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Worn Valve Guides


2old2fit's Avatar
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10-03-02, 06:41 PM   #1  
Worn Valve Guides

I have a '94 Chevy 4x4 with a 5.7 V8 that idles rough if I'm stopped a traffic light for more than a minute. Truck now has 76000 miles on it. Changed plugs, wires, rotor and distributor cap hoping that would solve the problem, but didn't. Just got it back from a repair shop to see what they thought was wrong. Said everything checks okay on the computer. Said he thought it might be worn valve guides which he said would run around $1300.

A little more background on the vehicle:

The set of plugs that I just took out appear to have carbon build up when comparing to the color pictures of used spark plugs in my repair manual.

Back in '97 at 30,700 miles (still under warranty) I asked the GM dealer's repair shop to look into the "rough idle at long stops". Their response on my invoice says " Scan check no codes, No problems at this time".

In '99 at 58,700 miles the vehicle was back to the GM dealer for what sounded like a broken rod, but ended up being a chunk of carbon that broke off and was banging around in the chamber. They decarboned the engine and charged me $125.

What do think I should do? The last repair shop suggested I just drive it until it gets worse.

Do you think it is worn valve guides?

Do I have any recourse against GM for a free repair since the problem was brought to their attention while still under warranty, but not diagnosed or repaired.

 
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10-03-02, 07:44 PM   #2  
the carbon buildup on the plugs is likely oil getting into the cylinder and sticking to the plug usually do to worn valve guides and needing valve guide seals replaced, after market valve guide seals are better quality than what they used from the factory originaly.
however i cant see this causing a rough idle after sitting at stops, but it is strange that a shop hasn't been able to find the problem, have they been able to reproduce the problem while they was looking at it?

 
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10-03-02, 07:55 PM   #3  
Sounds to me that to much fuel is entering the cylinders resulting in a rich condition.Could be a carb problem or the purge valve for the vapor recovery system.Possibly a fuel loaded vapor cannister.Valve guides don't cause carbon buildup,they cause oil fouling.I would run GM top engine cleaner through it and see what happens.

 
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10-04-02, 05:48 AM   #4  
Joe_F
This year truck is TBI injected, not carbed .

Start with the basics, including a full tuneup and filters. Make sure no vacuum lines are broken or misrouted.

Check the fuel pressure to be sure it's in spec...start with the simple stuff.

 
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10-04-02, 03:17 PM   #5  
You got me Joe had to many beers last night thought it said 1984, still may be a rich condition.I have a question for 2old2fit if you still had this idle problem from 30,700 miles why are you waiting untill 76,000 miles to attempt to press the issue?Ican tell you this GM has tightened the freebie belt,so it's not likely you will get recouse unless you have several reciepts showing this concern and then maybe not.

 
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10-04-02, 03:42 PM   #6  
I don't claim to be a gearhead or to know all the symptoms of engine ailments. The possiblity of worn valve guides was never presented as a possible problem until this week. I looked up some info on the web for valve guides and all the symptoms seem to be present. I just wonder why the "trained" repair person didn't offer the suggestion, or look into the possibility, when they had it in the shop at 30K miles rather than just looking for codes on the computer.

I don't do alot of start and stop driving in this vehicle, so it's not a problem I am faced with every day. I always assumed it was probably spark plug, wires, or rotor problem, not a major engine problem.

 
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10-04-02, 05:05 PM   #7  
Joe_F
First thing I would do is pull off the EGR valve and inspect it for carbon. Clean it out, install a new gasket and see if that helps. GM valves are known stuffers and this will give you jazz at idle like that.

Being that you already had carbonization issues (indicative of a bigger problem I believe), I would start here.

 
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10-05-02, 12:14 PM   #8  
Joe, I took off the egr valve and cleaned it up. Wasn't as bad as I was thinking it would be. Made a tremendous difference in the idle performance. Doesn't act like it is going to stall when I'm sitting at a light. I let it idle, like at a stop light, for about three minutes and it performed okay. Thanks for the help.

 
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10-05-02, 01:42 PM   #9  
Joe_F
Alternatively, you could have plugged it with a screw and if the vehicle ran fine without out in the loop, you'd know your problem was EGR related.

My Chevy Cavalier which I got from my grandparents was STUFFED with carbon (short trips) and I cleaned the valve. It got better, but was still pretty stuffed. A new one cured the jazz I was getting. I still have a few things to do on it.

 
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