Mercruiser 350 5.7 Low Compression #8 Cylinder

[BlizzmetKO]

Here's the link to the video of the sound when I put some compressed air on that cylinder. Can't figure out where its coming from. https://www.youtube.com/watch?v=wV54vFKxJbE

Any help would be appreciated. Thanks

 

[achris]

By the reverberation, that sounds like it's blowing into the crankcase. In which case, rings.

Chris.........

 

[BlizzmetKO]

It sounds like it’s higher then the crankcase. Could it be head gasket into the cooling?

 

[Bondo]

It sounds like it’s higher then the crankcase. Could it be head gasket into the cooling?

Ayuh,...... You have to listen through the various "Holes" in the motor,......

If it's leakin' into the coolin' passages, Pull a near by hose, 'n listen, it should be louder,.....
If it's an intake valve, the noise will be louder through the carb,....
An exhaust valve leak, louder through the exhaust,....

 

[BlizzmetKO]

Put some air on the cylinder again and getting some out of the pcv valves. Does that confirm getting by rings? Also go some more pictures with the borescope.

 

[BlizzmetKO]

Hey guys. I changed the oil a few days ago and added a can of restore. Been running it a and trying to free it up. I checked compression again today cold and found that the cylinder jumped to 120 and after running for a bit checked again and it was at 90. Trying to make sense of why it went down when warm but definitely my highest numbers yet by a wide margin. Any thoughts? Engine is bogging down at 2500 rpm. Which was happening all along. I thought it was due to the bad cylinder but now I’m thinking separate issue. Previous guy replaced icm with one from his truck. Should I replace back to the original or is it fuel related? Will post video. Thanks

 

[BlizzmetKO]

Here’s the link to the video showing it blogging down. I didn’t realize there is a second high pressure fuel pump. Thought now is that strainer could be clogged. Plugs look a bit black after pulling them.

https://m.youtube.com/watch?v=Lz24X4nSk-U&feature=youtu.be

 

[BlizzmetKO]

Figured out the low WOT and surging. I took apart the VST and found a lot of dirty gas and clogged screens for the high pressure pump. Solved the surging and now can rev up to redline no problem. Still having issues understanding higher compression when cold vs warm. Any thoughts?

 

[Scott Danforth]

my guess is you may have a crack somewhere if the compression is temperature related.