Why am i not getting good MPG?

[Longshot270]

Originally Posted by F150 Man 4Eva

Wow, this is getting pretty technical. Is there any definitive answer to the question, is my K&N setup helping or hurting me? And after all of this, I am assuming that getting lower MPGs on my custom perf. based against the canned tow tune isnt alarming.?.? Thanks again

The K&N setup isn't exactly hurting you but to eliminate the CAI drone Bill has to go to a stock cam advance curve which isn't as good for performance. I would expect that the tow program would have modified cam curves for more performance while also having a richer fuel map to help on towing. With a CAI you usually have to use the richer tow program to keep from running a lean engine. The stock cam settings may be what are lowering mpg.

I also remember that you are running big tires. They are effecting the spark timing by effecting the RPMs.
As Bill said earlier when the RPM is low the engine load goes up resulting in the spark timing getting dropped to lower the chance of detonation. By lowering the timing you also lower both performance and efficiency. If the truck isn't regeared then your timing is getting thrown off because the RPM's aren't high enough. Also since you are slinging around more rubber the load goes even higher, dropping the spark timing even more.