Engine - Detonation/Spark Knock

Bulletin No. 81-12

Article No. 81-21-13

Date: October 16, 1981

SUBJECT:
ENGINE DETONATION - SPARK KNOCK
OR PING

LIGHT TRUCKS
1982 E,F AND BRONCO UNDER 8500 GVW WITH 4.9L SIX CYLINDER ENGINE (EXCEPT CANADIAN LEADED FUEL USAGES)

WARNING: THIS MODIFICATION IS AUTHORIZED ONLY FOR THE LISTED ENGINE CALIBRATION. PERFORMING THIS MODIFICATION ON OTHER ENGINE CALIBRATIONS IS UNAUTHORIZED AND COULD CREATE LIABILITY UNDER APPLICABLE FEDERAL OR LOCAL LAWS.

When an engine detonation (spark knock or ping) is encountered on one of the aforementioned vehicles, the following steps should be taken:

1. Check the integrity of the engine emission components by ensuring that the vacuum hose system is not leaking and that all vacuum hose connections have been properly made.

2. Check the EGR valve as described in the Engine/Emissions Diagnosis Manual to determine if it is functioning properly.







3. Check the initial ignition timing and idle speeds and set them according to the decal on the vehicle. Check the distributor vacuum and mechanical advance. Chart "A" provides instructions to check vacuum and mechanical advance. Chart "B" is a spark advance reference chart.

4. Consult the decal on the vehicle to verify correct spark plug usage.

5. Inspect the entire exhaust system for leaks. Service if necessary.

If, upon completing the five steps noted above, the detonation condition still occurs, the distributor timing is to be retarded at 2 ° intervals (up to a maximum of 6 °) until the detonation condition is resolved. After retarding the distributor, re-check and reset the curb idle speed according to the decal on the vehicle.




If the initial ignition timing is retarded, obtain an Authorized Modifications decal and list the date, dealer number and alterations performed. Select a prominent place adjacent to the Vehicle Emission Control Information decal suitable for installing the Authorized Modifications decal. Clean the area, install the decal and cover it with a clear plastic decal shield.

It should also be noted that the 4.9L engine is available with an 8.0 and 8.9:1 compression ratio. All E/F-350's have an 8.0:1 compression ratio. Because of the difference in compression ratios, it is imperative that 8.9:1 compression ratio pistons are not substituted for 8.0:1 compression ratio pistons when major engine work is performed. Refer to TSB 80-16, Article 80-16-9, dated August 15, 1980 for specific charts on piston and short block applications in prior model 6 cylinder engines.