My 98 4.6 with 150,000 miles has developed a strong gas smell from the exhaust at startup. Also my mpg is erratic. I got 17 mpg on a recent trip but have got 12 mpg on the same route.I've had the truck for 120,000 mile and have never cleaned the EGR or replaced the O2 sensors but I have used Seafoam in it. The engine does not smoke at all and uses about a quart of oil every 3000 miles. Any help is greatly appreiciated.

 

have you tried the tune up and fuel filters and all that happy stuff

 

I replaced the plugs,wires,pcv,and fuel filter last summer. As far as I know that's a tune up on this engine.

 

If it is only at startup then its just running a bit rich. Have you checked everywhere for any gas leaks. Try this it may sound silly but it can work. Start the truck and allow it to idle for at least 30 mins. or longer. Don't touch anything just let it sit and idle. I had a friend leave his running (he forgot to shut it off) for at least 45 mins. and when he shut it off then got back in later he said he could not believe it runs better. I don't know if it will work but what the hell he even said his gas mileage is up a little. ??? . I get about 385-400 miles to a tank in my 4.6 1997 5 speed around 19-20 miles per gallon with 100,000 on the clock.