Fuel Injection System - Diesel GMC Magnavan G3500

DESCRIPTION

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

An electric fuel pump delivers fuel to the injection pump. The fuel pump is mounted on the left side of frame and pulls fuel from the fuel tank through a primary filter. The fuel is then pumped through a secondary filter mounted on firewall (pickups) or rear of air cleaner (vans) to the injection pump.

High pressure fuel lines carry the fuel to an injection nozzle in each cylinder. All fuel lines are the same length to ensure no variance in timing. Engine RPM is controlled by a rotary fuel metering valve. As the accelerator pedal is depressed, throttle linkage opens fuel 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. 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 (.5-.8 kg/cm 2 ) 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.

Scheme 162

FUEL INJECTION LINES

Eight high pressure fuel injection lines are routed from the injection pump to an injector in each cylinder. The lines are of equal length to prevent a difference in timing between cylinders. Lines are not interchangeable and are pre-bent by the manufacturer.

GLOW PLUGS

Glow plugs are small 6-volt heaters powered by 12 volts to give rapid heating. The glow plugs are operated by the electronic controller and cycle on when ignition switch is turned to the "RUN" position, prior to starting the engine. The glow plugs remain pulsing a short time after engine starting, then automatically turn off.

The glow system for the LH6 (light duty emissions version) is somewhat different from the system for the LL4 (heavy duty emissions version). The LH6 system has the same glow plugs, glow plug controller and "WAIT" lamp. However, there is no temperature inhibit switch. Instead, glow plug temperature inhibit is controlled by the ECM which receives temperature information from the coolant temperature sensor, located in the water crossover of the engine.

The computer then transposes this temperature information into a voltage signal which it sends to the cold advance relay, ignition circuit and glow plug controller. The cold advance relay is located at the junction block in the engine compartment on the right side of the cowl. For diagnostic information on the computer controlled system, see appropriate article in COMPUTER ENGINE CONTROLS section.

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

GLOW PLUG INHIBIT SWITCH

The LL 4 (heavy duty emissions version of 6.2L engine), is equipped with a glow plug inhibit switch. The inhibit switch is calibrated to open above 125°F (51.5°C) to prevent glow plug operation above this temperature.

Two types of inhibit switches are used. Switches can be identified by the color of their cap. A switch with a Black cap is a temperature-controlled switch. A switch with a Natural cap color is an optional switch which is always closed, allowing for more frequent cycling of the glow plugs.

GLOW PLUG AFTER-START

The glow plug controller provides glow plug operation after starting a cold engine. This after-start operation is initiated when the ignition switch is returned to "RUN" from the "START" position.

INJECTION NOZZLES

Each of the 8 combustion chambers is equipped with an 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.

VACUUM PUMP

A vacuum pump is mounted on the engine and provides vacuum for operating emission controls, transmission modulator (M40 only), cruise control and heater doors. The vacuum pump is either belt driven or gear driven.

The belt driven vacuum pump used on "G" and "P" models is bracket mounted to the right front of the engine. It has a pulley attached which is driven by the alternator belt. With the exception of the pulley, the vacuum pump is replaced as an assembly.

The gear driven pump, used on "R/V" models, is mounted at the top, rear of the engine. It is driven by a cam inside the drive assembly to which it mounts. The drive housing assembly has a drive gear on the lower end which meshes with the camshaft gear in the engine. The drive gear causes the cam in the drive housing to rotate.

HOUSING PRESSURE COLD ADVANCE (HPCA)

The HPCA circuit is used to improve cold starting and aid in emission control. On light duty emissions (LH6 models), an ECM signal is used to activate the HPCA circuit. On heavy duty emissions (LL4 models), 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 80°F (27° C), the circuit decreases housing pressure from 10 psi to zero (.7 to zero kg/cm 2 ). 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).

TESTING & DIAGNOSIS

Note. The 6.2L light duty emissions engine (LH6) uses the Diesel Electronic Control (DEC) system. For complete system testing and diagnosis of DEC system, see COMPUTERIZED ENGINE CONTROL section.

NORMAL GLOW PLUG CIRCUIT OPERATION

A normal functioning system should operate as follows

1. With ignition switch in the "ON" position, engine not running and at room temperature, glow plugs are on for 4 to 6 seconds, then off for about 4.5 seconds. Following this on and off cycle, the glow plugs are on for about 1.5 seconds and off for about 4.5 seconds. The glow plugs continue to cycle on and off in this time sequence for about 20 seconds
2. If engine is cranked during or after the above sequence, the glow plugs will cycle on and off for a total duration of 25 seconds after the ignition switch is returned from the crank position, whether the engine starts or not. The engine does not have to be running to terminate the glow plug cycling.

Note. Glow plug on and off times vary with engine temperature, system voltage and/or ambient temperature. Lower temperatures cause longer duration of cycling.

PRELIMINARY GLOW PLUG SYSTEM DIAGNOSIS

1. If system does not operate as described in «NORMAL GLOW PLUG CIRCUIT OPERATION»(/gmc/magnavan-g3500/1985-1993/remont/testing-diagnostics/#fuel-injection-system-diesel__normal-glow-plug-circuit-operation) , ensure glow plug system is correctly installed. Check all connectors are properly attached, clean and tight. Inspect engine harness ground connection. Ensure nut securing 4-wire connector at controller is tightened to 96 INCH lbs. (11 N.m), with connector fully seated and latched.
2. Ensure controller copper stud upper nuts are tightened to 96 INCH lbs (11 N.m). DO NOT tighten lower nuts. Ensure temperature switch connector in water crossover near front of engine is tightened to 48 INCH lbs. (5 N.m). Inspect "WAIT" lamp on instrument panel for tight connection and operation.

INHIBIT SWITCH (BLACK CAP)

1. Remove connector from inhibit switch when engine temperature is below 100°F (38°C), (Inhibit switch is located in water crossover near front of engine). Set ohmmeter on low range. Test across switch terminals. Switch should be closed (a reading of less than 1.0 ohm on meter.)
2. Test terminals to ground with a test light or ohmmeter on high range. Light should be off. Meter should show greater then 1.0 megohm. Replace switch if it tests open across terminals or if either terminal is closed to ground.
3. Disconnect plug from switch terminals when the engine is above 125°F (52°C). Change ohmmeter setting to highest scale or use a self-powered test light. Test across switch terminals. Test from each terminal to ground. Switch should be open (test light off or high ohm reading of greater than 1.0 megohm on meter). Replace switch if it is closed. When installing replacement switch, tighten to 17 ft. lbs. (23 N.m)

Glow Plug System Diagnosis (C/K, R/V, G, P). Scheme 163

If glow plug system does not operate correctly and all connections are intact and inhibit switch is operating, perform the following diagnostic tests

1. Connect an ammeter in series between glow plug controller and left bank of glow plugs (glow plug controller is located on top, rear of valve cover). (Scheme 164) "G" Series Van - Orange wire at controller is for left bank glow plugs. Red wire at controller is for right bank glow plugs. "C/K" Models - A pair of Grey wires are attached to glow plug controller. Color changes to Orange going to left bank glow plugs and Orange/Black going to right bank glow plugs. "R/V" & "P" Models - Information for "R/V" & "P" not available at time of publication. Use Fig. (Scheme 164) as a reference and trace wire from controller to left bank glow plugs.
2. Move ignition switch to the "RUN" position. Engine and accessories must be off and the glow plug system operating. Ammeter reading must be at least 55 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 each wire attached to a glow plug. Each glow plug wire should read about 14 amps.
4. If ammeter readings are as specified, glow plugs and wiring are okay. If reading is 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. Repeat above procedures for right bank of glow plugs.

NO ENGINE COLD START

Perform these diagnostic procedures if engine does not start when cold; "GLOW PLUG" light may or may not come on. Before proceeding, check fuel system to ensure it is okay. Ensure battery voltage is 12.4 volts or more with ignition switch in the "OFF" position. Check cranking speed is at least 100 RPM.

1. With the ignition switch off, use a voltmeter to measure the voltage at the battery stud (single wire) on the glow plug. (Scheme 164) If no voltage is present, repair battery to glow plug controller circuit.
2. If no voltage is present in step 1), disconnect the harness from all glow plugs. Use an ohmmeter to measure continuity between the glow plug terminals and engine block. Replace glow plug if measurement is greater than 2 ohms. Reconnect all glow plugs before continuing with diagnosis.
3. If voltage is present in step 1), turn engine ignition switch to "OFF" position and measure voltage at glow plug feed stud (twin lead) on glow plug controller. If battery voltage is present, relay contacts are shorted. Replace controller and all glow plugs.
4. With all glow plugs reconnected, place ignition switch in "RUN" position. Remove controller connector and check voltage at harness connector terminal "D". (Scheme 164)
5. If no voltage is present, repair open in ignition feed circuit to controller. If voltage is present, measure continuity between terminal "E" of the connector and the engine block (ground). If measurement is greater than one ohm, repair the ground circuit to the controller.
6. With ground circuit working properly in step 4), measure continuity between terminals "C" and "E" of the connector. (Scheme 164) If reading is greater than 2 ohms, go to step 6). If reading is less than 2 ohms, go to step 8).
7. If reading in step 5) is greater than 2 ohms, remove the connector from the temperature inhibit switch and measure the continuity between the two terminals on the switch. Switch is open above 125°F (51.5°C). If reading is less than one ohm, repair the glow plug circuit to the controller. If reading is greater than one ohm, replace temperature inhibit switch and return to step 6).
8. If reading in step 5) is less than 2 ohms, reconnect controller harness connector and ensure complete engagement. Connector locking latch should click over controller locking tab. With controller connector harness correctly connected, measure voltage at glow plug feed stud (twin lead) on glow plug controller, while turning ignition switch from "OFF" position to "RUN" position.
9. If no voltage is present, replace glow plug controller. If battery voltage is present, measure voltage at any one glow plug harness connector when turning ignition switch from "OFF" to "RUN" position. Test both right and left banks.
10. If no voltage is present in step 8), repair glow plug feed circuit to glow plugs. If battery voltage is present and instrument panel "GLOW PLUG" lamp does not come on, locate and repair bulb or circuit.

Scheme 164

GLOW PLUG CONTROLLER

The glow plug controller provides glow plug operation after starting a cold engine. This after-start operation is initiated when the ignition switch is returned to "RUN" from the "START" position. 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. It is NOT important that the engine starts. Return ignition switch to "RUN" position. Glow plugs should cycle on at least once.
2. If glow plugs do not cycle, disconnect controller connector (controller is located on top, rear of valve cover). Connect 12-volt test light between Purple/White wire terminal of harness connector (terminal "B") and ground ("G" van and "R/V" and "P" series, use solid Purple wire). With ignition switch in "RUN" position, test light should be off. Test light should glow when engine is cranked. (Scheme 164)
3. If test light does not operate as specified, repair short or open in engine harness Purple/White (Purple) wire. If test light operates properly but glow plugs did not cycle, replace controller.

INJECTION PUMP HOUSING LEAKAGE TEST

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 off 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 trapped air to escape. Watch for leaks after 10 minutes. If no leaks are observed after 10 minutes, 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 ready for use. If leaks are noticed, pump must be replaced.

Test Preparation

1. Remove injector nozzles 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. CAUTION: Use Nozzle Socket (J 36142) to remove and replace injection nozzle. Attach tool to 30mm hex portion of nozzle. Failure to do so will result in damage to the injector nozzle.
2. Connect injector nozzle to injection nozzle tester. Place clear plastic tubing on both fuel return fittings to prevent bleed-off 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 injector nozzle and coats all parts with test fluid.

Opening Pressure Test

1. Open tester shutoff valve 1/4 turn from closed position. Slowly depress tester lever and observe gauge. Note pressure at which needle of pressure gauge stops. Some injector nozzles may pop while other injector nozzles 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 nozzle which does not meet lowest acceptable pressure. Release tester pressure.

Leakage Test

1. Open tester shutoff valve 3/4 to 1 3/4 turns from a closed position. Blow dry injector nozzle tip. Slowly depress tester lever until pressure gauge reads 1400 psi (98 kg/cm 2 ). Maintain pressure for 10 seconds and observe injector nozzle tip.
2. A drop may form on end of injector nozzle, but should not drop off within a 10 second period. Replace injector nozzle if drop of test fluid drops from tip during the 10 second period. (Scheme 165) Release tester pressure.

Scheme 165

Chatter Test

Chatter for new and used injector nozzles may vary. With some used injector nozzles, chatter is difficult to detect during slow actuation of tester lever. Some injector nozzles may chatter louder than others. As long as there is chatter, the injector nozzle 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 nozzle chatters.
2. At fast lever movement, injector nozzle may emit a "hissing" or "squealing" sound rather than normal chatter. This is acceptable. These sounds indicate that injector nozzle needle moves freely and injector nozzle seat, guide and pintle have no mechanical defects. Replace any injector nozzle assembly which does not chatter.

Spray Pattern Test

The injector nozzles 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 nozzle nut and injector. Typical injector nozzle tester cannot deliver fuel with sufficient velocity to obtain proper spray patterns. DO NOT replace injector nozzle(s) based on 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 injector nozzles. 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 166) Reverse removal procedure to complete installation. Start engine and check for leaks.

Scheme 166

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-to-drive gear retaining bolts 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 167)
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. See «INJECTION PUMP TIMING»(/gmc/magnavan-g3500/1985-1993/remont/testing-diagnostics/#fuel-injection-system-diesel__injection-pump-timing) under ADJUSTMENTS in this article

Scheme 167

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 while aligning injection pump timing marks. (Scheme 167)
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. See «INJECTION PUMP TIMING»(/gmc/magnavan-g3500/1985-1993/remont/testing-diagnostics/#fuel-injection-system-diesel__injection-pump-timing) under ADJUSTMENTS in this article

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 nozzles(s). Always remove injector nozzle by placing remover on 30 mm hex flats of injector body to prevent damage to injector nozzle.

Remove caps from injector nozzles and fuel lines. Install injector nozzles(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. (Scheme 170)

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 shutoff 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 shutoff solenoid wire and install fuel tank cap. Start engine and allow to idle for 5 minutes. Check fuel conditioner filter for leaks.

Curb Idle

Set parking brake and block drive wheels. Warm engine to operating temperature. Install Tachometer (J-26925). Air cleaner must be in place and accessories turned off. Adjust low idle speed to specifications by turning low speed idle screw on pump. See IDLE SPEED (RPM) specifications table. (Scheme 168)

Fast Idle

1. Set parking brake and block drive wheels. Warm engine to normal operating temperature and install Tachometer (J-26925). Air cleaner must be in place and all accessories turned off.
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. Adjust to specifications. See «IDLE SPEED (RPM)»(/gmc/magnavan-g3500/1985-1993/remont/testing-diagnostics/#fuel-injection-system-diesel) specifications table. Turn off engine. Remove jumper wire and test equipment. Install fast idle solenoid connector.

Scheme 168

IDLE SPEED (RPM)

INJECTION PUMP TIMING

1. Original factory injection pump timing is designated in two ways. First, the injection pump is marked with a static timing mark (straight line scribed across both the pump flange and front housing). Then the injection pump timing is dynamically checked and marked with a dynamic timing mark (a circle scribed across both the pump flange and the front housing).
2. For the engine to be properly timed, the two halve of the dynamic timing mark (circle between pump flange and front housing) must be aligned. The engine must be off while the timing is being set. A service pump is not marked with a dynamic timing mark and should be timed using the static timing mark.
3. Check alignment of injection pump timing marks on top of engine front cover and injection pump flange. 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.

VACUUM REGULATOR VALVE

1. The vacuum regulator valve provides vacuum signals to control automatic transmission shift points. Vacuum setting of valve should be checked and adjusted periodically. Engine MUST NOT be running during the following adjustment procedure.
2. 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.
3. Insert 0.646" Gauge Block (J-33043-A) between gauge boss on injection pump and wide open stop screw on throttle lever (switch on position). (Scheme 169) NOTE: Always refer to Emission Control Label for correct gauge block size.
4. Rotate and hold throttle shaft against gauge 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.
5. Check adjustment by allowing throttle shaft to return to idle stop position. Then rotate throttle shaft back against gauge block. Vacuum gauge reading must be within 10.9-12.1 in. Hg. If vacuum is outside limits, reset valve.
6. With vacuum valve set, confirm detent switch point by reading resistance between Ignition (Pink with Black stripe wire) and detent terminal (Orange wire). Insert Switch Gauge (J-36142) between wide open stop pin and wide open stop screw on throttle lever. (Scheme 169)
7. Rotate throttle lever against switch gauge. There should be no continuity (infinite resistance). Release throttle lever and remove gauge. Rotate throttle lever to wide open throttle (lever stop screw touching pump stop pin).
8. Check switch for continuity. Switch must have zero to one ohm continuity before throttle reaches wide open position. If switch does not meet specifications, reset assembly by returning to step 1) and repeating entire procedure.

Scheme 169

FUEL FILTER

1. 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.
2. 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 2 minutes or until clear fuel is observed. Stop engine and close water drain valve.
3. 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. See «PURGING FUEL SYSTEM»(/gmc/magnavan-g3500/1985-1993/remont/testing-diagnostics/#fuel-injection-system-diesel__purging-fuel-system) under MAINTENANCE in this article.

Scheme 170

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:
• NORMAL GLOW PLUG CIRCUIT OPERATION
• INJECTION PUMP TIMING
• IDLE SPEED (RPM)
• PURGING FUEL SYSTEM