Tuning Facts - Understand Your 4Runner Like We Do at CAMTuning

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[CAMTuning]

Session 3:
What the ECU Is Doing When You See Throttle Closure

Sometimes when you’re reviewing a log, you’ll notice something that doesn’t quite match what your foot is doing.

The accelerator is down…
but the throttle isn’t fully open.

That can raise questions — especially if you’re new to looking at ECU data.

Let’s clear it up.

The Short Version

On the 2.4T Tacoma / 4Runner, the throttle is not a direct link to your foot.

It’s a torque management device.

This is not unique to Toyota.
Modern Ford and Volkswagen platforms use the throttle the same way — even at wide-open pedal.

The ECU uses throttle position as one of several tools to deliver the correct amount of torque for the current conditions.

Seeing throttle movement in a log is normal ECU behavior, not a problem by itself.

What Throttle Closure Is (And Isn’t)

Throttle closure is:

• A normal torque control strategy
• Used across modern OEM platforms
• Part of how the ECU keeps power smooth and predictable

Throttle closure is not:

• A malfunction
• A sign of engine knock
• The ECU “fighting” the tune
• Something unique to tuned trucks

If you’ve logged a modern Ford or VW, you’ve seen this before — even on factory or OEM-performance calibrations.

Why the ECU Uses the Throttle

The ECU is constantly balancing:

• Requested torque
• Available airflow
• Operating conditions (gear, speed, temperature)
• Drivetrain protection

If delivering more airflow would exceed its internal torque model, the throttle is one of the cleanest and fastest ways to stay in control.

Spark, boost, and throttle all work together — the ECU simply uses whichever tool makes the most sense at that moment.

How This Relates to Knock Learning

Knock control and torque control are closely linked.

If the ECU becomes more conservative under certain conditions, it may adjust torque delivery.

Throttle position is one of several ways it does this — alongside spark and boost control.

This doesn’t mean knock is occurring.
It means the ECU is managing output intentionally.

What To Do This Week

If you notice throttle movement in a log, look at it in context:

• Throttle angle vs pedal position
• Gear
• Intake Air Temperature
• KCLV and KCA trends

Single events don’t tell much.
Patterns do.

Closing Thought

Throttle closure isn’t something to eliminate.

It’s one of the tools modern ECUs — Toyota, Ford, and VW alike — use to keep power consistent, smooth, and repeatable in the real world.

Once you understand why it happens,
it becomes useful information — not a concern.

 

[CAMTuning]

Session 4:
Fuel Trims, Rich vs Lean, and Why Boost Changes Everything
Fueling is one of the clearest windows into how healthy a calibration really is—if you know what you’re looking at.
Modern Toyota ECUs manage fuel using two main correction layers:
Short-Term Fuel Trim (STFT)
Fast, real-time adjustments used during light-load, closed-loop operation to keep fueling on target.
Long-Term Fuel Trim (LTFT)
Slower, learned corrections that reflect how the engine typically behaves over time.
Together, they tell you whether the ECU is making small refinements—or compensating for a deeper mismatch.
Rich vs Lean (in simple terms)

• Lean = less fuel than expected
• Rich = more fuel than expected

Neither is inherently wrong on its own. What matters is where in the operating range it happens.
At cruise and light throttle, the ECU intentionally targets an efficient mixture and uses trims to stay there.
Under boost, the strategy changes.
Why enrichment under boost matters
As load and cylinder pressure rise, combustion temperatures increase. To protect the engine and maintain consistent torque, the calibration transitions away from trim-based correction and into a commanded enrichment strategy. At this time the fueling target will become richer (.75 to .85 lambda: 11-12.5:1 AFR on gasoline).

• There are no short-term fuel trims under boost
• The ECU relies on modeled airflow and commanded fuel targets
• Any learned long-term fuel trims can still be carried into higher load

If those learned trims are large, they can unintentionally influence fueling where accuracy matters most.
A healthy calibration:

• Has minimal long-term correction
• Transitions cleanly into enrichment
• Delivers predictable fueling under load without chasing compensation

Discussion encouraged:
What questions do you have about fueling, trims, or air/fuel behavior that you’ve never gotten a clear answer to?

 

[CAMTuning]

Session 5:
Shift Schedules: RPM vs Output Shaft Speed (And Why Your Truck Feels the Way It Does)
If you’ve ever thought “this truck should’ve shifted already” or “why did it short-shift there?” — this post is for you.
Most people assume automatic transmissions shift purely based on engine RPM.
In reality, modern Toyota transmissions care much more about Output Shaft Speed (OSS).
What’s the difference?

• Engine RPM tells you how fast the engine is spinning.
• Output Shaft Speed tells the transmission how fast the vehicle is actually moving through the gears.

OSS accounts for:

• Gear ratio
• Torque converter behavior
• Tire size
• Load
• Throttle input

That makes it a far more reliable signal for deciding when to shift.
Why this matters for drivability
Because shift schedules are often based on OSS:

• Two pulls to the same RPM can shift at different road speeds
• The truck may hold a gear longer under load, even at the same RPM
• Light throttle can cause earlier, smoother shifts
• Heavy throttle can delay shifts without increasing RPM targets

This is why changing engine power alone doesn’t always change how the truck feels to drive.
What tuning can (and can’t) influence
A refined calibration aligns:

• Torque delivery
• Throttle behavior
• Shift timing

When these agree with the OSS-based strategy, the result is:

• Fewer “busy” shifts
• More predictable downshifts
• Better part-throttle smoothness
• A transmission that feels like it’s anticipating your intent

Discussion encouraged:
Have you noticed situations where the truck feels like it “should’ve shifted” but didn’t—or shifted when you didn’t expect it to?

 

[CAMTuning]

Session 6: Rotating Weight: Why Bigger Tires Feel Like Lost Power (and How Tuning Gets It Back)

Let’s take a quick break from sensors, trims, and tables and talk about something you can feel immediately behind the wheel: rotating weight.

Earlier this week I had a Tacoma on the dyno running significantly heavier tire and wheel combo than stock. No engine changes. Same truck. Same dyno. The only variable was rotating mass.
(These tires are ~65lbs each, on factory wheels)
The baseline result was exactly what you’d expect:

• Lower measured power
• Slower acceleration
• A drivetrain that had to work harder to do the same job

But here’s the part most people miss.

That “lost power” isn’t gone — it’s being used.

Why rotating weight matters more than vehicle weight

Rotating mass (tires, wheels, driveshafts) doesn’t just need to be moved forward — it has to be spun. That means:

• More torque required to accelerate
• More load on the engine and transmission
• Slower rate of RPM change
• Heavier demand during shifts

This is why trucks often feel:

• Sluggish after tire upgrades
• Lazy to downshift
• Less responsive at part throttle

What the dyno showed

Despite the heavier setup, once calibrated correctly:

• Torque gains were equal to—or better than—stock-tire trucks
• Throttle response improved noticeably
• The power curve became smoother and more usable

The tune didn’t “add magic horsepower.”
It reclaimed efficiency that the stock calibration wasn’t designed to preserve with heavier rotating mass.


OEM calibrations are built for factory tires.
Once you change that equation, the strategy needs to change too.

The takeaway

Big tires don’t ruin performance — unaddressed calibration does.

When torque delivery, throttle behavior, and shift strategy are aligned for the added rotating mass, the truck stops feeling heavy and starts feeling intentional again.

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