Chevrolet 1980 Light Duty Truck Service Manual page 415

Condition
Engine Starts,Idles Rough,
W ithout A bnorm al Noise or
Smoke (C o n t'd )
Engine Starts And Idles
Rough With Excessive
Noise and/or Smoke
Engine Misfires But Idles
Correctly
Engine Will Not R eturn
To Idle
Fuel Leaks On G round -
No Engine M alfunction
Significant Loss o f Power
Possible Cause
Internal Fuel
Leak at N ozzle(s)
I
Fuel Supply Pump
M alfunctions
Uneven Fuel
D istribution to
Cylinders
Injection Pump Timing
Incorrect
N ozzle(s) Inoperative
High Pressure Lines
Incorrectly Installed
Plugged Fuel Filter
Incorrect Injection
Pump Timing
Incorrect or C ontam inated
Fuel
Internal Engine Damage
External Linkage Mis-
adjustm ent or Failure
Internal Injection Pump
M alfunction
Loose or Broken Fuel
Line or Connection
Internal Injection Pum p
Failure
Incorrect or C ontam inated
Fuel
Pinched or Otherwise
Restricted R eturn System
Fig. 6A-5--Diesel Diagnosis
ENGINE M E CHA NICAL
Correction
Disconnect fuel return system from nozzles
on one bank at a time. With the engine
running, observe the normal fuel seepage
at the nozzles. Replace any nozzle with
excessive fuel leakage.
Test the fuel supply pump. Replace if
necessary.
Install new or reconditioned nozzles, one
at a tim e, until condition is corrected as
indicated by normal idle.
Be sure tim ing mark on injection pum p
is aligned with mark on adapter.
With engine running, crack injection line
at each nozzle, one at a tim e. Use care
to direct fuel away from sources o f
ignition. Each nozzle should contribute
to rough running. If a nozzle is found
that does not affect idle quality or
changes noise and/or smoke, it should
be replaced.
Check routing o f each line. Correct as
required.
Replace filter.
Be sure that tim ing mark on injection
pump and adapter are aligned.
Flush fuel system and install correct
fuel.
Refer to Engine Diagnosis.
Reset linkage or replace as required.
Install replacem ent injection pum p.
Examine com plete fuel system,
including tank, supply, injection and
return system. Determine source and
cause of leak and repair.
Install replacem ent injection pum p.
Flush fuel system and install correct
fuel.
Examine system for restriction and
correct as required.
6 A -1 1
LIG H T T R U C K SER V IC E M ANUAL