Spark Plug - Cleaning/Replacement Guidelines

83chrysler7

Models


All Passenger Cars & Trucks
- Domestic & Import


Subject

Diagnosing Spark Plug Fouling & Failures


Index


FUEL

Date


April 8, 1983

No..

14-23-83
This bulletin briefly describes guidelines to accurately determine when spark plug cleaning or replacement is necessary.

As Technical Service Bulletin #14-03-83 describes, a special oil additive has been added to the factory fuel fill to prevent pre-delivery spark plug fuel fouling. Assembly plant introduction of the additive was December 15, 1982, to February 11, 1983.

Spark plugs remove from engines containing this fuel additive may be slightly shiny and oil wet in appearance. THIS IS A NORMAL CONDITION.

In depth spark plug fouling diagnosis is contained in the "Driveability Test Procedure" books under "No Start" and "Driveability Test Cold" and Technical Service Bulletin #14-44-82. A review of these two publications may be necessary to clarify any misunderstanding of spark plug fouling diagnosis.

Symptoms that may be caused by fouled or defective spark plugs are no start, rough and slow idle with engine miss, and surging and bucking with engine miss.

The following procedure should be used to determine whether spark plugs should be cleaned or replaced:

A. Engine Will Not Start

Check spark plugs for fouling. Clean them if necessary and reinstall in the engine ONLY if there is a satisfactory secondary ignition
spark and accelerator pump fuel spray as determined by following the Driveability Test Procedure for "No Start" testing.

A black and sooty appearance may not indicate a failed plug. These spark plugs can be cleaned and reinstalled in an engine.

B. Engine Starts, Runs Rough

Connect an ignition scope to engine and allow engine to warm up enough for choke to fully open.

1. Observe ignition firing lines on scope under load. Firing lines that are below 10 KV on one or more cylinders, but not all cylinders, may indicate a fouled plug.

2. If all firing lines are below 15 KV, and engine is not under load, apply a moderate load on the engine and observe the firing pattern. A firing line above 15 KV accompanied by an engine miss is an indication of a defective spark plug or open secondary wire.

A check of secondary wires for proper resistance should be made prior to cleaning of the spark plugs that indicated high firing voltage on the scope.

3. Any other scope patterns are not indications of defective spark plugs.

4. A black appearance is not an accurate indication of a fouled or defective spark plug.

Spark plugs will look black and wet after an engine has been started cold and/or operated for short periods while the choke is on.

Spark plug cleaning or replacement will probably not resolve driveability complaints such as sags, poor fuel economy, etc. Diagnosis and repair procedures described in the applicable "Driveability Test Procedure" should be followed for problem solving.

Spark plugs should only be cleaned or replaced when the symptoms justify this action. Conditions outlined in this bulletin and the test procedures described in the appropriate Driveability Procedure Manual should preclude incorrect servicing of the spark plugs.
Cleaning or replacement of spark plugs for unrelated symptoms or conditions under warranty may be cause for claim denial or charge back.

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