Fuel Injector: Testing and Inspection

Fig. 25 Fuel Injector Connections:

The fuel injectors are located in the top of the cylinder head between the intake/exhaust valves (Fig. 25).

A leaking fuel injector can cause fuel knock, poor performance, black smoke, poor fuel economy and rough engine idle. If fuel injector needle valve does not operate properly, engine may misfire and produce low power.

A leak in injection pump-to-injector high-pressure fuel line can cause many of same symptoms as malfunctioning injector. Inspect for leaks in high-pressure lines before checking for malfunctioning fuel injector.

WARNING:
- THE INJECTION PUMP SUPPLIES HIGH-PRESSURE FUEL OF UP TO APPROXIMATELY 120,000 kPa (17,400 psi) TO EACH INDIVIDUAL INJECTOR THROUGH HIGH-PRESSURE LINES. FUEL UNDER THIS AMOUNT OF PRESSURE CAN PENETRATE SKIN AND CAUSE PERSONAL INJURY. WEAR SAFETY GOGGLES AND ADEQUATE PROTECTIVE CLOTHING. AVOID CONTACT WITH FUEL SPRAY WHEN BLEEDING HIGH-PRESSURE FUEL LINES.
- DO NOT BLEED AIR FROM FUEL SYSTEM OF A HOT ENGINE. DO NOT ALLOW FUEL TO SPRAY ONTO EXHAUST MANIFOLD WHEN BLEEDING AIR FROM FUEL SYSTEM.

1. To determine which fuel injector is malfunctioning, run engine and isolate each cylinder using DRB III scan tool. The DRB scan tool lists the injector firing order in both cylinder numerical order (1-2-3-4-5-6), and actual firing order (1-5-3-6-2-4).

Fig. 26 Inspecting Injector Operation:

2. Note RPM drop for each cylinder. As an alternative, loosen high-pressure fuel line fitting at fuel injector connector tube (Fig. 26). Listen for a change in engine speed. After testing, tighten line fitting to 40 Nm (30 ft. lbs.) torque. If engine speed drops, injector was operating normally. If engine speed remains same, injector may be malfunctioning. Test all injectors in same manner one at a time.
3. Once injector has been found to be malfunctioning, remove it from engine and test it. Refer to Fuel Injector Removal/Installation.

WARNING: FUEL INJECTOR TESTERS CAN DEVELOP EXTREMELY HIGH PRESSURES. FUEL UNDER THIS AMOUNT OF PRESSURE CAN PENETRATE SKIN AND CAUSE PERSONAL INJURY. WEAR SAFETY GOGGLES AND ADEQUATE PROTECTIVE CLOTHING. AVOID CONTACT WITH FUEL SPRAY WHEN OPERATING INJECTOR TESTER.

Fig. 27 Fuel Injector Tester And Adapter Tool:

Fig. 28 Installing Injector To Adapter Tool 8301:

4. After injector has been removed, obtain bench-mount fuel injector tester OTC (SPX) part number 4210 (Fig. 27) (or equivalent). Install Special Tool number 8301 (Fuel Injector Adapter) to 4210 tester. Install fuel injector into 8301 adapter. Be sure tip of adapter tool 8301 is aligned to inlet hole at side of injector (Fig. 28) before tightening tool. Tighten tool 8301 to injector. Position container below injector before testing.
5. Refer to operating instructions supplied with pressure tester for procedures.
a. Check opening pressure or pop pressure. Pressure should be approximately 31,026 kPa (310 bars) or (4500 ± 250 psi). If fuel injector needle valve is opening (popping) too early or too late, replace injector.
b. Perform a leak-down test on injector. Apply pressure with injector tester. The injector should not leak (drip) fuel with pressure at approximately 20 bars (291 psi) lower than pop pressure.
c. Operate tester lever quickly several times to check injector spray pattern. Verify fuel is spraying from each injector nozzle hole. Injector should also spray evenly from each nozzle hole.
d. Pay attention to size and shape of spray plumes. They should all be equal. If possible, compare spray pattern to that of a new fuel injector with same part number. Checking each plume for consistency is an excellent indicator of injector performance. Even if only one nozzle hole is plugged, significant performance problems could result.
e. Look for burrs on injector inlet.
f. Check nozzle holes for hole erosion or plugging.
g. Inspect end of nozzle for burrs or rough machine marks.
h. Look for cracks at nozzle end.
i. Check nozzle color for signs of overheating. Overheating will cause nozzle to turn a dark yellow/tan or blue (depending on overheating temperature).
j. Look at end of injector tube where it meets injector. A small, shiny band should be seen at this point. The band should have a consistent thickness. If not, injector could be leaking into fuel return.
k. If any of these conditions occur, replace injector.