Valves floating? - 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 06-19-2019, 09:36 PM
calzplace calzplace is offline
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2004 GMC Envoy SLT XUV
Victory Red 4.2L I6 4X4
Join Date: Jul 2016
Location: Fargo, ND
Posts: 3
Valves floating?

This is a 2004 Envoy, 4.2L. It idles smoothly, but the valvetrain clacks a lot, and has sounded like this for a long time with no problems. 92k miles on the motor.

Recently it started to lose power, and now it won't go past 55mph on the highway. It feels more gutless than normal, has more throaty intake noise at around 2000 - 2500RPM.

It keeps downshifting while trying to get up to speed, so I first thought it was the torque converter, but it feels pretty solid in 1st gear. If I stay in 1st gear and rev it up to around 4500RPM it starts to pop and clack and immediately dogs out and loses power. I can back it off and it seems fine again, and then it will do the same thing consistently at 4500 and it doesn't seem to go past that.

Any thoughts as to what this is?

I checked for ODBII codes, and the computer showed no faults, and all the test history showed successes.

I've read that the valvesprings are notoriously weak on these, is it just floating the valves, and will need to rebuild the whole top end of the motor?

Thanks!
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  #2  
Old 06-20-2019, 10:23 AM
Grinder's Avatar
Grinder Grinder is offline
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2004 Chevy TrailBlazer LT
Indigo Blue Metallic 4.2L I6 4X4
Join Date: May 2011
Location: Sunbury , Pa
Posts: 51
Diagnose your fuel system ? Is it starved.
Fuel filter restriction - fuel pump pressure and volume is something i would look into.
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Old 06-20-2019, 10:42 AM
calzplace calzplace is offline
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2004 GMC Envoy SLT XUV
Victory Red 4.2L I6 4X4
Join Date: Jul 2016
Location: Fargo, ND
Posts: 3
That's worth a shot I suppose. I assumed that if it were low on fuel pressure, the computer would have shown that.
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  #4  
Old 06-20-2019, 10:53 AM
Grinder's Avatar
Grinder Grinder is offline
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2004 Chevy TrailBlazer LT
Indigo Blue Metallic 4.2L I6 4X4
Join Date: May 2011
Location: Sunbury , Pa
Posts: 51
Not really. If you were to run out out of fuel from an empty tank the computer wont leave a DTC if that happened.
The computer reads sensors and parameters and if something is outta sync within its programming then it would set a DTC not from lack of fuel would a code set.
I had a fuel filter clogged on a chevy truck i own and would shut off when driving when off the throttle.
Checked the fuel filter and it was restricted. Swapped out w/ new one all is good now.
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Old 06-21-2019, 03:34 PM
calzplace calzplace is offline
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2004 GMC Envoy SLT XUV
Victory Red 4.2L I6 4X4
Join Date: Jul 2016
Location: Fargo, ND
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Solved

I did replace the fuel filter, and it didn't help. I was really stumped on this one, so I took it to a shop. They determined it was a plugged catalytic converter! The way it behaved I would have never guessed that. And, no computer codes made this difficult too.
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Old 06-23-2019, 12:57 PM
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Grinder Grinder is offline
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2004 Chevy TrailBlazer LT
Indigo Blue Metallic 4.2L I6 4X4
Join Date: May 2011
Location: Sunbury , Pa
Posts: 51
Good , you found the culprit.
Although not a common problem it makes sense that Reduced Power you were describing would give that.
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