Guys I need help figuring out this engine rattle

[iamdub]

Today I am going to disable my fuel pump and turn the engine with the starter to see if I can replicate the sound.

Easy: Just hold the throttle pedal to the floor while cranking and it'll keep the injectors and spark plugs from firing.

I am hoping that pulling the heads I will find some problems with the lifters, push rods, or valvetrain.

Hoping for anything minimal.

if you have any other useful advice that would be great.

Use a large, blunt punch and hammer to give the heads of the exhaust manifold bolts a few good knocks to help shock 'em loose to reduce the chance of breaking them. Put a socket around them and beat on that a few times to shock the surrounding iron of the manifold flange. If you have a small, relatively weak impact gun (or turn your air pressure way down), a few hits towards tightening before loosening and maybe repeating a few times back and forth can help. No need to rush this part cuz you'll surely negate any time saved when you have to fight broken bolts.

 

[TollKeeper]

Having just gone thru collapsed and exploded lifter, and a pushrod in the shape a letter Z. Just start in the valve cover, both sides. Relative easy, and you dont even have to pull the intake (at least on my LH6 I didnt).

Go in there and look for loose rockers, or even a pushrod sitting off to one side (both of these I found on cylinder #1 intake).

The baffling question is, if it was a pushrod, lifter, or stripped rocker, you would have a MIL light for a misfire on a cylinder. You didnt mention this that I saw.

 

[Dustin Jackson]

@iamdub Thank you for that advice!

@TollKeeper I do have a code for cylinder 6 misfire, I don't know if I mentioned it in this thread or not but I will be focusing my inspection on the passenger side for sure.

 

[FasterBass]

Easy: Just hold the throttle pedal to the floor while cranking and it'll keep the injectors and spark plugs from firing.

really?! This would make top end soak easier

 

[iamdub]

really?! This would make top end soak easier

I speaketh the trutheth. No need to pull fuses, unplug stuff, etc. It's a GM feature called "Clear Flood Mode". Prior to my engine refresh, I used to use it all the time to prime my oil system to help a ticking lifter when starting my Tahoe after it sat for a week or three. You hold the pedal to the floor (there's a specified minimum throttle- like 80% or something, but flooring it is easiest) and turn the key. You can hold it but it'll automatically stop cranking the starter after ten seconds to let it cool.

 

[Dustin Jackson]

I was not able to replicate the sound by just turning the engine with the starter.

I can vouch, pedal to the floor while cranking won’t start it.

 

[FasterBass]

I speaketh the trutheth. No need to pull fuses, unplug stuff, etc. It's a GM feature called "Clear Flood Mode". Prior to my engine refresh, I used to use it all the time to prime my oil system to help a ticking lifter when starting my Tahoe after it sat for a week or three. You hold the pedal to the floor (there's a specified minimum throttle- like 80% or something, but flooring it is easiest) and turn the key. You can hold it but it'll automatically stop cranking the starter after ten seconds to let it cool.

Well goll-e thanks for the info!

 

[Dustin Jackson]

Got the intake manifold and valve cover off on the passenger side today. I wasn't able to find anything wrong, I took the pushrods for #6 out and they all look nice and straight. The rockers for #6 look the same as the rest of them. I am a little confused, I thought I would see some evidence of damage by now. Tomorrow I will pull the head and hopefully see something wrong.

Here are a couple videos I took today:

And here is a clip of my lady turning the motor over for me. As you can see it appears that the valves for #6 work just fine, How do you disable the fuel pump? I pulled fuse #20 and the fuel pump relay but as you can see the fuel pump still works..

What are your guys thoughts here?

 

[Fless]

Did your lady floor the accelerator pedal while cranking, to use clear flood mode? (Or as Dad would have called it, "the footfeed." )

 

[Dustin Jackson]

Did your lady floor the accelerator pedal while cranking, to use clear flood mode? (Or as Dad would have called it, "the footfeed." )

@Fless I told her to but I think that just disables the injectors, but doesn’t turn the fuel pump off.