Engine - Hard Start, Knocking Noise, Poor Driveability
Group: 23Number: 96-02
Date: Feb. 22, 1996
Subject:
Turbo Diesel Engine, Hard Starting
Model(s):
All with (Engine Code AAZ)
Canada Only 1993 -->
Condition
Turbo Diesel engine starts hard (may be accompanied by the following symptom(s):
^ Unstable idle
^ Lack of power
^ Surging at constant speeds
^ High fuel consumption
^ Engine noise (knocking)
Service
Note:
Prior to working on any fuel system, always review fuel system "Rules for cleanliness" and "Cautions and Warnings" in the appropriate Repair Manual.
Warning!
Fire Hazard. When working on fuel systems, Do NOT smoke or work near heaters, open flame, sparks or anything that can ignite fuel or fumes
If a vehicle exhibits the described condition:
1. Check the Gravity Vent valve for proper position (see Technical Bulletin 20-95-05 dated Oct. 11, 1995).
- Check for air bubbles in the clear fuel supply line between the fuel filter and the Diesel injection pump
If large bubbles can continuously be seen in the fuel line, check the fuel system for leaks as follows:
- Disconnect fuel return line from Diesel injection pump
- Attach VAG 1274 with an adapter line to the injection pump in place of the fuel return line
- Remove fuel supply line at the tank and clamp closed using a suitable clamp
- Build pressure in line from 1.0 to 1.5 bar
Caution!
Relieve pressure slowly before releasing clamps from fuel lines.
Note:
It may be necessary to pump up the system several times due to air in the system that becomes compressed when the system is pressurized
If pressure continually drops:
- Locate leak using a soapy water solution, then eliminate the cause of the leak
Note:
^ The leak can be further isolated by clamping the fuel supply line downstream of the fuel filler
^ The return line can be pressurized by connecting the adapter to the fuel supply line. The return and supply lines at the fuel tank as well as the supply line at the fuel filter outlet must be clamped
- Inspect the (black) one way check valve located on the fuel supply line at the top of the fuel sender unit for leakage or blockage. Replace as necessary, (let the engine run at idle for several minutes)
Caution!
Do not attempt to modify or delete the one way check valve
After check valve replacement, if air bubbles are still visible in the fuel supply line:
- Replace the fuel filter and control valve mounted on the fuel filter (do not transfer control valve to new filter)
Note:
Always use new gaskets and hose clamps
2. Clean the metallic filter (screen) inside the air inlet of the air filter outlet
When procedure applies to vehicles within warranty use the following:
Part Identifier: 23A1
Labor Operation: 23A1005 60 T.U.
If air bubbles have been eliminated and the condition still exists:
- Check basic adjustments of accelerator cable (see group 20), idle and residual fuel delivery, full load adjustment, and pump timing (if necessary) as outlined in group 23 of the appropriate Repair Manual