Loud Engine Noise... Maybe Serious Issue?

[Kwing]

I have an '07 Tahoe LT 2wd with the 5.3. Bought it 2 years ago with 130k, have 194k now. Earlier this year (march or april) my wife was driving it to work daily and started complaining of a banging noise when she accelerated. I drove it and it sounded like a rough AC compressor clutch, so i had her kick it on and off while i watched the clutch, at which point I noticed the 2-3 inches of travel the engine had on RPM change. Motor mounts were TOAST.

Fast foward to 2 weeks ago, I FINALLY replaced the motor mounts. That job is NOT for the faint of heart or weak of back. Made a world of difference (duh). No shimmy, shake, or vibration. But I'll be darned if that banging sound ain't still there.

However, now that the motor isn't doing riverdance, I have a terrifying suspicion of what it is. I'm not going to share my suspicion, I'll just list the symptoms and let you all judge it.

It's typically on acceleration, but not always. Sometimes it does it at idle. Usually within the first 10-15 minutes of running, but sometimes later. It's a banging sound, definately under the hood. When it makes the sound, the engine noticably shakes and hesitates like a BAD missfire, but just briefly. The other day i went to pull off from a light and it made the sound machine gun style and I had NO power until the sound/shake stopped.

The sound is almost exactly like the sound of a 2lb sledge on a 1/8" walled 2" steel pipe laid against concrete. Metallic, loud, and almost hollow sounding.

So give me your thoughts based on that or at least some directed questions. I'm afraid saying more at this stage before you opinions can start forming would negate open minded responses.

 

[Doubeleive]

I have an '07 Tahoe LT 2wd with the 5.3. Bought it 2 years ago with 130k, have 194k now. Earlier this year (march or april) my wife was driving it to work daily and started complaining of a banging noise when she accelerated. I drove it and it sounded like a rough AC compressor clutch, so i had her kick it on and off while i watched the clutch, at which point I noticed the 2-3 inches of travel the engine had on RPM change. Motor mounts were TOAST.

Fast foward to 2 weeks ago, I FINALLY replaced the motor mounts. That job is NOT for the faint of heart or weak of back. Made a world of difference (duh). No shimmy, shake, or vibration. But I'll be darned if that banging sound ain't still there.

However, now that the motor isn't doing riverdance, I have a terrifying suspicion of what it is. I'm not going to share my suspicion, I'll just list the symptoms and let you all judge it.

It's typically on acceleration, but not always. Sometimes it does it at idle. Usually within the first 10-15 minutes of running, but sometimes later. It's a banging sound, definately under the hood. When it makes the sound, the engine noticably shakes and hesitates like a BAD missfire, but just briefly. The other day i went to pull off from a light and it made the sound machine gun style and I had NO power until the sound/shake stopped.

The sound is almost exactly like the sound of a 2lb sledge on a 1/8" walled 2" steel pipe laid against concrete. Metallic, loud, and almost hollow sounding.

So give me your thoughts based on that or at least some directed questions. I'm afraid saying more at this stage before you opinions can start forming would negate open minded responses.

no check engine light?

 

[Kwing]

no check engine light?

None. I even hooked up the code reader to check for historical codes and the log is clear.

 

[Doubeleive]

None. I even hooked up the code reader to check for historical codes and the log is clear.

that's not good, sounds like time for a compression test

 

[Kwing]

that's not good, sounds like time for a compression test

I have no problem running a compression test. That's actually reasonable. What scares me is the end game. What is your thought in going that direction?

 

[kbuskill]

I would check the torque converter to flywheel bolts.

Had a big block one time that the torque converter bolts loosened up on and when you would first start it in the morning it sounded like it had a rod knocking but after it warmed up the sound went away.

 

[thompsoj22]

cam chain/tensioner/guide coming apart? the fact that it is intermittent opens the possibility of repairing it before it grenades. Your not really giving much to go on but if gremlins are taking a 2lb sledge to engine components it wont be long til you now exactly what is making the noise

 

[Doubeleive]

I have no problem running a compression test. That's actually reasonable. What scares me is the end game. What is your thought in going that direction?

well I don't know, if your sure that it is the engine and it's loosing power and making a slapping noise, but yet no CEL, then I would do a compression test and maybe pickup one of those cheapy inspection camera's at harbor freight and start digging deeper, any metal fragments in the oil? can you take a video of the sound from the engine compartment and post it up? some engine noise is normal and some is not, my 03 Silverado has a tick that comes and goes it may start up and idle just fine for a few minutes and then begin to tick tick tick, rev it and it goes away till it idles down and it comes back, it has done it for years, lately it has stopped doing it the last 2-3 oil changes, it's just a noisy lifter and it's fairly common the engine runs fine and it's not worth tearing it down to eliminate.

 

[Kwing]

The flywheel bolts are an interesting thought. Although I feel like that would either be rythmic or more consistant (as in I could get it to perform on demand, which I can't).

It's definately not a lifter type noise. I can rule that out right away. I know that noise.

The only thing I could think of in the timing set that would make a noise like this would be a couple missing teeth and the chain catching up, which would puke rods all over the pavement as soon as it happened. It's just too loud for that possibility.

I guess I'll dive into the other symptoms now that flirst blush is out of the way...

I have oil pressure issues going on too. Oil pressure is riding at 40 (straight up, in the middle) going down the freeway. Every once in a while it jumps to the 3/4 mark where it usually rides, but then drops back to halfway. It has done this twice before. The first time was shortly after we bought it. That wound up being a bad pressure sensor.

The second time i had to run a gunk treatment on the oil change to get it to normalize. Now that it's back, my fear is that there's some nasty stuff in my oil (i just did an oil change with the motor mounts).

What I'm getting at is that it almost sounds and feels like I've got a valve sticking open on #8 and slapping the piston.

I was hoping there was some common issue on the 5.3 that could make this easy. I've got 20 years worth of countless 5.7's under my belt, but this is only my second 5.3. I was basically grasping at straws.

I guess it's time to grab a scope, pull the worst plug on the truck to get to, and dive in.

Bummer

 

[Doubeleive]

The flywheel bolts are an interesting thought. Although I feel like that would either be rythmic or more consistant (as in I could get it to perform on demand, which I can't).

It's definately not a lifter type noise. I can rule that out right away. I know that noise.

The only thing I could think of in the timing set that would make a noise like this would be a couple missing teeth and the chain catching up, which would puke rods all over the pavement as soon as it happened. It's just too loud for that possibility.

I guess I'll dive into the other symptoms now that flirst blush is out of the way...

I have oil pressure issues going on too. Oil pressure is riding at 40 (straight up, in the middle) going down the freeway. Every once in a while it jumps to the 3/4 mark where it usually rides, but then drops back to halfway. It has done this twice before. The first time was shortly after we bought it. That wound up being a bad pressure sensor.

The second time i had to run a gunk treatment on the oil change to get it to normalize. Now that it's back, my fear is that there's some nasty stuff in my oil (i just did an oil change with the motor mounts).

What I'm getting at is that it almost sounds and feels like I've got a valve sticking open on #8 and slapping the piston.

I was hoping there was some common issue on the 5.3 that could make this easy. I've got 20 years worth of countless 5.7's under my belt, but this is only my second 5.3. I was basically grasping at straws.

I guess it's time to grab a scope, pull the worst plug on the truck to get to, and dive in.

Bummer

sometimes a valve spring may break, it's known the happen on the engines with v4 mode, not sure of that is a feature on the 07?, they can be fixed by using air pressure in the plug hole which keeps the valve lifted

 

[kbuskill]

sometimes a valve spring may break, it's known the happen on the engines with v4 mode, not sure of that is a feature on the 07?, they can be fixed by using air pressure in the plug hole which keeps the valve lifted

I am glad my '08 did not come with the broken valve spring option

 

[Kwing]

sometimes a valve spring may break, it's known the happen on the engines with v4 mode, not sure of that is a feature on the 07?, they can be fixed by using air pressure in the plug hole which keeps the valve lifted

Mucho good to know, because YES the 07 has v4 mode. Doesn't hardly work worth a poop (above 1500rpm it goes to v8 no matter what), but it's there.

Guess it's worth pulling the valve cover while i'm in there with the scope.

I hadn't thought of a valve spring. Never broke one on an sbc. I've dropped plenty on harley motors and sbf's, but if it is it would be my first GM. Good info!

 

[iamdub]

I'm with Ken on checking the flywheel and torque converter bolts, but mainly flywheel.

No, it won't necessarily always be a constant sound. A friend finally checked his flywheel after parking his truck for an intermittent knocking sound. Rhe only constant was when it did it, it was under load. Sometimes he'd drive it to work for a few days with no noise. The flywheel had a crack about 1/3 the way around the crank bolt holes.

Buuuuuut... The engine hesitating is what throws me off of that trail and points me towards a valvetrain issue. It also sounds like intermittent detonation. Have access to a Tech2 or a scanner that reads live data?

 

[kbuskill]

I'm with Ken on checking the flywheel and torque converter bolts, but mainly flywheel.

No, it won't necessarily always be a constant sound. A friend finally checked his flywheel after parking his truck for an intermittent knocking sound. Rhe only constant was when it did it, it was under load. Sometimes he'd drive it to work for a few days with no noise. The flywheel had a crack about 1/3 the way around the crank bolt holes.

Buuuuuut... The engine hesitating is what throws me off of that trail and points me towards a valvetrain issue. It also sounds like intermittent detonation. Have access to a Tech2 or a scanner that reads live data?

The hesitating doesn't make me flinch from my previous statement...

If the knock sensors pick up the knocking of the flywheel/torque converter bolts then the ECU will cut the timing severely which will definitely make it stumble.

 

[Doubeleive]

So if he stuck that camera in the inspection hole this would be something that could maybe be ruled in or out right?

 

[Kwing]

Ok, I've bought into the idea that the converter bolts are a possibility. The knock sensor argument is compelling. Although I would think the ECU would register a disturbance that significant and regularly occuring.

Regardless, it's easy enough to check, so it's on the list.

Keep 'em comin'!

 

[iamdub]

The hesitating doesn't make me flinch from my previous statement...

If the knock sensors pick up the knocking of the flywheel/torque converter bolts then the ECU will cut the timing severely which will definitely make it stumble.

Good point. I didn't factor that. Them knock sensors can be sensitive! I recall a guy was having KR issues and found it was due to fine vibes from his gear drive timing set.

 

[iamdub]

Ok, I've bought into the idea that the converter bolts are a possibility. The knock sensor argument is compelling. Although I would think the ECU would register a disturbance that significant and regularly occuring.

Regardless, it's easy enough to check, so it's on the list.

Keep 'em comin'!

When it comes to knock, the ECU is quite passive. When I run 87 octane and mash the throttle on a hot day (which is 330+ days a year here), I can hear detonation for a second or so until the PCM responds with retarded timing. This will happen numerous times with no codes being thrown. I've watched a live data stream when doing this and can see knock counts jump up followed by significant timing retarding.

I guess it would have to be consistent knocking under lower engine loads where knock really shouldn't happen before the PCM considers it a fault and throws a code and SES light. Well, it'd probably be a flashing SES light in this instance, but still. BTW, I find mine knocks much less with 89 or higher. Good tuners can vouch that these things prefer 89 or higher.

 

[kbuskill]

So if he stuck that camera in the inspection hole this would be something that could maybe be ruled in or out right?

Quite possible. I would put the front wheels on ramps (unless you have access to a lift) chock the wheels front and rear, set the parking brake, put the transmission in neutral, remove the inspection cover and try moving the torque converter back and forth (rotationally speaking) with a long screw driver and see if there is any slop. You could also try getting a wrench onto the bolts to see if they are tight. This wouldn't completely rule out a cracked flywheel but perhaps the inspection camera might be able to get a look.

The inspection cameras are so small and convenient now. Here is one I have been eyeballing but haven't bought yet...

https://rover.ebay.com/rover/0/0/0?mpre=https://www.ebay.com/ulk/itm/173355960294

I still have the big, comparatively speaking, HF inspection camera. It's handy but not able to get into really small areas.

 

[Kwing]

So I finally bit the bullet and bought a scope. Didn't dig deep enough to start pulling plugs, but I got a purty good look at the converter and flywheel. I have no movement or visible damage on the flex plate or converter. For fun, I also got a good 360 look all around the trans, bell housing, and between the intake/block and firewall. Nothing loose, no debre, none of that nonsense.

So I guess it's time to pull the plugs and maybe the valve covers and have a look.