7.3 IDI is a naturally aspirated diesel engine used in Ford pickup trucks F250 and F350 from 1988 to 1994 till its discontinuation.
Earlier versions have non-turbo indirect fuel injection and turbocharger with the intercooler in 1993-mid 1994 models.
What is Fuel Economy of 7.3 IDI? 7.3 IDI non-turbo or naturally aspirated has an average of 8-12 miles per gallon (mpg) fuel economy in city/highway areas. While with a turbocharger and intercooler, it can go up to 14-16 mpg. However, it also depends on other factors like your driving style, loading conditions, transmission system, maintenance schedule, and timing of the fuel injectors. You can improve its mileage by reducing wind resistance, reducing acceleration, and upgrading the older exhaust system.
It is a highly reliable engine and still in use by various owners by adopting aftermarket solutions to make it turbocharged and upgrade its performance.
However, modern pickup trucks have better fuel injection to improve the fuel economy and reduce emissions to fulfill EPA requirements.
7.3 IDI has two versions available according to their air intake system and is significantly different in their performance.
Ford F250/350 from 1988 to 1993 has 7.3 IDI engines without turbochargers. It means they have a naturally aspirated system that relies on atmospheric pressure to pull in the air.
Therefore, they lack the performance leaving 20-25% of their intake fuel unburnt from the cylinders. It results in black smoke, reduced power, and poor mileage.
Naturally aspirated 7.3 IDI engine has fuel economy from 8-12 mpg depending on several factors.
Having a 1989 F250 with the same engine, one of my friends has reported fuel economy as low as 6 mpg. Therefore, exact figures can vary according to the truck’s current condition.
With turbocharger and intercooler
1993-1994 model F250/F350 has 7.3 IDI with a turbocharger installed. Aftermarket solutions are available for the engine to get a turbocharger and intercooler.
It increases air intake to the cylinders resulting in increased burning. As a result, it increases the power of the truck and improves fuel consumption.
It can go up to 14-16 mpg. There have been reports of mileage as high as 18 mpg by introducing several modifications, but it is an exceptional case. It can also vary according to driving in city and highway areas.
Is Ford 7.3 IDI a fuel-efficient engine?
Ford 7.3 IDI is a reliable engine with good power and torque ratings in the late 1980s to early 1990s.
However, it has poor fuel efficiency due to the absence of a turbocharger and an efficient fuel injection system.
As a result, Ford discontinued it due to increased requirements from EPA regarding fuel economy and emissions.
Although the turbocharged variant of 7.3 IDI improved the figures a bit, it was insufficient to continue its production for future generations.
Therefore, they replaced it with a 7.3 power stroke engine with the same bore size with new electronics and computer programming to have better performance.
What factors affect the fuel economy of the Ford 7.3 IDI engine?
Several factors affect the fuel economy of your Ford 7.3 IDI engine. Therefore, you cannot quote an absolute figure regarding its fuel consumption.
However, you can present a range or average value after a long trip depending on the factors given below:
Loading or towing condition is a single important factor affecting the fuel consumption of 7.3 IDI engines. For example, Ford F250 is a ¾ ton, and F350 is a 1-ton pickup truck.
Loading them up to their payload capacity will reduce fuel economy even under 10 mpg.
Similarly, towing a fully furnished trailer with the truck will also give you fewer miles per liter.
I got a 9 mpg mileage by towing 12000 lbs with my 1991 F350. However, the best figure I got is 16 mpg driving on the highway under mildly loading conditions.
Regular maintenance or tuning
Regular preventive maintenance also plays a significant role in the mileage of a diesel engine. 7.3 IDI has a schedule for tuning, oil change, fuel filter replacement, and air filters.
If you follow the instructions and properly maintain the truck, you will get better fuel economy.
Otherwise, I have met with drivers complaining about poor mileage as low as 6-7 mpg of their F250/F350 trucks with 7.3 IDI engines.
Older vehicles have automatic transmissions with fewer gear ratios. Therefore, they have lesser mileage than manual transmissions that allow you to change gears in a more optimum way.
Upgrading it with a 7.3 IDI engine will improve the fuel economy. For example, E4OD with lockup converter will improve mileage by 2-3 mpg than C6 automatic transmission.
Fuel consumption also depends on your driving style. For example, if you keep on accelerating hard all the time at higher speeds like above 70 miles per hour (mph), it will result in black smoke, an indication of a lot of unburnt fuel from the exhaust.
As a result, you will get a poor mileage of 10-12 mpg.
However, going soft on the accelerator and driving at 60-65 mph will significantly improve the economy to 14-16 mph under the same loading conditions.
Therefore, it is the easiest way to save money in terms of fuel by driving at mid speeds to avoid extended idling.
Fuel injectors timing
Fuel injection timing also plays a vital role in improving the fuel economy of the diesel engine.
They enhance or retard the timing according to specific operating conditions.
However, retarded timing reduces fuel consumption and emissions, while enhanced timing provides better power ratings.
You can visit the expert mechanic to get optimum timing of fuel injectors for better results.
Wind friction or drag also impacts the fuel economy of the Ford engine.
If you drive too fast, air resistance will be significant, and the engine has to do more work to keep it going at the same speed.
Similarly, if you drive F250/F350 without a tonneau cover, the truck bed will act as a bucket to capture air resulting in drag force.
You can improve the fuel economy by 1-2 mpg by driving at medium speeds and installing a cover on the truck bed.
Highway or city areas
Driving in highway areas is smooth with no sudden brakes or frequent stops. On the other hand, city areas have crowded places with more traffic and slower speeds.
Therefore, you will get better mileage on highways than in city areas. Therefore, manufacturers often mention separate figures for driving in city and highway areas.