Fuel Injection System - 6.2l Diesel GMC Cab & Chassis R2500

COMPONENT TESTING

Note. Specific component testing information not available. Refer to any tests performed during REMOVAL & INSTALLATION or OVERHAUL procedures

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.

A mechanical fuel pump, mounted on right of engine, 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.

Scheme 25

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 at camshaft speed. 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 26

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 Plug System Diagnosis (C/K, R/V, G, P). Scheme 27

Glow plugs are threaded into each cylinder's combustion chamber. Glow plugs are small heaters that assist in cold starting. The glow plug controller/relay (mounted on top-rear of engine) cycles 12 volts to these 6-volt heaters, which causes them to heat rapidly. After the engine starts, glow plugs continue to cycle on and off for about 25 seconds, depending on coolant 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. The circuit is controlled by a 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.

DIAGNOSIS OF "WATER IN FUEL LIGHT"

"WATER IN FUEL LIGHT" DIAGNOSTIC

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 (an induction type meter may be used) with Red or Orange wire leading from top of controller to left bank of glow plugs. If using an in-line ammeter read both banks at once. DO NOT cut wire.
2. Operate system and note ammeter reading. Repeat procedure for right bank of glow plugs. On pickups, reading must be at least 55 amps. On vans, reading must be at least 50 amps.
3. If ammeter reading is correct, glow plug system is operating correctly. If ammeter reading is less than specified, one or more glow plugs is inoperative. Go to next step.
4. Check individual glow plug leads by connecting ammeter in series with Green wire that feeds glow plug. Operate system and note ammeter reading. Repeat procedure for each glow plug.
5. On pickups, each individual wire should have a reading of about 14 amps. On vans, reading is about 13 amps. If ammeter readings are correct, glow plugs and harness are okay. Problem is elsewhere. If readings are less than normal, go to next step.
6. On those glow plugs with less than normal readings, check for continuity through harness by disconnecting glow plug lead and connecting a 12-volt test light from connector to ground. Operate glow plug system.
7. If test light glows, harness 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 probe on battery stud (single Red wire) on glow plug controller. If test light glows, go to next step. If test light does not glow, locate and repair open circuit between battery and glow plug controller.
2. With ignition off, place test light probe on glow plug feed stud (2 Orange or Red wires) on glow plug controller. If test light glows, relay contacts are shorted. Replace glow plug controller and all glow plugs. If test light does not glow, go to next step.
3. 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. Connect all glow plugs before going on to next step.
4. 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.
7. If test light glows, replace glow plug controller. If test light does not glow, remove temperature inhibit switch connector and check for continuity through switch.
8. Switch should be open above 125°F (52°C). 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 Wiring System Diagram. Scheme 28

GLOW PLUG CONTROLLER

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. 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 described, 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 (.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 stops.
2. Maximum pressure observed is opening pressure. Lowest acceptable pressure is 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. Replace injector if drop of test fluid drops from tip. A drop may form but not drop off within specified time period. (Scheme 29) Release tester pressure.

Nozzle Leakage Test A drop of test fluid may form but not drop off within 10 seconds. Courtesy of General Motors Corp. Scheme 29

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 nozzle 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 and needle 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 bracket from 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 Screens (J-29664-1) in cylinder heads.
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 30) Reverse removal procedure to complete installation. Start engine and check for leaks.

Scheme 30

Removal (Pickup)

1. Disconnect negative battery cables. Remove intake manifold. Install Screens (J-29664-1) in cylinder heads. 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.
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. (Scheme 31)
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.

Injection Pump Timing Mark Locations Cylinder No. 1 must be set at TDC. Courtesy of General Motors Corp. Scheme 31

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 31)
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.

1. Disconnect negative battery cables. Disconnect fuel line clip. Remove fuel return line. Remove fuel injection line. Cap all openings.
2. Using Injector Remover/Installer (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 "C" and "K" models, fuel conditioner filter is located on engine side of cowl. On "G" and "P" models, filter is mounted on rear of inlet 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 2 minutes. 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 32)
2. Remove connector from fast idle solenoid. Run 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.

Idle Speed Adjustment Energize solenoid when adjusting fast idle. Courtesy of General Motors Corp. Scheme 32

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. Loosely assemble throttle position switch to fuel injection pump with throttle lever in closed position. Disconnect throttle position switch connector. Attach an ohmmeter 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). NOTE: Switch point must be set only while rotating switch body in clockwise direction.
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 exists, switch is set properly. However, if there is continuity, then switch must be reset by returning to step 1 and repeating entire procedure. (Scheme 33)

Throttle Position Switch Adjustment Rotate clockwise until continuity occurs. Courtesy of General Motors Corp. Scheme 33

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. 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 34) 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 34)
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.

Vacuum Regulator Valve Adjustment Valve must be set while rotating valve body in clockwise direction only. Courtesy of General Motors Corp. Scheme 34

DIESEL ENGINE FUEL FILTERS

The diesel engine fuel filter is an inline filter which combines several different functions. It acts as a filter, water separator, water detector, water drain and a fuel heater.

The first stage of the filter element is a water coalesor. The coalesor element combines small droplets of water into larger drops. The water collects in the bottom of the filter element for draining. The fuel then passes through the second stage of the filter element which is a paper filter.

The filter acts as a water detector by turning on the "WATER IN FUEL" light on the instrument panel. The probe of the water detector will touch water when 65 ml (2.2 fl. oz.) of water has collected in the filter. This completes a circuit through the water to the cover assembly which turns on the "WATER IN FUEL" light.

Note. If "WATER IN FUEL" light comes on and system is not purged of water, fuel injection system damage may result.

When light comes on, filter should be drained as soon as practical, but within 1-2 hours of engine operation. A water drain is located in the bottom of the fuel filter assembly. By opening water drain valve, water collected in the bottom of filter element can be drained.

A fuel heater is located in the fuel filter assembly to help prevent fuel waxing. The heater thermostat turns the heater on at about 0°C (32°F) and off at about 30°C (80°F). The heater uses 7 to 13 amps depending on fuel temperature.

Draining Fuel Filter

1. Turn off engine and apply parking brake. Remove fuel filler cap to release any pressure or vacuum in the fuel tank. Place suitable container under filter drain hose. CAUTION: The water/diesel fuel mixture is flammable, and could be hot. To help avoid personal injury and/or property damage, do not touch the fuel coming from the drain hose, and do not expose the fuel to open flames or sparks. DO NOT overfill container. Heat can cause fuel to expand. If container is too full, fuel could be forced out of the container. This could lead to a fire and the risk of personal injury and/or vehicle damage.
2. Open drain valve 2-3 turns. Start engine and allow it to idle for 1-2 minutes or until clear fuel is observed. Stop engine and close drain valve.
3. Install fuel filter cap. Dispose of the drained mixture in a proper manner.

Fuel Filter Replacement

1. Remove or disconnect fuel filler cap to release any pressure or vacuum in the fuel tank. Remove or disconnect both bail wires. Drain fuel from filter by opening air bleed and water drain valve. Allow fuel to drain into suitable container. Remove or disconnect fuel filter element.
2. Clean any dirt from fuel sealing surfaces of the filter element and the filter adapter.
3. Install or connect new filter element. Install or connect bail wires. Close drain valve. Install or connect 3 mm inside diameter hose to the air bleed port. NOTE: If engine is to be cranked or started with air cleaner removed, take care not to let objects fall into engine. If engine is running, suction can pull loose objects into engine. Objects pulled or dropped into engine can cause costly damage.
4. Install or connect other end of hose into a suitable container. Disconnect fuel injection pump shut-off solenoid wire. Crank engine for 10-15 seconds, then wait 1 minute for starter motor to cool. Repeat until clear fuel is observed coming from air bleed. Close air bleed.
5. Install or connect injection pump solenoid wire.
6. Install or connect fuel filler cap. Start engine and allow to idle for 5 minutes. Check fuel filter for leaks.

Fuel Filter Assembly Component Replacement

All component parts of fuel filter assembly are serviceable. These components include filter adapter, restriction switch, fuel heater, and the water sensor. Always replace damaged or worn O-rings, gaskets, or seals. After replacing components, bleed air from filter to save cranking time. Start engine and check for leaks after replacing components.

FUEL CONDITIONER 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 and open hood. 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. Shut engine off 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 35

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, 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:
• ELECTRICAL SYSTEM DIAGNOSIS