Engine (Federal) - Detonation Fix

86mitsubishi01

SUBJECT:

2.6L TRUCK (FEDERAL) DETONATION FIX
NO. STB-86-08-004

DATE August, 1986

MODEL 1985 and 1986 Truck
PURPOSE This bulletin tells how to correct a "ping" or detonation that can occur in a 1985 or 1986 Federalspecification Truck with 2.6L engine.

SYMPTOM The engine detonates (pings) on light acceleration between 30-60 mph. The condition usually occurs on vehicles with more than 4,000 miles, and it seems to be most prevalent in the southern tier of states.

PROBABLE CAUSE
1. The EGR valve is sticking or plugged.
2. The ignition timing is out of specification.
3. The ignition advance curve is not compatible with the local fuel blend.

CORRECTIVE ACTION
1. Check the EGR valve for proper operation as described on Page 25-11, 1986 Truck Service Manual. Replace if necessary.

2. Check the ignition timing. Adjust if necessary to the middle of the specification range (5-9 degrees BTDC).

FIGURE 1:

3. If the above steps fail to correct the condition, then replace the original-equipment distributor vacuum controller with a California-specification vacuum controller MD607969. Figure 1 on Page 2 shows how to identify the controller. Procedure for replacing the vacuum controller is on Pages 8-64 and 8-67, 1986 Truck Service Manual.
WARRANTY INFORMATION Normal warranty procedures apply.
Labor Operation Code: 08 15 66 50
Time Allowance: 0.2 hr