Mechanics

CHEVY INTEMITENT ROUGH RUNNING

1998 Chevrolet Silverado

Engine Performance problem
1998 Chevy Silverado V8 Four Wheel Drive Automatic 157000 miles

intemittent rough running, Error code cylinder 1 misfire. Changed plugs wires rotor and cap. Still same problem. Put GM injector cleaner in and then yesterday it started doing it again and felt like it was running on 4 cylinders. Floored it for a while and it cleared up. Then excellerating onto the highway it happened again. Floored it for a while and again it cleared up.
Seems to happen under load like excellerating or towing.
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Kenfranklinl
July 17, 2009.



3 things left to check=1.) compression test it in all cylinders, 2.) fuel, check pressure, 3.) carbon in the intake ports....

Go here and checkout our video.
http://www.2carpros.com/articles/how-to-check-fuel-system-pressure-and-regulator

FUEL DELIVERY Fuel Pressure Regulator (CSI) Fuel pressure regulator is mechanically controlled by internal spring pressure. Regulator is adjusted at factory and is not serviceable. If fuel pressure is too low, check for restricted delivery line. Also, check fuel pump pressure and volume. If fuel pressure is too high, check for restricted fuel tank return line or fuel filter. If no faults are found and pressure is too high or too low, replace fuel pressure regulator. Fuel Pressure Regulator (SFI) Fuel pressure regulator is a vacuum -controlled diaphragm type, which uses manifold vacuum to modify fuel pressure to compensate for engine load fuel requirements. Connect fuel pressure gauge to fuel pressure service port. Start engine and note fuel pressure. Disconnect vacuum hose from fuel pressure regulator. Fuel pressure should increase 4-10 psi (.28-.70 kg/cm 2 ). If pressure does not increase 4-10 psi (.28-.70 kg/cm 2 ), check for presence of manifold vacuum at signal line. If vacuum is not present, check for kinked, cut or split vacuum hose or plugged throttle body vacuum port. If vacuum is present and no pressure change occurs, replace fuel pressure regulator. Fuel Pump Oil Pressure Switch (Back-Up Circuit) To test fuel pump oil pressure switch (fuel pump back-up circuit), start engine. With engine running, disconnect fuel pump relay. If engine stalls, fuel pump oil pressure switch is faulty. If vehicle continues to run, switch is okay. FUEL CONTROL Fuel Injector Circuit Diagnosis 1. If powertrain OBD system check has been performed, go to next step. If powertrain OBD system check has not been performed, perform powertrain OBD system check. See POWERTRAIN OBD SYSTEM CHECK in TESTS W/CODES - 5.0L article. 2. Turn ignition switch to LOCK position. Disconnect fuel injector harness connectors. Using a test light connected to ground, probe appropriate injector ignition feed circuit at injector harness connector. Turn ignition switch to RUN position. If test light illuminates, go to next step. If test light does not illuminate, go to step 7). 3. Connect Fuel Injector Test Light (J-34730-350) to fuel injector harness connectors one at a time. Crank engine while observing test light. If test light does not flash at each injector, go to NOTE: For fuel system pressure testing, see BASIC TESTING - 5.0L article. NOTE: If injectors are dirty, they should be cleaned using approved injector cleaning procedure before performing INJECTOR BALANCE TEST.next step. If test light flashes at each injector, perform inject coil test. See INJECTOR COIL TEST. 4. If fuel injector test light illuminates constantly while engine is being cranked, go to next step. If fuel injector test light does not illuminate constantly while engine is being cranked, go to step 6). 5. Install fuel injector test light on affected circuit. Turn ignition switch to LOCK position. Disconnect PCM/VCM harness connectors. Turn ignition switch to RUN position. If test light illuminates, go to step 8). If test light does not illuminate, go to step 11). 6. Check injector control circuit for open or short to voltage between PCM and injector harness connectors. If open or short exists, go to next step. If open or short does not exist, go to step 9). 7. Repair open or short to voltage in injector control circuit between PCM and injector harness connectors. After repairs are complete, go to step 12). 8. Repair short to ground in injector control circuit, between PCM and injector harness connectors. After repairs, go to step 12). 9. Check PCM/VCM harness connectors for poor connections. If poor connection exists, go to next step. If poor connection does not exist, go to step 11). 10. Repair connections as necessary and go to step 12). 11. Replace PCM/VCM and go to next step. 12. Using scan tool, clear DTCs. Attempt to start engine. If engine starts and continues to run, go to next step. If engine does not start and continue to run, go to step 2). 13. Let engine idle until normal operating temperature is obtained. Retrieve DTCs. If no DTCs are present, system is okay at this time. If any DTCs are present, perform appropriate DTC test. See TESTS W/CODES - 5.0L article. Injector Balance Test 1. If powertrain OBD system check has been performed, go to next step. If powertrain OBD system check has not been performed, perform powertrain OBD system check. See POWERTRAIN OBD SYSTEM CHECK in TESTS W/CODES - 5.0L article. 2. If injector coil test has been performed, go to next step. If injector coil test has not been performed, perform injector coil test. See INJECTOR COIL TEST. 3. If engine coolant temperature is greater than 201 °F (94 °C), go to next step. If engine coolant temperature is not greater than 201 °F (94 °C), go to step 5). 4. Allow engine to cool to less than 201 °F (94 °C) and go to next step. 5. Install fuel pressure gauge. Turn ignition switch to RUN position then to LOCK position. Bleed air from fuel pressure gauge. Using scan tool, energize fuel pump. If fuel pressure reading is 60-66 psi (4.2-4.6 kg/cm 2 ), go to next step. If fuel pressure reading is not within specification, perform fuel system diagnosis. See BASIC TESTING - 5.0L article. 6. Turn fuel pump off. Observe fuel pressure gauge. If fuel pressure remains constant, go to next step. If fuel system does not remain constant, perform fuel system diagnosis. See BASIC TESTING - 5.0L article. 7. Disconnect fuel injectors harness connector. Using Fuel Injector Adapter (J-34730-3A), NOTE: Perform step 7) on each injector.connect Fuel Injector Tester (9J-39021) to fuel injector. Connect fuel injector tester power leads to appropriate battery terminals. Set amperage supply selector switch on fuel injector tester to Balance Test 0.5-2.5 amp position. Turn ignition switch to RUN position then to LOCK position. Record fuel pressure reading (first reading). Energize injector by depressing PUSH TO START TEST button on injector tester and hold until fuel pressure gauge stabilizes. Record fuel pressure reading (second reading). Subtract first reading from second reading (this result is pressure drop valve). Add pressure drop valve for each injector together and divide total by 4. If any injector's drop valve is greater or less than average drop valve by 1.5 psi (.1 kg/cm 2 ), replace faulty injector(s) as necessary. If no injector's drop valve is greater or less than average drop valve by 1.5 psi (.1 kg/cm 2 ), injector balance test is okay at this time. Injector Coil Test 1. If powertrain OBD system check has been performed, go to next step. If powertrain OBD system check has not been performed, perform powertrain OBD system check. See POWERTRAIN OBD SYSTEM CHECK in TESTS W/CODES - 5.0L article. 2. Turn ignition off. Relieve fuel pressure. Connect Fuel Injector Tester (J-39021) to battery voltage. Connect Injector Switch Box (J-39021-210). Set amperage on fuel injector tester to 0.5 amp. Connect DVOM to fuel injector tester. Connect scan tool to data link connector and monitor engine coolant temperature. If coolant temperature is 50-95 °F (10-35 °C), go to step 4). If coolant temperature is not as specified, go to next step. 3. Allow engine to warm or cool as necessary. If engine coolant temperature is now 50-95 °F (10- 35 °C), go to next step. 4. Using fuel injector tester, press PUSH TO START TEST button and monitor DVOM reading. Perform this test to each injector. Voltage reading should be 5.44-7.53 volts. If voltage reading is as specified, go to next step. If voltage reading is not as specified, perform injector balance test. See INJECTOR BALANCE TEST. 5. Replace faulty injector nozzle and poppet assembly and then proceed to next step. 6. Using scan tool, clear DTCs. Start engine. If engine starts and continues to run, go to next step. If engine does not start or starts and dies, go to step 2). 7. Warm engine to normal operating temperature. Using scan tool, retrieve DTCs. If DTC(s) exists, perform appropriate DTC(s) test. See TESTS W/CODES - 5.0L article. If DTC(s) do not exist, system is okay at this time. WARNING: In order to prevent flooding of cylinder and possible engine damage, relieve fuel pressure before performing injector coil test procedure. WARNING: In order to prevent flooding of cylinder and possible engine damage, relieve fuel pressure before performing injector coil test procedure.

Merlin2021
Jul 18, 2009.