91 4.3 rattle at mid range

Hey all I have a 1991 blazer auto 4x4 4.3 that is driving me nuts. When you start the engine cold and drive off it has a mid range rattle. stop the truck and the rattle goes away. It only rattles while you drive and its
consistant with the rpms. Im thinking it could be the rockers hammering but if it was the rockers then wouldnt they hammer at idle while the trucks in park? What is confusing me is the fact that it only rattles when the engine is cold and in gear. So far I have gave it a tune up, changed the oil (the sound changed its tone after the oil change, which leads me to think that it may be the rocker arms) and replaced the TPS (thinking maybe timing/fuel issue) ANY AND ALL Ideas would be greatly appreciated Thnks Steve
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Sounds like an exhaust situation, loose baffle or hanger.
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nah, I crawled under it and checked. everythings tight

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Get your Gasoline from a different station!
seeray28 wrote:

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its not the gas ( I have tried several different brands and ratings) Tonite I took off the valve cover and loosened up a rocker and started te engine. the sound is Definitly a rocker. now my question is Why would the rockers make noise only when they are cold and at mid range. this weekend I plan on getting new rockers installed and hopefully that will cure the problem

you
but
in
tone
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I
Sounds more like a collapsed lifter. H
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warms
away.
You get to get dirty, pull the valve covers off one side at a time, fire the beast up and use your thumb on the rocker arm over the push rod moving from one to the next. You'll now when you find the right one, assuming it is a collapsed lifter. also that particular one might not have as much oil squirting as the rest. Usually a collapsed lifter is quieter when the oil is cold and thick, then when its hot and thinner. You might be able to narrow which side down before pulling the valve covers with a stethoscope, or a long extension one end against the valve cover, one against your ear. A collapsed lifter makes noise because there is gap between the rocker and valve because the lifter and push rod aren't keeping pressure on it, the same basic noise you get with solid lifters if they aren't adjusted correctly, ie too loose, or the noise you get when you back the valve adjustment off on hydraulics before cranking them back down to zero lash and a 1/2 turn more. One thing you might try first, is a quart of Marvel Mystery Oil in the crankcase for a little while and then another oil change and filter. It could just be gummed up, everyone gets lucky once in a while. Drive easy while the Marvel is in there, it will thin the oil out. Another question comes to mind, does this rig have an oil pressure gauge, what's the oil pressure hot and cold. Whitelightning
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Whitelightning wrote:

Too much Work
Simpler to Take a Broom stick... Cup your hand around the handle at one end put your Ear to your hand. Now put the other end on the Valve cover Move it around and when The ticking sound gets the loudest , you are Right over top of the Noisy tappet No need to even get dirty , Nor remove the valve cover Works as if u were using a Stethoscope
Be care not to touch moving parts.. if it is not a tappet, Then move the stick around the engine till u here the noise Via the BROOM STICK
also that particular one might not have as much oil

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ok thanks, ill look into it in the a.m. Steve

idle.
culprit?????????????????
the
from
a
oil
stethoscope,
ear.
and
and
easy
gauge,
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forget the broom handle, get a mechanic's stethoscope, about 20 bucks from Snap-On or Mac (or borrow one from a neighbor) much more precise and accurate
Besides you can use it later to decide which belt pulley to replace when one goes South
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Occaisional use stethoscope I use cost $2.49 located here: http://www.harborfreight.com/cpi/ctaf/Displayitem.taf?itemnumberA966
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