Can the AIP's cause bad fuel economy without a fault code?

Hi everyone,
2016 Tundra 5.7L 70K miles
Let me say, first of all, I love my truck. However, it appears that it has been possessed by evil forces.
I'm battling a recent big jump in fuel usage. Consumption has gone from an average 15 mpg (17hwy/12city) since new to an average of 9 mpg. Yikes! Driving habits and load have not changed. I been working on this for about 4 months and have checked/replaced all the obvious culprits:

• New WIX Air filter
• Tire pressures
  
• Vacuum smoke tested (so tight it holds pressure)
• OBD analysis of STFT, LTFT, air flow etc. appeared normal
• New rear shocks
• New tires (lower RR)
• Checked for brake drag / calipers all ok
• Oil change ( I know, just a CYA)
• Spark plugs replaced (old plug gaps were a bit high with age)
• Cleaned throttle body
• MAF replaced
• AFR sensor$ replaced
• Injectors removed and professionally cleaned

One thing that seems strange is that after each engine component change I usually reset the ECU with a battery disconnect and initial mileage would be a reasonable number for the first 20 – 30 miles then get slowly worse.
Possibly ECU might be compensating for STFT trim, perhaps with eventual higher LTFT set point?)

Any ideas on what else I should look into?

I am wondering if the Air Injection pumps can fail and be letting air into the induction side without dropping a code? Kinda like a vacuum leak.

Your help would be much appreciated!

Thanks!

Alan

 

And you going by the truck or hand calculating at fill up? Maybe the truck isn’t calculating MPG correctly?

 

doing both and I have found that the ECU computer tends to be within a few percent of my manual calc's. besides you can never be certain you topped it off at the same point anyway. thx

 

40% increase in fuel consumption is aLOT. If fuel trims are all single digits, my first guess would be a failing sensors that the ecu uses to set fuel flow (maf, iat,map,clt,etc.)When dealing with issues like this, you need to look at o2 readings and FTs. If the ecu is getting bad sensor data it doesn’t up the trims. For example, 20* air gets a lot more fuel than 80* air for the same air flow volume. Also need a reader to confirm ecu is not staying in open loop.
So bad data can force a rich mixture without raising FTs. However, the upstream o2 sensors will show the rich mixture. If the o2 sensor is bad, the FTs usually show it.

Could also be a leak

 

uuuuufff.... If you have an expensive OBD 2 reader, get a full-on diagnostic. If you don't the auto parts stores always have them handy. Have them run a full diagnostic and write down them codes if any. May also be a transmission code that's pending, that's keeping you from shifting past 4th gear. I would second what @lr172 stated about O2 sensors. More specifically the upstream ones/Pre cat. My Celica dropped from 32 to 20 when my oxygen sensors started to go. My Tundra's haven't been replaced as of yet.

 

Thanks, I had my local mechanic do a drive test with a higher level OBD diagnostic running on board and except for a minor difference in the Bank 1/Bank 2 fuel trims they concluded there were no issues. I changed the AFR sensors anyway as you can see from the list of changes. Upstream O2 sensors are actually AFR sensors. Other than the shop charges for that work they were the most expensive part. I have the OBDLinkSX on my laptop and have done a bit of EFI research. The YT Car Care Nut guy has some good vid's. However, I still can't find the issue. Good idea in the tranny issue, I will look.
I am wondering about some sort of drag issue. Is it possible for the front diff to be an issue. I have changed the rear diff fluid last year to an Amsoil full synthetic but not the front diff yet. I guess I will do that next...

 

My truck is 2wd, so I wouldn't know.. someone else with a 4x4 can chime in on that. I would assume the mechanic with a higher level OBD 2 would look at any possible faults besides the usual ones....

 

Wel, if mileage dropped 40% and mechanic says no issues, it is tim to find a new mechanic. You need to find and address the issue, as extended running with excessively rich mixtures will burn up the cats.

did he observe the o2 readings while driving? You cannot diagnose this type of issue with only FTs.