Ferm and other vortec guys I need help!
 

My 99 tahoe has had what I thought to be some rocker arm noise. I pulled the passenger bank valve cover a month ago and turned the second one back about a quarter turn. That seemed to fix it. It was ran about 3 to 3.5 qts low when I found the remote oil filter lines leaking. Replaced and all has been well or so I thought. The last couple weeks the noise has come back with the cold weather. today I was driving down the road and it started to miss on a cylinder. I came back to the house and got a number 6 cylinder misfire code. I change the spark plugs, cap, rotor, button and wires. #6 was wet with fuel and all others looked good on burn. after all that I still have the miss. New plug is wet like the old one.


I tried to do a compression check and got 75 I think on that cylinder and 100 on the one behind it. This was coil wire off and turning it over at full throttle. I say I "think" 75 because it held once and then after that got only a bouncing needle while having someone else turn the engine over. I'm not a hundred percent sure my gauge is working right and I need to know where to go from here. Could this be in the head or valve train and not a piston/lower block issue? God I hope so. I'm just trying to make it through hunting season and ultimately get another year is out of it to pay off the wife's car and get something newer.


let me know where to go from here....this engine has about 60k on it.when we rebuilt it I replaced everything. ..heads...crank...pistons..rods....etc...etc...

The only other thing i can think to add is in addition to the tapping when starting cold i have heard what i can only describe as a metallic sound similar to an ac compressor clutch going out. It wasn't the ac though it was in that passenger bank valve cover. I'm going to pull the valve cover tomorrow after work but wanted to check in first on what to look for.

recheck with another compression tester, go ahead and pull all the plugs and check compression on all of them

Wet plug and low compression could be a stuck lifter. I've had ALOT of problems out of federal mogul/sealed power lifters. Theres 2 manufacturers out there for lifters for the OEM hydraulic roller cams, FEDERAL MOGUL/SEALED POWER, and MELLINGS. MELLINGS was the OEM manufacturer for these lifters and is all I use in them. Also get a better gauge as the compression should be up around 125-175 depending on engine health. I would remove the valve covers, get ready for a mess, and adjust the valves the old fashioned way. Start it up, let it idle, and back them off until they hammer, then tighten them down till it stops, and go another 1/4 turn. For the cylinder thats wet and throwing the code, start by backing the rockers off a turn on that cylinder and see what that does. And I know the book calls for 1/2-1 turn of preset, but I have had nothing but problems with anything more than a 1/2 turn, so I stick with a 1/4 turn to be safe.

But start with the basics. If it has compression, even only 60 lbs, it should still fire. If the plug is wet, it is either a hung poppet(if your running the old style injectors still) which is flooding the cylinder and washing the rings down, or a valve isn't opening allowing the air fuel in or out. A collapsed lifter could be at fault, but I wouldn't expect to see the wet plug with a collapsed lifter unless it is still cracking open some(just not much).

If all else fails, remove the check valve from the compression tester hose and set it up so tou can use it to pressurize the cylinder. Rotate the engine around to TDC and blow some air into the cylinder. Listen to see if you hear air rushing out the intake, exhaust, crankcase, or if the engine rolls around. You can find a compression leak in a hurry with compressed air.

Thanks guys!

Another possibility is carbon sticking a valve.... Be cautious.... If it IS carbon you can end up w valve piston contact.... Did a head job on Mom's 98 z71 for that very reason.

alright here's where I'm at so far I did the reverse pressure test with my shop air...150psi...number umber 6 at TDC on compression stroke. There was a little air out of the oil fill on the valve cover but the majority came out of my exhaust.

latest development is I pulled the valve cover and have a collapsed lifter. Rocker arm was so loose it was turned sideways and not touching the valve. But that doesn't explain my compression loss through the exhaust. So I'm thinking while I have the intake off inspecting the lifter Journal I'm going to go ahead and pull that head to look for a burnt valve stuck causing the lifter to crush. What do y'all think?

pull the rocker arms and retest. i've seen this twice back when ethanol 1st hit the pumps. the goo in the tanks at the station gummed up the valves which hung them open, and allowed the rocker to kick off. a collapsed lifter normally will not hang a valve open, or cause a rocker to fall off the valve stem. sounds to me like a gummed up valve caused the valve to stick open, and give enough play to allow the rocker to kick off. also, replace the pushrod while your there. i HIGHLY DOUBT a collapsed lifter caused this.