06 mileage drop after spark plug changes, no codes, no leaks, help???

[06sport88]

I have an 06 4.0 sport ranger that has had a drop in gas mileage & power after some tuning up. No codes are thrown.

Tuneup was replacing spark plugs & seafoaming (1/3 in gas, 1/3 in oil, 1/3 in brake booster hose).

MPG calculated every single tank by starting with a 0 mileage trip meter, filling up & diving the trip mileage by gallons of gas. The very next tank after the tuneup resulted in a 3 MPG drop, every tank thereafter continued with the 3 MPG drop.

Diagnostic Info:
- No codes
- Smoke test showed no leaks

Tuneup after this issue:
- Spark plug changes (tried a couple different motorcraft plugs, then autolite plugs, then just had the dealership do the change)
- Changed oil & filter (a few times)
- Changed fuel filter
- Cleaned MAF
- Cleaned IAC
- Cleaned throttle body
- Cleaned EGR
- Replaced front O2 sensors

I'm running out of ideas. Any help?

 

[Big Jim M]

Oh yeah

I have an 06 4.0 sport ranger that has had a drop in gas mileage & power after some tuning up. No codes are thrown.

Tuneup was replacing spark plugs & seafoaming (1/3 in gas, 1/3 in oil, 1/3 in brake booster hose).

MPG calculated every single tank by starting with a 0 mileage trip meter, filling up & driving the trip mileage by gallons of gas. The very next tank after the tuneup resulted in a 3 MPG drop, every tank thereafter continued with the 3 MPG drop.

Diagnostic Info:
- No codes
- Smoke test showed no leaks

Tuneup after this issue:
- Spark plug changes (tried a couple different motorcraft plugs, then autolite plugs, then just had the dealership do the change)
- Changed oil & filter (a few times)
- Changed fuel filter
- Cleaned MAF
- Cleaned IAC
- Cleaned throttle body
- Cleaned EGR
- Replaced front O2 sensors

I'm running out of ideas. Any help?

Checking the milage on every tank is comendable. We all should do the same.
Before the 3mpg drop did you drive zackly the same? Was the rout the same? Have you added more stop and go or shorter trips? Have you MOVED?

If you had it to the dealer, I'm sure he tried to get all your money he could. Sooo I'm guessing the thing is running as built. That's why I think you should investigate any change in driving patterns.
Big JIm

 

[06sport88]

Checking the milage on every tank is comendable. We all should do the same.
Before the 3mpg drop did you drive zackly the same? Was the rout the same? Have you added more stop and go or shorter trips? Have you MOVED?

Comendable? haha thanks, I was thinking more like a bit OCD.

Driving routine is still the same.

The most accurate comparisons are the long highway trips cruising at a consistent speed, I still get about 3 MPG less then I used to.

Before: Averaged 17 MPG a tank. Never hit below 16 MPG with the exception of offroading or towing.
Now: Average 13-14 MPG a tank. Never hit 15 MPG.

The fact that my "now" best is lower than my "old" worst solidifies the possibility of it being a change in driving routine.

If you had it to the dealer, I'm sure he tried to get all your money he could. Sooo I'm guessing the thing is running as built. That's why I think you should investigate any change in driving patterns.
Big JIm

Dealership was a waste of time, they basically said "If there were any problems there would be a code, and it's a truck it will get bad mileage."

I explained to them my concern wasn't the low mileage, but the sudden swift drop in mileage would imply that SOMETHING is not right. They just fell back on the idea that there are no code so there is no problem. I wasn't going to argue too much to try and convince the dealership to take my money.

 

[06sport88]

Bump.