Hello guys,
I have some issues with FJ Cruiser 2010, namely too much fuel consumed. Yes I know, drive slower....I have LC100, LC200, 4runner....and other.
I know this is very old topic. However I have spent over 2 years building and moding my FJ. today I was drivind 130km/h and avaraged 30L/100km [80mph/8mpg].
I have no modified intake, but a snorkel. My engine is 30k km old [replaced recently/old one was doing same bad milage] . I run 34" tyres, roof rack and tent. Weight about 2400kg.
I had a 4runner with same setup and it was 18L/100km at 140-150km/h. Same engines, same tyres. LC100 and 200 also performes about 18L...
My car is bought as a near junk, rebuild and engine replaced. Can the ECU have been modded that it influences the MPG!?
Thanks.
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If all your other Toyotas — heavier, even larger — outperform your FJ massively on fuel consumption, something is absolutely wrong mechanically or electronically. If you haven't gotten your problem solved yet.....go over these 5 areas:
1. Tire Size and Gearing Correction
Problem:
You have 34" tires.
Did you regear your differentials? Or recalibrate your speedometer/ECU for the new tire diameter?
Impact:
If you run stock gears (like 3.91 or 4.10) with big 34s:
The engine is working way harder at highway speeds.
Transmission stays in wrong gears.
ECU sees wrong wheel speeds → fueling can be wrong.
Test:
GPS-check your true speed at 100 km/h.
Compare with what your speedometer shows.
If there's a big difference (e.g., speedo says 100, but you're only doing 88 km/h), your MPG reading is totally wrong too — you’re driving slower but burning extra fuel spinning heavy tires.
Solution:
Regear to 4.56 or 4.88 depending on your use (daily vs. off-road heavy).
Reprogram tire size into ECU if possible (Toyota Techstream software can do it, or via a tuner).
2. Aerodynamic Drag
Problem:
Roof rack + tent + snorkel are absolute killers for fuel efficiency.
At 130 km/h (80 mph):
Drag force increases exponentially (not linearly).
The FJ is a brick already — you're adding massive air resistance.
But...
Even with the roof rack and snorkel, your 4Runner did WAY better — so aero drag alone can't explain the terrible 30L/100km.
3. ECU Tune or Sensor Malfunction
You mentioned possible ECU modification. YES — it could absolutely ruin your fueling.
If someone previously:
Flashed a richer performance map
Deleted oxygen sensors (cat-delete tune)
Disabled closed-loop fuel control
Or did a "off-road" tune with super-rich fueling
…it would dump fuel into the engine at all RPMs, destroying MPG.
Tests to run:
Check Long-Term Fuel Trims (LTFT) via OBD-II scanner.
Normal = within ±5%.
If you see -20% trims → ECU is correcting too rich mixture.
Read Air-Fuel Ratio (AFR) live at cruise speed:
Should be ~14.7:1 at cruise.
If it's 12:1 or 11:1 = you're running insanely rich.
Solution:
If trims or AFR are wrong: stock flash the ECU back to OEM Toyota calibration.
Techstream dealer tool, or find a good Toyota tuner who can verify your ECU file.
4. Mechanical Drag: Brakes, Bearings, Driveshaft
Not very common, but:
Dragging brakes, bad wheel bearings, driveshafts at wrong angles (post-lift or axle swap) can absorb horsepower constantly.
Jack up each wheel: spin by hand — should turn freely.
Driveshaft vibration or binding = friction = fuel burn.
5. Fuel System / Sensors
Some supporting things to check:
MAF Sensor dirty? → Overfuels.
O2 sensors old or slow? → Rich or lean readings.
Fuel injectors leaking? → Bad spray pattern = poor combustion = worse MPG.
Hope that's useful.
