Go ahead, what do you think this sound is...

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RoyR
Posts: 3
Joined: Thu Jul 31, 2014 4:48 pm

Go ahead, what do you think this sound is...

Unread post by RoyR » Thu Jul 31, 2014 4:56 pm

Engine number 2 (GM3800 Series II) - lasted about two years.

Driving to work yesterday, felt like it was down on power, no noises. Pushed it a bit, thinking it may be a clogged injector. It would shift down, RPM to 5000, but it would not have the same power as usual.

Eventually made it home, going up the hill there was a new sound, like a burst of air escaping from the cylinder head. That stopped, and this is how it sounds now.

http://youtu.be/e3OgcXy82PQ

I have done the following, what should I do next?

1. Compression Test - the compression numbers are 175 up to 190...
2. Removed upper and lower intake.
3. ...

Harmonic balancer feels tight...not sure how to test it. Note: There was a power loss preceding this event, compression was good and spark in all six cylinders. The noise was significantly loader at cylinder 6, placed the stethoscope on the rocker bolt....

http://s118.photobucket.com/user/roy_ro ... 4.jpg.html

http://s118.photobucket.com/user/roy_ro ... c.jpg.html

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carriedi
Posts: 2280
Joined: Wed Apr 10, 2013 12:42 pm
Location: Oregon

Re: Go ahead, what do you think this sound is...

Unread post by carriedi » Thu Jul 31, 2014 9:54 pm

is that an exhaust leak? have you checked your exhaust back pressure? Loose spark plug? did taking the valve cover off change the sound of the noise?

RoyR
Posts: 3
Joined: Thu Jul 31, 2014 4:48 pm

Re: Go ahead, what do you think this sound is...

Unread post by RoyR » Fri Aug 01, 2014 10:07 am

This was the sound with the cover on.....I can't recall if the noise was louder on the intake or exhaust valve (cylinder 6 using the stethoscope). With the performance loss, I have to think the exhaust valve is stuck, but it sure looks like the pushrod as moving correctly.

1. Do I remove the valves for 6,
2. Take the head off,
3. Drop the pan and look if I can see anything?
4. How do you test a lifter?
5. Does the frequency of the noise match the cam revolutions, or the crankshaft?

http://youtu.be/uUrpO0y7Q9Y?list=UUe1CT ... P121MvBKtg

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carriedi
Posts: 2280
Joined: Wed Apr 10, 2013 12:42 pm
Location: Oregon

Re: Go ahead, what do you think this sound is...

Unread post by carriedi » Fri Aug 01, 2014 10:41 am

without being there to actually hear where the noise seems to be coming from, I would think that sounds like a rod knock. Sometimes a cracked flex plate or loose flex plate bolts will make that kind of noise.

a lifter noise is more of a ticking sound. your noise seems deeper in the engine.

I would have the engine running and, one by one, individually disable each cylinder to see if I could make the noise change. If you have one cylinder that changes the sound that would be the cylinder with the problem. with the cylinder working it will knock under the pressure of combustion. when you take away the combustion pressure the knock should change.

here's the thing though, normally a rod knock makes noise but it doesn't cause a loss in power while you are driving. or a sound like a burst of air escaping. but, stranger things have happened. I have been in this business a very long time and things still surprise me.

RoyR
Posts: 3
Joined: Thu Jul 31, 2014 4:48 pm

Re: Go ahead, what do you think this sound is...

Unread post by RoyR » Fri Aug 01, 2014 10:52 am

I did pull the fuel injectors to each piston, and noise stayed the same...with the stethoscope, it was clear the culprit is cyl 6. I've also had a misfire code on cyl 6 previously.

It's definitely not rodnock, I know how that one sounds...engine number two here!

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