Declining MPG - requesting diagnosis help (1 Viewer)

[tlin]

Over the past ~2 years, my average MPG has steadily dropped from ~15 to ~12.5 as my ride currently sits.

I only ever look at the avg as recorded by the truck, I don't self-calculate it.
I've never reset it.
I've checked the engine air filter, she's clean.
Same tires - air pressure ~38psi.
Since selling our cabin, I've only hunted/camped twice and neither time involved airing down.
Driving style hasn't changed and I'm the only one who drives it.

133K miles, regular oil/oil filter changes every January and August.
I'm overdue to change spark plugs but nothing else comes to mind from a maintenance need standpoint.

I replaced brake rotors and pads all around, I'm considering asking a shop to take it all off and replace it back after ensuring everything goes back clean/right/tight and all mating surfaces are free of debris possibly creating some friction (I won't claim it's impossible I didn't do a perfect job - anything's possible).

A gentlemen (local GX club on FB with a 460) did a carbon cleaning and states his MPGs are now UP ~2 mpg. I didn't find any mention of carbon cleaning in this forum but thought I'd share that.

Any thoughts/recommendations? Love the rig, not getting as much trail/camping time as when I kept it up north but I'd really like to get this bugger figured out.

Cheers!

 

[Rednexus]

12.5 mpg is super low and I usually beat that towing our camper. It should be quite a bit higher.

I'd suggest throwing a OBDII reader that can give you sensor readings and reporting back. Things like looking at long term fuel trim etc will be helpful to know where you are as a "baseline". I would also not be surprised if your upstream O2 sensors, there are problems with the MAF sensors, leaky injectors, etc. It could be any number of things really, but may not actually be a big deal to address.

Regarding carbon cleaning, I've done it using Seafoam on my GX and several other vehicles. It can help on older vehicles where the owner drives very conservative and rarely hits full throttle. It's pretty easy to do a Seafoam treatment and may help with any carbon buildup you might have but I'd be pretty surprised if it carbon buildup the sole reason your MPG dropped.

 

[tlin]

Zero codes. Dumped in some liqui moly, planning on new plugs, cleaning injectors, and getting my brakes inspected.

Cruising on the freeway this morning @ 65mph, onboard showed only 15-18 mpg while cruising...barely touching the gas!

At some point this'll get figured out - hoping this helps others.

 

[Rednexus]

The rig can have issues that won't throw a code. For example it won't throw a rich code until it's adding 25% more fuel than the default ECU mapping calls for. That would cause your poor MPG issues but could be caused by any number of things. Checking the long and short term fuel trims would be a starting point to IDing the issue.