Carbon build up or bent valve?? - Chevy TrailBlazer, TrailBlazer SS and GMC Envoy Forum



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Go Back   Chevy TrailBlazer, TrailBlazer SS and GMC Envoy Forum > 2002 - 2009 TrailBlazer/Envoy Tech > 02-09 Vortec 4.2L I-6 Engine and Drivetrain > OEM Issues

OEM Issues Original Equipment Repairs and/or Problems

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  #1  
Old 06-13-2010, 04:51 PM
1tm315 1tm315 is offline
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Carbon build up or bent valve??

I did a compression check on my 2005 I6 envoy and found that cylinder # 2 has only 30 PSI. I followed a suggestion from someone and sprayed some oil into the cylinder and ran the compression check again, with the same results. Thus, I was told that this is not a ring problem but a valve problem.

I have since taken the intake manifold and valve cover off and inspected the top end. Everything is extremely clean and I cannot detect any loose or missing parts along the valve train. I had someone crank the motor while I inspected the valve springs and I did not see anything noticeably wrong?? I did however discover that there is aircoming out of the # 2 intake port??

None of the others had leaks... The only thing I can think of is a bent intake valve but how could it be bent if there is no noticeable damage when inspecting the top end?? Could it be carbon built up on one of the intake valves? Is it possible to have that much carbon build up that it could keep the valve from seating? How do valves bend and not come lose and drop into the cylinder? anyway to get carbon off the valve without taking the head off?
If I take the head off and find that it is just carbon and get it cleaned off, do I have to get it re-surfaced or can I simply put it back on with a new head gasket?


Thanks!
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  #2  
Old 06-13-2010, 05:04 PM
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RayVoy RayVoy is offline
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A lot of products out there for cleaning carbon. Give one of them a try.
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  #3  
Old 06-13-2010, 06:54 PM
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Agreed. I use Seafoam.
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  #4  
Old 06-13-2010, 07:08 PM
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Quote:
Originally Posted by 1tm315 View Post
... The only thing I can think of is a bent intake valve but how could it be bent if there is no noticeable damage when inspecting the top end?? Could it be carbon built up on one of the intake valves? Is it possible to have that much carbon build up that it could keep the valve from seating? How do valves bend and not come lose and drop into the cylinder? anyway to get carbon off the valve without taking the head off?....
As I told you in your other nearly identical post, the most probable cause is some sort of carbon build-up holding the valve open a little. The I6, as far as I know, is a non-interference engine, so the chance that the valve is bent is low (short of a rod breaking).

And yes, valve stems CAN bend without the head of the valve breaking off.

The fact that there is SOME compression indicates the valve is only open a very small amount, IMO.
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  #5  
Old 06-13-2010, 09:03 PM
1tm315 1tm315 is offline
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Carbon build up or bent valve??

thanks everyone! Now the real question... Can I get the carbon off the valve WITHOUT pulling the head? will it harm the motor to run it in its current condition while I try the seafoam?? The engine light flashes when you run it any length of time. Obviously, I would rather put the valve cover and intake manifold back on and try to knock the carbon deposit off with the seafoam than pull the head. I have heard horror stories of broken head bolts in this forum.

Thanks again!
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Old 06-13-2010, 10:17 PM
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Is it me, or are the people on here tonight not paying attention.

We would not suggest using the Seafoam if it was going to damage the engine.

The suggestion to try the Seafoam was to save you taking the engine apart.

If the Seafoam does not work, you will probably have to have the engine taken apart.

I will not suggest that you tackle this, it is a very labour intensive procedure.
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Old 06-13-2010, 10:32 PM
1tm315 1tm315 is offline
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I was indeed paying attention... You misunerstood the question.
I was asking if running the engine with the low compression/valve problem would damage the engine, not the seafoam. I know what seafoam is/does...

Would you recommend running the engine with 30psi in #2 cylinder while trying to knock a posible carbon deposit off with the seafoam?

I was told you should not run the engine if the ses light was flashing. Is this true?

Sorry I was not clearer with my question.
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  #8  
Old 06-13-2010, 10:41 PM
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Quote:
Originally Posted by 1tm315 View Post
I was indeed paying attention... You misunerstood the question.
I was asking if running the engine with the low compression/valve problem would damage the engine, not the seafoam. I know what seafoam is/does...

Would you recommend running the engine with 30psi in #2 cylinder while trying to knock a posible carbon deposit off with the seafoam?

I was told you should not run the engine if the ses light was flashing. Is this true?

Sorry I was not clearer with my question.
Sorry, having a bad night.

You are correct, running an engine with a flashing light is not recommended. It may damage the cat.

Therefore, I can not recommend that you do it.

However, after saying that to you, I would still try it if it was my truck.
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  #9  
Old 06-13-2010, 11:48 PM
1tm315 1tm315 is offline
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Thanks Ray!
I like living on the edge so I will probably try it too! How will it damage the cat converter and so what if it does?? can't I just replace the cat if that happens? what does the cat do anyway? I never really paid much attention to their function other than remembering they had something to do with emissions...
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  #10  
Old 06-13-2010, 11:48 PM
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Quote:
Originally Posted by 1tm315 View Post
I did a compression check on my 2005 I6 envoy and found that cylinder # 2 has only 30 PSI. I followed a suggestion from someone and sprayed some oil into the cylinder and ran the compression check again, with the same results. Thus, I was told that this is not a ring problem but a valve problem.

I have since taken the intake manifold and valve cover off and inspected the top end. Everything is extremely clean and I cannot detect any loose or missing parts along the valve train. I had someone crank the motor while I inspected the valve springs and I did not see anything noticeably wrong?? I did however discover that there is aircoming out of the # 2 intake port??

None of the others had leaks... The only thing I can think of is a bent intake valve but how could it be bent if there is no noticeable damage when inspecting the top end?? Could it be carbon built up on one of the intake valves? Is it possible to have that much carbon build up that it could keep the valve from seating? How do valves bend and not come lose and drop into the cylinder? anyway to get carbon off the valve without taking the head off?
If I take the head off and find that it is just carbon and get it cleaned off, do I have to get it re-surfaced or can I simply put it back on with a new head gasket?


Thanks!
OK, you have the intake manfold off. Screw in an adaptor in the spark plug hole and apply compressed air (100 psi, with piston @ tdc) and see if you hear hissing at either the intake or exahust valve area. This can tell you a lot. A broken ring also can cause problems with compresson and oil added to the spark hole will not change it.
Please respond with the results
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