Help - 14 MPG to 11 MPG. Out of ideas :-/ - Toyota FJ Cruiser Forum
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post #1 of 29 (permalink) Old 12-22-2018, 01:43 PM Thread Starter
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Help - 14 MPG to 11 MPG. Out of ideas :-/

Here is what is going on. I have a auto 2008 FJ with 137k miles, for the last 3 years I have been averaging 220 miles per tank. Last month I dropped to 190-200 after blowing a rear seals/bearings...or so I thought this was the cause.

while tearing down the rear I noted both rear calipers had pretty good grip on the rotors while removing them even though they were soaked in gear oil (I could also smell the gear oil burning when coming to a stop). Installed new rear bearings, seals, parking shoes, pads, and rotors. Then dialed in the parking brake cable which I regret not replacing as its fairly stretched out.

The end result is now 175 miles per tank.

Power feels about the same, though it feels like I do need more throttle input to maintain the same speed.

Here is some telemetry:
water temp 185-193f
Air intake temps average between 40-67f
Transmission fluid temp 140-155f
tires 36 psi
Washington state with 92 fuel


within the last 8k miles I have done:
rear end bearings brakes as mentioned above
front and rear gear oil
front wheel bearings
all new suspension parts (same ride height)
spark plugs
cleaned maf
cleaned air filter (k&n, nearly no oil sprayed on it)
new battery group 31


other things to mention:
No engine codes
rear hub temps are sub 100 after stopping, rotor pad surface is 180ish, rotor hub is a little less (170ish but cant get a good reading through wheel), outside pad/caliper 200-220ish.
front are a little warmer, but not much.
oil changes between 3k/4k
transmission does have a bit of a whine when center console removed, and a little "chirp" on up shift when cold between 2k-3k rpm slight uphill.
I let my truck hit at minimum 120 water temp before rolling off
extended the factory battery cables with hydraulic crimper/solder to fit group 31 battery so this should be solid
replaced serpentine pulleys about a year ago
rear calipers pressed into bore very smoothly
no trouble starting cold or warm


Thinking of throwing a few new parts at it:
ignition coils
new plugs
fuel pump? (starts fines, revs like a high compression 4.0, idles very smooth around 600)
o2 sensors?


and again this is very recent... my tires are the same, lift is the same. I don't think it is related to rear wheel bearing job... just a really good timing coincidence.


Any ideas would be appreciated


Thanks in advance.
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post #2 of 29 (permalink) Old 12-22-2018, 03:35 PM
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Re: help - 14mpg to 11mpg. out of ideas :-/

Winter blend gas.

After Monday and Tuesday even the calender says WTF


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post #3 of 29 (permalink) Old 12-22-2018, 10:58 PM Thread Starter
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Re: help - 14mpg to 11mpg. out of ideas :-/

dont think winter gas blend would be this bad, never had this issue in the past.
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post #4 of 29 (permalink) Old 12-23-2018, 02:24 AM
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Re: Help - 14 MPG to 11 MPG. Out of ideas :-/

Impressive list, and grasp of temps on so many parts/systems! Did you clean your throttle body? No other idea other than fuel blend...my mpg always takes a hit in winter. If you donít figure this out, and it improves when summer blend return youíll have your answer



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post #5 of 29 (permalink) Old 12-23-2018, 05:08 AM
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I know this sounds too simple, but your latest loss is between 1-2 mpg, which, although frustrating, could have a simple cause. Any changes to tire pressure or truck weight due to mods or cargo increases? Don't discount that the mere onset of cold weather season could be a factor as well as the seasonal fuel blend and telemetry you have presented.

36 PSI is lower than I like to roll for highway driving. Cold weather, altitude changes, or heavy mods and cargo can cause you tires to a have lower PSI than you intended. Sometimes my TPMS light will come on in the mountains and then automatically return to normal at sea level. Airing down even 5 psi could conceivably reduce efficiency by that much. Even adding winter snow chains and other cold weather supplies as cargo or taking an occassional passenger more often can reduce my mileage efficiency by 10%.

Try increasing to 42 psi if your tires and configuration allow for it. I would also drive stripped down of cargo for one refueling cycle just for a scientific baseline and piece of mind. This might help recoup 1 or 2 mpg's until spring or until you find another root cause for lagging performance.

Last edited by i12c; 12-23-2018 at 05:22 AM.
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post #6 of 29 (permalink) Old 12-23-2018, 07:37 AM
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Re: Help - 14 MPG to 11 MPG. Out of ideas :-/

I read years back that FJs were losing mpg because the thermostat was going bad. Now I`m not sure how accurate this is but just throwing it out there if you want to check it out

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post #7 of 29 (permalink) Old 12-23-2018, 09:51 AM
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Re: Help - 14 MPG to 11 MPG. Out of ideas :-/

Maybe consider switching the thermostat as it's a mechanical spring/disc that lets coolant through. Switch back to a Toyota filter. K&N won't help and more than likely to cause gunk down the line. Minimize your idle times. Not sure how long it takes to get to 120* water temp (2 minutes?), but if it's freezing temp you can do a longer start up procedure, but on regular days, shorter idle times have helped (20-30 seconds) and take it easy until your gauges show your up to temp. Bad spark plug gaps might not effect mileage on a whole, but may help the performance in the end. Give it a go! Lastly, make sure to grease any thing in the drive train that needs it. I get about 16mpg year round and 14mpg with A/C on and I'm on heavy wheels and tires. 14 to 11mpg is definitely out of place.
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post #8 of 29 (permalink) Old 12-23-2018, 12:13 PM
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Re: Help - 14 MPG to 11 MPG. Out of ideas :-/

This has been covered here many times in the past, but the #1 cause of poor fuel economy in vehicles with fuel - feedback mixture control systems is fuel-air sensors and oxygen sensors that have reached the end of their useful lives, which is typically around 85k to 120k Miles.

The fuel-air sensors and the mass airflow sensors work together to maintain a 14.7:1 fuel/air ratio. A contaminated MAF will not provide accurate data on the mass of air entering the engine, and worn-out fuel-air sensors will not provide accurate data on the volume of fuel that needs to be injected to achieve the magic 14.7:1 ratio.

1. Make absolutely sure that you have cleaned the tiny, well-concealed MAF sensor elements, and not just the match-head looking intake air temp sensor.

2. Replace both fuel-air sensors, using only OEM Densi parts.

Then, meticulously record your actual fuel consumption over at least four complete tank fills in miles-per-gallon, and not just some nebulous “miles per tank” number.

Post your results here.
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post #9 of 29 (permalink) Old 12-24-2018, 10:47 AM Thread Starter
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Re: Help - 14 MPG to 11 MPG. Out of ideas :-/

Quote:
debFJVT previously said: View Post
Impressive list, and grasp of temps on so many parts/systems! Did you clean your throttle body? No other idea other than fuel blend...my mpg always takes a hit in winter. If you donít figure this out, and it improves when summer blend return youíll have your answer
No I have not. I can give it a look over. Will be posting some more info shortly.
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post #10 of 29 (permalink) Old 12-24-2018, 10:54 AM Thread Starter
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Re: Help - 14 MPG to 11 MPG. Out of ideas :-/

Quote:
i12c previously said: View Post
I know this sounds too simple, but your latest loss is between 1-2 mpg, which, although frustrating, could have a simple cause. Any changes to tire pressure or truck weight due to mods or cargo increases? Don't discount that the mere onset of cold weather season could be a factor as well as the seasonal fuel blend and telemetry you have presented.

36 PSI is lower than I like to roll for highway driving. Cold weather, altitude changes, or heavy mods and cargo can cause you tires to a have lower PSI than you intended. Sometimes my TPMS light will come on in the mountains and then automatically return to normal at sea level. Airing down even 5 psi could conceivably reduce efficiency by that much. Even adding winter snow chains and other cold weather supplies as cargo or taking an occassional passenger more often can reduce my mileage efficiency by 10%.

Try increasing to 42 psi if your tires and configuration allow for it. I would also drive stripped down of cargo for one refueling cycle just for a scientific baseline and piece of mind. This might help recoup 1 or 2 mpg's until spring or until you find another root cause for lagging performance.
chains, booster pack, survival gear, ammo, air comp, medical supplies, and recovery gear are in my rig year round. I have about 300 lbs added.

Did 400 miles since original post, brought psi up to 40 since it was mostly highway... yet me fuel economy dropped even more. tires are rated up to 80 psi, I think I have something else going on. I will post more below shortly.
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