Loud Engine Noise... Maybe Serious Issue?

[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.