Improving Fuel Economy for a GM 4.3 TBI

I’m just now getting to around to driving the 1990 GMC K1500 more, a little over a year after I bought it. Based on other 4.3 5-speed trucks I’ve owned, including the 1991 C1500, I know this transmission and engine combo can get good gas mileage for a full-size truck. The two tanks I had on the ’91 were were 20.3 mpg and 18.2 mpg.

So I was surprised to see 13.4 mpg for my first “tank” in this truck. I say “tank” because it was only 196 miles and 14.7 gallons, and this truck has the larger 34 gallon tank. So it wasn’t even a full tank and most of it was spent driving around my yard and property moving brush. But still, I’ve gotten better gas mileage than that in an extended cab truck with a 350 V8, the 1990 K2500.

Date Miles Gallons MPG
8/26/2019 196.9 14.656 13.4
5/2/2020 371.2 25.543 14.5
Historical Fuel Economy for 1990 GMC K1500

However, I still expected better. Even my second tank with much more road and highway driving was only 14.5 mpg. So I’m on a mission to improve the fuel economy for the truck. Here are a few things I plan on doing:

  • Rebuild throttle body (I used this kit on the ’92 C1500)
  • Ultimate TBI mods
  • TBI Airflow Enhancer
  • New plugs, wires, rotor, and rotor cap (maybe, these might have been replaced just before I bought it)

I’ll either update this post or create a new one to document any changes in gas mileage as I make these improvements.

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