Engine - Loss Of Power Or Erractic Idle, Crank Sprocket

91mitsubishi07

NO. TSB-91-11-011

DATE July, 1991

MODEL 87-91 Precis


SUBJECT:
CRANKSHAFT SPROCKET WEAR


PURPOSE

A loose crankshaft sprocket may cause a Precis to lose power or idle erratically. This bulletin provides diagnosis and correction procedures.

Figure 1:

CONDITION

The crankshaft sprocket (timing belt sprocket) is keyed to the crankshaft by means of flat areas on the sprocket. These flat areas may become worn and distorted allowing the crankshaft sprocket to rotate slightly on the crankshaft (Figure 1).

Figure 2:

DIAGNOSIS

Carbureted vehicles:

With a breaker bar and socket on the crankshaft sprocket bolt, try to rotate the crankshaft back and forth slightly. If the crankshaft feels like it has some freeplay AND rotates slightly without moving the crankshaft pulley (or timing belt), the flats could be worn (Figure 2).

Fuel Injected vehicles

Using the Multi-Use Tester, check the airflow sensor frequency and injector duration at idle. Normal air flow sensor frequency is approximately 40 hz and normal injector duration will be between 2.8 and 3.3 ms. A worn crankshaft sprocket will cause those readings to be about twice as high due to the change in camshaft timing.



PARTS INFORMATION

PART NAME PART NUMBER YEAR/MODEL

CRANKSHAFT SPROCKET 23120-21000 87-89 PRECIS

23120-24000 90 --> PRECIS


WARRANTY INFORMATION

Standard warranty procedures and coverage apply.


OPERATION OPERATION MODEL MODEL TIME NATURE CAUSE
CODE YEAR ALLOWANCE CODES CODE


REPLACE 87 - 89 1.2
23122ROO CRANKSHAFT GEAR PRECIS N13 C11
SPROCKET 90 --> 1.0


CORRECTIVE MEASURE

Remove the crankshaft sprocket following the procedures shown in the Service Manual. Inspect the crankshaft sprocket and crankshaft mating surfaces for wear. Replace as needed.