So I posted recently about a cylinder 6 misfire, thinking it was probably a fuel injector. Instead I found that when a compression test was run, it could only withstand 40PSI. Right now I have the motor kinda torn down (intake manifold and valve covers are removed), and I really don't want to remove the rear head if I don't have to. You guys have any idea what it could be, maybe something easier that I could check first?

 

With engine tore down that far you might as well pull the head and inspect. Worst case it could be is a hole in piston but probably a bad valve.

 

So, im curious... What would be the fix for this? New head?

 

Doesn't NEED to be a new head, but the cost of pulling the head, getting it to a machine shop, and getting new valves placed while getting the heads clean... you probably would be better off just getting a new set of heads for these engines.

Unless you are doing the work yourself, in which case you are just cleaning and replacing the parts, and making sure it's not warped in any way

 

If it's a bad valve you can send the head out and they will machine the valve seat and replace the valve, but its probably cheaper to find another head. I would have done a leakdown test before tearing anything apart. It would have told you if you have a bad intake valve, bad exhaust valve, bad piston/rings or possible bad gasket. If you have minimal leakdown but low compression that points to valvetrain problem, broken valve spring, worn cam lobe, etc.

 

Also, did you test the compression on the other cylinders and did you use a quality compression tester? If you used a harbor freight compression tester I can almost guarantee the reading is incorrect.

 

Just a massive pain because its the back head, the bolts holding the exhaust manifold on are in such an awkward angle. I'll yank it tomorrow though.

I had a shop do it, they said all 5 of the other ones were close to 160PSI.

 

Remove the dog bone mounts and tip engine forward to get easier access to back bolts .

 

This was super helpful, thanks.

Wound up getting it all off, pics here: https://imgur.com/a/iVap8lm

There's some graphite from the head gasket left, I circled it in red. I think it was head gasket, just want to get your opinions on it since it's my first time dealing with low compression.

 

With the cylinder head upside down and spark plug in put water in the combustion chamber and see if it holds water or if it leaks in either the exhaust or intake runner on the dead hole.