2008 gmc Sierra cylinder 6 missfire and backfiring out intake

Two common places to find the pcv valve is the intake manifold or the cam cover. There have been engines, principally Ford, where it has been located directly in the crankcase.

Regardless of the location there will be a hose connecting the intake manifold to usually the cam or rocker cover with the valve found at one end or the other.

The 24-valve overhead system is a "low-maintenance"
design. Routine adjustments are no longer
necessary, however, measurement should still take
place when trouble-shooting performance problems,
or upon completion of a repair that includes removal
and installation of the valve train components or
injectors.
(1) Disconnect battery negative cables.
(2) Remove cylinder head cover (Refer to 9 -
ENGINE/CYLINDER HEAD/CYLINDER HEAD
COVER(S) - REMOVAL).
(3) Using the crankshaft barring tool #7471-B,
rotate crankshaft to align damper TDC mark to
12:00 o'clock position.
(a) If both number one cylinder rocker levers are
loose, continue to next step.
(b) If both number one clylinder rocker levers
are not loose, rotate crankshaft 360 degrees.
(4) With the engine in this position, valve lash can
be measured at the following rocker arms: INTAKE
1-2-4 / EXHAUST 1-3-5. Measure the valve lash by
inserting a feeler gauge between the rocker arm
socket and crosshead (Fig. 32). Refer to VALVE
LASH LIMIT CHART for the correct specifications. If
the measurement falls within the limits, adjustment/
resetting is not necessary. If measurement
finds the lash outside of the limits, adjustment/resetting
is required.
VALVE LASH LIMIT CHART
0.152 mm ( 0.006 in.)
MIN.
0.381 mm (0.015 in.)
MIN.
0.381 mm (0.015 in.)
MAX.
0.762 mm (0.030 in.)
MAX.
note:
If measured valve lash falls within these
specifications, no adjustment/reset is necessary.
Engine operation within these ranges has no adverse
affect on performance, emissions, fuel economy or
level of engine noise.
(5) If adjustment/resetting is required, loosen the
lock nut on rocker arms and turn the adjusting screw
until the desired lash is obtained:
² INTAKE 0.254 mm (0.010 in.)
² EXHAUST 0.508 mm (0.020 in.) Tighten the
lock nut to 24 Nm (18 ft. lbs.) and re-check the valve
lash.
(6) Using the crankshaft barring tool, rotate the
crankshaft one revolution (360°) to align the
damper TDC mark to the 12 o'clock position.
(7) With the engine in this position, valve lash can
be measured at the remaining rocker arms: INTAKE
3-5-6 / EXHAUST 2-4-6. Use the same method as
above for determining whether adjustment is necessary,
and adjust those that are found to be outside of
the limits.
(8) Install the cylinder head cover (Refer to 9 -
ENGINE/CYLINDER HEAD/CYLINDER HEAD
COVER(S) - INSTALLATION).
(9) Connect the battery negative cables.

Hi there:

Rocker Arms & Pushrods

Removal & Installation

3.1L & 3.4L Engines
Left Side

1. Before servicing the vehicle, refer to the precautions section.
2. Drain the cooling system to a level below the coolant pipe on the front of the engine.
3. Remove or disconnect the following:
   NOTEKeep the pushrods in order. Intake pushrods are 5 3 / 4 inches long and exhaust pushrods are 6 inches long.
   
   
   Negative battery cableSpark plug wiresHeater bypass pipePositive Crankcase Ventilation (PCV) valve and hoseRocker arm cover
   
   
   Rocker arms and pushrods
   

To install:

1. Lubricate all the valvetrain components with engine oil.
2. Install or connect the following:
   
   Pushrods and the rocker arms. Torque the bolts to 24 ft. lbs. (32 Nm).Rocker arm cover using a new gasket. Torque the rocker cover bolts to 89 inch lbs. (10 Nm).PCV valve and hoseHeater bypass pipe. Torque the screw at the water pump to 106 inch lbs. (12 Nm), the bolt at the cylinder head corner to 18 ft. lbs. (25 Nm) and the nut to 18 ft. lbs. (25 Nm).Spark plug wiresNegative battery cable
   
3. Refill the cooling system.
4. Start the vehicle and verify no leaks.

Right Side

1. Before servicing the vehicle, refer to the precautions section.
2. Remove or disconnect the following:
   NOTEKeep the pushrods in order. Intake pushrods are 5 3 / 4 inches long and exhaust pushrods are 6 inches long.
   
   
   Negative battery cableAlternator bracket on 2005 modelsSpark plug wires from the spark plugs and the upper intake plenum wire retainerPower brake booster vacuum pipe from the intake plenumAccessory drive beltAlternator, if necessaryIgnition coil assembly and Evaporative Emissions (EVAP) canister purge solenoid as an assemblyRocker arm cover
   
   
   Rocker arms and pushrods
   

To install:

1. Lubricate all the valvetrain components with engine oil.
2. Install or connect the following:
   
   Pushrods and the rocker arms. Torque the bolts to 24 ft. lbs. (32 Nm) plus an additional 30 degree turn.Rocker arm cover using a new gasket. Torque the rocker cover bolts to 89 inch lbs. (10 Nm).Ignition coil and EVAP solenoid assemblyAlternator, if removed. Torque the bolts to 37 ft. lbs. (50 Nm).Accessory drive beltPower brake booster vacuum pipe to the plenumSpark plug wiresNegative battery cable
   
3. Start the vehicle and verify no leaks.

Hope this helps.

First, check your firing order. Then check the routing of the plug wires. Those that are twisted around each other need to be untwisted. You may have a condition of cross fire which can have a couple sources. The wires that run parallel to each other for any distance must cross once only. Also make sure plug boots are fully seated on plugs, and the distributor connenctions are fully down.

At night, start the vehicle up and in the dark using care around the fan, look for arcing at the plugs, at the wires themselves and across towers on the distributor. Even new wires can be leaky to high voltage. Watch for glow in the vicinity of any corner or edge.

If vavle train is noisy, resetting valve lash will quiet it down some and may alleviate some of the backfiring too. it entails warming up the engine, removing the valve covers/rocker covers, covering the push rod ends with foil, and with engine operating, backing the nut on each each rocker one at a time, until a clatter is heard, then in 1//4 turn increments, pausing at each increment to let engine stabilize, until the nut is 1 turn tight past clatter.

If the issue of backfiring is a bent valve or burned valve this may help isolate that valve as well as any popping at idle will coincide with the clatter of that particular valve.

If you have the air pump, don't ovelook that as a source of the noise too. Look to see if the back side of the valve at the back of the engine on the distribution piping has rusted out.

With the Engine in the number 1 firing position, adjust the exhaust valves for cylinders number 1, 3, 4, and 8 and the intake valves for cylinders number 1, 2, 5, and 7.
Turn the valve rocker arm nut counter clockwise until the valve lash is felt in the valve pushrod.
Turn the rocker arm nut clockwise until all of the valve lash is removed (zero valve lash).
Zero valve lash can be felt by moving the valve pushrod up and down between your thumb and forefinger until there is no more up and down movement of the valve pushrod.
When all the valve lash is removed, then turn the valve rocker arm nut clockwise 1 additional turn (360 degrees).


With the engine in the number 6 firing position, adjust the exhaust valves for cylinders number 2, 5, 6, and 7 and the intake valves for cylinders number 3, 4, 6, and 8.

Follow the same steps as above.

The bolts should have thread lock on them when installing, and the torque is done in 2 steps. 33 ft lbs. and then 90 deg. after that on the second pass. 3.1L Engine CAUTION
Observe all applicable safety precautions when working around fuel. Whenever servicing the fuel system, always work in a well ventilated area. Do not allow fuel spray or vapors to come in contact with a spark or open flame. Keep a dry chemical fire extinguisher near the work area. Always keep fuel in a container specifically designed for fuel storage; also, always properly seal fuel containers to avoid the possibility of fire or explosion. LEFT SIDE (FRONT)

1. Properly relieve the fuel system pressure.
2. Disconnect the negative battery cable.
3. Drain the cooling system into a suitable container.
4. Disconnect the top half of the air cleaner assembly, then remove the throttle body air inlet duct.
5. Remove the exhaust crossover pipe heat shield and crossover pipe.
6. Disconnect the spark plug wires from spark plugs and looms then route the wires out of the way.
7. Remove the rocker arm (valve) covers.
8. Remove upper intake plenum and lower intake manifold.
9. Remove the left side exhaust manifold.
10. Remove oil level indicator tube. NOTE: When removing the valve train components they must be kept in order for installation in the same locations they were removed from.
    
11. Remove rocker arms nut, rocker arms, balls and pushrods.
12. Unfasten the cylinder head bolts evenly, then remove the cylinder head from the engine compartment. Remove and discard the gasket. To install:
    
13. Clean all the gasket surfaces completely. Clean the threads on the cylinder head bolts and block threads.
14. Place the cylinder head gasket in position over the dowel pins on the cylinder block so the words THIS SIDE UP are showing.
15. Coat the bolt threads lightly with sealer, then install finger-tight.
16. Tighten the cylinder head bolts in sequence to 33 ft. lbs. (45 Nm). With all the bolts tightened make a second pass tightening all the bolts an additional 90°.
17. Install the pushrods, rocker arms, balls and rocker arm nuts in their proper locations. Tighten the rocker arm nuts to 18 ft. lbs. (25 Nm).
18. Install the lower intake manifold and upper intake plenum.
19. Install the rocker arm (valve) covers.
20. Install the oil level indicator tube. Insert the dipstick.
21. Connect the spark plug wires to spark plugs and looms.
22. Install the left side exhaust manifold.
23. Install the exhaust crossover pipe and heat shield.
24. Refill the cooling system.
25. Install the top half of the air cleaner assembly and the throttle body air inlet duct.
26. Connect negative battery cable.
27. Start vehicle and verify that there are no leaks. Fig. 20: Cylinder head mounting and bolt tightening sequence - 3.1L engine
    

RIGHT CYLINDER HEAD (REAR) CAUTION
Fuel Injection systems remain under pressure, even after the engine has been turned OFF. The fuel system pressure must be relieved before disconnecting any fuel lines. Failure to do so may result in fire and/or personal injury.

1. Relieve the fuel system pressure.
2. Disconnect the negative battery cable.
3. Drain the cooling system.
4. Remove the top half of the air cleaner assembly and remove the throttle body air inlet duct.
5. Remove the exhaust crossover pipe heat shield and crossover pipe.
6. Raise and safely support the vehicle.
7. Detach the Oxygen (O2) sensor connector.
8. Disconnect the exhaust pipe from the exhaust manifold.
9. Remove the right side exhaust manifold.
10. Carefully lower the vehicle.
11. Disconnect the spark plug wires from spark plugs and wire looms and route the wires out of the way.
12. Remove the rocker arm (valve) covers.
13. Remove upper intake plenum and lower intake manifold. NOTE: When removing the valve train components they must be kept in order for installation in the same locations they were removed from.
    
14. Remove rocker arms nut, rocker arms, balls and pushrods.
15. Unfasten the cylinder head bolts evenly, then remove the cylinder head from the engine compartment. Remove and discard the gasket. To Install:
    
16. Clean all the gasket surfaces completely. Clean the threads on the cylinder head bolts and block threads.
17. Place the cylinder head gasket in position over the dowel pins on the cylinder block so the words THIS SIDE UP showing.
18. Coat the bolt threads lightly with sealer, then install finger-tight.
19. Tighten the cylinder head bolts in sequence to 33 ft. lbs. (45 Nm). With all the bolts tightened make a second pass tightening all the bolts an additional 90°.
20. Install the pushrods loosely retained with the rocker arm assemblies. Make sure all pushrods are in the correct locations. Coat the ends of the pushrods with prelube. The intake rods are marked yellow and are 5 3?4 inch long. The exhaust pushrods are marked green and 6 inches long. balls and rocker arm nuts. Tighten the rocker arm nuts to 18 ft. lbs. (25 Nm).
21. Install the lower intake manifold and upper intake plenum.
22. Install the rocker arm (valve) covers.
23. Connect the spark plug wires to spark plugs and wire looms.
24. Raise and safely support the vehicle.
25. Install the exhaust manifold.
26. Connect the exhaust pipe to the exhaust manifold.
27. Carefully lower the vehicle.
28. Connect the Oxygen (O2) sensor wiring.
29. Install the exhaust crossover pipe and heat shield.
30. Refill the cooling system.
31. Install the top half of the air cleaner assembly and the throttle body air inlet duct.
32. Connect negative battery cable.
33. Start vehicle and verify that there are no leaks.

from autozone.com

ADJUSTMENT

22R and 22R-E
See Figures 3, 4, 5 and 6

1. Start the engine and warm it up to normal operating temperature.
2. Turn the engine OFF . Remove the air cleaner and housing, along with the hot air and cold air intake ducts.

CAUTION Components will be hot. The engine head, block and radiator will be very hot.

1. Remove any other hoses, cables, or wires attached to the valve cover. The valve cover (or cylinder head cover) is the domed steel item with the oil filler in it.
2. Remove the small nuts holding the valve cover, then lift the cover off. Retrieve the rubber gasket and put it aside; it can be reused if not damaged or crushed out of shape. Beware of hot oil dripping from the inside of the cover.
3. Use a large wrench on the crankshaft pulley bolt to turn the engine clockwise until the timing mark on the pulley to 0 on the scale. Turning the engine will be easier if the spark plugs are removed, but this is not required.

CAUTION Do not attempt to align the engine by using the ignition switch to turn the engine. Doing will splash hot oil onto everything in the area, including you.

1. Check that the rockers on No.1 cylinder are loose and the rockers on No.4 are under tension. (No.1 is closest to the radiator; No. 4 is closest to the firewall.) If this is true, the engine is aligned with No.1 piston at top dead center. If it is not true, turn the engine one full revolution clockwise and realign the timing mark at zero; recheck the rockers.
2. Adjust the clearance 0.008 in. (0.20mm) intake and 0.012 in. (0.30mm) exhaust. Insert a feeler gauge and check for proper clearance between the top of the valve stem and the bottom of the rocker arm on the No. 1 intake valve. To adjust, loosen the locknut on the end of the rocker arm and turn the adjusting screw until the clearance is correct. Tighten the locknut and recheck the clearance; there should be a slight drag felt when the feeler gauge is pulled through the gap. Repeat the procedure for No 1 exhaust, No 2 intake and No. 3 exhaust.

Fig. Fig. 3: Adjust the clearance of half the valves, do the arrowed ones first

Fig. Fig. 4: Use a gauge to measure the distance between the stem and the rocker arm

Fig. Fig. 5: Hold the adjusting screw in position, then tighten the locknut

1. Turn the crankshaft pulley one full rotation clockwise until the marks align at 0 and for the remaining valves.

Fig. Fig. 6: Adjust the second set of valves the same as the first

1. Clean the valve cover thoroughly with a lint-free rag. Wipe any oil off the cylinder head edges in the area of the valve cover gasket.
2. Fit the gasket into the valve cover, making sure it is not crimped or twisted. If the half-moon rubber plugs came out of the valve cover, clean them and apply sealant to the part of the plug contacting the valve cover; install the half-moon plug.

The use of sealants on the valve cover gasket is not recommended.

1. Install the valve cover onto the head. Make certain is squarely seated and not pinching any adjacent wires or cables.
2. Install the valve cover retaining nuts. Tighten them to 43-60 inch lbs. (5-7 Nm) This is little more than finger-tight; overtightening will deform the cover and cause leaks.
3. Connect the lines, hoses and cables which were removed for access. Make certain electrical and ignition wires are firmly held by their clips or brackets.
4. Install the air cleaner with the hoses and duct work.
5. If still in place, remove the wrench and socket from the crankshaft pulley.

had a similar hard-running problem with a 96 ES 3.8 V6; pulled the front valve cover and rocker-arm tube over #5 had split and no longer controlled the i/o valves. had to replace and re-machine #5 valves in the head.

Most pcv valves are stuck in the rocker cover, with a hose attached to it. There isn't much to them, a rattling ball valve, about 2 inches long, 1/2 wide.

I would check the valves for number 6. If one or both are burned, stuck or out of adjustment it would cause your problem. If a cam lobe for that cylinder is burned or badly worn it could be the culprit.