George Schreffler
Newbie
Looking for help with ideas to diagnose and fix my 1998 Chevy K1500 5.7L L31 misfire. The situation and actions I have taken to date appeaser below. Any thoughts on where to go next would be appreciated.
Symptom - Cylinder 5 misfire at all engine speeds - P0300 DTC; no other DTCs. Diagnosed with Snap On Solus Pro scan tool.
New GM L31 replacement engine (old engine had a crack in cylinder 5 and the same P0300 misfire in cylinder 5 only)
New GM multi-port fuel injection (MPFI) meter replaced central sequential port fuel injection (CSFI) meter
New crankshaft position sensor. Ran crankshaft position sensor system variation learn procedure.
Ignition system inspections and tests
Other inspections and tests
George
Symptom - Cylinder 5 misfire at all engine speeds - P0300 DTC; no other DTCs. Diagnosed with Snap On Solus Pro scan tool.
New GM L31 replacement engine (old engine had a crack in cylinder 5 and the same P0300 misfire in cylinder 5 only)
New GM multi-port fuel injection (MPFI) meter replaced central sequential port fuel injection (CSFI) meter
New crankshaft position sensor. Ran crankshaft position sensor system variation learn procedure.
Ignition system inspections and tests
- New spark plugs with correct gap.
- New distributor cap and rotor.
- Ignition wires and coil wire passed resistance test.
- Tested for arcing, cross-firing, and electro-magnetic interference with no issues found.
- Swapped spark plugs and ignition wires to different cylinders. Misfire remains on cylinder 5.
- Tested spark on cylinders 1, 3, 5, and 7. Adequate spark on all cylinders.
- Distributor and camshaft position sensor. No defects apparent in visual inspection. Replaced with known good distributor and camshaft position sensor from another truck. Misfire remains on cylinder 5. Cam retard offset on both distributors set to zero and confirmed with scan tool.
- Ignition coil and ignition control module. Replaced with known good units from another truck. Misfire remains on cylinder 5.
- Fuel pump delivers 60 psi and system holds 55 psi after shutting off pump.
- New fuel filter.
- Fuel injector balance test. Pressure 1 = 55 psi on all 8 cylinders. Pressure 2 = 28 psi on all 8 cylinders. Average pressure drop 27 psi on all 8 cylinders.
- Fuel injector coil test. Steady reading on all 8 injectors. Readings range from 6.9 to 7.1 volts.
- Inspected connectors at the vehicle control module and fuel injectors. No apparent deformities or other problems affecting the connection.
- Checked injector ignition feed circuits with a test light. Test light illuminated for all circuits.
- Checked fuel injector circuit with an injector test lamp. Flashed correctly for each injector.
Other inspections and tests
- Searched and tested for vacuum leaks. None found.
- Inspected and cleaned all grounds. No corrosion or other issues found.
- Monitored all engine sensor data with scan tool (engine in open and closed loop). Idle air control (IAC), throttle position (TP), engine coolant temperature (ECT), manifold absolute pressure (MAP), exhaust gas recirculation (EGR), all within typical values.
- Long term fuel trim on Bank 1 was 154 counts. Typical value is 127 counts.
- Heated oxygen sensor Bank 1, Sensor 2 voltage varied widely just like Sensor 1. Bank 2, Sensor 2 was steady as expected for the H02S downstream from the catalytic converter. This variation indicates to me that there is too much unburned fuel in the exhaust in Bank 1, probably from the misfiring cylinder 5.
George