Idle Speed Drop Test
A defective or clogged injector may be the cause of hard starting, rough idling and running, knocking, or loss of power. An idle speed drop test is used to identify faulty injectors.
To test:
| 1. | Run the car at fast idle. On 1985 models pull the cold start handle out. On later models pull the cold start handle out to the first detent. |
| Fig. 3-1. | Open end box wrench (Volkswagen special tool no. 3035 or equivalent) being used to loosen fuel union nut at the injector. |
|
| 2. | Slightly loosen one of the fuel union nuts on a fuel injector pipe, either at the pump end or the injector end, as shown in Fig. 3-1, above. |
WARNING-
Loosen the nut only about one-quarter to one-half turn to limit the amount of fuel leakage. The fuel injection system operates at very high pressure. Keep hands and eyes clear. Wear heavy gloves and eye protection.
|
WARNING-
Fuel will be expelled. Do not smoke or work near heaters or other fire hazards. Have a fire extinguisher handy.
|
| 3. | Observe the condition of the idle. Idle speed should roughen and drop, due to loss of pressure at that injector. No change indicates that the injector was already malfunctioning. |
| 4. | Tighten the fuel union nut and torque it to 25 Nm (18 ft. lb.). Repeat the test for the other three injectors. |
CAUTION-
Diesel fuel is damaging to rubber. Wash or wipe off any fuel that spills on hoses, wiring, and rubber steering and suspension parts.
|
Injectors which fail the test should be rebuilt or replaced. See 5.6 Injectors.
|