# 8 cyl zero compression

[A97obs]

After all these days repairs small fixes this that.. and getting my rocker lash and preload correct . I decided to pull out my compression checker on this dead horse to see why the riugh idle and no power and nothing like the first 7 of 8 cylinders making you feel good until cyl 8 hits 0 psi ZERO

So I’m wondering is “0” even a possibility or could something else have failed causing that or something fixable every cylinder almost hit 150 psi


Here’s my and I tested cyl 8 three times ..
And I guess it’s time for a donor or rebuild
I’ll drive it on 7 cylinders the rest of the summer idc it still moves , or until I park it . I drive it to work and drove it 2 hour back when I purchased the truck .. No smoke no weirdness just no power and a noticeable miss. This sucks

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[A97obs]

No blow by, no oil spewing from exhaust, no red white or blue smoke
So could this be a bad valve or compression ring gone

 

[A97obs]

Now what~ nothing like getting had on a purchase .
Decided to check all the cylinders today everyone single one 1-7 was looking good until # 8 . It didn’t seem like it ran that way when I got it aside from all the small fixes I had to do ps pump rad leak and charcoal canister missing. The rocker noise that came along must have been the point and time possibly when the failing cylinder went.
It’s just weird truck didn’t stumble or idle that way at first until the rocker chatter . That’s been done and gone since I changed oil twice and adjusted the preload . It still had a rough miss idle.
I just wonder what could cause zero psi and is is that even possible to have No compression zero , or might I be in luck and it could be a combination of valve train issues . I know on cyl 8 I did pull the push rod to check it when I was looking for issues , maybe it’s not centered on a lifter causing no compression or is this as simple as it gets No compression is literally piston ring failure ?

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[GoToGuy]

You've done a total or dynamic compression test. Step two is to a compression Leakdown check / test. Are familiar with that type? Where you input a regulated pressure and read how effective the compression is, and or identify where what the broken or worn parts are. By identifying where the input pressure is escaping from. Crankcase worn rings, exhaust - exhaust valve, throttle body- intake valve.
There's probably tons of you tube vids. Do you have a cheap borescope, stick in spark plug hole?

 

[evilunclegrimace]

Put compressed air to the suspect cylinder. If you hear air coming out of the tail pipe you have a exhaust valve problem, if you hear air coming out of the Throttle body you have an intake valve problem, if you hear air coming out of the dipstick tube, oil fill cap or PCV grommet you have a piston ring problem

 

[95burban]

Put compressed air to the suspect cylinder. If you hear air coming out of the tail pipe you have a exhaust valve problem, if you hear air coming out of the Throttle body you have an intake valve problem, if you hear air coming out of the dipstick tube, oil fill cap or PCV grommet you have a piston ring problem

Loosen the rocker arms also before you do this. Great advise

 

[Sean Buick 76]

Yes leak down test time

 

[termite]

Post in thread 'Rocker arms loosening 93 5.7 tbi' https://www.gmt400.com/threads/rocker-arms-loosening-93-5-7-tbi.69210/post-1443095

 

[termite]

You've done a total or dynamic compression test. Step two is to a compression Leakdown check / test. Are familiar with that type? Where you input a regulated pressure and read how effective the compression is, and or identify where what the broken or worn parts are. By identifying where the input pressure is escaping from. Crankcase worn rings, exhaust - exhaust valve, throttle body- intake valve.
There's probably tons of you tube vids. Do you have a cheap borescope, stick in spark plug hole?

Post in thread 'Rocker arms loosening 93 5.7 tbi' https://www.gmt400.com/threads/rocker-arms-loosening-93-5-7-tbi.69210/post-1443095

 

[A97obs]

Loosen the rocker arms also before you do this. Great advise

That’s was the fix, for some reason I could not find this post to respond on. I thought it was deleted or replied on one of my other topics and resolve the matter at the rocker nuts were too tight. I re adjusted lash and preload now I have 145-150 psi on all 8

I also had corroded dist cap terminals and points on the rotor were shot plugs were trashed I did a full tune up
So far so good ~ topic can be closed
Thanks for all the support prior to my response