Lost MPG, help understanding vacuum readings and cat converters

Afternoon all! So it looks like I'm just about beat on this one I'm hoping a fresh set of eyes can help me look at the clues from a different angle to come up with a solution.

First what am I driving:

• 2008 Tundra 5.7L 2wd with ~170k miles

What started me digging into this engine?

• I have consistently maintained a mixed driving MPG of 17-18 and interstate 70mph of 20-21 mpg since I got this truck. These MPGs are based off the computer and generally confirmed within -2% from manual computations. The important thing though is rock solid reliability for 13 years.
• In August I lost 2 mpg between tanks, manual computations confirmed by computer reset, with no changes to the truck at all.
• In February I lost 2 more mpg, manual confirmed by computer reset, once again not changes to the truck.
• I'm now at 13.5-14.5 mixed driving and highway of 14.5-15.5 mpg. That's a lot of money these days!

What have I looked at?

• Plugs had ~60k miles on them, replaced all 8 with no effect
• No DTCs are pending or thrown.
• Long term trim was ~10% bank 1 ~6% bank 2
  • Upstream 02 sensors were borderline on a few tests so I installed new Denso's on both upstream banks
  • Long term trim relearned at ~7% and ~8% respectively.
  • Change in mpg within uncertainty of calculations ~0.5mpg mixed and highway
• Temperature check on Cat converters with IR thermometer
  • At idle after ~20 minutes
    • outlet = ~380 F
    • Inlet = >605 F
  • So I thought, maybe it's a clogged cat...
• Connected vacuum gage through brake booster line
  • 700 RPM = 24.0" with a +-1.5" flutter
  • 1000 RPM = 24.0" with a +-1.5" flutter
    
  • 1500 RPM = 24.0" with a +-1.5" flutter
    
  • 2000 RPM = 23.5" with a +-1.5" flutter
  • 2500 RPM = 23.0" with a +-1.5" flutter
  • 3000 RPM = 22.5" with a +-1.0" flutter
  • 3500 RPM = 24.0" no flutter
  • 4000 RPM = 24.0" no flutter
  • The flutter causes me a little heartburn but I haven't notice any valve guide issues. I'm also not certain that working through brake booster line is a great choice on this truck. Even so, I wouldn't expect a worn guide to cause that much loss of mpg.
  • The slight drop in vacuum was concerning but the sudden rise to 24.0" with the flutter disappearing leads me to think my cats are fine but there is something I don't understand in this engine.

Edit because I forgot a few things:

• MAF was replaced and throttle body cleaned at same time as 02 sensor replacement.
• Brake rotors were checked for temp differences after first MPG lost and rechecked after second MPG loss. For fun I checked again today and still consistent between all rotors.

So what would you look at next? Do you see an answer to my puzzle that I'm missing? I'm a 283, 327, 350 guy so I get the basics but this engine has enough complexity to leave me scratching my head on what I should be looking at.

Thank you anyone for thoughts, I could sure use a brain storming session.

Edit of an edit just to keep additional information in one spot:

• This thread has helped me find a bad carrier bearing bushing.
• Ran back pressure tests on both banks, both show <1 psi.

 

Drive around for ten minutes then check the temperatures of all your brake discs with your IR gun, you may have something extremely simple like a sticky caliper. Have you greased your U-joints lately? How about servicing the transfer case and differentials?

Start with the inexpensive and simple stuff first.

 

Thank you audiowize, all great points.

I forgot to discuss sone of those in my first post.

• I did check all rotors early on and they were all equivalent.
  Pulled wheels and inspected all four bearings with no noticeable drag. Front passenger had slight difference in sound so I went ahead and replaced it, no change
• Differential was serviced ~40k miles ago, I can pull and look at it again though.

• Ujoint was inspected with no noticeable play but not greased, I don’t believe it has zerks.

Thanks again!

 

The U-joints have grease, I would definitely squirt some in there.

Is your long term fuel trim adding or subtracting fuel?

 

+ LFT on both sides.

As far as the Ujoints go, you had me questioning everything! I just double checked and these are fully sealed units, no zerk to be seen. Maybe they switched on later model years?

 

I know from experience that you will notice a big power loss from a clogged cat. I add a 1987 F150 with the 351HO. It had a Holley double pumper and the factory set the floats too high which ended up clogging the cats. When I took it in the service advisor thought it drove fine. I asked if he had driven a HO. He said no and I said trust me it is not right. After they diagnosed and replaced the cats he called and said it runs like a raped ape.

 

If there are no U joint zerks on your 08, then someone has replaced the u joints. This would be something I would look into.

 

Clean the throttle body and intake thoroughly. Also, the MAF sensor. These are quick to do, not difficult, and may fix your problem.

 

Mike, thank you great ideas for sure. Unfortunately I forget to mention both were done, I cleaned both once then replaced the MAF since it reported a constant flow of ~16-1.8 g/s even with the engine off. Turns out the new new unit does the same though and when I hooked up to a 2010(today) I got the same result as well. Wasted money on that one.

AudioWize, chat doesn't carry well so no sarcasm at all here but I must have won a prize then. That drive train is all OEM and the U-Joints are sealed as sealed can be. Now the 2010 I was just toying with at lunch has zerks but it's a crew cab and 2010 saw powertrain changes including a redesign of rear end bearings. Maybe 2010 saw the zerk additions? Pretty sad mine doesn't include that nice feature, love pumping a little grease in with each oil change. You did put me on to something though, the center support bearing bushing is toast. Bearing feels OK but maybe....

Edited because I hit enter too dang fast.

 

I have a 2008 and it has zerks on the u joints. Someone has been through your driveline, can you tell what kind of u joints they installed?

The OE joints are Spicer, and if you see something in there like Duralasts or something off brand, that could be your answer.

 

Sounds like your truck is running well. The only things that come to my mind regarding mpg that you haven't covered are a fuel leak (which you'd likely have smelled and noticed by now), or accessory drag - any chance AC, alternator, idler pulley, ps pump, etc. are starting to wear and create more drag on the engine?

I didn't see you mention the air filter, but from the sounds of it you probably tend to that quite regularly.

 

Okay I guess I'll jump in and poke something thats not mentioned.
1.)Tire wear
2.)Tire Pressure
3.) Alignment
How are those?

and a few added bonus know some parts were mentioned but just want to confirm.

4.) the inner brake pads hows the wear between the inner and outer per wheel
5.) parking brake is it adjusted right and not dragging

Gremlins
6.) battery terminals clean and tight
7.) does the MPG change if you disconnect the battery for 30mins and while it's unplugged cycle the key on and off twice every 10mins
8.) do you always go to the same fuel station or do you go where ever

 

I have a 08’ Crewmax 4wd and would kill for your mpg’s! I’ll blame it on some good old northeast winter blend gas and my lead foot. I have no idea what part of the country you are in.
However, I have 200k on mine and had a passenger front cat go at about your current mileage. No codes were thrown, only found it when I noticed a little rattle. When I pounded the cat, I heard the guts rattle. Might be worth a try.

 

Dang we got active!

• Audiowize.
  • I've been responsible for every repair done on this truck, if those U-joints were changed someone stole my truck stuck new u-joints in and returned. I could use more vandals like that in my life. Interesting we have different U-Joints on the same year, Mid year redesign maybe. Have you had your truck from day 1?
• Jernik.
  • The air filter is spotless as can be, I always try to start small because I hate tossing out money. Drag isn't a bad idea. Original Idler et al still on the truck, it might be a good time to pull the belt and see if there are any toast bearings. I like the way you think.
• NueveTundra
  • Tire pressure, wear, are GTG. No unusual pulling or near wear so I think alignment is AOK too.
  • Brakes, I haven't looked at the inner pad in a while. Newish pads but worth a look see. Parking brake doesn't have any drag I can feel by hand and I would think that would show up as extra heat or the classic burnt brake smell. I might pull them just to be 100% sure when I replace my carrier bearing though.
  • Battery is GTG
  • I've reset the computer with no change in economy but never using your battery/ignition trick. Heck I'll give it a shot and see.
  • No I mix it up between three or four stations and across state lines. I would love to blame my local source but I don't think that's it
• Malinois
  • I'm feeling more and more like a clogged cat is my most likely culprit. It's the addition of the vacuum flutter that has me thrown on going to far. I beat on them a bit for lunch (no rattle) but I'm thinking maybe it's time to setup a back pressure gage to replace an 02 sensor for a bit. You having a failure at similar mileage only points me more towards it as an option.

Thank you all! If nothing else we're getting one complete list of possibilities going for future confused DIY'rs

 

For anyone following along at home, we have an exciting new chapter!

Ran back pressure tests on both banks, both show <1 psi. Doesn't sound like a plugged cat to me. Still confusing though to see an extreme temp difference on the input vs output with the input being higher. Shaking my head here. So back to square 1ish, odd vacuum flutter, unusual temp response from cats, poor mileage, no apparent cause.

I'll look at accessories and change carrier when it's delivered. Anyone with other obscure tests throw them at me, I'm up for some good engine digging!

 

It could be worth running some potent injector cleaner through your tank (it also doesn't cost a lot). If the fuel trims are pretty much constantly adding fuel, that could indicate fouling in one or more injectors, and that will definitely mess with your fuel economy.

 

A quick google shows this thread: https://www.tundratalk.net/threads/grease-points.87073/page-2
They say 2WD does not have zerks. 4WD does.

 

So I have the same gas mileage as you reported OP. Although mine has 279k and is crewmax 4x4. I get like 13.5-14.5 town and 17-19 Hwy, but I don't drive that much so I usually see 14.

So for ltft on both sides are around 3-6%. Vaccum is around what you see. If you only get only a marginal increase in mgp between town/Hwy it sounds like either its older Fuel injectors or clogged cats.

So if you checked cats then check FI. But the question is how do you check FI pressures? I wonder if you can see that via Techstream. Or can only be seen by hooking up a FI pressure gauge.

Also I would also check fuel pump pressure. Cause if your FI are working good. Then the Fuel pump may be dying a slow death.

 

So I think there is a way from Techstream to check out Fuel Injections number. And also do a fuel test. Now sure if I can get these test on a 2007 Tundra though.

 

The way I have seen injectors tested on the vehicle is to pressurize the fuel system with a pressure gauge attached, then pulse an injector a set number of pulses and read the pressure drop, then repeat for all injectors.

Personally I would just run a high end cleaner through a few tanks of gas (maybe BG 44K or ATS 505CRF).

 

Thanks Barynavb, So when you get similar pressure readings do you see a constant gage flutter as well? To me that screams problem but with variable valve timing I just don't know.

I'll fire up Techstream to compare your readings to mine. Nice to have something to reference that's real world. To be honest, it doesn't look bad to pull the rails. It could be worth my time to just run some pressurized cleaner through each injector to test. A good cleaning never hurt and seeing spray difference can tell a ton more than numbers to my eyes.

Still confused by my cat temps though, something just doesn't make sense. No more working on this one for a week or so though but I'll be back to it soon enough.

 

Post your injectors readings...I'll take some time to get mine and we can compare. Also any other readings you think are relevant Maf, TPS, ITC, whatever.. maybe even take a video and post it. We can compare and see whats the odd one out.

 

Good morning! I played with Techstream but I couldn't find a way to pull the values for all of my injectors. Injector 1 was simple but 2-8 well if they are there as data points I sure couldn't find them. I went ahead and did a screen grab for all sensors, who know maybe someone will catch something I'm missing. I'm not seeing anything but there's a lot here I just don't have any baseline info for. I did try one more test on a whim, I forced the lockup solenoid on and off. I confirmed a 150 RPM rise and drop at ~1500 RPMs. That's within what I consider normal.

All of the values below were taken at idle in park.


Here's to a fast Friday and long weekend.

 

I have been browsing and ran across your post. I am a Ford guy, my son owns the Tundra in my profile. I have a fleet of fords and spend a little time with scanners and learning about the fuel systems and studying the numbers. My thoughts are your fuel trims are way too high. Both long term and short term are adding fuel.
baraynavab posted his lt trims at 3-6% which in my experience is pretty normal. If you have graphing capabilities graph the 02 sensors in closed loop at idle and 1500 rpm. The rear 02 sensors should be a somewhat flat line the front should be pretty active. I don't know about Toyota, but in my Fords, rear 02 problems have a big influence on fuel trims. Fuel injectors and 02 sensors would be my suspects.