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argo · 09-14-2014, 03:51 PM

I have been lurking on this forum for a while and have seen a few mileage discussions regarding these cars, or similar ones, and there is quite a mixed consensus about their efficiency potential. I rescued this particular car from my parents. I actually drove this car to high school back in 1992. The car had been sitting mostly and relegated to spare car duty. I wanted a backup family car for my 1992 Diesel Suburban, so I offered to buy it. My parents gave it to me because I always fixed it for them for free. So the price was right but the old girl needed some help.

Nobody would ever accuse the LO3 5.0L (305 TBI) V8 of being a rocket in a 4500 lb car, especially when pulling 3.08 gears, but it was particularly sluggish when I brought it home and it had no heat and it only managed 13 MPG. I gave it a tuneup, replaced the thermostat (I installed a 205* unit instead of the factory 190* thermostat), I replaced the worn out O2 sensor and re-calibrated the TPS down to 0.62v at idle to make the computer run the engine a little leaner. I also replaced the tires with Yokohama Geolander HT/S tires in the LT 215-75-R15 and run them at the full 50 psi. This doubled my fuel economy to 26 mpg highway on a trip to Disneyworld with the family on a 2,100 mile round trip. Around town it is averaging about 20 MPG. I recently took a trip to building supply liquidator in Readding PA to buy replacement windows for my house and despite the weight of 10 windows (2 of which ended up on the roof rack) it averaged 23.1 MPG for the trip. I can do better, but since I try to keep with the flow of traffic and generally cruise at 5 MPH over the limit I think these numbers are reasonable as a starting point. Since I live in a rural area and sometimes need to travel on unimproved roads, lowering the car is not an option. Also, as a mechanic/shop teacher I always travel with about 100 lbs of tools in my traveling tool box. I intend to modify the TBI unit for more efficiency by installing smaller injectors and boosting the fuel pressure to compensate because higher pressure with smaller injectors should provide better atomization. I plan to use the injectors for the 4.3L V6 and a pump for an LT1. I might convert to a 6.2L diesel like my Suburban has. I custom built that for fuel economy and get 27 mpg with the Sub. Stay tuned...

09-14-2014, 03:51 PM	#1 (permalink)
argo Diesel Fume Junkie! Join Date: Nov 2008 Location: Sussex County, DE Posts: 4 Thanks: 0 Thanked 4 Times in 4 Posts	1992 Caprice Wagon Fuel Economy Project I have been lurking on this forum for a while and have seen a few mileage discussions regarding these cars, or similar ones, and there is quite a mixed consensus about their efficiency potential. I rescued this particular car from my parents. I actually drove this car to high school back in 1992. The car had been sitting mostly and relegated to spare car duty. I wanted a backup family car for my 1992 Diesel Suburban, so I offered to buy it. My parents gave it to me because I always fixed it for them for free. So the price was right but the old girl needed some help. Nobody would ever accuse the LO3 5.0L (305 TBI) V8 of being a rocket in a 4500 lb car, especially when pulling 3.08 gears, but it was particularly sluggish when I brought it home and it had no heat and it only managed 13 MPG. I gave it a tuneup, replaced the thermostat (I installed a 205* unit instead of the factory 190* thermostat), I replaced the worn out O2 sensor and re-calibrated the TPS down to 0.62v at idle to make the computer run the engine a little leaner. I also replaced the tires with Yokohama Geolander HT/S tires in the LT 215-75-R15 and run them at the full 50 psi. This doubled my fuel economy to 26 mpg highway on a trip to Disneyworld with the family on a 2,100 mile round trip. Around town it is averaging about 20 MPG. I recently took a trip to building supply liquidator in Readding PA to buy replacement windows for my house and despite the weight of 10 windows (2 of which ended up on the roof rack) it averaged 23.1 MPG for the trip. I can do better, but since I try to keep with the flow of traffic and generally cruise at 5 MPH over the limit I think these numbers are reasonable as a starting point. Since I live in a rural area and sometimes need to travel on unimproved roads, lowering the car is not an option. Also, as a mechanic/shop teacher I always travel with about 100 lbs of tools in my traveling tool box. I intend to modify the TBI unit for more efficiency by installing smaller injectors and boosting the fuel pressure to compensate because higher pressure with smaller injectors should provide better atomization. I plan to use the injectors for the 4.3L V6 and a pump for an LT1. I might convert to a 6.2L diesel like my Suburban has. I custom built that for fuel economy and get 27 mpg with the Sub. Stay tuned...