Hello all new to th forum and have ran into a dead end. I've got a 97 expedition 4" lift and 35" BFg a/t. The rig had a factory 4.6 and the previous owner put in a 99 5.4, I've fixed a lot of sensors that wheren't hooked and have a gryphon with custom tunes for the motor/trans. It has 21/2" exhaust with a Holley terminator muffler and theres no cats (not my doing). I just replaced the stock 8.8 with a 9.75 that has 3.73 gears because I pull my camper which is 6k and I haul cars off and on. I run full syn oil in the motor and the diff.
Here's the problem. When I got this rig a year ago it had 7" of lift and 37" ssr on it. I drove it a lot like that and got on average 16mpg highway and 11-12 city. Well I took the 3" body lift off and stuck the 35's on and took a hit in highway mpg but my city went up. I'm averaging 13-14 in town and 5-8 highway. Then only codes I've come up with where p0420 p0430 and p1000. All the codes are taken care of now and the mpg hasn't changed. I'm pulling about 15-1600 rpm's going 60-65 and 18-1900 going 70-75 and the mpg is bad. I can't for the life of me under stand why the change I figured my highway would atleast stay the same. Only thing I can think of is the egr??
Here's the problem. When I got this rig a year ago it had 7" of lift and 37" ssr on it. I drove it a lot like that and got on average 16mpg highway and 11-12 city. Well I took the 3" body lift off and stuck the 35's on and took a hit in highway mpg but my city went up. I'm averaging 13-14 in town and 5-8 highway. Then only codes I've come up with where p0420 p0430 and p1000. All the codes are taken care of now and the mpg hasn't changed. I'm pulling about 15-1600 rpm's going 60-65 and 18-1900 going 70-75 and the mpg is bad. I can't for the life of me under stand why the change I figured my highway would atleast stay the same. Only thing I can think of is the egr??
