Q: I have a bus that contain a Cummins engine and Allison transmission. The problem is that the vehicle does not exceed the speed 80 Km/h / 50 mph.

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look of power , the bus does not have enough RPM which result in limiting the bus speed MAX of 80 Km/h.
My car has an automatic transmission.

Hi there. Check the fuel filter and the fuel water separator for if they are old and need changed. Check the fuel water separator for a valve on the bottom and if there is a valve, if you can open it, let some of the fuel out as it would be full of water. Check the air filter to the engine. If the air filter gets dirty, then the engine will starve it self and not operate properly. Also, check the fuel rail pressure and make sure that the pressure is accurate and not low. If the air filter, fuel filters, and fuel water separator are good and there is good fuel pressure, then the throttle position sensor on the foot pedal has lost its counts and would need replaced. I recommend seeking out a professional, such as one from Your Mechanic, to help you with your bus acceleration issue.

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