1999 Vortec engine. Out of nowhere the car lost power, shudders a bit like it's missing a cylinder and has a knock like you can't believe.
Anyone have or ever heard of this? It's not a Cracked Rocker, I looked.
The engine has 100K miles on it. The oil was changed regularly, with the Valve cover off, the Head is immaculate so it's not a lubrication problem.
I'm thinking a stuck Lifter, I added some marvel mystery oil to the oil and down the Intake to sit over night, The knock got a lot quieter. didn't run it for a few days as I mulled some ideas around and next time I started it, it was back to very loud with popping up through the Intake.
I'm leaning toward Stuck Lifter or Valve but I'm not sure. NO Codes After letting a mechanic look at it he listened and played a bit and he's stumped. He mentioned something about these engines have a Balancer on the Crank that can loosen but would that cause the noise and bad running to come and go?
I hate to open this engine up and start tearing it down without a true direction as to what to shoot for.
Any thoughts? any at all??

 

Another quickie.. Is ther esome type of Balancing piece on teh Crank other than the Harmonic balancer on teh outside. Anything that might have broken loose and bangs around internally? I guess after I do a compression test I will know whether it is top end or bottom. This is just a Hard knock but the other symptoms lead me away from a lower end issue.

 

take the valve covers off and watch each valve while its running, sounds like you have a intake valve stuck slightly down or broken valve spring causing piston to tap the intake valve causing the knock noise you are hearing, and also causing the popping coming up through the intake which is compression bypassing partially opened intake valve.

 

That's what I suspect too. I attempted to get the valve cover off. The harness starddles the Cover in so many places and I didn't want to pull them all off, I wanted the engine to still run. I could have slipped the cover off if I could have figured out how the Filler Neck comes out of the Cover. I ran my fingers under the cover and all the Rockers seemed intact. That's all I could determine at that point.
It's weird because after pouring some Marvel Mystery oil in the intake as well as add it to the oil, it quieted down ( not totally) for hours of idling in the driveway. I added more down the intake to let it soak the Lifteres more and a few days later the Harsh heavy knock is back. I also ran some water in teh intake to get rid of any Carbon buildup. Didn't help any. I guess after watching the Valves.. the next step is to pull the Head on that side. It sounds like a rod knock .. I guess a piston smacking a Valve would have that deep knock sound. The fact that it comes and goes makes me think it can't be the lower end.

OH this V6..an interference engine??

 

you just simply unscrew and pull the oil fill spout off the valve cover. get a stethoscope and probe on the side of the head itself and then on the block around where the crank is at along the side, you should be able to determine if its in the head or in the rods or main bearings.

 

Tearing down to inspect the rockers and push rods takes only about 2 hrs tops. Before you look for too many miracles in an additive, take a Saturday and just tear down to really see. Most it will cost you is your time and a few cheap gaskets.

Here's a few lessons I have learned (above the normal) for a quick tear down to the heads:

Remove the air cleaner and the filter housing.
remove sepentine belt
Remove the fan - remove a/c compressor and lay it over to the side (the coolant lines will flex). Loosen the ac/power steering bracket and slide it forward (don't forget the nut at very bottom and 1 on the side behind the power steering pump). With the upper radiator hose removed and egr line disconnected, you can now remove the drivers side valve cover gasket.

Passenger side:
Go ahead and remove the alternator and bracket from the front of the engine.
Take your time and lay the harnesses to the side - they are not really that bad once you can really see them and how they are connected - just dont yank on them.
You can remove the valve cover by snaking it up and forward even when some of the harnesses are laying over it. Use care when removing the oil filler tube - they get a bit brittle with age. It should rotate and pop out. If you do break it (I did last month), they are about $13 and an over night delivery at the Chevy dealer.

Now you can inspect your valve train - I don't recommend running the engine, but you can turn it over (disconnect the coil) without affecting your timing at this level of tear down. I have done this when I torque down rocker arms - I torque, turn over the engine a few revs and then recheck the torques.

 

On an earlier post, when the noise occured, I asked about the removal of the Filler . I could rotate it about an 1/8th of a turn. After that I was sure it was going to break.

So which one of you guys are coming over to help??
As My signature says. These newer engines and their harnesses and Bracketry gets me nervous. I have torn down many engines in my day and have fabricated and put v8's in cars that had 4 cylinders in them. I am very mechanical but all this crap packed into a very tight engine compartment just isn't my cup of tea. Heck, it took me two hours to TRY and get the valve cover off and back on the passenger side.
It's on the passenger side for sure. I used a broom handle to my ear to try and get an idea of where it was coming from but it was a heavy knock. I'm guessing middle of engine on passenger side so I will really observe the rocker movement there.

Could a lifter or valve get so hung up that a Piston coming up and smacking the Valve wouldn't free it enough not to get hit again??

 

Where do you live?

 

Long Island

Wading River, NY

sorry for the late reply, I was away for a 4 day weekend

 

Have you pulled the spark plugs on that side yet?