Zero compression on 1 cylinder help please

[Jesseyourcalipers]

1999 gmc Sierra 1500 4.3 vortec from a 2003 silverado. Check engine blinking misfire cylinder 1. Exhaust Billowing grey smoke, rough idle, oil on spark plug 1. Did compression test and it’s dead zero. All other good compression except for cylinder 5 which is same side as cylinder 1 but at least has compression. I’m thinking broken piston or rings. Will not be rebuilding will be looking at dealerships. But is dead zero compression possible with broken rings or piston? I re checked multiple times all dead zero zero movement all other cylinder 160 except number 5 which was 60. Would bad heads cause a dead zero?

 

[supton]

I’d pull the valvecover and look for a stuck open valve.

Can you rig up a leakdown test? or just pressurize somehow? zero compression should be easy to hear where it is going, if you are not cranking.

 

[KGMtech]

Broken valve? get a inexpensive borescope and put into cylinder # 1 should tell the story.

 

[spasm3]

i'd pull a valve cover as mentioned above. See if the valve is working on that dead cylinder.

Whats the mileage on this engine?

 

[Jesseyourcalipers]

i'd pull a valve cover as mentioned above. See if the valve is working on that dead cylinder.

Whats the mileage on this engine?

Little over 200k

 

[Jesseyourcalipers]

I’d pull the valvecover and look for a stuck open valve.

Can you rig up a leakdown test? or just pressurize somehow? zero compression should be easy to hear where it is going, if you are not cranking.

I’d pull the valvecover and look for a stuck open valve.

Can you rig up a leakdown test? or just pressurize somehow? zero compression should be easy to hear where it is going, if you are not cranking.

What would I hear with a zero compression? What do you mean? With the spark plugs all out I did the compression test one by one. Every cylinder besides #1 you can hear the gallop. The chuuh chuuh chuuh chuuh chuuh. But as soon as I put the gauge on 1 and try to crank it sounds like a free flowing spin no chuuh chuuh etc.

 

[supton]

What would I hear with a zero compression? What do you mean? With the spark plugs all out I did the compression test one by one. Every cylinder besides #1 you can hear the gallop. The chuuh chuuh chuuh chuuh chuuh. But as soon as I put the gauge on 1 and try to crank it sounds like a free flowing spin no chuuh chuuh etc.

The compressed air has to go somewhere. That hissing out of intake, exhaust or oil fill is the clue.

But if you get nadda as you say, I would be looking for a new inspection port on the side of the motor, as that too could explain this situation.

 

[Kira]

What would I hear with a zero compression?

Leak down tests are done at each cylinder with both valves closed.
You put your ear near the exhaust pipe to listen for a burnt/broken exhaust valve and at the throttle body to detect a bad/broken intake valve.

 

[supton]

If cylinder one isn’t pushing any air, whatsoever, then maybe the piston is broken, big hole in it, or the rod snapped.

How was it running before? did this start suddenly, or had it been poorly running for a while?

 

[clinebarger]

If this happened all the sudden?.....I'd suspect a broken valve spring. Pull the valve cover to inspect......And don't run it anymore or you risk the valve dropping into the cylinder.

 

[Soft Cars]

Pull the valve cover to check the cylinder 1 springs and have a borescope ready to drop in through the spark plug hole. If enough of the valve is missing, it could cause a large loss of compression.

Alternatively or in conjunction with the above, you could pressurize cylinder 1 with air pressure and listen to the exhaust pipe. If you hear air coming from the exhaust, that's an indication of a burnt exhaust valve. If you hear air coming out of the throttle body, that's an indication of a burnt intake valve. If you hear air coming out of the oil fill hole, that's an indication of worn piston rings.

If you have any of the cylinders pressurized, you need to have a wrench on the end of the crankshaft to keep the engine from turning over. Usually a long 1/2" drive flex ratchet with the matching socket for the crank pulley/harmonic balancer bolt.

 

[sloinker]

200k miles? I wouldn't invest too much money unless it is something dead easy and cheap to repair. Remanufactured long blocks can be had for a couple grand.

 

[clinebarger]

Just pop the two #1 Rockers off....Then pressurize with air.

 

[Chris142]

Many years ago my friend had a car with a 307 Chevy in it. Developed a miss. We took the valve covers off and found a pushrod had gone through a rocker and was holding a valve open. Fast easy fix

 

[Dinoburner]

While you have the valve covers off crank the engine over to see if the valves are opening and closing. If not r then the the cam is suspect. Of course if there is a broken valve spring it will be visible and as Clinebarger said don`t turn the engine over.

 

[Jesseyourcalipers]

By

While you have the valve covers off crank the engine over to see if the valves are opening and closing. If not r then the the cam is suspect. Of course if there is a broken valve spring it will be visible and as Clinebarger said don`t turn the engine over.

popped cover off. Springs and rods look fine. Turned it over and rockers all flicker in order. Will probably be getting borescope to really make sure but I’m sure it’s the piston. Thank you for your help.

 

[Jesseyourcalipers]

While you have the valve covers off crank the engine over to see if the valves are opening and closing. If not r then the the cam is suspect. Of course if there is a broken valve spring it will be visible and as Clinebarger said don`t turn the engine over.

popped cover off. Springs and rods look fine. Turned it over and rockers all flicker in order. Will probably be getting borescope to really make sure but I’m sure it’s the piston. Thank you for your help.

 

[Jesseyourcalipers]

Many years ago my friend had a car with a 307 Chevy in it. Developed a miss. We took the valve covers off and found a pushrod had gone through a rocker and was holding a valve open. Fast easy fix

This gave me hope and popped the cover. Everything looked okay and turned it over and all rockers and valves flutter like normal. Thank you for your reply though

 

[Dinoburner]

popped cover off. Springs and rods look fine. Turned it over and rockers all flicker in order. Will probably be getting borescope to really make sure but I’m sure it’s the piston. Thank you for your help.

Good news the cam and springs are ok.