Section V. TROUBLESHOOTING - TM-10-3930-627-120048

TM 10-3930-627-12

Section V. TROUBLESHOOTING

symptoms at the same time. Also. a single symptom

4-9. General

may have one of several possible causes. Use table 4-2

This

section

provides

general

guidance

mainly as a checklist, rather than as a sole source of

troubleshooting the truck. Table 4-2 lists some possible

information while troubleshooting. Entries in table 4-2

problems which might occur, with the probable cause,

assume trouble has developed in normal use of the

and possible remedy for each. Troubleshooting

truck, Consider also accumulated time since new or

successfully will basically depend on the skill, experience

since last overhaul, and possible poorly done

and personal observations of the man checking the

maintenance work in deciding the most probable cause.

truck. Remember that a single defect may cause several

Table 4-2. Troubleshooting

Malfunction

Probable cause

Corrective action

a. Discharged battery.

a. Charge battery.

1. Starter does not crank engine.

b. Bad starter

b. Replace starter, paragraph 4-34.

c. Loose or dirty battery cable connections. c. Clean and tighten connections,

paragraph 4-33.

a. Check ignition & repair defects

2. Starter cranks, engine will not

a. Ignition failure.

start.

noted, paragraph 4-35, 4-36, 4-37.

b. Fuel system failure.

b. Check fuel pump. paragraph 4-26.

carburetor paragraph 4-22. and

fuel supply. Correct as needed.

c. Carburetor over-or underchoked.

c. If overchoked. gas will drip from

carburetor. Wait five minutes

and start without using choke.

a. Governor setting

a. Adjust governor, paragraph 4-23.

3. Engine lacks power, exhaust

b. Late ignition timing.

b. Correct ignition timing, paragraph 4-35.

color, and idle are normal.

c. Fuel supply restricted.

c. Check fuel line and shut off valve., fuel

pump, paragraph 4-26, and adjustment

of carburetor. Correct as needed.

4. Engine lacks power, black exhaust

Carburetor flooding

Replace carburetor, paragraph 4-22.

smoke and strong odor of gasoline.

a. Lean fuel mixture.

a. Adjust carburetor, or replace

5. Engine backfires on acceleration.

carburetor, paragraph 4-22 or

fuel pump, paragraph 4-26 as needed.

b. Refer to direct support maintenance.

Sticky valves.

c. Advance ignition timing, paragraph 4-35.

Late ignition timing.

a. Add required coolant.

Coolant level low.

6. Engine overheats.

b. Replace pump, paragraph 4-30.

Water pump bad.

c. Replace radiator, paragraph 4-30.

Radiator clogged.

a. Normal. No action necessary.

Battery fully charged.

7. Ammeter shows low charging rate.

b. Tighten belt, paragraph 4-30.

Drive belt loose.

c. Replace defective unit, paragraph 4-31,

Alternator or regulator bad

8. Ammeter shows high charging rate,

Regulator bad.

Replace regulator, paragraph 4-32.

battery charged.

a. Replace switch.

9. Neither head nor taillight will light.

a. Bad switch.

b. Blown fuse.

b. Replace fuse.

c. Burned out lamps.

c. Replace lamps.

10. Brakes do not release.

Bad brake master cylinder.

Replace master cylinder, paragraph 4-40

11. Spongy or soft brake pedal feel.

Air in brake hydraulic system.

Bleed brakes.

4-3