Ccc Tests W/o Codes GMC Cab & Chassis R2500

DESCRIPTION

Note. Most Computer Command Control (CCC) problems are the result of mechanical breakdowns, poor electrical connections, or damaged vacuum hoses. Before considering the CCC system as a possible cause of problems, check ignition high tension wires, fuel supply, electrical connections, and vacuum hoses. Failure to do so may result in lost diagnostic time.

The Computer Command Control (CCC) system controls engine operation and lowers exhaust emissions while maintaining good fuel economy and driveability. The CCC system is designed to maintain a 14.7:1 air/fuel ratio under all engine operating conditions. When the ideal air/fuel ratio is maintained, the catalytic converter can control oxides of nitrogen (NOx), hydrocarbon (HC), and carbon monoxide (CO) emissions.

The CCC system consists of the following sub-systems: Fuel Control, Data Sensors, Electronic Control Module (ECM), Electronic Spark Timing, Electronic Spark Control, AIR Management, Exhaust Gas Recirculation, Evaporative Emission Control, Torque Converter Clutch (TCC), Diagnostic System.

System Check Flow Chart. Scheme 83

Flow Chart. Scheme 84

HOW TO USE THIS TROUBLE SHOOTING ARTICLE

The Trouble Shooting section should be used only AFTER the SYSTEM CHECK chart procedures have been performed to verify that

1. On-Vehicle Diagnostics are working.
2. There are no trouble codes stored, or only intermittent ones.
3. Fuel control system is operating properly as verified by Field Service Mode Check.

Verify customer complaint and locate the correct symptom below. Check items indicated under that symptom. These procedures will normally lead to a component system on the vehicle, such as EGR, EST, TCC, etc. These are covered in the Component charts.

The flow charts are located in the TBI CEC TESTING article in this section. If the first flow chart leads you to another flow chart, all the test charts are in the TBI CEC TESTING article. If a flow chart leads you to trouble shooting procedures, that information will be in this article.

Check items indicated under that symptom. These procedures will normally lead to a component system on the vehicle, such as EGR, EST, TCC, etc. These sytems are covered in the component charts.

Several of the following symptom procedures call for a careful visual check. Visual check should be performed CAREFULLY and THOROUGHLY as it can correct a problem without further checks or diagnosis. This check should include

1. Vacuum hoses for splits, kinks and proper connections, as shown on Emission Control Information label.
2. Air leaks at throttle body mounting and intake manifold.
3. Ignition wires for cracking, hardness, proper routing, and carbon tracking.
4. Wiring for proper connections, pinches, and cuts.

Note. If engine cranks but will not run, see CHART A3 - ENGINE CRANKS BUT WON'T RUN chart in the TBI TESTS W/ CODES article in this section.

SYMPTOM DEFINITION

Intermittent problem(s) may or may not turn on "SERVICE ENGINE SOON" light. Code(s) may or may not be stored.

POSSIBLE CAUSE & CORRECTION

1. Check for poor mating of one connector to another. Terminals may not be fully seated. Check for improperly formed or damaged terminals. Check wire to terminal connections.
2. If visual check doesn't find cause of problem, drive vehicle with voltmeter connected to suspected circuit and ground. If voltage reading changes as problem occurs, problem may be in that circuit.
3. Check for loss of trouble code memory by disconnecting TPS. Idle engine until "SERVICE ENGINE SOON" light comes on. Code 22 should be stored when ignition is turned off. If not, ECM is faulty.
4. Check for electrical system interference caused by a defective relay or an ECM driven solenoid or switch. They can cause a sharp electrical surge. Problem will usually occur when faulty component is operated.
5. Check for improper installation of electrical accessories such as auxiliary lights, 2-way radios, etc.
6. Make sure EST wires are kept away from spark plug wires, distributor wires, distributor housing, ignition coil and alternator. Ensure wire from 453 to distributor has a good ground.
7. Check ignition secondary wiring for short to ground.
8. Check circuits 419 and 451 for intermittent shorted to ground.
9. Check ECM power grounds.
10. Check for incorrect or defective CALPAK or PROM.

Engine cranks but doesn't start for a long time. Engine eventually runs, or engine starts but immediately dies.

POSSIBLE CAUSE AND CORRECTION

1. Check for water contaminated fuel.
2. Check fuel pressure, see CHART A6 - FUEL SYSTEM PRESSURE TEST chart in the TBI TESTS/CODES article in this section.
3. Check TPS for sticking or binding.
4. Check EGR operation. See EGR SYSTEM CHECK chart chart in the TBI TESTS/CODES article in this section.
5. On Astro, Safari, and "S" Series trucks, check fuel pump relay; connect test lamp between pump test terminal and ground. Test lamp should be on for 2 seconds following ignition on. On 7.4L engines and some 5.0L engines, the fuel module circuit activates the fuel pump for 20 seconds after ignition is turned on. If circuit is not functioning, a hot, hard start condition may result.
6. Check for faulty in-tank fuel pump check valve that would allow fuel to drain back into tank
7. With ignition off, disconnect fuel line at filter.
8. Remove fuel tank filler cap and connect radiator test pump to line. Apply 15 psi (1.05 kg/cm 2 ) pressure. If pressure holds for 60 seconds, check valve is okay.

Check ignition system for

1. Proper output signal.
2. Worn distributor shaft.
3. Bare and/or shorted wires.
4. Pick-up coil resistance and connections.
5. Loose ignition coil ground.
6. Moisture in distributor cap.
7. Remove spark plugs. Check for wet plugs, cracks, wear, improper gap, burned electrodes, or heavy deposits. Repair or replace as necessary.
8. If engine starts but then immediately stalls, open distributor by-pass line. If engine then starts and runs, replace distributor pick-up coil.
9. If hard start occurs with engine at normal operating temperature, see CRANK SIGNAL DIAGNOSIS chart in the TBI TESTS/CODES article in this section.
10. Check fuel pump cycle system on 8500-10,000 GVW vehicles with 5.7L and 7.4L engines.
11. Check EST circuit No. 423 for short to ground.

Momentary lack of response as accelerator is depressed. May occur at any vehicle speed. Usually most severe when first trying to make vehicle move. May cause vehicle to stall if severe enough.

1. Perform careful visual check.
2. Check fuel pressure. See CHART A6 - FUEL SYSTEM PRESSURE TEST chart in the TBI TESTS/CODES article in this section.
3. Check for water contaminated fuel.
4. Check TPS for binding or sticking.
5. Check fuel pump cycle system.
6. Check ignition timing.
7. Check alternator output voltage. Repair if less than 9 or more than 16 volts.
8. Check for open HEI ground circuit No. 453.
9. Check canister purge system.
10. Check EGR valve operation. See EGR SYSTEM CHECK chart in the TBI TESTS/CODES article in this section.
11. Check for incorrect or defective CALPAK or PROM.

As determined by actual road test, fuel economy is significantly lower than expected. Also, fuel economy is much lower than had been previously shown by an earlier road test.

1. Check thermostat for proper heat range or improper operation (always open).
2. Check fuel pressure. See CHART A6 - FUEL SYSTEM PRESSURE in the TBI TESTS/CODES article in this section.
3. Check ignition timing.
4. Check TCC for proper operation. See TORQUE CONVERTER CLUTCH chart in the TBI TESTS/CODES article in this section.
5. Check non-CCC related items such as tire pressure, clogged air cleaner, engine compression, owner's driving habits, etc.
6. Perform SYSTEM CHECK.

Engine continues to run after ignition is turned off, but runs very rough. If engine runs smoothly, check ignition switch and adjustment.

1. Check for leaking injectors: Apply 12 volts to fuel pump test terminal to turn fuel pump on and to pressurize system. See appropriate CHART A5 - FUEL PUMP RELAY CIRCUIT DIAGNOSIS chart in the TBI TESTS/CODES article in this section.
2. Visually check injectors and TBI unit for leaks.

Fuel ignites in intake manifold, or exhaust manifold, making a loud popping noise.

1. Check EGR operation for being open at all times. See EGR SYSTEM CHECK chart in the TBI TESTS/CODES article in this section.
2. Check output voltage of ignition coil.
3. Check for crossfire between spark plugs (distributor cap, plug wires, and proper routing of plug wires).
4. Check for intermittent condition in primary ignition system.
5. Check ignition timing.
6. Check for faulty spark plugs, plug wires and/or plug boots.
7. Check for proper valve timing.
8. Check engine compression (leaking or sticking valves).

Engine runs unevenly at idle. If severe enough, vehicle may shake. Engine may display varied idle RPM ("hunting"). Either condition could be severe enough to cause stalling. Engine idles at incorrect speed.

1. Check ignition timing.
2. Check part/neutral switch circuit. See PARK/NEUTRAL SWITCH DIAGNOSIS chart in the TBI TESTS/CODES article in this section.
3. Check for leaking injector.
4. Check fuel pressure. See CHART A6 - FUEL SYSTEM PRESSURE TEST chart in the TBI TESTS/CODES article in this section.
5. Check injector delivery (too rich or too lean)

If rough idle only occurs HOT, check for

1. Vacuum leaks: Block idle air passage using Plug (J-3047). If closed throttle engine speed is above 650 RPM, locate and correct vacuum leak (disconnected thermostatic vacuum hose or cruise control hose).
2. Park/Neutral Switch operation. See PARK/NEUTRAL SWITCH DIAGNOSIS chart in the TBI TESTS/CODES article in this section.
3. Sticking throttle shaft or binding linkage causing high TPS voltage (open throttle indication). ECM cannot control idle if this condition exists. Monitor TPS voltage (1.2 volts with throttle closed).
4. Roughness, stoppage, and/or hard starting as a result of EGR flow being allowed during idle. See EGR SYSTEM CHECK chart in the TBI TESTS/CODES article in this section.
5. Battery cables and ground straps should be clean and secure. Erratic voltage supply will cause IAC valve to change position, causing poor idle quality.
6. If system voltage is below 9 volts or greater than 17.8 volts, IAC valve will not move.
7. On 2.5L engines, ECM should compensate for power steering loads. Loss of this signal would be more noticeable under parking conditions where power steering loads are greatest. See POWER STEERING PRESSURE SWITCH TEST chart in the TBI TESTS/CODES article in this section.
8. MAP sensor. With ignition on and engine off, compare voltage reading of MAP sensor with that of known good vehicle. Voltage readings should be within 400 millivolts of each other.

OR

Start and idle engine. Disconnect sensor connector. If idle improves, substitute a known good MAP sensor, and repeat test while checking the following

1. Check A/C compressor, A/C relay, or A/C signal. See A/C CLUTCH CONTROL DIAGNOSIS chart or A/C "ON" SIGNAL DIAGNOSIS chart in the TBI TESTS/CODES article in this section.
2. A/C refrigerant pressure too high. Check for overcharge or faulty cycling switch.
3. Check PCV valve for proper operation.
4. Perform compression check.
5. Inspect oxygen sensor for silicon contamination from fuel, or use of improper RTV sealant (sensor will have White, powdery coating that will result in high, but false, signal voltage). In return, the ECM will reduce amount of fuel delivered, causing a severe driveability problem.
6. Check AIR management system for intermittent induction of air to exhaust ports while system is in "Closed Loop".
7. Monitoring system will help identify the cause of the problem. If the system is running lean, see CODE 44 - LEAN EXHAUST INDICATION flow chart. If the system is running rich, See the CODE 45 - RICH EXHAUST INDICATION flow chart. These tests are in the TBI TESTS/CODES article in this section.

Excessive odors (high concentrations of CO and HC) that are more noticeable when engine is under load and at normal operating temperatures.

1. High fuel pressure. See CHART A6 - FUEL SYSTEM PRESSURE TEST chart in the TBI TESTS/CODES article in this section.
2. Ignition timing.
3. Fuel loaded canister.
4. PCV valve for blockage and correct operation.
5. Condition of spark plugs, plug wires, and distributor cap.
6. Lead contamination of catalytic converter (suspect if fuel filler neck restrictor has been removed).

Engine power variation under steady throttle or cruise condition. Feels like vehicle speeds up and slows down without changing accelerator pedal position.

Using a "SCAN" tool, ensure vehicle speed matches VSS reading. If tool is not available, or if readings do not agree, check

1. Intermittent EGR operation during idle condition. See EGR SYSTEM CHECK chart in the TBI TESTS/CODES article in this section.
2. Ignition timing.
3. In-line fuel filter for obstruction.
4. Fuel pressure. See CHART A6 - FUEL SYSTEM PRESSURE TEST chart in the TBI TESTS/CODES article in this section.
5. Alternator output. Repair if less than 9 volts or more than 16 volts.
6. TCC operation. See TORQUE CONVERTER CLUTCH chart in the TBI TESTS/CODES article in this section.
7. Inspect oxygen sensor for silicon contamination from fuel, or use of improper RTV sealant (sensor will have White, powdery coating that will result in high, but false, signal voltage). In return, the ECM will reduce amount of fuel delivered, causing a severe driveability problem.
8. Remove spark plugs and check for cracks, wear, improper gap, burned electrodes, or heavy deposits. Check condition of distributor cap, rotor, and plug wires.

Engine delivers less than expected power. Little or no increase in speed when accelerator pedal is depressed part way.

Compare vehicle to another vehicle of similar design. Ensure vehicle has actual problem. Remove air cleaner and replace filter if dirty or plugged. Check the following if problem still exists

1. Ignition timing.
2. Restricted fuel filter, contaminated fuel, or improper fuel pressure. See CHART A6 - FUEL SYSTEM PRESSURE TEST chart in the TBI TESTS/CODES article in this section.
3. ECM grounds.
4. EGR operation to ensure EGR valve is not open (or part open) all the time. See EGR SYSTEM CHECK chart in the TBI TESTS/CODES article in this section.
5. Alternator output. Repair if less than 9 volts or more than 16 volts.
6. Valve timing. Perform compression test.
7. Proper or worn camshaft.
8. Exhaust system for restriction
9. With engine at normal operating temperature, connect vacuum gauge to convenient intake manifold vacuum port.
10. Disconnect EGR solenoid electrical connector, or connect EGR valve directly to vacuum source (by-passing switches and/or solenoids).
11. Run engine at 1000 RPM and record vacuum reading.
12. Slowly increase speed to 1500 RPM and note vacuum reading at steady 2500 RPM.
13. If vacuum at 2500 RPM decreases more than 3 in. Hg from reading at 1000 RPM, inspect exhaust system for restrictions.
14. Disconnect exhaust pipe from engine and repeat previous 2 steps. If vacuum still drops more than 3 in. Hg with exhaust disconnected, check valve timing.

A mild to severe ping, usually worse under acceleration. Engine makes sharp metallic knocks that change with throttle opening.

Check for obvious overheating problems

1. Low coolant.
2. Loose water pump belt.
3. Restricted airflow to radiator, or restricted water flow through radiator.
4. Fuel quality (proper octane rating).
5. Correct PROM (MEM-CAL).
6. Closed thermostatic air cleaner device.
7. Ignition timing (ESC check).
8. Low fuel system pressure. See the CHART A6 - FUEL SYSTEM PRESSURE TEST in the TBI TESTS/CODES article in this section.
9. EGR system not opening. See EGR SYSTEM CHECK chart.
10. Proper transmission shift points and TCC operation. See TORQUE CONVERTER CLUTCH chart in the TBI TESTS/CODES article in this section.
11. Incorrect engine parts (camshaft, cylinder heads, pistons, etc.).
12. Remove carbon with Top Engine Cleaner (12345089).
13. On vehicles over 8500 GVW with 5.7L or 7.4L engine and dual catalytic converter system, check for exhaust restriction in rear converter area.

Steady pulsation or jerking that follows engine speed, usually more pronounced as engine load increases. The exhaust has a steady spitting sound at idle or low speed.

Check for missing cylinder by

1. Disconnecting IAC motor connector. Start engine. Remove one spark plug at a time.
2. If there is an RPM drop on all cylinders, proceed to ROUGH, UNSTABLE, OR INCORRECT IDLE, STALLING trouble shooting.
3. If there is no RPM drop on one or more cylinders, or excessive variation in drop, check for spark on suspected cylinders using ST-125 Spark Tester (J-26792).
4. If there is no spark, remove spark plugs in suspected cylinders and check for cracks, wear, improper gap, burned electrodes, and heavy deposits.
5. Check spark plug wires by connecting an ohmmeter to each end of wire. If ohmmeter reading is greater than 30,000 ohms, replace wire(s).
6. Check ignition coil and secondary voltage using ST-125 Spark Tester (J-26792).
7. Check for restricted fuel filter, contaminated fuel, or low fuel pressure. See CHART A-6, FUEL SYSTEM PRESSURE TEST chart in the TBI TESTS/CODES article in this section.
8. Check valve timing. Perform compression test.
9. Check distributor cap and rotor for moisture, dust, cracks, or burns.
10. Remove rocker covers. Check for bent push rods, worn rocker arms, broken valve springs, or worn camshaft lobes.