Cylinder Compression

[docstoy]

If problem seems to be on #1 and #8 , then back valves adjustment on those 2 cylinders, leave spark plugs out, rotate crankshaft , air should just be flowing thru sparkplug hole , if stillno air flow (compression) install spark plug for that cylinder , air will either come out around rings or valves this will help isolate direction you need to go.

 

[katwood16]

I was thinking the same so I backed my valves off and check with no plug in and the thing is still piss poor on both those cylinders. I reinstalled all the plugs but those two, hoping I could hear better but no. With the plugs in the two bad cylinders and none other what am I hoping to hear?

 

[Road Trip]

Sorry for making two different threads after a couple hours on this one I was unsure anyone was gonna answer me.

Hello katwood16,

Everyone writing responses in here is just volunteering their time, experience, & effort in order to help fellow GMT400
enthusiasts. And they are fitting these contributions into whatever time is left over after running their own business/
shift at the plant/or working their honeydo lists. Or even working on their own rides. Or deep in a rabbit hole trying to
come up to speed on a rarely seen problem. :0)

In English, after waiting a short period of time you may come to the conclusion that nobody is going to respond, but
the coverage here is somewhere between very good and excellent. It make take awhile, but that's because people would
rather research first and then toss out an idea vs just a quick guess that may or may not be relevant.

You are new here, so if you plan on keeping this truck for the long term, you should consider starting a 'build thread'.
This really helps the remote troubleshooters, for the context of what's already been done to the truck is available in
order to help figure out why the latest problem started occurring. (And not have to research several different threads
in order to build this knowledge base.) It may not seem like it, but I hate guessing in public, so if I don't have enough
information to work with a lot of times I'll decide to not respond.

So you haven't done anything wrong, but I'm just trying to explain how this forum seems to work, and how you can
help us help you. (For what it's worth, when lurking I found this forum to be exceptional, so much so that it's the
first forum I've ever joined.)

Best of luck, and that build thread will help to overcome the seeming apathy that multi-thread generation can bring on.

Cheers --

 

[katwood16]

Thanks for letting me know I will compile a thread from beginning to end to provide more context. This is my first Forum I have joined and it has been excellent so I want to do what I can to help you guys help me.

 

[docstoy]

I would be hoping to hear air movement thru the valves (intake or exhaust ) or thru the crankshaft area if going by the rings, or if you have long block together , thru intake or exhaust port at cylinder head or lower area of engine, I've never tried that with oil pan installed think it would be difficult. Should hear air movement somewhere then if not would suspect ring alignment on piston . And that's if you backed valve adjustment off so valves should be seated

 

[katwood16]

With the valves all the way backed off, the plugs only in 1 and 8, and my ear to the throttle and exhaust manifold, I can hear air coming through the throttle.