Diesel MPG Accuracy & Calibration


Until calibrated, fuel and mileage estimates  for Diesel vehicles may be as much as 3x off.  It is necessary to perform the fuel calibration procedure detailed in the user manual for all diesel vehicles. 

 Also, most Diesel engines do not function in a closed loop manner.   For example, there is no attempt to keep the air to fuel ratio a constant as in a closed loop gasoline fuel system.  For such vehicles, the fuel and mileage estimates may appear inaccurate.  This is the nature of the open loop diesel engine.  As a result Instanteous gauges may read incorrectly during deacceleration.   However, if calibrated, UltraGauge will provide reasonable average results. 

Fuel calibration is manidatory with diesel engines.

Because the Air to Fuel ratio is allowed to widely vary in most Diesel engines,  and can vary  from 14 to as much as 70, Ultragauge will not be able to provide accurate fuel useage estimates.  As such, gauges such as Instantenous MPG and Gallons/hour, should only be used to provide relative fuel estimates.  Gauges such as Distance to Empty & Time to Empty should not be relied upon.


Please also note that Diesel vehicles typically support few gauges.  The OBDII standard was created for emmission purposes and in general manufacturers are required to make available via the OBDII, parameters used in meeting emissions.  Since Diesels operate in an open loop, few parameters are needed and few guages are available via the OBDII interface.

Please check the Gauge Availability estimator to determine which guages are potentially available for your Diesel.

Please note that Ford Diesels are not supported