Poor fuel economy

[Chantz]

On the subject of fuel mileage, I have a 1989 Sub that gets about 12mpg on the highway and about 8-10mpg in town. I recently replaced the plugs, but didn't gap them. Would this be wise to go back and do so? Also, my truck was giving me codes for running rich and an EGR/MAP sensor problem, and now it says it's running lean (code 44). Any reason for this? It has recently been pretty cold (-25 through -30 for a week and a half), but I'm not sure what would have caused this. As well, I've heard that fuel additives can be harmful, as they may remove carbon that is keeping a seal in the cylinders, and that you tend to burn more oil when you use them.

And if anyone has any general tips on how to improve mileage, then I'd be open to suggestions Thanks

[1999burbanite]

I have a 1999 burban and I was getting 9-10.5mpg city/hwy. I put on a K&N air filter and a flowmaster 50 series delta flow muffler. Those two changes took me to 11.5-12.5 in the city. I haven't yet had the chance to go for a long haul to get my freeway mpg yet.

[bigjimdaddy]

consider yourself lucky i only get 9 to 10 mph with 7.4 L. less if towing

[Jimbozcrazy]

I have a 1999 1500 Burb 4X4, I drive like a saint; I mean like an old gray haired, not motivated to go ANYWHERE fast saint and I cant seem to get more than 10.2 MPG out of this pig. It's got a 5.7 Vortec engine with a K&N filter and 3" Flowmaster cat back system on it. The engine runs cold, real cold... thinking that it might not even have a thermostat. Going to check today and make sure it has one, if I can get 13mpg out of this thing, I'd be ecstatic!

Any help or advise would appreciated. (And yeah... I already read the one about driving a smaller vehicle)

[j cAT]

Originally Posted by Jimbozcrazy

I have a 1999 1500 Burb 4X4, I drive like a saint; I mean like an old gray haired, not motivated to go ANYWHERE fast saint and I cant seem to get more than 10.2 MPG out of this pig. It's got a 5.7 Vortec engine with a K&N filter and 3" Flowmaster cat back system on it. The engine runs cold, real cold... thinking that it might not even have a thermostat. Going to check today and make sure it has one, if I can get 13mpg out of this thing, I'd be ecstatic!

Any help or advise would appreciated. (And yeah... I already read the one about driving a smaller vehicle)

the thermostat should be regulating the engine temp at 190deg f.If lower the MPG will suffer.

If you have a loud exhaust this will cause the timing to be retarded. also large sized exhaust pipes have been reported to cause engine issues.

using throttle body cleaner only clean the throttle body and IAC.

Using only MAF cleaner spray the small sensing wires to clean them of contamination. only a slight film of oil/dirt will cause inaccurate metering of air to intake.

DO NOT TOUCH THESE SMALL SENSING WIRES .

you should get 15mpg with that vehicle.