Help identify sound

[Damian]

The truck started making this noise the other day and I can't figure out where it's coming from.
http://i53.photobucket.com/albums/g...64-AF5B-5AF03278F017-631-0000001D4A59C69A.mp4

 

[DaveP]

Re: Help identify sound

Does it run correctly? If it's missing (hard to tell in the vid) or not running smoothly, it sounds like an exhaust valve isn't opening fully, or at all. The 'pop' you hear is the pressure being released back through the intake tract when the intake valve opens on the afflicted cylinder. Rev it up a bit. If the 'pop' becomes rhythmic with engine RPM, ie every time, it's an exhaust valve isn't opening.

 

[Damian]

Re: Help identify sound

When Jr takes a nap, I'll go try that.

It runs good when it's warming up, starts running weird when you accelerate when it's up to temp.

 

[Damian]

Re: Help identify sound

I finally revved the motor and the popping sound does increase as RPMs go up. It sounds like its coming from the drivers side, still hard to tell for sure. I'll pull the valve covers off again and check the valve lash again.

Is there any aftermarket nuts for the stock rockers that won't back themselves out? In less than 1k miles I had to set valve lash again. Im not wanting to do this all the time.

 

[SY2455]

Re: Help identify sound

It almost sounds like a pushrod is hitting the valve cover. Are the rocker arm studs pulling out?

 

[Don W.]

Re: Help identify sound

To me it's to heavy and random to be a rocker. How about a loose torque converter or flex plate?

 

[SY2455]

Re: Help identify sound

To me it's to heavy and random to be a rocker. How about a loose torque converter or flex plate?

Don , I was thinking along that too until I read that, he yet again had to adjust his rocker arms in the thrid posting.

 

[DaveP]

Re: Help identify sound

Ok, my turn: An exhaust valve isn't opening, for whatever reason. When the pressure in the cyl is released into the intake when the intake valve opens on the afflicted cyl it makes that 'pop'.

 

[Don W.]

Re: Help identify sound

OK, but a) a loose rocker taps every time, not randomly. Unless maybe one lifter is bad somehow And b) Nuts don't loosen on their own. The stud will pull and/or a non self-locking nut might back off but that's it IMHO

To me it's just to heavy a knock. Something else going on. But that's just my opinion.

Question: What procedure is being used to adjust the rockers? How much pre-load?

 

[DaveP]

Re: Help identify sound

Had another thought, but I'm not as confident with this one as the exhaust valve not opening: Firing order, or cross-fire between plug wires, or the inside of the distributor cap is carbon-tracked.

 

[Damian]

Re: Help identify sound

I tightened the nut down until the pushrod wouldn't spin by fingers and then did another half a turn. When I did this procedure last time, engine ran smooth as a baby's ass, even with solid mounts.

I wasn't able to pull the valve covers off tonight, should be able to sometime tomorrow. I'll check the rocker studs as well.

 

[Don W.]

Re: Help identify sound

Interesting Dave. But wouldn't cause a miss? Motor seems to be idling smooth.

I would really like it if he could cut individual cylinders and see if the noise goes away. Or gets worse.

And I'm still confused. Why, again, is it not a loose TC or flex plate? They aren't related to rockers. Crawl under the truck and listen at the TC cover.

 

[Damian]

Re: Help identify sound

That's what I thought at first and couldn't find anything hitting the fan. The noise is coming from the front of the engine for sure.

 

[DaveP]

Re: Help identify sound

To me it's just to heavy a knock. Something else going on.

I've heard this noise on at least twenty different engines. Marine engines develop water leaks into the hot section ot the exhaust manifolds. When the engine is shut down, and allowed to sit, water enters the port, and the valve gets stuck. On restart, usually the push rod bends, and the valve stays where it's at.

Another variant is the valve train gets loose, rocker breaks, push rod comes out of lifter, etc. "For whatever reason" the exhaust valve remains closed at all times.
When the piston comes up on exhaust, pressure is built to compression-stroke level. Then the intake valve opens, the pressure is released, and you get the 'pop' of the pressure being squeezed through the just-open crack of the intake valve into the intake manifold.

Could also be ignition maladies causing a gross timing error (like 120º of error) in one cyl.

 

[DaveP]

Re: Help identify sound

The noise is coming from the front of the engine for sure.

Could it be coming from the intake? The turbo inlet? Or the air filter? When the boat engines do it, the noise emanates from the air cleaner. So did my big block El Camino when it broke a rocker. Each of the 3 times it did it.

 

[DaveP]

Re: Help identify sound

Interesting Dave. But wouldn't cause a miss? Motor seems to be idling smooth..

Ahhh, but it's not idling smooth. You can hear it stumble when it makes the pop. So it has something to do with with something that interrupts smooth combustion. Like ignition or valve action.

This is not a new noise for me. I feel like driving over there and pulling the valve covers right now and taking a look.

 

[Don W.]

Re: Help identify sound

That's what I thought at first and couldn't find anything hitting the fan. The noise is coming from the front of the engine for sure.

Crankshaft dampener? Remove serpentine belt and see if it goes away.

 

[Damian]

Re: Help identify sound

I'll go out and a little bit and and see if the noise is coming from the turbo or intake manifold. This noise is kinda hard to pinpoint.

 

[Don W.]

Re: Help identify sound

Ahhh, but it's not idling smooth. You can hear it stumble when it makes the pop. So it has something to do with with something that interrupts smooth combustion. Like ignition or valve action.

This is not a new noise for me. I feel like driving over there and pulling the valve covers right now and taking a look.

Better ears than I got Dave... :rotf:

 

[DaveP]

Re: Help identify sound

I'll go out and a little bit and and see if the noise is coming from the turbo or intake manifold. This noise is kinda hard to pinpoint.

Can you do another vid, please? Begin with it idling and popping like the first vid, then slowly advance the throttle up to about 2-2,500 RPM with it still running. I'd like to hear how the pops change with increase with RPM.

Thanks.