Engine Controls - Basic Diagnostic Procedures - 8.1L: Other Chevrolet Silverado 1500 HD

Testing & Diagnostics 5 illustrations ~1316 words

Cylinder Compression Pressure

Check engine mechanical condition with compression gauge, vacuum gauge, or engine analyzer. See engine analyzer manual for specific instructions. For compression specifications, see ENGINE COMPRESSION SPECIFICATIONS table. Install and tighten spark plugs to 11 ft. lbs. (15 N.m).

Application	Specification - psi (kPa)
Normal Compression Pressure	(1)
Minimum Compression Pressure	(1)
Compression Variance	(2)
(1) Lowest compression reading should not be less than 70 percent of highest compression reading. No cylinder compression reading should be less than 100 psi (689.5 kPa). (2) Information is not available from manufacturer.

(1)	Lowest compression reading should not be less than 70 percent of highest compression reading. No cylinder compression reading should be less than 100 psi (689.5 kPa).

(2)	Information is not available from manufacturer.

ENGINE COMPRESSION SPECIFICATIONS

Cylinder Combustion Pressure Leakage

Disconnect negative battery cable. Remove spark plugs. Install Cylinder Head Leakdown Tester (J-35667 A). Measure each cylinder on compression stroke, with both valves closed.
Apply air pressure to cylinder leakdown tester. Record cylinder leakage readings for each cylinder. Any cylinder with 25 percent leakage or more requires service.
Inspect following primary areas in order to properly diagnose a leaking cylinder. If air is heard from intake or exhaust system, remove valve rocker arm cover of suspect cylinder head. Ensure that both valves are closed. Inspect cylinder head for a broken valve spring or remove and inspect suspect cylinder head. If air is heard from crankcase system at crankcase oil filler tube, remove piston from suspect cylinder. Inspect piston and connecting rod assembly. Inspect engine block. If bubbles are observed in radiator, remove and inspect both cylinder heads. Inspect engine block.
After performing test, remove leakdown tester. Install spark plugs and reconnect negative battery cable.

Exhaust System Backpressure

Before replacing any components, check exhaust system for restrictions. Use vacuum gauge or low pressure (0-5 psi) gauge to check exhaust system.

If vacuum gauge is used, connect vacuum gauge hose to intake manifold vacuum port and start engine. Observe vacuum gauge. Partially open throttle and hold steady. If vacuum gauge reading slowly drops after stabilizing, exhaust system should be checked for restriction. If using low pressure gauge, connect gauge in following manner

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.

Preliminary Checks

Before performing following tests, check battery condition, engine cranking speed and for adequate fuel in tank. Perform diagnostic system check following any repairs. See DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS - 8.1L AVALANCHE, SIERRA, SILVERADO, SUBURBAN & YUKON XL article.

Perform diagnostic system check. See «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(ref-158433-S21464854222003092600000) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS - 8.1L AVALANCHE, SIERRA, SILVERADO, SUBURBAN & YUKON XL article. After performing diagnostic system check, go to next step.
Crank engine for 15 seconds. Does scan tool display any DTCs that failed this ignition? If yes, diagnose affected DTCs. See «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(ref-158433-S36149293242003092600000) in SELF-DIAGNOSTICS - 8.1L AVALANCHE, SIERRA, SILVERADO, SUBURBAN & YUKON XL article. If DTCs are not set, go to next step.
Does scan tool display any Body Control Module (BCM) or Vehicle Theft Deterrent (VTD) DTCs? If yes, diagnose affected DTCs. See appropriate BODY CONTROL MODULES or ANTI-THEFT SYSTEMS article in ACCESSORIES & EQUIPMENT. If no, go to next step.
Observe engine speed parameter with scan tool, while cranking engine. Is engine RPM indicated on scan tool? If yes, go to next step. If no, diagnose ignition system. Go to «ELECTRONIC IGNITION SYSTEM»(ref-152876-S08811986612003030100000) under IGNITION SYSTEMS.
Turn ignition on, with engine off. Probe both sides of PCM 1 fuse located in underhood fuse/relay block with a test light connected to a good ground. Does test light illuminate on at least on side of fuse? If yes, go to next step. If no, go to «IGNITION RELAY»(ref-153339-S40257399102003041600000) under IGNITION SYSTEMS in SYSTEM & COMPONENT TESTING - 8.1L AVALANCHE, SIERRA, SILVERADO, SUBURBAN & YUKON XL article.
Monitor ignition 1 signal parameter with a scan tool. Is ignition 1 signal parameter at battery voltage? If yes, go to next step. If no, go to step 10 .
Command fuel pump ON with a scan tool. Does fuel pump operate? If yes, go to next step. If no, go to «FUEL PUMP ELECTRICAL CIRCUIT DIAGNOSIS»(ref-153339-S42480524892003041600000) under FUEL SYSTEMS in SYSTEM & COMPONENT TESTING - 8.1L AVALANCHE, SIERRA, SILVERADO, SUBURBAN & YUKON XL article.
Turn ignition off. Install fuel pressure gauge. The fuel pump operates for about 2 seconds when ignition is turned on. Fuel pressure must be observed when fuel pump is operating. Turn ignition on, with engine off. Observe fuel pressure while fuel pump is operating. Is fuel pressure within 55-62 psi (385-425 kPa)? If yes, go to next step. If no, go to «FUEL SYSTEM PRESSURE TEST»(ref-152876-S29682748142003030100000) in FUEL SYSTEMS.
Check if ECT sensor is close to actual engine temperature. Check duct work between MAF sensor and throttle body for air leaks. Check for restricted exhaust system. Check for a malfunctioning MAF sensor, causing a no-start or a stall after a start condition. If you suspect this, disconnect MAF sensor. PCM will default to speed density in order to calculate engine load and intake air flow. If disconnecting MAF sensor corrects condition and connections are okay, MAF sensor is faulty. If disconnecting MAF sensor does not correct the condition, check for fouled spark plugs or for an engine mechanical problem. Compare MAP/BARO parameters to another vehicle. Parameter values should be close to each other. Repair as necessary. After repairs, go to step 11 .
Test ignition 1 voltage circuits that are supplied by PCM 1 fuse for an open or for a short to ground. Replace fuse, if necessary. Did you find and correct condition? If yes, go to step 13 . If no, go to next step.
Inspect for poor connections at harness connector of PCM. Did you find and correct condition? If yes, go to step 13 . If no, go to next step.
Replace PCM. See appropriate REMOVAL & INSTALLATION article. After replacing PCM, go to next step.
Clear DTCs with a scan tool. Turn ignition off for 30 seconds. Attempt to start engine. Does engine start and continue to run? If yes, go to next step. If no, go to step 2 .
Warm engine to normal operating temperature. Observe Capture Info with a scan tool. Are there any DTCs that have not been diagnosed? If yes, diagnose affected DTC(s). See «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(ref-158433-S36149293242003092600000) in SELF-DIAGNOSTICS - 8.1L AVALANCHE, SIERRA, SILVERADO, SUBURBAN & YUKON XL article. If no DTCs are set, system okay.

FUEL SYSTEM PRESSURE RELEASE

WARNING

Remove fuel tank cap and release fuel system pressure before servicing any fuel injection related components. After releasing fuel system pressure, a small amount of fuel may be released when servicing fuel lines, fuel pump or fuel connections. Cover fuel system components with a shop towel before disconnection. DO NOT allow fuel to contact engine or electrical components.

CAUTION

Fuel system is under pressure. Pressure must be released prior to servicing fuel system.

Disconnect negative battery terminal. Loosen fuel filler cap to release fuel tank vapor pressure. Connect Fuel Pressure Gauge (J-34730-1A) to fuel pressure test port. Wrap a shop towel around fitting while connecting gauge to avoid spillage. Install gauge bleed hose into an approved gasoline container. Open valve on gauge to bleed system pressure. Fuel connections are now safe for servicing. Drain any fuel remaining in gauge into an approved gasoline container.

IGNITION SYSTEMS

Note. For additional ignition system and component diagnosis, see IGNITION SYSTEMS in SYSTEM & COMPONENT TESTING - 8.1L AVALANCHE, SIERRA, SILVERADO, SUBURBAN & YUKON XL article.

CAMSHAFT POSITION SENSOR

For testing procedures and specifications, perform appropriate diagnostic test. See DIAGNOSTIC TROUBLE CODE DEFINITIONS in SELF-DIAGNOSTICS - 8.1L AVALANCHE, SIERRA, SILVERADO, SUBURBAN & YUKON XL article.

CRANKSHAFT POSITION SENSOR

Scheme 14

Scheme 14: ELECTRONIC IGNITION SYSTEM

Scheme 15

Scheme 16

Scheme 17

Scheme 18

IDLE SPEED & IGNITION TIMING

Idle speed and ignition timing are controlled by PCM. Incorrect idle speed are normally caused by dirty throttle plate or vacuum leaks. Ensure all vacuum components are functioning properly.