I actually understand it all. (You duplicated one paragraph) I've already read the "How to Perform an ACDelco TEC" post as well as how to change the lifters.

The mil is not flashing and it doesn't come on (steady) unless I let it sit idling for like 5 minutes or longer when it is warmed up. It doesn't do it in the morning when I let it idle to warm the interior while I clean the dew off the windows. I can hear the rpm get lower and the engine idling rougher when it does happen.

I just got this vehicle and I haven't even inspected a spark plug yet, that's next on the list I think. I'll take a good look in the resonator to see if there's any signs of excessive blow by. It did just pass smog here in CA.

To give you an idea of what I purchased.

I just pulled 1.5 litres out of the tranny today as it was overfilled.
(Using an Ortho Home Defense battery powered spray handle and some 1/4" drip line, It worked great!)

It had a K&N air filter. Apparently the last owner thought "lifetime" meant you never had to check it.

I'm sure you've seen my fuel tank picture? I'm waiting on an empty tank to tackle that. I've already got all the parts.

The vehicle is actually pretty undamaged inside and out. The owner tried to take good care of it though it doesn't seem they were very good at the mechanical stuff.

 

[Mooseman]

I'll take a vid with my phone. Can I upload vids here or do I have to stick it on youtube and link it?

YT and post the link please.

The mil is not flashing and it doesn't come on (steady) unless I let it sit idling for like 5 minutes or longer when it is warmed up.

That sounds like what I had. From what I can tell, it cleared itself up. No more misfires.

Very Slight Miss at Idle

Yesterday on the TB, at 117k km, saw the CEL come on and code came up for P0304. Fired up Torque and it was missing on cylinder #4 but only at idle or stopped at a light. It's not a big miss since I can't feel it at all and it's just a couple of misses per refresh cycle. While driving...

gmtnation.com

If you can, check the live data misfire counts at idle and higher RPM.

 

[Sqrly]

When I was a kid phones was on the wall in the kitchen!

Anyways, here's a video. The fan blew on the phone at the sides but otherwise the sound is pretty good.

 

[mrrsm]

Nicely Done... Sounds more like you MIGHT have a Cracked Flex-Plate. If you move the Camera under the area adjacent the underside of the Bell Housing and Pull (Gently...Pry) Out the Round, S/S View Port Cover... perhaps we can get more audible confirmation. I am basing this impression on the fact that the sound volume increased as your camera moved closer to the Firewall on the rear passenger side while filming.

 

[Sqrly]

Wouldn't a cracked flex plate make the same noise regardless of the engine temperature? When first started and running at the higher idle speed, it does not make this noise. Now that I'm paying more attention to it, I can also hear it during light accelleration. Stop and go, 25-35 mph, taking the kids to school stuff.

Also, there is nothing between the head and the camera on that side. Unlike the resonator on top and the intake on the drivers side. Perhaps that accounts for the change in the sound.

I saw the round metal pop out plugs on the bottom of the bellhousing last time I was under there. One is about 2" in diameter. Next time I'm under it I'll pop those out and look and listen. I still need to check the fluids in the transfer case and diffs.

 

[Mooseman]

A cracked flexplate sounds more like irregular pinging. That sounds more like valvetrain. Maybe timing chain? Another possibility is the beginning of rod knock. You feel anything when you put your hand on the valve cover at the front? Any noise coming from the open oil cap?

Maybe someone else have any ideas?

 

[Sqrly]

Back to my original question, does it really matter?

Is this a normal sound for a high mileage engine of this type?

This is my first I6 and I don't really know what it's supposed to sound like. I'm used to Honda 4 cyl and SB V8s. The frequency and smoothness of the sound make me think valve train too.

Is the tensioner on the cam chain hydraulic or a spring? Does it even have a cam chain tensioner? I've no idea how the VVT on the ex side works. I know what it does but not how. How do I even check the oil pressure? (I know that last one is on here somewhere, I haven't read up on that yet.)

There's so many possiblities and so many things I don't know about this engine. The priority right now is just figuring out how time sensitive this issue is. I've been tinkering with this thing since we got it. I've taken the last few days off from working on it.

It's never going to be driven a lot or very far. This ones job is ferrying kids to school and an occasional trip to home depot. It probably won't ever get 50 mi from home now that we have it.

This vehicle replaced a 94 Mazda pickup that someone else totalled for us. That 8 spark plug cast iron Ford I4 is practically bullet proof but it sounded, and felt like, it was idling on 3 cyl when it got warmed up. I never did figure that one out and it always ran fine and passed smog with no issues.