Light Throttle Hesitation or Misfire - keywords 4.3 5.0 5.7 accelerate backfire buck chuggle code decelerate detonation DTC hard harsh hot injector L30 L31 L35 launch miss noise surge

The following diagnosis might be helpful if the vehicle exhibits the symptom(s) described in this PI.

The customer concern may be a miss, buck, or fishbite type feeling on a deceleration.

1. This condition can usually be duplicated just after a smooth gradual acceleration, cresting a hill, or just after the TCC engages.
2. This condition will not occur on a cold engine, it becomes more evident at normal operating temperature.
3. A rough idle or poor idle quality may also be noticed.
4. Scan data may look normal with only random misfires showing up in misfire data.
5. This condition will vary in intensity from just a light bump to a severe buck. The bump or buck caused by this condition can induce a driveline clunk or ringing of the propshaft. The driveline clunk or ringing may be misinterpreted as a transmission or driveline concern.
6. This condition is similar to, but far more harsh than the miss/buck/surge created when the CMP offset is set incorrectly.

1. Question the customer and verify if there has been any previous repairs made to the vehicle that may have allowed the improper installation of the injectors.
2. Use the Tech 2 and verify the CMP retard is set correctly. Use the current SI procedures for Camshaft Retard Offset Adjustment and adjust as needed.
3. If the SI procedures have been completed for the vehicle symptom duplicated, and the diagnostics are inconclusive, it is possible that the SCPI / CPI injector nozzle(s) are not in the proper cylinder location. There is no apparent correlation between the number of improper nozzle locations and the severity of condition.
4. If improper injector installation is suspected, remove the Upper Intake Manifold and inspect the injector positions. The engine cylinder numbers are molded into the Injector Fuel Metering Block. Verify the individual cylinder injector poppet positions correspond with the engine cylinder numbers marked on the Fuel Metering Block. Evaluate the customer concern after the injectors are installed into the proper cylinders.

Please follow this diagnostic or repair process thoroughly and complete each step. If the condition exhibited is resolved without completing every step, the remaining steps do not need to be performed.