Intermittent miss and knocking coming from exhaust

[KCTurbos]

Well I was spending some time on the dyno today. We loaded up a more aggressive tune and ran the truck hard. Truck was making great power during the run... but when I came back down to idle I could tell the truck was missing.

Autoenginuity shows no codes. Passed buzz test. Cylinder cont shows normal. So i drove it home. It smoke pretty good and make a bunch of racket, then seem to run fine. It would miss and then run fine.

I got home and looked into it more. No puffing out the oil fill (very little blow by). No puffing from air intake. Engine seems to idle "ok" but you can tell something is off.


Its making a weird popping/knocking sound that you cant really hear over the sound of the motor... but you can hear it coming out the exhaust. Since it is coming out the exhaust I am guessing maybe bent exhaust valve. Maybe I had a valve kiss the piston. :doh:



Anyone ever heard this noise before? I made a video of the noise coming out the exhaust. (it was dark so no picture, only sound)

https://www.youtube.com/watch?v=ZZ0thgvatmA&feature=youtu.be




Anybody have some wisdom for me?

 

[Bushwood_6.0]

Sounds like a bent push rod or valve. Hopefully just a push rod...
I had a good buddy with a 7.3 make a pass at the track and the trans slipped and over Revd. I followed it back to the pits with the golf cart and made the same sound exactly coming from the exhaust. Tore into the next day Ended up being a very bent push rod.

 

[KCTurbos]

Well the problem is intermittent... the miss comes and goes.

The earlier video was when the truck was not "missing hard" and the power contribution balance was good...


I went out to run some more tests and now... the truck has a "hard miss" and the knocking sound has turned into a hissing noise with puffs of smoke coming out the exhaust. Also the power balance test shows a few weak cylinders :shrug:

Here is a pic of the balance test

Here is the video now that the knocking is gone and you can hear hissing and smoke puffing out the exhaust.
Hissing out exhaust - YouTube



Maybe its just and injector lease:

 

[6 L chevy eater]

Are u running HD springs and push rods?

 

[dieselflash]

Have you done a relative compression? Definitely sounds like a valvetrain concern.

 

[SEABEE08FX4]

Well I was going to say sounds like a pushrod too, but the noise wouldn't change if that was it. That would have been the cheapest fix though for sure.

 

[strokin6L]

Damn charlie....that sucks! Sounds like you're almost in the same boat I am. Do a leak down test to determine a bent valve. That's how I found out I have a bad intake valve/seat. The leak down test showed air pushing out the intake side. That's why #3 cylinder has a miss and low compression.

 

[KCTurbos]

No relative compression test yet.


I am going to pull off the valve covers this afternoon and see if I can find out any more.


I am leaning towards a bad lifter, possibly spun and is taking out the cam. Anybody have any good advice on how to tell if you have a bad lifter without pulling the head/motor?

 

[webb06]

No relative compression test yet.


I am going to pull off the valve covers this afternoon and see if I can find out any more.


I am leaning towards a bad lifter, possibly spun and is taking out the cam. Anybody have any good advice on how to tell if you have a bad lifter without pulling the head/motor?

I thought lifter noise was more of a squeak or tick.

I wouldn't think you could hear a lifter noise through the exhaust

 

[SEABEE08FX4]

You'll have to pull the head to tell that, no way around it.

 

[KCTurbos]

You'll have to pull the head to tell that, no way around it.

GRRRR... Thanks

I thought lifter noise was more of a squeak or tick.

I wouldn't think you could hear a lifter noise through the exhaust

I think you are right.


I am going to tear more into it later... listen more carefully... and see what I can hear with the motor warm vs cold. It was late last night when I was trying to diagnose. I could have missed a squeak or tick from the engine bay. It did sound slightly off but not like a rod knock coming from the engine bay.

 

[swinky]

If it was a lifter you would know it. These things sound awful and most of the time quit running when a lifter has failed.

 

[Strokethis34]

Mine ran great when my lifter decided to stop spinning and make a flat spot. Pull the lpop gears out and inspect them for signs of scoring from lifter material.?

 

[Cutting-Edge Diesel]

How does it sound when cranking it? Have you cranked it with the jumper wire so it won't fire and will just crank? If its a push rod or bent valve it will normally have a hard spot or loose spot when cranking.

Normally a lifter won't cause a miss. You usually don't know it until you get a needle Bearing in your lpop. Or it starts squeaking

 

[KCTurbos]

Well... one of the cylinders is dead.


http://youtu.be/zZJidN_5ruI

I am praying for a rocker arm or push rod... but I doubt it.

 

[MrOneEyedBoh]

How did you determine that.

 

[KCTurbos]

How did you determine that.

If you watch the video above you can hear a "skip" in the motor... which is a sign that I have a dead cylinder.

 

[Cutting-Edge Diesel]

What I call a dead cylinder is one that isn't firing when running. (Just how I see it might be what was confusing him)

What you have is one that has a hard spot. Normally in my experience is from a liquid in the cylinder or something causing a valve to not open. I wouldn't think it would be a lifter since it happened all at once during a dyno run. Pull the valve covers and look at the push rods and bridges.

 

[KCTurbos]

Well... I am not very good at reading the power balance charts... but according to people much smarter than I, it looks like cylinder number 4 is dead. You can hear the in the video i posted where you just hear the truck turning over and it sounds like it is skipping... that is usually a sign that a cylinder has low compression.

I pulled the valve cover and everything looks normal, but there is a weird faint sound like something is not right (slight tapping). I pulled the injector plug on cylinder 4 just to verify that was the dead cylinder.

Cylinder 4 not firing - YouTube



Then I took off the oil rail to get a better look. You can still hear the dead miss and a "poofing" sound. But the valve train seems to be moving ok.

Valves dead miss - YouTube




I took off the rockers and the push rods and those look good :doh: I was really hoping it was just a bent push rod...

When the truck was running I pulled the oil fill cap to check and see if compression was slipping past the rings/piston... Nope... had very little blow by and no one cylinder was puffing out more than the others. So I would assume not the rings.

A bad lifter should not cause a dead miss... right? It would just cause the valve to open "slightly" later and and close earlier... but not a dead miss??? or am I wrong?

Am I right to now assume that it is a valve issue?


Next I am going to try to do a leak down test and see if I can hear where the air is going. I just need to get the right parts... or try to make something. Anybody have any good ideas on that?

 

[Cutting-Edge Diesel]

It's hard for me to tell but in the second video is it hissing?