Engine - Diagnosing Performance Problems
Subject: EngineKey Points: Diagnosing Performance Problems
Group: 10
Number: 82-03
Date: November 5, 1982
Engine performance complaints
^ Engine, when cold, does not run on all cylinders
^ Engine surges/misses on acceleration springs are tested before installation
^ Engine does not run on all cylinders during load changes
^ Engine misses or lacks power at high rpm
Diagnosis sequence
- check the ignition distributor cap and rotor for correct seating and wear
^ if OK,
- check the valve springs for possible breakage
Note:
Usually, on this engine, a broken valve spring will not cause engine noise
- test drive vehicle in 3rd gear, and accelerate engine to 5000 rpm. Decelerate to 2000 rpm; then accelerate using full throttle
^ The engine should accelerate smoothly without any bucking, missing or surging
If engine runs rough, a valve spring may be broken (the camshaft housing must be removed to check)
To find the broken spring. use a screwdriver and try to push each valve down. A valve which has a broken spring can be moved down several millimeters. A valve which has the springs intact cannot be easily depressed
Note:
To replace a broken valve spring. it is not necessary to remove the cylinder head. Set the piston to TDC at which point the valve spring can be removed and new one installed
Note:
As of engine No. 43D 3026 - 43D 5451 the valve springs are tested before installation.