For 1990-2009 cars

# Poor Acceleration from a Stop or Detonation in Gear at a Stop - keywords code DTC low MIL ping

Subject: | Poor Acceleration from a Stop or Detonation in Gear at a Stop

Models: | 1996-2007 All General Motors Passenger Cars and Light Duty Trucks

This PI is being superseded to update model years and instructions. Please discard PIP3144A.

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

### Condition/Concern:

Customer concern of poor acceleration, detonation or "ping" at idle in drive or reverse, and/or possible DTC P0101, P0106 and/or P0121 set in the PCM. The vehicle will perform properly after attaining a speed of about 30 - 40 mph. The condition may also be described by the customer or the dealer as a hesitation, stall when putting into gear, surge on acceleration (similar to hitting fuel cut or rev limit). The ultimate cause may be a non-holding torque converter stator or damaged stator support shaft within the automatic transmission.

Note: A torque converter or stator spline concern will not effect engine operation in park or neutral i.e. misfire or rough idle.

### Recommendation/Instructions:

The following checks should be performed in the event that normal engine driveability checks have not resolved the detonation or "ping" at idle in drive or reverse, lack of power from a stop, stall, surge on acceleration and or hesitation complaint.

The IAC counts throttle angle and/or MAP voltage and KPA should be compared to a like vehicle in park and in gear after reaching operating temperature. If the counts and map are high or throttle angle is open excessively in comparison this may be a result of high engine load and a torque converter and or stator support shaft related concern.

If the above information does not lead to a resolve follow torque converter diagnostics listed below.

The transmission oil cooler outlet line (line to the cooler) should be checked for excessive heat. The Tech II scan tool may be helpful on vehicles equipped with the transmission fluid temperature sensor in the cooler line (mainly front wheel drive). On vehicles that do not have the temperature sensor in the cooler line a temperature probe should be used to check the temperature. The temperature readings should be compared to a like vehicle with the same powertrain option content.

A stall test (brake torque) may point to a damaged torque converter, the stall RPM speed will be lower then a like vehicle. However, poor engine performance will also produce a lower stall speed RPM.

If the torque converter stator or stator support is suspect, the transmission should be removed and THE STATOR SUPPORT SHOULD BE INSPECTED FOR SPLINE DAMAGE. If the stator support splines are damaged the transmission should be repaired and new torque converter installed. If damage is not present on the stator support the concern is either internal to the torque converter stator or an engine performance concern.

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.