Possible Causes & Corrections
WARNING: This page is about a different car, the 2003 GMC Sierra, 2003 GMC Cab & Chassis Sierra, 2003 Chevrolet Silverado, and 2003 Chevrolet Cab & Chassis Silverado. However, it is still accessible from the selected car via links, so may be relevant.
Check the following items:
- Search for bulletins.
- Compare scan tool data at idle with scan tool data list. See PID VALUE CHARTS in PID VALUE CHARTS - SILVERADO & SIERRA article.
- Inspect ECM grounds for being clean, tight and in the proper locations.
- Remove and inspect air filter element for dirt or for being restricted.
- Inspect Fuel Rail Pressure (FRP) sensor. Observe FRP with scan tool. The FRP should be between 1.1-1.4 MPa. If not, inspect for high resistance in FRP sensor circuits or FRP sensor.
- Test for an intermittent FRP sensor signal by wiggling the harness between the sensor and ECM with ignition on and engine off, while monitoring parameter with scan tool.
- Observe FRP sensor and fuel pressure regulator commanded percent at idle. FRP should be near 40 MPa, and commanded percent should be near 40 percent. If command is high, a fuel pressure or sensor problem exists.
- Inspect for an intermittent Crankshaft Position (CKP) sensor signal.
- Inspect CKP sensor reluctor wheel. Remove CKP sensor and attempt to move the reluctor wheel front to back or side-to-side with a probe. If there is any movement, the reluctor wheel retaining bolts are loose.
- Inspect for proper crankcase ventilation. See EMISSION SYSTEMS & SUB-SYSTEMS in SYSTEM & COMPONENT TESTING - 6.6L SIERRA & SILVERADO - DIESEL article.
- Perform fuel injector balance test using a Tech 2 scan tool.
- Inspect for a restricted fuel filter.
- Inspect for a restriction in fuel return system.
- Inspect for a contaminated fuel condition.
- Inspect for a sticking fuel pressure regulator. The symptom for this condition will be an idle surge of at least 100 RPM. This surge will be from 50 RPM above or below the desired idle speed. See FUEL SYSTEM DIAGNOSIS - HIGH PRESSURE SIDE under FUEL SYSTEMS in BASIC DIAGNOSTIC PROCEDURES - 6.6L SIERRA & SILVERADO - DIESEL article.
- Inspect engine mechanical for cylinder compression. Low compression can be caused by sticking or leaking valves, worn camshaft lobes, valve timing, bent push rods, worn rocker arms, or broken valve springs. Check for excessive oil in the combustion chamber, caused by leaking valve seals.
- Inspect for incorrect basic engine parts, such as camshaft, cylinder heads, pistons, connecting rods, or bearings.
- Inspect exhaust system for damaged or collapsed pipes, exhaust manifold for a collapsed inner wall, and mufflers for heat distress or possible internal failure.
- Electromagnetic Interference (EMI) on the reference circuit can cause an engine miss condition. A scan tool can usually detect EMI by monitoring the engine RPM. A sudden increase in RPM with little change in actual engine RPM change indicates that EMI is present. If a problem exists, inspect routing of high voltage components, such as fuel injector wiring near the sensor circuits.
- Inspect the Park/Neutral Position (PNP) switch circuit.
- Inspect for a short to 5-volt circuit on one of the fuel injector control circuit between ECM and FICM.
- Inspect for faulty motor mounts.
- Inspect intake and exhaust manifold passages for casting flash.