Engine Controls - Basic Testing - 5.7L: Other Chevrolet Suburban C2500

Compression

Check engine mechanical condition using a compression gauge, vacuum gauge or engine analyzer capable of performing a relative compression test. If using engine analyzer, see engine analyzer instruction manual for availability and description of relative compression feature.

Exhaust System Backpressure

Before replacing any components, check exhaust system for restrictions. Use a vacuum gauge or a low-pressure (1-5 psi) pressure gauge to check exhaust system.

If using a vacuum gauge, connect gauge to intake manifold vacuum, and start engine. Observe gauge while holding throttle steady at 2000-2500 RPM. If vacuum gauge reading slowly drops after stabilizing, exhaust system may be restricted.

Check At Oxygen Sensor

Remove oxygen sensor. Install backpressure tester in place of oxygen sensor. After test is completed, coat oxygen sensor threads with anti-seize compound before installation.

DEFINITION

No-start is defined as engine cranks okay but does not start. Engine may fire a few times.

Note. Before performing following tests, check battery condition, engine cranking speed and fuel supply.

Ignition System

1. Disconnect tachometer wire at distributor tachometer terminal (if equipped). A shorted tachometer or tachometer circuit prevents vehicle from starting. Ensure TP sensor and coolant sensor codes are not present, and sensors are not out of calibration.
2. Check for battery voltage at "+" terminal of ignition coil with ignition on. (Scheme 398)and (Scheme 399). Repair as necessary.
3. Connect Spark Tester (ST-125) to end of one plug wire. Crank engine. If spark is present, check fuel delivery.
4. If spark does not occur, disconnect 4-wire EST connector at distributor and check for spark at ignition coil tower using Spark Tester (ST-125). If spark now occurs, check cap and rotor for damage or wear. Check for open in coil wires.
5. If spark does not occur, reconnect EST connector. Leave spark tester connected to coil tower for remainder of test. Disconnect ignition coil Black 2-wire connector, and check voltage on "C" and "+" terminals with ignition on.
6. If voltage on both terminals is 10 volts or greater, go to next step. If voltage on both terminals is less than 10 volts, repair wire from module "+" terminal to "B" terminal on coil Black 2-wire connector. If voltage is less than 10 volts on "C" terminal only, check for open or short to ground in circuit from "C" terminal of ignition module to ignition coil. If circuit is okay, problem is faulty coil or coil connections.
7. Connect voltmeter between ground and tachometer terminal at coil with ignition on. Tachometer terminal may be taped back against harness. If voltage is greater than 10 volts, go to step 9).
8. If voltage is 1-10 volts, replace ignition module and check for spark at coil tower using Spark Tester (ST-125). If voltage is less than one volt, repair open in tachometer lead or tachometer connector. After repairs, recheck voltage at tachometer terminal.
9. Connect test light between ground and tachometer terminal. Crank engine. If test light remains on (steady), go to next step. If test light flashes, replace ignition coil with a known-good unit and recheck for spark. If spark does not occur, reinstall original ignition coil and replace ignition module.
10. Remove distributor cap. Unplug ignition module pick-up coil connector. Connect voltmeter between ground and tachometer terminal. Turn ignition on. Using jumper wires, connect positive end of a known-good 1.5-volt battery to terminal "P" of module. Observe voltmeter at tachometer terminal as negative end of test battery is momentarily grounded to distributor housing.
11. If voltage at tachometer terminal does not drop, check ignition module ground. Check for open in wires from ignition coil to module. If all is okay, replace ignition module.
12. If voltage at tachometer terminal drops, check for spark at spark tester as jumper is removed from terminal "P". If spark does not occur, go to next step. If spark occurs, check pick-up coil connections. Check for 500-1500 ohms resistance at pick-up coil leads. Ensure leads are not shorted to ground. Repair as necessary.
13. Test ignition module with module tester. If module tests okay, check ignition coil wire. If module tester is not available, replace ignition coil, and touch terminal "P" again. If spark occurs, system is okay. If spark does not occur, reinstall original ignition coil, and check coil wire from distributor cap. If no problem is found, replace ignition module.

Fuel System (TBI)

1. Before checking fuel system for a no-start condition, check ignition for adequate spark. Check for proper fuel pump pressure (9-13 psi) and capacity (one pint in 30 seconds). See the «A-7, BASIC FUEL SYSTEM CHECKS»(ref-20098-S29792494072001010200000) .
2. Crank engine, and watch for injector spray. If injector spray occurs, go to step 5). If no spray occurs, disconnect injector harness. Check for battery voltage at harness with ignition on. Battery voltage should be present on one injector terminal. If battery voltage is not present, check for blown injector power fuse. If battery voltage is present on both terminals, check for wires shorted together.
3. If battery voltage is present on only one terminal, connect injector test light to injector harness. Crank engine, and note light. If light flashes, check for stored PCM codes. See «DIAGNOSTIC CIRCUIT CHECK»(ref-20098-S26640417142001010200000) . If no codes are present, refer to HARD START symptom in «TESTS W/O CODES - GASOLINE»(ref-20057) article in this section. If light does not flash, momentarily touch test light from battery voltage to PCM RPM reference terminal (circuit No. 430 - Purple/White wire).
4. Each time test light is removed from PCM RPM reference terminal, injector test light should flash. If test light does not flash, check for open in RPM reference wire or injector drive (ground) circuit. If wiring is okay, replace faulty PCM. Before replacing PCM, check PCM power and ground circuits.
5. Disconnect injector harness, and crank engine. If injector spray or leakage occurs, a no-start condition may be caused by excessive fuel being delivered during cranking. Repair faulty injector or injector seal. If no spray or leakage occurs, refer to HARD START symptom in «TESTS W/O CODES - GASOLINE»(ref-20057) article in this section.

Scheme 395

Scheme 396

Scheme 397

1. Check if Code P1221 is stored. If code is present, diagnose code first. Check TP sensor voltage. If TP sensor voltage is greater than 2.5 volts at closed throttle, see Code P0118. Check ECT sensor reading. If ECT sensor reading is -30°C, see Code P0118. See «TESTS W/CODES - 5.7L»(ref-20086) article.
2. Turn ignition off for 10 seconds. Turn ignition on. Listen for fuel pump operation. Fuel pump should operate for 2 seconds. If fuel pump operates, go to next step. If fuel pump does not operate, check fuel pump relay and circuit. Proceed to the «SYSTEM/COMPONENT TESTS - 5.7L»(ref-20084) article.
3. Disconnect injector connector at intake manifold. Connect Injector Test Light (J 34730) to wiring harness connector. Crank engine. If injector test light flashes, go to next step. If injector test light does not flash or stays on steady, go to step 6).
4. Disconnect one spark plug wire. Install Spark Tester (ST-125). Crank engine and check for spark. If spark is present, go to next step. If spark is not present, proceed to the «C-4, BASIC IGNITION SYSTEM CHECKS»(ref-20098-S09522618212001010200000) .
5. Reconnect spark plug wire. Turn ignition off. Relieve fuel pressure. See «FUEL SYSTEM PRESSURE RELIEF»(ref-20098-S14095796462001010200000) . Connect Fuel Pressure Gauge (J 34730-1). Turn ignition on. Fuel pressure should be 55-61 psi (3.9-4.3 kg/cm 2 ) when fuel pump stops. Pressure should hold steady. If fuel pressure is as specified and holds steady, check injectors. See «SYSTEM/COMPONENT TESTS - 5.7L»(ref-20084) article. If fuel pressure is not as specified, go to «A-7, BASIC FUEL SYSTEM CHECKS»(ref-20098-S29792494072001010200000) .
6. If injector test light does not illuminate, go to next step. If injector test light stayed on steady, check for short to ground in injector circuit. If circuit is okay, check injector resistance. Injector resistance should be greater than 1.3 ohms. If resistance is as specified, replace VCM-A. If resistance is not as specified, replace faulty injector.
7. Turn ignition off. Disconnect coil high voltage wire. Disconnect3-pin crank sensor harness connector. Turn ignition on. Using test light connected to battery, momentarily touch test light to Yellow wire crank sensor harness connector terminal. If injector test light flashed, check for faulty crank sensor harness connection or faulty crank sensor. If injector test light does not flash, go to next step.
8. Turn ignition off. Check for open or grounded Yellow wire to crank sensor or faulty VCM-A connector. If wire or connector is okay, remove injector test light.
9. Turn ignition on. Using test light connected to ground, probe engine harness connector. If test light illuminates on one of the terminals, go to next step. If test light illuminates on both terminals, repair short to voltage in circuit. If test light does not illuminate on either terminal, repair open between ignition coil Pink wire to VCM-A.
10. Turn ignition off. Reconnect injector connector. Disconnect Red VCM-A connector. Turn ignition on. Using test light connected to ground, probe VCM-A terminal No. RE3. If test light illuminates, check for faulty VCM-A connector or faulty VCM-A. If test light does not illuminate, check for faulty VCM-A connector or open in circuit.

FUEL SYSTEM PRESSURE RELIEF

TBI Unit

Fuel pressure is relieved and drops to zero when ignition is turned off. To minimize risk of fire and personal injury, cover area to be disconnected with a shop rag.

TBI

1. Turn ignition off for 10 seconds. Turn ignition on, and listen at fuel tank for fuel pump operation. Pump should run 2 seconds (20 seconds on models with fuel module). If fuel pump runs, go to next step. If fuel pump does not run, go to step 7).
2. If fuel pump runs, turn ignition off. Verify fuel tank has fuel. Relieve fuel pressure. See «FUEL SYSTEM PRESSURE RELIEF»(ref-20098-S14095796462001010200000) . Remove air cleaner, and plug air cleaner vacuum ports (if equipped). Disconnect fuel line between throttle body and fuel filter. Install Fuel Pressure Gauge (J-29658-D) and Adapter (J-2968A-85) between steel fuel line and flexible hose, on outlet side of fuel filter.
3. Turn ignition on, and note reading on pressure gauge. If fuel pressure is 9-13 psi (.63-.91 kg/cm 2 ), no problem exists. If pressure is less than either of the low readings, go to step 5). If pressure is greater than either of the higher readings, turn ignition off, and bleed fuel pressure. Disconnect fuel return line downstream of pressure gauge. Insert return line into a gasoline container.
4. Turn ignition on. If pressure is now as specified, correct restriction in fuel return line between disconnected point and fuel tank. If fuel pressure is greater than either of the higher readings, check for restricted return line (including fuel filter) downstream of pressure gauge. If no restrictions are present, replace fuel pressure regulator assembly.
5. Check for restricted fuel line between in-tank fuel pump and pressure regulator. If fuel line is okay, disconnect injector connector. Turn ignition on. Gradually pinch fuel pressure gauge outlet hose. Note pressure. CAUTION: DO NOT pinch off fuel return line completely. DO NOT allow fuel pressure build-up to exceed specification, as damage to fuel pressure regulator may occur.
6. If pressure is greater than 13 psi (.91 kg/cm 2 ), replace fuel pressure regulator. If pressure is less than 9 psi (.63 kg/cm 2 ), check for faulty fuel pump or incorrect part. Check fuel pump coupling hose and pump inlet filter in fuel tank. On models with dual fuel tanks, check for faulty fuel tank selector valve and meter switch.
7. Apply 12 volts to fuel pump test connector. For fuel pump test connector location, see underhood engine component views under COMPONENT LOCATIONS in «SYSTEM/COMPONENT TESTS - 5.7L»(ref-20084) article. If fuel pump now runs, repair open in fuel pump relay drive or power circuit or repair faulty fuel pump relay. To test relay, see «SYSTEM/COMPONENT TESTS - 5.7L»(ref-20084) article.
8. If fuel pump does not run with 12 volts applied to fuel pump test connector, repair open in fuel pump power or ground circuit, or repair faulty fuel pump.

FIELD SERVICE MODE CHECK

Note. Assembly Line Data Link (ALDL) connector may also be referred to as Data Link Connector (DLC). SERVICE ENGINE SOON (SES) light may also be referred to as Malfunction Indicator Light (MIL).

Note. Oxygen sensor may cool off while engine idles, causing system to enter open loop. To restore closed loop mode, run engine at part throttle several minutes and accelerate from idle to part throttle several times.

This test confirms proper fuel system operation and verifies closed loop operation. Clear codes and perform this test after any repair is completed. When performing this test, always engage parking brake and block drive wheels. Parking brake on FWD models does not hold drive wheels.

1. Start engine. With engine running, ground diagnostic test terminal "B" of DLC. (Scheme 404)and (Scheme 405). In closed loop mode, Malfunction Indicator Light (MIL) flashes once per second.
2. In open loop, light flashes 2.5 times per second. A lean exhaust is indicated if light is usually off. A rich exhaust is indicated if light is usually on.

HEI-EST DISTRIBUTOR

Note. Only basic ignition timing is adjustable in HEI/EST ignition system.

Spark

1. If factory tachometer is connected to ignition coil tachometer terminal, disconnect it before performing tests. When removing spark plug wire from spark plug, twist and pull on boot. DO NOT pull on wire.
2. Using Spark Tester (ST-125), check for spark at coil wire (if applicable) and at each spark plug wire. Check spark plug wire resistance on suspect wires. Resistance should not be greater than 30,000 ohms.

Ignition Coil Power Source

Turn ignition on. Use voltmeter to check voltage between terminal "B" of ignition coil and ground. If battery voltage does not exist, check for open circuit, blown ignition fuse or defective ignition switch.

Ignition Coil Resistance

1. Remove coil connectors and secondary coil wire. In test "A", use high ohmmeter scale. (Scheme 398) Resistance value should be very high (infinite). If reading is not infinite, replace coil.
2. In test "B", use low ohmmeter scale. Reading should be very low (near zero ohms). If reading is not near zero ohms, replace coil. In test "C", use high ohmmeter scale. Continuity should exist. If no continuity exists, replace coil.

Scheme 398

Distributor Pick-Up Coil Short & Resistance Checks

1. Disconnect pick-up coil leads from module. Using ohmmeter, check pick-up coil resistance. Connect ohmmeter to distributor housing and either pick-up coil lead (step 1 in illustration). (Scheme 399) Flex pick-up coil leads by hand to check fo r intermittent short to ground. If reading is not always infinite, replace pick-up coil.
2. Connect ohmmeter between pick-up coil leads (step 2 in illustration). (Scheme 399) Check for intermittent open by flexing wire s and connectors. If resistance is not 500-1500 ohms, replace pick-up coil.

Scheme 399

Tach Pulse (RPM) Signal

Connect scan tester to DLC. RPM should be indicated on tester when engine is cranked or running. Tach pulse (RPM reference) will be indicated as a voltage signal when a DVOM connected to battery voltage is used to backprobe circuit No. 430, PCM terminal. (Scheme 398)and (Scheme 399). If tach pulse signal is not present, vehicle will not run.

IDLE SPEED & IGNITION TIMING

Ensure idle speed and ignition timing are set to specifications. For specifications, see SPECIFICATIONS - 5.7L article. For adjustment procedures, see ADJUSTMENTS - 5.7L article.

A-1, MALFUNCTION INDICATOR LIGHT (MIL) INOPERATIVE

1. If MIL does not illuminate with ignition on and engine off, attempt to start engine. If engine starts, go to step 3). If engine does not start, check fusible links at battery. Also check PCM fuse. If fusible links or PCM fuse are blown, repair short to ground.
2. If fusible links and PCM fuse are okay, turn ignition on and check power circuits to PCM, including keep-alive memory and ignition feed. See appropriate WIRING DIAGRAM in the «WIRING DIAGRAMS»(ref-20098-S05910863262001010200000) section at the end of this article for power terminal identification. If power to PCM power terminals is not available, check for open in power circuits. If power to PCM power terminals is available, check for poor PCM ground circuits. If circuits are okay, replace faulty PCM.
3. Turn ignition off. Disconnect PCM connectors. Turn ignition on, and connect PCM MIL driver terminal to ground using a test light. See See appropriate WIRING DIAGRAM in the «WIRING DIAGRAMS»(ref-20098-S05910863262001010200000) section at the end of this article for power terminal identification.
4. If MIL is now on, repair MIL driver terminal connections at PCM, or replace faulty PCM. If MIL stays off when test light is used to ground MIL driver terminal, check for blown instrument panel fuse, faulty bulb, open in MIL driver circuit between PCM and bulb, short in driver circuit to voltage or open in ignition feed to MIL.

A-2, MIL ALWAYS ON OR WON'T FLASH CODE 12

1. Turn ignition on, engine off. If MIL does not illuminate, see A-1, MALFUNCTION INDICATOR LIGHT (MIL) INOPERATIVE. If MIL is on, ground DLC test terminals "A" and "B". Code 12 should flash. If Code 12 does not flash, go to next step. If Code 12 now flashes, problem is no serial data. Check serial data circuit for open or short to ground, or short to voltage between PCM and DLC terminal. If circuits are okay, replace faulty PCM or PROM (MEM-CAL).
2. Turn ignition off. Disconnect PCM connectors. Turn ignition on. If MIL is on, check for short to ground in MIL driver circuit between MIL and PCM driver terminal. see scheme 6 Also, see appropriate WIRING DIAGRAM in the «WIRING DIAGRAMS»(ref-20098-S05910863262001010200000) section at the end of this article for terminal identification.
3. If light is off with PCM connectors disconnected, turn ignition off. Reconnect PCM connectors. Turn ignition on with engine off and diagnostic terminal not grounded. Using a test light connected to ground, backprobe PCM terminal circuit to DLC terminal "B". see scheme 6 If MIL does not flash Code 12, go to next step. If MIL flashes Code 12, check for open in DLC test terminal "B" circuit to PCM. If circuit is okay, check for open in DLC terminal "A" circuit to PCM and PCM ground. see scheme 6
4. Check PROM (MEM-CAL) for proper installation. If installation is okay, replace PCM using original PROM (MEM-CAL). Recheck for Code 12. If Code 12 is not present, replace PROM (MEM-CAL). If Code 12 is present, system is okay.

Diagnostic Circuit Check & Work Flow Chart (5.7L). Scheme 400

SUMMARY

If faults were not found while performing BASIC DIAGNOSTIC PROCEDURES, proceed to TESTS W/CODES - 5.7L article. If no hard codes are found in self-diagnostics, or vehicle does not have a self-diagnostic system, proceed to TESTS W/O CODES - GASOLINE article for diagnosis by symptom (i.e., ROUGH IDLE, NO START, etc.) or intermittent diagnostic procedures.

Wiring Diagram ("C" & "K" Series Pickup, Sierra, Suburban, Tahoe & Yukon - 5.7L With A/T - 1 Of 3). Scheme 401

Wiring Diagram ("C" & "K" Series Pickup, Sierra, Suburban, Tahoe & Yukon - 5.7L With A/T - 2 Of 3). Scheme 402

Wiring Diagram ("C" & "K" Series Pickup, Sierra, Suburban, Tahoe & Yukon - 5.7L With A/T - 3 Of 3). Scheme 403

Wiring Diagram ("C" & "K" Series Pickup, Sierra, Tahoe & Yukon - 5.7L With M/T - 1 Of 2). Scheme 404

Wiring Diagram ("C" & "K" Series Pickup, Sierra, Tahoe & Yukon - 5.7L With M/T - 2 Of 2). Scheme 405

Wiring Diagram ("P" Series - 5.7L With M/T - 1 Of 2). Scheme 406

Wiring Diagram ("P" Series - 5.7L With M/T - 2 Of 2). Scheme 407

Wiring Diagram ("P" Series - Commercial & Motorhome - 5.7L With 4L80-E - 1 Of 3). Scheme 408

Wiring Diagram ("P" Series - Commercial & Motorhome - 5.7L With 4L80-E - 2 Of 3). Scheme 409

Wiring Diagram ("P" Series - Commercial & Motorhome - 5.7L With 4L80-E - 3 Of 3). Scheme 410

Wiring Diagram ("P" Series - Cutaway - 5.7L - 1 Of 3). Scheme 411

Wiring Diagram ("P" Series - Cutaway - 5.7L - 2 Of 3). Scheme 412

Wiring Diagram ("P" Series - Cutaway - 5.7L - 3 Of 3). Scheme 413

Wiring Diagram (Van - 5.7L With 4L60-E - 1 Of 3). Scheme 414

Wiring Diagram (Van - 5.7L With 4L60-E - 2 Of 3). Scheme 415

Wiring Diagram (Van - 5.7L With 4L60-E - 3 Of 3). Scheme 416

Wiring Diagram (Van - 5.7L With 4L80-E - 1 Of 3). Scheme 417

Wiring Diagram (Van - 5.7L With 4L80-E - 2 Of 3). Scheme 418

Wiring Diagram (Van - 5.7L With 4L80-E - 3 Of 3). Scheme 419