Tune-Up - Diesel GMC Pickup R2500

VALVE ARRANGEMENT

1. I-E-I-E-I-E-I-E (Left bank, front-to-rear).
2. E-I-E-I-E-I-E-I (Right bank, front-to-rear).

VALVE CLEARANCE

The 6.2L engine uses hydraulic lifters with roller followers. Valve lash is not adjustable.

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 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 temperature.

6.2L Firing Order. Scheme 1

INJECTION PUMP TIMING

1. All 6.2L engines are timed both statically and dynamically at assembly. The dynamic timing marks are half circles. Static timing marks are straight lines. Whenever possible use dynamic timing marks to adjust injection pump timing. If a replacement pump is to be used, adjust injection timing using static marks.
2. 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 marks on injection pump with marks on front cover. Tighten nuts to 30 ft. lbs. (41 N.m) and adjust throttle linkage.

Scheme 2

1. Set parking brake and block drive wheels. Warm engine to normal operating temperature and install Tachometer (J-26925). Adjust curb idle speed screw on pump to obtain curb idle speed. (Scheme 2)
2. To adjust fast idle speed, 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 engine off. Remove jumper wire and test equipment. Install fast idle solenoid connector.

IDLE SPEED

THROTTLE POSITION SWITCH (TPS)

1. Remove air cleaner and vacuum hoses. Disconnect TPS connector. Install jumper wires between TPS and harness. Turn ignition on, with engine off. Install a gauge block with.646" (16.4 mm) clearance, between gauge boss on injection pump and wide open stop screw on throttle shaft. Rotate and hold throttle lever against gauge block. (Scheme 3)
2. Using a digital voltmeter, measure and record voltage reference from terminals "A" to "C". Measure and record TPS voltage from terminals "B" to "C". Divide TPS voltage by voltage reference, this will give voltage ratio. Voltage ratio should be within one percent of voltage ratio specification on Emission Control Label.
3. If adjustment is necessary, loosen attaching screws. Rotate TPS until correct voltage ratio is obtained. To check TPS voltage, release throttle lever to idle position. Measure voltage between terminals "B" and "C".
4. Voltage should be approximately one volt at closed throttle. Rotate throttle lever against gauge block. Voltage should return to voltage ratio within one percent of specification. If at closed throttle voltage is not less than one volt, or voltage ratio cannot be obtained, replace TPS.

Scheme 3

TPS VOLTAGE RATIO SPECIFICATIONS (6.2L)

Heavy Duty Emissions (VIN J)

1. Loosen vacuum regulator valve so that it is free to rotate on fuel injection pump. Connect vacuum pump and apply 18-21 in. Hg vacuum to bottom port.
2. Attach vacuum gauge to top vacuum port. Install a gauge block with .646" (16.4 mm) clearance between gauge boss on injection pump and wide open throttle valve stop screw on throttle lever (switch on position).
3. Rotate throttle shaft and hold it against gauge block. Valve must be set while rotating valve body in a clockwise direction only. Slowly rotate vacuum regulator valve clockwise (facing valve) until vacuum gauge reads 11-12 in. Hg. Hold valve body in this position, and tighten mounting screws to 54 INCH lbs. (6 N.m).
4. Check by releasing throttle shaft, allowing it to return to idle stop position. Rotate throttle shaft back against gauge block and determine if vacuum gauge reading is 11-12 in. Hg vacuum. If vacuum reading is outside specifications, reset valve.
5. Confirm detent switch point by reading resistance between ignition terminal Pink/Black wire and detent terminal Orange wire. Insert Switch Gauge (J-36142) between wide open stop pin and wide open stop screw on throttle lever.
6. Hold throttle at WOT. Meter should show no continuity. Release throttle lever. Remove gauge. Slowly rotate throttle to WOT. Meter should show continuity just before throttle reaches WOT. If specifications are incorrect, repeat entire procedure.

EMISSION CONTROL

See EMISSIONS section.

FUEL INJECTION

All 6.2L engines are equipped with General Motors diesel fuel injection.

BATTERIES

All models use Delco batteries. All V8 diesel vehicles use two 12-volt, negative ground, sealed-top batteries. One battery is located on each side of engine compartment and they are wired in parallel.

BATTERY SPECIFICATIONS (1)

STARTER

STARTER SPECIFICATIONS

ALTERNATORS

On 6.2L, alternator supplies current to both batteries.

ALTERNATOR SPECIFICATIONS

ALTERNATOR REGULATOR

All models are equipped with Delco nonadjustable regulators, integral with alternator.

REGULATOR SPECIFICATIONS

BELT ADJUSTMENTS

BELT ADJUSTMENT - TENSION IN LBS. (KG) USING STRAND TENSION GAUGE

SERVICE INTERVALS

REPLACEMENT INTERVALS

CAPACITIES

FLUID CAPACITIES

SYSTEM REFRIGERANT CAPACITIES