What the Heck!? She's Mad At Me

I got an 07, double cab, 4 liter, 4x. I neglected the thing as I have about 145k and finally got to doing long awaited maintenance last weekend. I changed fluids in both diffs, transfer case, trans flush, spark plugs and changed the serpentine belt. Before the maintenance, I averaged 19 mpg. Since then I've been getting 15-16 mpg. I didn't expect to get better gas mileage but certainly didn't expect it to get worse either. Any ideas?

 

You disconnected the battery, the computer is learning the drive style all over.

 

Thx for the response. I did not disconnect the battery for any reason and don't have a computer that tells me mileage. I do the old fashioned method, calculate it by mileage and how many gallons I've added. Thanks again.

 

Did you put Denso or NGK plugs back in?

 

Denso. Thanks

 

Hmm. Not trying to be insulting, but did you check the gap on the plugs? Also, check under the hood to see if there is a vacuum hose loose or disconnected. Also, check the air filter assembly where it sandwiches together. It may not have gone back together and have a gap throwing off the airflow. I can't see where any of the fluid changes would have caused an issue. Almost has to be related to changing the plugs - at least to me it does.

 

Strange...doesn't make sense.

 

How many tanks of fuel have you tracked? Can you run another tank thru it to verify that you truly lost 4 mpg?

 

Also, is this a K&N air filter or just a paper air filter? If it is a K&N might be too much oil on the MAF sensor.

 

I was also thinking maybe spark plug gap. Did you get Denso K20HR-U11 plugs?

 

I like the vacuum hose idea. Even if you didn't unplug any, just doing all that work around older hoses could have knocked one loose or cracked one.

None of the fluid changes or spark plug changes should cause that big of a difference.

 

There would be a CEL if a hose was off.

 

I truly appreciate all of your questions and insight.

No offense taken, I did check gap and all were at .041. I crosschecked the type of plugs from Chris4x4's how to post and dealer, where I purchased them and they are Denso K20HR-U11.

I did go out and peek for loose hoses and a possible improperly sealed air filter. Filter housing looked good but what I did notice is where the intake goes out through engine compartment has a bad foam seal. I did take it apart to do plugs but it appears that it was that way since build judging by how the foam is pressed. I am at the moment running an oiled K&N filter (since reading here I have an AFE Prodry S on the way). I did notice that when I did do the maintenance last weekend, it seemed I had too much oil on the filter and had to wipe housing down.

I have ran two tanks since my maintenance and will see what the future brings.

I am worried that I may have a bad MAFS since seeing oil and combining that with some questions here. If it is a MAFS, what about does that cost and is it a fairly simple project?

Thanks again!

 

What oil(s) did you use for the fluid changes?

My only other guess is maybe the computer is adjusting to the new plugs

 

Get some MAF cleaner, pull the MAF off and spray it the cleaner on the MAF sensor. DON'T touch the wires inside the MAF. Put it back on. Clean the K&N filter and lightly oil it or wait for the Pro Dry. You can get a roll of seal gasket at Autozone or O'reilly's, etc and fix the gap for the intake at the fender. I am not a betting man, but I feel like that will resolve your issue. Either way, let us know so that if someone else has the issue, they can refer to this thread.

 

Diffs- A dealer sold synthetic Penzoil, 75-90 (something like that) with a bottle of Toyota LS
Transfer- the same Penzoil
Transmission-Toyota ATF WS

 

Put everything back.

 

No kidding! Hopefully cleaning MAFS does it!

 

OP...not trying to troll you but there was a thread just like this last year and it turned out the guy put his belt on inside out so it was slipping...

 

Did not even think of that. Even if it is not the issue, that is a good idea to check.