Compression Test for Chuff

You can very easily make a sort of leakdown tester out of the compression gauge - just unscrew the gauge from the hose and put a air hose fitting on then just hook it up - instant cylinder pressure. It'll most likely turn the engine some, so be careful. Going to need to crank it over to where both valves are closed first of course. Woln't really give you a leak down rate, but it'll immediately show you if a valve is leaking - you'll hear the air hissing out.

For a better set use a tee to keep the gauge hooked up and put a valve on the air line so you can shut it off and time the leakdown rate.

May or may not actually find out anything useful though - chuff can be caused by many things that are hard to find, such as a lifter, worn cam lobe, etc.

riotwarrior said:

I was a little over a mile from home when I heard KaBoOm in a bad way...and lots of smoke and knocking from engine. I pulled over and let it run, I know better n to shut **** down...won't start when away from home = TOW BILL
Hope that helps....

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Thanks. I wanted to get an idea of what noises, smoke, etc.

I'll add my .02, then maybe you'll have enough cents to repair some stuff.
I'm just at the end of rebuild on a 7.3.
My #8 cylinder had a stuck ring, 2nd ring IRRC, and this cylinder had to be sleeved.
Did not have a cavitation issue, just a spot in the wall that couldn't be "cleaned" up by boring .030.
My problem with the engine was a lot of oil usage and blow by. 1qt to 100 miles.
Looking back I'm glad I rebuilt the engine. Don't think my oil usage would have gotten much better but using some Auto-RX might have helped that issue.
That's only if you didn't want to spend a bunch of money...

you can do a wet compression test to see if the ring is the issue, squirt some heavy oil into the bad cylinder and do another test, if the pressure is higher it is at least partially a ring problem. Good luck.

Brad S. said:

I'll add my .02, then maybe you'll have enough cents to repair some stuff.
I'm just at the end of rebuild on a 7.3.
My #8 cylinder had a stuck ring, 2nd ring IRRC, and this cylinder had to be sleeved.
Did not have a cavitation issue, just a spot in the wall that couldn't be "cleaned" up by boring .030.
My problem with the engine was a lot of oil usage and blow by. 1qt to 100 miles.
Looking back I'm glad I rebuilt the engine. Don't think my oil usage would have gotten much better but using some Auto-RX might have helped that issue.
That's only if you didn't want to spend a bunch of money...

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I have been reading about the Auto RX recently. Seems like a good way to clean things up. I have some issues to resolve first. This one I just did compression on is a chuffer so I have a machine shop cleaning up some used heads for me. When they are ready to go on I can get the heads opened up and hopefully get some more answers. It's my daily so I'm not sure how much more testing I will be doing since heads are getting pulled pretty much for sure.

marmot said:

you can do a wet compression test to see if the ring is the issue, squirt some heavy oil into the bad cylinder and do another test, if the pressure is higher it is at least partially a ring problem. Good luck.

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I appreciate all the help with all the test options. Good to know I can narrow down the problem. I figured the chuff was a bad valve for sure based on my research.... Could it be other things causing it? I'm gonna post a video today of it for ***** and gigs.

marmot said:

you can do a wet compression test to see if the ring is the issue, squirt some heavy oil into the bad cylinder and do another test, if the pressure is higher it is at least partially a ring problem. Good luck.

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Be cautious of this as it may LIGHT off and thus you end up with it running...even one fire of the cylinder can ruin a compression tester.

Oil fired engines AKA Diesels are not usually done wet ...maybe someone with more exp will chime in, however I would NOT attempt this myself.

JM2CW

Here is a video of the "chuffing" noise.... listen for the sound change....

Notice how the sound changes? That is not a sound adjustment from the phone. I wanted that sound change to be in the video that is why it is long. My understanding is that the sound change is due to the valve rotating in its' seat. Not sure if you could hear this, but there is a slight change in idle when the chuff is louder and then the idle bumps up just slightly when the noise gets lower.

My landlord owned a 6.9 and had a construction company in his day so he has been around the block many, many times. He suggested it may be a worn cam lobe or bad lifter. He pulled a lifter out of his 6.9 that looked like a mushroom on the end. Said he wasn't sure he would be able to remove it. I guess I need to test further to narrow this down. I was certain based on research and the threads here that the chuff was from a bad valve/spring/guide and because it could be heard from the exhaust it was probably an exhaust valve. If that logic is wrong, let me know. It sounds like maybe there is a bad injector mixed in there also? In the meantime I will attempt some of the tests suggested to narrow it down further if possible when I get time...freakin' snow!!! Thanks guys!

EDIT I wanted to note that this chuff was not present at the time I test drove this truck. The engine idled smoothly without smoke, leaks, etc. When I came back and bought it a week later it had not been run as far as I know and chuff was magically there and the engine idle quality has deteriorated significantly since purchase. Bought the truck bought a month ago.

No reason for a "wet test" compression test. We have an incredible amount of oil being squirted up under the pistons for cooling. That oil is creating a wet seal on the rings better than pouring any oil sown a glow plug hole. Just do the comp test on a warmed up engine and those cylinders will be well wetted by the cooling jets.