Learn me: engine knock (or pre-cursor build thread to BB swap GMT900)

I got rid of my 85 k20 suburban earlier this year for something a bit more modern - a 2008 k20 suburban, something that would be a bit more reliable and not prone to failure as often and gain the benefit of some modern creature comforts. 6L90E LQ4 without VVT or DOD so this thing should be robust as a freight train and with only 60k miles on it, I should not have to touch this engine. (ideally the whole point of a buying a newer tow vehicle)

however about 3,000 miles later or so. I have developed a knock... it is only when the engine has warmed up to operating temp and under acceleration of the engine, it is not vehicle speed dependent but engine acceleration (not engine braking or decel). It is most pronounced between 1500-2000 rpm when holding at a steady rpm or blipping the throttle.

At first, I checked the bellhousing and block areas with a stethoscope. I thought it was the flexplate, so I popped the inspection cover off and starter to check the tq converter bolts - they were tight with no signs of witness marks and from what I can see no cracks, everything good and peachy.

so after ruling this part out I move upstream, and I check for exhaust leaks (found none!) so I start unplugging coils to see if the noise goes away and cyl 5 (middle rear driver side head) goes quiet when unplugged. I can rev it and you don't hear it or if you do its soooo verrrrryyy faint. I even swapped coils (for E36 M3s and giggles) still no change.

so I changed the oi l, no metal there and 1st oil change since I got the truck (came with an oil change done upon trade it at the dealer I got it from) knock sound still present.

Then to rule out anything valvetrain, I popped the valve cover off and rotated the engine by hand to see the valves go through intake/exhaust, nothing abnormal - actually the cylinder head is so clean it looks like the engine is brand new. ZERO gunk - nothing.

I want to do a compression test next but I feel that's a waste of time, the truck runs fine and has no performance issues. I get about 9-11mpg but that's partially the 265/75 tires on it and short distance driving.

so TL;DR -> Am I looking at a wrist pin knock or rod knock? what else can I check?

If I have to pull this engine to overhaul it, I am putting a 8.1L big block in because even with a 6 speed the high revving peaky SBC is still kind of a dog when towing 5000lbs and it lacks the low end grunt I'd desire for driveability when towing. Also I don't know how to rebuild v8s properly, rotaries are fine but I never seem put together a pushrod v8 correctly...

HOWEVER the other problem is that I don't see this well documented which makes me believe it may not work. I am still doing some research on that though but people do the duramax swap for a duraburb for this gen but that comes at a hefty price tag.

Slightly collapsed pistons are very common on LS motors, but that generally shows up when the engine is cold. Same for broken exhaust manifold bolts, although if the manifold is actually cracked, it can do different things. They will occasionally knock the top of the cam lobe off, but that should have nothing to do with pulling the load from a cylinder. Sometimes modern engines are just a bit noisy, with their little short pistons and all. I'd drive it until the noise is unmistakeable.

Check the torque on the spark plug, just for E36 M3s and giggles.

First thing I'd do is remove the serpentine belt and see if the noise goes away.

While doing that I would inspect the damper, water pump, fan clutch and all the accessories.

I'd also pull the spark plug and make sure it looks good, and probably put a new one in to rule out any cracks or misfires. Plus a look at the business end of it may reveal something (oil, missing pieces, etc).

Noises can travel through the driveline and be deceiving at times. Also, if the problem is something driving or driven by the belt it may just be a coincidence that small variation in engine speed cause by the coil being off #5 is enough to quite down the noise.

As an example I had a knock on a Dodge Ram recently that seemed to be either the flex plate, or internal, but ended up being a bad waterpump. The knock was the impeller hitting the housing.

In reply to Streetwiseguy:

I did check that, and all good there. tight like a tiger. I put new plugs on it (and ensured they were all gapped properly) only a few months ago and the noise is super annoying, its one of those things like once you hear it you can't unhear it.

also I am thinking maybe a cracked skirt, since it doesn't affect performance?

I do need to replace the serp belt so I can pop that off and see.... but it doesn't make sense that killing the power to the #5 coil would quiet it, I would rule out accessory drive with that one I feel.

A cracked skirt will show up worse pretty quickly. A slightly shrunk one will rattle for a decade.

Streetwiseguy wrote: A cracked skirt will show up worse pretty quickly. A slightly shrunk one will rattle for a decade.

I should just turn the volume up on the radio?

Id send some oil to blackstons. Ive seen a few lose a cam bearing and the only symptom was noise u til the E36 M3 hot the fan.

My buddy broke a piston on his goat, and chased a rattle noise for a while, driving it the whole time. Turns out a chunk of the piston was be8ng held on by the ring. Yanked the piston and rod and got a new one from s&d and dropped it in and kept driving.

Also as much as i love the 496 i would bother swapping to one, just get to 6.0 tuned. Torque management makes them seem like a dog, dialing it back makes a big difference, and having driven a 8100 burb, it didnt feel stronger than multiple 6.0 ive driven, probably because of gm also neutering it qith tq management

I dont have torque management... do I? I thought that only came with the vvt engines. I would send the oil out but i just emptied it with my other oils of the vehicles. Do'h!

Also the 496 makes lq4 peak power at about 2000 rpm. I hate winding the small block when towing.

The struggle im having for 496 swap is the cam/crank signal. I need to convert it from 24x to 58x for the ecu which requires a different reluctor wheel and im unsure on the cam wheel too. I need to educate myself on these parts and systems a bit more.

fidelity101 wrote: I dont have torque management... do I? I thought that only came with the vvt engines.

Torque management has nothing to do with VVT. The ECM just pulls spark timing at the low end to keep the auto transmission alive. Dial it back or remove it entirely and it'll feel like a rocket ship comparatively. Be warned though, it could (and note, I say "could") shorten transmission life. Not definite.

NickD wrote:

fidelity101 wrote: I dont have torque management... do I? I thought that only came with the vvt engines.

Torque management has nothing to do with VVT. The ECM just pulls spark timing at the low end to keep the auto transmission alive. Dial it back or remove it entirely and it'll feel like a rocket ship comparatively. Be warned though, it *could* (and note, I say "could") shorten transmission life. Not definite.

With a 2009 vehicle, torque control is more than that- it uses the electronic throttle as the main torque controller. Unless GM is doing something really odd- your pedal is a torque request. And it then starts by giving you a specific throttle position at the main knob.

So for that trans limit- that goes into the desire throttle position more than spark, as it's always better to have the spark as advanced as it reasonably can be.

NickD wrote:

fidelity101 wrote: I dont have torque management... do I? I thought that only came with the vvt engines.

Torque management has nothing to do with VVT. The ECM just pulls spark timing at the low end to keep the auto transmission alive. Dial it back or remove it entirely and it'll feel like a rocket ship comparatively. Be warned though, it *could* (and note, I say "could") shorten transmission life. Not definite.

keep the auto transmission alive? its a 6L90?! this small block can't hurt this. well maybe if I neutral drop it a bunch but you get the idea.

fidelity101 wrote:

NickD wrote:

fidelity101 wrote: I dont have torque management... do I? I thought that only came with the vvt engines.

Torque management has nothing to do with VVT. The ECM just pulls spark timing at the low end to keep the auto transmission alive. Dial it back or remove it entirely and it'll feel like a rocket ship comparatively. Be warned though, it *could* (and note, I say "could") shorten transmission life. Not definite.

keep the auto transmission alive? its a 6L90?! this small block can't hurt this. well maybe if I neutral drop it a bunch but you get the idea.

That's always been the official reason for torque management: to preserve transmission and drivetrain component longevity.

hrmm, oh well.

I will be borrowing a friends boroscope tonite and see if anything good turns up.