Fuel Injection System - Diesel GMC Pickup R2500

COMPONENT TESTING

Note. See TESTING .

DESCRIPTION

The General Motors 6.2L diesel engine uses a mechanical high pressure rotary pump, gear driven by camshaft at camshaft speed. It injects a precisely metered amount of fuel to each cylinder at the proper time.

An electrical fuel pump, mounted on left side of frame, pulls fuel from fuel tank through a primary filter. Fuel is pumped through a secondary filter mounted on firewall (pickups) or rear of air cleaner (vans) to the injection pump. High pressure fuel lines carry fuel from pump to an injection nozzle in each cylinder. All fuel lines are the same length to ensure that there is no variance in timing. Engine RPM is controlled by a rotary fuel metering valve. As accelerator pedal is pushed down, throttle linkage opens metering valve to allow increased fuel delivery.

AIR INDUCTION SYSTEM

Intake manifold is always open to atmospheric pressure. Intake manifold has a single inlet for drawing air through an air filter assembly mounted above. Manifold consists of 8 branches, one leading to each cylinder.

DIESEL INJECTION PUMP

The high pressure diesel injection pump is mounted at top of engine, below intake manifold. The pump is gear driven by camshaft. Pump precisely governs time and amount of fuel injection.

A built-in fuel pressure regulator and transfer pump picks up fuel at pump inlet, pushing it through a passage to the pump head. The pump head distributes fuel at transfer pump pressure (8-12 psi) to metering valve, governor and automatic advance mechanisms. Fuel then passes to rotary fuel metering valve and into a charging passage. As pump shaft rotates, fuel is directed at high pressure through each delivery pipe to an injector. Pump is not serviceable and must be exchanged in the event of a malfunction.

Scheme 37

FUEL INJECTION LINES

Eight high pressure fuel injection lines are routed from injection pump to an injector in each cylinder. The lines are of equal length but are bent differently to maintain equal length, prevent any difference in timing from cylinder-to-cylinder and aid installation. Lines are not interchangeable and are pre-bent by manufacturer.

GLOW PLUGS

Glow plugs are small 6-volt heaters operated by the Electronic Controller. Glow plugs cycle on and off, powered by 12 volts to give rapid heating. Glow plug light on dash should illuminate as glow plugs cycle on and off.

Glow plugs cycle for approximately 25 seconds with ignition on regardless if engine is running or not. On and off cycling varies with system voltage and engine temperature.

Note. Any attempt to by-pass relay with jumper wire may result in glow plug failure.

INJECTION NOZZLES

Each engine cylinder combustion chamber is equipped with one injection nozzle. The injection nozzle has a single fuel inlet fitting and 2 fuel return fittings (one on each side of fuel inlet fitting). The nozzle is threaded into the cylinder head. Injection nozzles are spring loaded and calibrated to open at a specified fuel line pressure. The combustion chamber end of the nozzle has a replaceable compression seal and carbon stop seal.

Note. Injection nozzles used in "G" models are shorter than ones used in all other models. Use of incorrect nozzles will damage cylinder heads.

VACUUM PUMP

Vacuum to operate accessory systems on diesel vehicles is provided by a vacuum pump which is located at the rear of the block and driven by the cam. The engine should never be operated without the vacuum pump in place, as it is also the oil pump drive.

HOUSING PRESSURE COLD ADVANCE (HPCA)

The HPCA circuit is used to improve cold starting and aid emission control. On light duty emissions, an ECM signal is used to activate the HPCA circuit. On heavy duty emissions, the HPCA circuit is controlled by a coolant temperature switch located on rear of right-hand cylinder head. The circuit advances injection timing about 4 degrees when the engine is cold.

When engine temperature is below 95°F (35°C), the circuit decreases housing pressure from 10 psi to zero. At the same time, the fast idle solenoid is activated. When the temperature switch opens, the HPCA circuit is de-energized and housing pressure rises, retarding pump timing. The temperature switch will close again when engine temperature falls below 85°F (30°C).

DIESEL FUEL HEATER

This option is used to heat fuel when ambient temperature is below 20°F (6-°C). This prevents wax crystals from building up and blocking the fuel filters. The heater is located along the right side of the intake manifold and uses a resistance wire spiralled around the fuel line.

PRELIMINARY DIAGNOSIS

Glow plug system preliminary diagnosis should be performed only after ensuring that glow plug system is correctly installed. Check that all connectors are properly installed and that all connections are clean and tight.

This procedure is used to determine if a problem exists in the glow plug system itself, or elsewhere in the electrical system. This procedure should always be completed before performing ELECTRICAL SYSTEM DIAGNOSIS .

1. Connect ammeter in series with Red or Orange wire at top of glow plug controller to left and right banks of glow plugs. Operate glow plug system and note ammeter reading.
2. On pickups, reading must be at least 55 amps. On vans, reading must be at least 50 amps. If ammeter reading is within specification, glow plug system is operating correctly. If ammeter reading is not within specification, one or more glow plugs is inoperative.
3. Check individual glow plug leads by connecting ammeter in series with Green wire. Operate glow plug system. On pickups, each glow plug wire should read about 14 amps. On vans, reading is about 13 amps.
4. If ammeter readings are as specified, glow plugs and wiring are okay. If reading was less than specified, check for continuity by disconnecting glow plug lead and connecting a 12-volt test light from connector to ground. Operate glow plug system.
5. If test light glows, wiring is okay. Replace glow plug(s). If test light does not glow, repair or replace harness. Retest glow plug(s) for proper operation.

ELECTRICAL SYSTEM DIAGNOSIS

Perform this diagnostic procedure if engine does not start when cold. "GLOW PLUGS" light may or may not come on. Check fuel system to ensure it is okay. Ensure battery voltage is 12.4 volts or more with ignition switch off. Check that cranking speed is at least 100 RPM.

1. Connect 12-volt test light to ground. Place test light lead on battery stud (single Red wire) on controller. If test light does not glow, repair open circuit between battery and controller.
2. If test light glows, place test light lead on glow plug feed stud (2 Orange or Red wires) on controller. If test light glows, relay contacts are shorted. Replace controller and all glow plugs.
3. If test light does not glow, disconnect harness from all glow plugs. Connect test light to battery (12-volt source) and touch each glow plug terminal. Test light should glow. Replace glow plug(s) if light does not glow.
4. Connect all glow plugs. With ignition switch in "RUN" position, connect 12-volt test light to ground. Remove controller connector and check voltage (from ignition switch) at terminal "D" of harness connector.
5. If test light does not glow, repair open circuit from ignition switch to controller. If test light glows, connect test light to battery (12-volt source) and check for ground at terminal "E" of harness connector.
6. If test light does not glow, repair open in ground wire to terminal "E" of connector. If test light glows, connect test light to battery (12-volt source) and check terminal "C" of harness connector. If test light glows, replace glow plug controller.
7. If test light does not glow, remove temperature inhibit switch connector and check for continuity through switch. Switch should be open above 125°F (52°C).
8. If continuity exists, repair open circuit in harness between glow plugs and terminal "C" of harness connector. If no continuity exists, replace inhibit switch.

Engine (VIN C) Wiring System Diagram. Scheme 38

Engine (VIN J) Wiring System Diagram. Scheme 39

Glow Plug System Diagnosis (C/K, R/V, G, P). Scheme 40

A faulty controller may result in excessive White smoke and/or poor idle quality immediately after starting. The following procedure checks for proper operation of controller circuit. Ensure coolant temperature is below 80°F (27°C) before beginning test.

1. Place ignition switch in "RUN" position and allow glow plugs to cycle. After 2 minutes crank engine for one second. Return switch to "RUN" position. Glow plugs should cycle on at least once.
2. If glow plugs do not cycle, disconnect controller connector. Connect 12-volt test light between terminal "B" (Purple wire) of harness connector and ground. With ignition switch in "RUN" position, test light should be off. Test light should glow when engine is cranked.
3. If test light does not operate as specified, repair short or open in engine harness Purple wire. If test light operates properly but glow plugs did not cycle, replace controller.

INJECTION PUMP HOUSING FUEL PRESSURE

1. Remove injection pump and drain all fuel. Connect an air supply line to fuel inlet fitting. Be sure air supply is clean and dry. Seal return line fitting. Completely immerse pump assembly in a container of clean test oil.
2. Apply 20 psi (1.4 kg/cm 2 ) to pump. Leave pump immersed for 10 minutes to allow any trapped air to escape. Watch for leaks after 10 minutes. If no leaks are observed, reduce air pressure to 2 psi (.14 kg/cm 2 ) for 30 seconds.
3. If there are still no leaks, increase pressure to 20 psi (1.4 kg/cm 2 ) again. If no leaks are observed, pump is serviceable. If leaks are noticed, pump must be replaced.

Test Preparation

1. Remove injectors from engine. Clean carbon from tip area of nozzle with soft brass wire brush. DO NOT use steel brush or motorized brush to clean nozzle tip. Damage to nozzle tip may result.
2. Connect injector to injection nozzle tester. Place clear plastic tubing on each fuel return fitting to prevent leakoff from being confused with leaks. Close tester shutoff valve to pressure gauge.
3. Fill tester with test fluid. Fill and flush nozzle assembly with test fluid by operating tester lever briskly and repeatedly. This purges air from nozzle and coats all parts with test fluid.

Opening Pressure Test

1. Open tester shutoff valve 1/4 turn. Slowly depress tester lever and observe gauge. Note pressure at which needle of pressure gauge stops. Some injectors may pop while other injectors may drip (this is not a leak).
2. Opening fuel pressure should not fall less than the lowest limit of 1500 psi (105 kg/cm 2 ). Replace any injector which does not meet lowest acceptable pressure. Release tester pressure.

Leakage Test

1. Open tester shutoff valve an additional 1/2 to 1 1/2 turns. Blow dry nozzle tip. Slowly depress tester lever until pressure gauge reads 1400 psi (98 kg/cm 2 ). Maintain pressure for 10 seconds and observe nozzle tip.
2. A drop may form on end of injector, but should not drop off within a 10 second period. Replace injector if drop of test fluid drops from tip during the 10 second period. (Scheme 41) Release tester pressure.

Scheme 41

Chatter Test

Chatter for new and used injectors may vary. With some used injectors, chatter is difficult to detect during slow actuation of tester lever. Some injectors may chatter louder than others. As long as there is chatter, the injector is acceptable.

1. Close tester shutoff lever at pressure gauge. Slowly depress lever and note whether chatter can be heard. If no chatter is heard, increase speed of lever movement until it reaches a point where injector chatters.
2. At fast lever movement, injector may emit a "hissing" or "squealing" sound rather than normal chatter. This is acceptable.
3. These sounds indicate that injector needle moves freely and that injector seat, guide and pintle have no mechanical defects. Replace any injector assembly which does not chatter.

Spray Pattern Test

The injectors used with this system have several features which make pattern testing difficult. These features include longer nozzle overlap, greater pintle to body clearances, and an internal wave washer between injector nut and injector. Typical injector testers cannot deliver fuel with sufficient velocity to obtain proper spray patterns. DO NOT replace injector(s) because of spray pattern.

Removal

1. Disconnect negative battery cables. On vans, remove engine cover. On all models, disconnect air cleaner at valve cover. Remove crankcase vent bracket.
2. Loosen vacuum pump hold-down clamp. Rotate pump to gain access to intake manifold bolts. Remove injection line clips and intake manifold. Install Protective Covers (J-29664-1) in intake ports.
3. Remove injection line clips. On vans, raise vehicle (for left bank). On all models, disconnect and cap injection lines at injectors. Remove lines at pump. Tag lines for reassembly reference. Cap all openings.

Installation

Remove caps and install injection lines. Ensure lines are properly positioned. (Scheme 42) Reverse removal procedure to complete installation. Start engine and check for leaks.

Scheme 42

Removal (Pickup)

1. Disconnect negative battery cables. Remove intake manifold. Install Protective Covers (J-29664-1) in intake ports. Remove fuel injection lines. Disconnect throttle cable and detent cable (if equipped). Disconnect wiring, fuel return line, fuel supply line, and fuel injection lines at pump. Cap all openings.
2. Remove A/C hose retainer bracket (if equipped). Remove oil filler tube and vent hose assembly. Remove grommet. Scribe or paint an alignment mark on front cover and injection pump flange.
3. Rotate engine to remove injection pump retaining bolts that are accessible through oil filler neck hole. Remove injection pump mount nuts. Remove injection pump and gasket.

1. Install new injection pump gasket. Align locating pin on injection pump hub with slot in injection pump driven gear. At the same time, align injection pump timing marks. Cylinder No. 1 must be set at TDC. (Scheme 43)
2. Attach injection pump to front cover. Alignment marks made during removal must be aligned. Tighten nuts. Attach pump to drive gear and tighten bolts. Reverse removal procedure to complete installation. Check injection pump timing.

Scheme 43

Removal (Van)

1. Disconnect negative battery cables. Remove engine cover and intake manifold. Rotate snorkel up and remove air cleaner inlet hose. Remove hood latch. Disconnect cable and move aside.
2. Remove windshield washer bottle, fan shroud bolts and upper fan shroud. Disconnect rubber hose from oil fill tube. Disconnect oil fill tube attaching nuts and remove oil fill tube. Remove oil fill tube grommet.
3. Rotate engine as necessary and remove pump drive gear bolts. Remove fuel filter and bracket including line to injection pump. Disconnect wire looms from injection lines and injection lines at brackets.
4. Disconnect oil pan dipstick tube from left cylinder head. Disconnect electrical connections at injection pump. Disconnect detent cable (if equipped). Disconnect accelerator cable.
5. Remove injection lines. Tag lines for reassembly reference. Cap all openings. Disconnect fuel return line. Scribe or paint a mark on front cover and pump flange. Remove injection pump mount nuts. Remove injection pump. Cap all openings.

1. Install new injection pump gasket. Align locating pin on injection pump hub with slot in injection pump driven gear. At the same time, align injection pump timing marks. (Scheme 43)
2. Attach injection pump to front cover. Alignment marks made during removal must be aligned. Tighten nuts. Attach pump to drive gear and tighten bolts. Reverse removal procedure to complete installation. Check injection pump timing.

Disconnect negative battery cables. Disconnect fuel line clip. Remove fuel return line. Remove fuel injection line. Cap all openings. Using Injector Socket (J-29873), remove injector(s). Always remove injector by placing remover on 30 mm hex flats of injector body to prevent damage to injector.

Remove caps from injector and fuel lines. Install injector(s). Install fuel line. Install fuel return line and fuel line clip. Connect battery cables. Start engine and check for leaks.

1. On "R" and "V" models, fuel conditioner filter is located on engine side of cowl. On "C", "K", "G" and "P" models, filter is mounted on rear of intake manifold, under air cleaner. It is accessible by removing engine cover.
2. Remove fuel tank cap to release pressure or vacuum in tank. Place drain pan under drain hose to collect fuel. Drain fuel from filter by opening both air bleed and water drain valves. Using a screwdriver, release fuel conditioner bail wires. Remove filter.

1. Clean filter mount pad. Install new filter element and snap on bail wires. Close water drain valve. Attach a 1/8" inside diameter hose to air bleed and place other end in drain pan.
2. Disconnect fuel injection pump shut-off solenoid wire. Crank engine for 10-15 seconds. Allow starter to cool for one minute. Repeat procedure until clear fuel comes out of air bleed hose.
3. Close air bleed. Connect injection pump shut-off solenoid wire and install fuel tank cap. Start engine and allow it to idle for 5 minutes. Check fuel conditioner filter for leaks.

IDLE SPEED

1. Set parking brake and block drive wheels. Warm engine to normal operating temperature and install Tachometer (J-26925). Adjust low idle speed screw on pump to obtain curb idle speed. (Scheme 44)
2. Remove connector from fast idle solenoid. Connect an insulated jumper wire from battery positive terminal to solenoid terminal to energize solenoid. Open throttle to ensure plunger is fully extended.
3. Adjust fast idle speed by turning plunger hex head. Turn off engine. Remove jumper wire and test equipment. Install fast idle solenoid connector.

Scheme 44

IDLE SPEED (RPM)

INJECTION PUMP TIMING

1. Check alignment of injection pump timing marks on top of engine front cover and injection pump flange (half circles on California models and scribe marks on Federal models).
2. If timing marks are not aligned, loosen 3 retaining nuts, and align mark on injection pump with mark on front cover. Tighten nuts to 30 ft. lbs. (41 N.m) and adjust throttle linkage.

THROTTLE POSITION SWITCH (TPS)

1. Disconnect TPS connector. Loosen TPS mounting screws. Connect an ohmmeter or 12 volt test light between Ignition (Pink wire) and EGR (Yellow wire) of TPS switch.
2. Insert proper "switch-closed" Gauge Block (J-33043-A) between gauge boss on injection pump and wide open stop screw on throttle shaft. NOTE: Always refer to Emission Control Label for correct gauge block size.
3. Rotate throttle lever and hold wide open throttle stop screw against gauge block. Rotate TPS until there is continuity between terminals. Hold switch body at this position and tighten mounting bolts to 53 INCH lbs. (6 N.m).
4. Release throttle lever and allow it to return to idle position. Remove "switch-closed" gauge block and insert "switch-open" gauge block. Rotate throttle lever against "switch-open" gauge block. There should be no continuity between terminals.
5. If no continuity is present, switch is set properly. If continuity is present, then switch must be reset by returning to step 1) and repeating entire procedure. (Scheme 45)

Scheme 45

VACUUM REGULATOR VALVE

The vacuum regulator valve provides vacuum signals to control automatic transmission shift points. Vacuum setting of valve should be checked and adjusted periodically, using the following procedure. Engine MUST NOT be running during this procedure.

1. Loosen vacuum regulator valve so it is free to rotate on pump. Attach a hand-held vacuum pump and apply 20 in. Hg. vacuum to bottom port of valve. Attach vacuum gauge to top port of valve.
2. Insert Gauge Block (J-33043-A) between gauge boss on injection pump and wide open stop screw on throttle lever (switch on position). (Scheme 46) NOTE: Always refer to Emission Control Label for correct gauge block size.
3. Rotate and hold throttle shaft against gauging block. Slowly rotate vacuum regulator valve body clockwise (facing valve) until vacuum gauge reads 10.9-12.1 in. Hg. Hold valve body at this position and tighten mounting screws.
4. Check adjustment by allowing throttle shaft to return to idle stop position. Then rotate throttle shaft back against gauging block. Vacuum gauge reading must be within 10.9-12.1 in. Hg. If vacuum is outside limits, reset valve.
5. With valve vacuum set, confirm detent switch point by reading resistance between Ignition (Pink with Black stripe wire) and Detent (Orange wire). Insert Switch Gauge (J-36142) between wide open stop pin and wide open stop screw on throttle lever. (Scheme 46)
6. Rotate throttle lever against switch gauge. There should be infinite resistance. Release throttle lever and remove gauge. Rotate throttle lever to wide open throttle (lever stop screw touching pump stop pin).
7. Check switch for continuity. Switch must have zero to one ohms continuity before throttle reaches wide open position. If switch does not meet these specifications, reset assembly by returning to step 1) and repeating entire procedure.

Scheme 46

FUEL FILTER

Water in fuel filter should be drained every 5000 miles or when "WATER IN FUEL " warning light glows. Diesel fuel can damage asphalt and painted surfaces. Always place a drain pan under drain hose to collect fuel.

1. Stop vehicle and turn engine off. Apply parking brake. Remove fuel tank cap. Open water drain valve 2-3 turns. Start and allow engine to idle for 1-2 minutes or until clear fuel is observed. Stop engine and close water drain valve.
2. Install fuel tank cap. If "WATER IN FUEL" warning light comes on after driving a short distance or if engine runs rough or stalls, a large amount of water may be present in fuel tank. Purge fuel system.

Scheme 47

PURGING FUEL SYSTEM

1. Park vehicle on a level surface. Place drain pan under drain hose to collect fuel. Open drain valve 3-4 turns. With fuel tank cap installed and using air nozzle, apply 3-5 psi (.21-.35 kg/cm 2 ) through fuel return hose at injection pump.
2. Contaminated fuel will be forced out of tank via filter drain hose. Continue to drain fuel until clear fuel is observed. Entire fuel tank may have to be drained. Close drain valve. Install fuel return hose.

Note. If vehicle is equipped with dual tanks, perform purging procedure on each tank.

TORQUE SPECIFICATIONS

TORQUE SPECIFICATIONS

See also:
• TESTING
• ELECTRICAL SYSTEM DIAGNOSIS