This bulletin involves rotating all engine exhaust valves, replacingthe valve spring retainer locks with a new design to increase valverotation at lower rpm, inspecting/replacing the MAP sensor (asnecessary), and decarbonizing the combustion chamber.
The customer may experience occasional engine misfire (rough-running engine) during certain vehicle operating conditions.
In addition, MIL illumination may also have occurred due to DTCP0300 – Multiple Cylinder Misfire. Various single cylinder misfire DTCsmay also be present. If the frequency of misfire is high, thepowertrain control module (PCM) may place the engine in “limp-in” mode.
The misfire condition may be caused by one or more engine exhaustvalves that are slow to close due to a buildup of carbon on the valvestem.
1. This condition may occur when the engine is not allowed to run atengine rpms that are greater than 3,500. At 5,000 rpm or higher, theengine exhaust valves will rotate if not impeded by high carbondeposits. Low engine rpms and high carbon deposits are associated withshort-trip driving where the engine is not allowed to fully warm tonormal engine operating temperatures.
Cold ambient temperatures will increase engine warm-up time andincrease the likelihood of carbon deposit buildup on the stem of theengine exhaust valve. Fuel detergent quality may also contribute to thecondition; the customer may want to try a different brand of fuel.
2. Verify that the engine misfire condition is not caused by faulty engine mechanical or electrical components.
3. If the engine mechanical and electrical systems are operating properly, perform the Repair Procedure.
1. Relieve the fuel pressure.
2. Remove the upper intake manifold.
3. Remove the cylinder head cover(s).
4. Remove the rocker arm and shaft assembly.
5. Clean and mark the tip of each exhaust valve stem at the 12 o’clockposition with a paint marker. The paint mark will be used later toassist with determining the amount of valve rotation.
6. Remove the spark plugs.
7. Rotate the crankshaft clockwise, until the number 1 piston is at Top Dead Center (TDC) on the compression stroke.
8. Install the compression tester spark plug adapter in cylinder #1spark plug hole. With the air hose attached to the spark plug adapter,apply 90 to 100 psi air pressure. This is to holdthe valves into place while servicing the components.
9. Using a valve spring compressor tool (MD 998772A) with the valvespring adapter (6527 or equivalent), slightly compress the exhaustvalve spring to release tension against the valve and valve springretainer (see Figure 1).
10. Remove the valve spring retainer locks and discard the locks.
Note: It is important that the valve rotation section of this repair procedure be performed.
Caution: Only grab the valve stem tip, being careful not to cause damage.
11. Using needle-nose pliers, grab the tip of the valve stem and rotatethe exhaust valve 90° (move the mark to the 3 o’clock position).
12. Install two new valve spring retainer locks (P/N 53022277AA).
13. After installing the locks, release the tension on the valve spring and verify proper installation.
14. Remove Special Tool MD 998772A (1) and the spark plug adapter tool.
15. Repeat steps 7-14 on the remaining five cylinders using the firingsequence 1-2-3-4-5-6. Make sure the piston is at TDC in each cylinderof the exhaust valve spring retainer lock that is being removed. Whenall the exhaust valves have been rotated 90° and all the exhaust valvespring retainer locks have been replaced, proceed to the next step.
16. Install the rocker arm and shaft assembly.
17. Install the cylinder head cover(s).
18. Install the upper intake manifold
MAP Sensor Inspection:
1. Inspect the MAP sensor — Figure 2 for LX models or Figure 3 for CS models.
a. If the MAP sensor is the new style, no further action is necessaryfor the MAP sensor. Proceed to Decarboning Combustion Chamber andValves.
b. If the MAP sensor is the old style, proceed to the next step.
2. Replace the MAP sensor with P/N 05033310AC for LX models or P/N04896003AB for CS models. If the vehicle is a CS model, be sure the newsensor opening is facing a downward direction when installed and onlyuse one fastener.
When complete, proceed to Decarboning Combustion Chamber and Valves.
Decarboning Combustion Chamber and Valves:
Caution: Do not use the Premium Air Intake Cleaner provided with kit 05174566AA for this service action.
Note: Use both fuel tank additives.
1. Pour the Premium Fuel System Cleaner from kit P/N 05174566AA and Combustion Clean P/N 05183546AA, into a full fuel tank.
2. Start the vehicle’s engine and allow it to reach normal operating temperature.
3. Disable the fuel pump by removing the fuel pump relay.
4. Disconnect the fuel supply line quick disconnect fitting from the fuel rail.
5. Install the appropriate adapter, either #31814 or #31815. Be sure toengage the adapter completely (push until a “click” is noticed).
6. Pour the Premium Combustion Chamber Cleaner from kit P/N 05174566AA, into the cleaning canister.
7. Suspend the fuel injector cleaning apparatus under the hood. Theregulator knob must be fully counterclockwise to the off position.Connect the cleaning apparatus service hose to the supply adapter.
8. Turn the regulator knob clockwise to the recommended cleaningpressure (58 psi). Be sure there are no leaks before starting theengine.
9. Start the engine and run at normal idle (or fast idle, 1,200-1,500rpm, to shorten service time) until the product has been used up andthe engine stalls.
10. When the engine stalls, turn the ignition off.
11. Disconnect the cleaning apparatus and adapter.
12. Reconnect fuel line and the fuel pump relay.
13. Turn the ignition key to the on position to energize the fuel pump.Check for leaks. Start the engine and run for at least 2 minutes toclear the fuel system of any residual product.
14. Using the DRBIII or the Star-SCAN, erase any engine DTCs.
1. In a safe vehicle operating location that will allow the vehicle tobe driven safely and at the posted speed limit, accelerate the vehicleuntil the engine reaches 4,500 rpm.
2. Hold the engine speed at this rpm for 15 seconds.
3. Slow down and, in a safe location, pull to the side of the road. Allow the engine to idle for five seconds.
4. Repeat steps 1 through 3 five more times.
Courtesy of ALLDATA.
Engine Builder Staff
Latest posts by Engine Builder Staff (see all)
- Ringbrothers to Debut One-of-a-Kind 1966 Chevrolet Chevelle - Oct 21, 2014
- Elgin Industries Celebrates 95th Anniversary - Oct 20, 2014
- PRW Welcomes New Customer Service Sales Manager - Oct 20, 2014