Chevrolet 1980 Light Duty Truck Service Manual page 416

6A-12 ENGINE M E C H A N IC A L
Condition
Significant Loss o f Power
(C o n t'd)
Noise - " R ap" From One
or More Cylinders
Noise - Significant
Overall Com bustion Noise
Increase With Excessive
Black Smoke
Noise - Internal or
External
Possible Cause
Plugged Fuel Tank Vent
Restricted Supply
Plugged Fuel Filter
External Compression
Leaks
Plugged N ozzle(s)
Internal Engine Problem
Air in Fuel System
Air in High Pressure
Line(s)
N ozzle(s) Sticking Open
or with Very Low Blowoff
Pressure
Internal Engine Problem
Timing Not Set To
Specification
Internal Engine Problem
Injection Pump Housing
Pressure Out o f Specifi­
cations.
Internal Injection Pump
Problem
Fuel Supply Pump,
A lternator, Water Pum p,
Valve Train, Short
Block, Etc.
Fig. 6A-6--Diesel D iagnosis
Correction
Remove fuel cap. If "hissing" noise is heard,
vent is plugged and should be cleaned.
Examine fuel supply system to determ ine
cause of restriction. Repair as required.
Remove and replace filter.
Check for compression leaks at all nozzles
and glow plugs, using " Leak-Tec" or
equivalent. If leak is found, tighten nozzle
clamp or glow plug. If leak persists at a
nozzle, remove it and reinstall with a new
carbon stop seal and compression seal.
Remove nozzles, check for plugging and
have repaired or replaced.
See Engine Section 6A.
Check for leaks and correct.
Crack line at nozzle(s) and bleed air at
each cylinder determ ined to be causing
noise. Use care to direct fuel away from
sources of ignition and be sure to carefully
retighten lines.
Replace the nozzle(s) causing the problem .
See Engine Section 6A.
Align tim ing marks on adapter and injection
pum p.
Check for presence o f oil in the air crossover
If present, determ ine cause and correct. See
Engine Section 6A for disassembly and
inspection procedures.
Check housing pressure as described in
Section 6A 5. If incorrect, replace fuel return
line connector assembly.
Replace pump.
See appropriate section o f Service Manual
for inspection, disassembly and repair pro­
cedures.
LIG H T T R U C K S ER V IC E M ANUAL