4.3L LU3 Engine Hot Soak Hesitation Low Power - accelerate hot no speed

When servicing the vehicle with the VIN you entered, the following diagnosis might be helpful if the vehicle exhibits the described symptoms.

Hesitation at launch after a 10-20 minute hot soak at hot ambient. More prevalent when going from reverse to drive while truck is still rolling.

It is a normal condition when the ambient temperature is above 90°F and the vehicle was driven to operating temperatures and then parked for a short time period (10-20 minutes). The engine software and calibrations are set up to prevent spark knock which could lead to other engine concerns. To prevent the spark knock, the calibration looks at Inlet air (hotter on M/L van applications), coolant temperature, knock sensor and transmission torque management values and takes away spark when the engine and coolant temperatures are at high enough temperatures to create spark knock. The calibration also looks at the transmission torque values and makes adjustments to spark when necessary on any gear shifts. Another obvious value that removes spark would be if the knock sensor was recording any activity. When you add to this the load of the cooling fan and the A/C clutch and the customer is doing a parking lot maneuver after a hot soak they will notice some lower performance which can be attributed to the calibration performing as designed to protect the engine and transmission.

Compare this unit to a like unit. If the results are the same, this is normal and is designed to protect the engine/transmission.

One other possibility would be if you noticed knock sensor activity during this maneuver which should show up for a brief moment. If you have verified the knock system performance to be correct, then it could be caused by the balance shaft rattle being interpreted as a knock. Remove the balance shaft gear for diagnostic purposes. If the condition is gone a balance shaft rattle kit is being developed and will be available sometime in August to September, 2003.

Please follow this diagnosis 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. If these steps do not resolve the condition, please contact GM TAC for further diagnostic assistance. This diagnostic approach was developed for the vehicle with the VIN you entered and should not be automatically be used for other vehicles with similar symptoms.

(03 Chevrolet Blazer 2WD/4WD) and (03 Chevrolet S10 Pickup 2WD/4WD) and (03 GMC Jimmy 2WD/4WD) and (03 GMC Sonoma Pickup 2WD/4WD) and (03 Chevrolet Silverado/GMC Sierra) and (03 Chevrolet Astro/GMC Safari) and (Chevrolet Express/GMC Savana)