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Discussion Starter · #1 · (Edited)
I have two problems:
1.) I have a tapping noise that comes and goes. Sometimes its really loud and other times its quite. I noticed when replacing the spark plugs that the valve cover is leaking alittle bit around the back two spark plugs. I plan on replacing the gasket with gasket maker next week. Is it possible that the tapping im hearing is actually air leaking out the gasket? And if not when i take the vavle cover off what should I look for to see if the valves are bad?

2.) I also have noticed when I first start the truck it has a very strong fuel smell from the exhaust and you can still smell it after its been idleing for awhile. Any ideas?


Is it possible that a sicky lifter could cause both problems???
 

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Discussion Starter · #2 ·
Nobody has any ideas or thoughts????:surprised:
 

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Valve cover leak and tapping are two different problems.
It may take a little longer to do the job but I'd reccommend you use the correct GM gasket to fix the leak instead of gasket maker. Gasket maker is ok for emergency repairs but it doesnt always seal as well as a gasket.
The tapping could be a lifter if it comes and goes. Possibly a build-up of oil sludge affecting the lifters performance. Try some "Marvel Mystery Oil" in the oil. I've used this stuff for years to get rid of top end noises. The viscosity is lower than regular oil and it has the abillity to loosen build up of sludge sticking to internal engine parts.
Another solution may be to do an engine flush/cleaning of the oil system and an oil change.
These are inexpensive methods that hopefully will solve the problem, if they dont work you may have to dig into the engine to repair it.
 

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Discussion Starter · #4 ·
I already bought the Marvel Mystery Oil and am putting that in the gas and with the next oil change which is coming up next week. The noise does come and goes. sometimes its really loud and other times it quiet or not there at all. Could this also cause the fuel smell in the exhaust? Thanks for the input!:great:
 

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I don't want to scare you but it could be a sticky valve :neutral: or a bad lifter
 

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Yea, a stickey lifter could allow the valve to release unburnt gasses.
Like Davandy says it could also be a bad lifter or valve.
If you still have the ticking after the marvel mystery oil you might want to do a compression bleed down on the suspect cylinder.
 

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When is it load, and when is it quiet?
A collapsed lifter usually makes noise when the engine is cold before it gets pumped up with oil. After its run, it will quiet down. I wouldn't think a collapsed lifter would cause an exhaust odor in the exhaust. if a lifter is collapsed, its just not going to allow that valve to open fully.
Is the sound a ticking, or does it sound like b.b.'s rattleing in a can?
Maybe a catalytic converter coming apart. Cats can make some funny noises when they come apart and if its going bad and no burning the spent fuel in the exhaust...That might be the source of your rattle and smell..
just my .02..
 

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i posted another reply but i dont see it so I'll say it again...
the 4.2 is an overhead cam engine so we can throw the lifter theory out the window.
i was also thinking, could it be an exhaust leak, and the o2s are seeing a lean condition and dumping fuel?
Cam chain? im not sure how they are tensioned in that engine, but if its hydraulic, it could fail the same way a lifer does...
just throwing ideas out there..
90k okn a 3 year old truck, i doubt its a valve or a valve spring.
 

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Discussion Starter · #9 ·
Its always there, sometimes I can only hear it when I give it gas.( one time its real quiet and others its really loud.) And sometimes its right when I start it and the truck is idling its really loud, and thats cold start or after I have been driving for awhile.
So your saying the inline 6 does NOT have lifters?

I have tried to pinpoint the origin of the noise and it sounds like its coming from under the throttle body. Thats why I thought it was a vavle tapping. But then my brother thought it could be a sticky lifter. An exhaust leak is a possibility. What would be the best way to check for that? ( I am guessing soapy water wont work) And the truck was in the shop about 2 months ago and the O2 sensors were reading fine. Granted they could have went bad since then.

And the fuel smell: I was with a friend who has an Envoy and when he started his, it also had a fuel smell at first. Is this a normal thing?
 

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over head cam engines don't use pushrods or lifters. depending on the set-up, the cams either directly contact the top of the valve (shim under bucket) or use a cam follower type set up. The follower is spring loaded and rides on the cam and then pushes the valve down.
If I'm not mistaken, the 4.2 is a shim under bucket style valve drive. No lifters, no pushrods.
spray around the area you think is leaking with carb clean. maybe its an intake leak if you say it seems like its coming from under the TB. I'm not sure where that is in relation to everything else on the motor, but couldn't hurt. the idle will go up if its an intake leak and you suck carb clean up there.
loud ticking that changes with engine speed and load sounds like exhaust leak. I blew a header gasket this summer out on my stang while driving home from VT. by the time I got home, it had burnt out my valve cover gasket and t started weeping...i just remembered that tonight while I was in teh garage hooking up a battery tender to my car. made a mess on my new valve covers and ceramic headers...:no:
i think your exhaust ports are much farther way from your valve covers on the I6 than on my V8...but its something to look for.
I'm just putting it out there...it might sound stupid, but hey...if it turns out to be something like that, you'll be glad you didn't yank your head off and have a valve job done.
 

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Discussion Starter · #11 ·
Update

Just wanted to update as to what the problem was. It was an exhaust leak. I guess when a certain mechanic reassemble my exhaust where the cat connects to the exhaust manifold down pipe he didnt tighten the one bolt( b/c it was a pain in the a$$ to get to). I tighten it up and the noise went away and there was no fuel smell. And the MPG went from 13mpg back up to 19mpg. It came back a couple of days later so I decided to just change the plange gasket on it and its been fine since.

Thank you SlimyAvocado for your input and help!!
 
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