FJ Cruiser 2010, rebuild, BAD GAS MILAGE - modded ECU? (2 Viewers)

[bartwarot]

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.

 

[iwashmycar]

At 80mph with all that stuff on it, 8mpg is a little low, but I gotta say...not by much.

Things to look at.

Wheel alignment
Brake calipers - any sticking pistons? This is common as they age on these.
Tires and the tire pressure can have an affect.
Engine temp...is it cold where you are? Does it warm up quick and maintain temp? If not, check thermostat.
Plugs in good shape?
Throttle body clean? MAF clean?

If its running high RPM at that speed, might want to regear.

Lastly, if you are gauging fuel economy by looking at your trip odometer and gas pump, then that is incorrect. Your tires are oversized so they will make it seem like you are traveling less than you actually are. Need to measure your distance traveled using GPS or other more accurate means.

 

[Rockslinger]

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.

View attachment 3831712

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.

 

[-MaTTi-]

Reprogram tire size into ECU if possible (Toyota Techstream software can do it, or via a tuner).

I have never heard/seen this option, have you seen with your own eyes?

 

[Rockslinger]

I have never heard/seen this option, have you seen with your own eyes?

After checking with an old Toyota tech.... actually, you can’t reprogram tire size directly via Techstream. So you're right in being skeptical, but you can correct speed sensor pulse counts.

Tuning software or OBDII tuners can help — some allow tire size entry.

Bottomline the fuel usage being that high is NOT normal — the speedometer should be checked for accuracy; scan fuel trims, and investigate ECU tune history.