There is NO activity on the GMC Yukon Chevy Tahoe forum. I signed up months ago and there has been no replies and no new threads in months.
I use to own a 1997 GMC Yukon I ordered it from the factory with a fuel economy chip. It was getting 18.5 mpg in town and 24 on the highway when I sold it with 200,000. miles on it.
Now I own a 1999 Chevy Tahoe. This is identical to the GMC Yukon only difference is I get poor gas mileage it probably has NO fuel economy chip. I bought it used with 95,000. miles on it. It was getting about 17 to 18 mph when I first bought it then the mpg went down down down. The service engine light came on and Auto Zone pulled code on the computer and it said I have an air leak.
Gas mileage was down to 9 mph. A new gas cap bought the gas mileage up to 11 mph. I disconnected the battery cable over night and put it on again next morning and the service engine light went off. The heater has not getting very hot in the winter and the thermostate guage reads 120 degrees. I replaced the old thermostate with a new 195 degree thermostate and gas mileage came up to 14 mpg the dash guage was reading 140 degrees. Next I replaced the temperature sensor that tells the computer how hot the engine is the dash guage now reads 160 degrees and gas mileage came up to 15.1 mpg in town and 17.2 on the highway. Next I put in a new high CFM air filter no change in the mpg. New sparks plugs did not change MPG either. The engine now has 108,000. miles on it.
Engine back fires when I start it. I park in the garage all night next morning it back fires. I stop at the grocery store or a restaurant for 45 minutes engine back fires when I start it. Back fire is small now but in colder weather the back fire was louder.
What else can I do to get my mpg up much higher???
I would love to have 24 mph like the GMC had.