1999 Chevy Tahoe 99 Tahoe low compression on #4 cyl

Tiny
1SLOV6
  • MEMBER
  • 1999 CHEVROLET TAHOE
  • V8
  • 4WD
  • AUTOMATIC
  • 12,000 MILES
99 Tahoe has about 120K on t. I had the misfire code on cylinder 4. I did all the normal tune up stuff and still had the misfire. Fuel pressure was ok. I did a compression check and all cylinders were 175-180 EXCEPT #4. Which was 120. Whats the next step?
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Saturday, October 24th, 2009 AT 3:16 PM

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Tiny
OBXAUTOMEDIC
  • EXPERT
Hello,

Ok, next step.

Do another compression check on the #4 cylinder and right it down then sqirt a little oil into the cylinder and check compression again.

If compression increases then you have bad rings.

If compression remains the same then there is a problem with the Valves or possibly the head gasket.

Also what did the plug look like when you pulled it?

Mark S

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Saturday, October 24th, 2009 AT 3:26 PM
Tiny
1SLOV6
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OK.I tried it again a couple more times today. Same result. I am not losing any coolant and no oil in the coolant.I guess the heads gotta come off now? Or is there anything I could "try" to bandaid it with?
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Sunday, October 25th, 2009 AT 5:08 PM
Tiny
OBXAUTOMEDIC
  • EXPERT
Ok, so wet test results were same as dry. Right?

If so then there are a couple possibilities.

One is the valve spring has failed and compressed so the valve isn't closing all the way. This you can check by taking the valve cover off and using a tale measure a small narrow one you can measure and get a rough height on the the #4 cylinder springs, then the others and compare.

Another cause could be build up on the valve. You can remove the exhaust manifold and look at the valves to see if the are closed completely or not.

If a valve has broken a small piece off then you may not see that till head comes off.

One other thing, have you noticed an increase in radiator pressure or it sounding like it is boiling over into the overflow tank.

I have see this more on fords than chevy. But, the head gasket blows between the cylinder and a coolant port and this shows no oil in coolant nor coolant in oil, but does push exhaust though coolant system. You can check by starting vehicle and opening coolant overflow tank if it is bubbling and has an oder of exhaust then you do have a blown head gasket.

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Sunday, October 25th, 2009 AT 8:59 PM

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