Spark Plugs - Oil Fouling/Misfire on Hard Acceleration

88chrysler13

Models


1978-1989 MMC Engines With Jet Valves


Subject


Oil Fouled Spark Plug(s) Miss & Bucking Under Hard Acceleration


Index


FUEL


Date

October 17, 1988

No.


18-17-88


C18-21)
This bulletin updates Technical Service Bulletin 5/14/88 and serves as a reminder that driveability problems may be caused by mechanical problems as well as fuel system problems.

FIGURE 1:

SYMPTOM/CONDITION

One or more (seldom occurs to more than one cylinder) spark plugs will be oil fouled and may show ground and center electrode erosion due to overheating (Figure 1).

Under hard acceleration (wide open throttle) engine will miss and buck.

FIGURE 2:

This condition may result from a jet valve failure. The jet valve failure is characterized by one of the causes outlined below (refer to Figure 2 for description):

^ Oil leaking past the oil seal and valve stem.

^ Oil leaking past the valve body and oil seal.

^ Oil leaking past the O-ring seal between the valve body and cylinder head which may be caused by a torn or cut Oring.

FIGURE 1:

DIAGNOSIS

Remove and inspect all spark plugs. If a spark plug is found to be heavily oil fouled and/or appears to have the electrodes eroded or overheated, proceed to jet valve removal procedure below (Figure 1).
PARTS REQUIRED

Jet Valve Assembly (as required) PN MD009440
O-Ring (as required) PN MD009786
INSTALLATION PROCEDURE

1. Remove only the jet valve of the cylinder showing the spark plug oiling or overheating. Follow the jet valve removal procedures outlined in the respective model year service manual using Miller Special Tool #MB-998310.

FIGURE 2:

2. Push jet valve open and inspect the valve stem just under the valve head. If oil residue and excessive carbon buildup are present, the Jet Valve Assembly, PN MD009440, will have to be replaced (Figure 2).

If no residue or carbon buildup is present, inspect the O-ring for rips, tears, or deformity. O-ring can be replaced separately with PN MD009786.

If no tear or deformity is found, remove the adjacent jet valves until the defective one is found. This is possible in some cases because oil from a leaking jet valve will migrate through the jet air passage in the cylinder head, which will falsely indicate a cylinder with a good jet valve as being bad.

FIGURE 3:

3. Inspect jet piece pocket by looking down into jet piece. If pocket has any buildup of burnt oil residue or carbon, it must be cleaned completely using the following procedure (Figure 3).

a. Remove spark plug.

b. Place piston on top dead center of compression stroke (both valves closed).

c. Use a thin stiff bristle brush to clean jet piece (a distributor cap terminal brush works well). A thin metal rod (coat hanger) can be used to loosen heavy deposits.

d. Direct compressed air in jet piece. The loosened deposits will be blown out of the jet piece and spark plug hole. Eye protection is recommended when performing this operation.

e. Reinspect cleaned jet piece. If cracking or erosion is seen in the area of the jet air orifice (Figure 3) or the deposit cannot be cleaned adequately, the cylinder head will require replacement.

4. Install new spark plug of proper heat range and gap setting.

5. Start engine and allow to fully warm up. Check for oil leaks and adjust idle speed if necessary.
POLICY: Information only