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2006 gmc envoy_denali_xl
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16 Posts
Discussion Starter #1
I need some help. I thought I fixed the knocking issue but it has come back. I was towing our travel trailer back to the storage unit with the gas light on. Just before I got to the gas station the engine started knocking. I filled up and the knocking continued. I got home and checked all the spark plugs and wires. I had replaced all but the front two on the passenger side. So I went ahead and changed those. The knocking didn't start again the next day till I got on the highway. I put a can of seafoam in the gas tank and engine. Problem solved. This was about 3 weeks ago. Yesterday I filled up with gas and picked up the camper to take it to the dealer. No knocking noise. After that we drove up the highway to get something to eat while they worked on the camper and the knocking came back. It gets louder with acceleration. Any ideas? I posted a video of it running idle http://youtu.be/pCpgKNp4vOk I need to get this fixed before our camping trip at the end of the month.
 

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2004 chevy trailblazer_ls
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333 Posts
Try doing the SeaFoam again but do it through the brake booster hose. If you search here there is a thread with pictures.
This will get all the carbon out and then (if it were me) pour some SeaFoam, Lucas injector cleaner (also cleans carbon) or similar product in the gas tank.
Take a look at your throttle body and make sure it isn't carboned up, too.
I've seen carbon knocks come back but not in that short a time frame, and the vehicles that did it were driven very short distances regularly back and forth.
 

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2003 gmc envoy_sle_xl
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59 Posts
A true "knock" will not be fixed with a can of anything. It's a sign of deeper mechanical issues. You need to properly diagnose the issue. A used oil analysis can be a BIG help. Blackstone labs in Ohio is a very good place to send it. I've used them for Cars, boats, and aircraft. The oil can give you a "snapshot" of the health of the engine and be a clue into a possible bearing, rod, piston(amongst others) issue. It's about $25 for the test and etiology.
 
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