| Subject: | Diagnostic Tips for DTC P0300 Engine Misfire Detected and Cylinder Leakage Testing |
| Models: | 2004-2006 Chevrolet Colorado |
| with 3.5L I-5 Engine (VIN 6 - RPO L52) |
The purpose of this bulletin is to provide technicians with diagnostic tips for DTC P0300 and cylinder leakage testing.
Diagnostic Tips for DTC P0300
If DTC P0300 sets, follow DTC P0300 diagnostics in SI. The following tips may also be helpful:
| • | Isolate the cylinder or cylinders responsible for the P0300 misfire code and determine if the misfire can be moved to another cylinder by swapping components such as spark plugs, ignition coils and fuel injectors. |
| • | If misfire is random, diagnose for possible mechanical noise that may be misinterpreted as a misfire. |
| • | If diagnostics lead to suspect cylinder head valve seats, conduct a cylinder leakage test utilizing a cylinder leakage tester following the manufacturer instructions and Cylinder Leakage Test procedure in SI. |
Diagnostic Tips for Cylinder Leakage Test
When performing a cylinder leakage test, the following tips may be helpful:
| • | Carefully follow the manufacturer's instructions for J 35667-A Cylinder Head Leakdown Tester (or equivalent automotive cylinder leakage tester) and Cylinder Leakage Test procedure in SI. |
| • | The cylinder must be at TDC on the compression stroke when testing to ensure that all the valves are fully closed. |
| • | If holding the crankshaft balancer bolt with a wrench, regulate shop air to the J 35667-A to 345-414 kPa (50-60 psi) to reduce torque on the crankshaft balancer bolt when air is applied. For other equivalent cylinder head leakdown
testers, refer to the manufacturer's instructions. |
| • | An alternative to holding the crankshaft balancer bolt with a wrench would be to use the EN-46547 Flywheel Holding Tool. A breaker bar with socket is another alternative. |
| • | If intake valve seat leakage (rare) is suspected, verify by listening for air leakage inside the intake runner. |
| | Important: If excessive cylinder leakage is NOT observed, the cause of the misfire condition is NOT engine mechanical related. Misfire diagnosis should focus on fuel and electrical for cases where excessive leakage is not observed.
|
| • | The majority of vehicles will not experience an intake valve seat erosion condition. Expect a variation between cylinders if valve seat erosion has occurred. |
| • | Use the labor code and time provided in the Warranty Information section of this bulletin to receive credit for performing cylinder leakage diagnostics. |
Warranty Information
Important: Cylinder leakage test results must be documented on the repair order.
For vehicles repaired under warranty, use:
Labor Operation
| Description
| Labor Time
|
J7520
| Cylinder Leakage Diagnostics
| 0.8 hr
|
