2016 CR-Z Sprintex – fueling issues (large injectors, MAF vs AFM Fuel / deadtime limitations)

Title:

2016 CR-Z Sprintex – Idle fueling issues (large injectors, MAF vs AFM Fuel / deadtime limitations)

Post:

I’m looking for some guidance on idle fueling behavior with a supercharged CR-Z setup.

Vehicle / setup:

• 2016 Honda CR-Z (manual)
• Sprintex supercharger (positive displacement, with bypass)
• KTuner
• DeatschWerks 550cc injectors (also tested a smaller ~410cc set previously)
• Previously running a Takeda Momentum intake (MAF closer to throttle body), now reverted to stock airbox and stock MAF curve

  Takeda Intake also had PCV pre-MAF which may have been contributing to problems. OEM is after MAF

Background:

The car was e-tuned, but I’ve had ongoing issues with idle fueling.

• Initially, fuel trims were very large (±30–50%)
• In the final revision, trims were limited to ±10% (Clamped), which made things look better, but didn’t actually resolve the underlying behavior
• AFR at idle can be brought near stoich, but only with large negative correction
• CMD AFR Vs AFR not tracking well with finished e-tune

Current state (after reverting hardware changes):

I reverted to:

• Stock intake
• Stock MAF curve

Now:

• Idle AFR ≈ stoich
• STFT is still heavily negative (around -25 to -30%)
• Changes to the AFM Fuel table (low mg/stk cells) have very little effect on trims
• Deadtime changes do affect behavior, but not enough to bring trims into a reasonable range
• Missing Injector Scaling in Ktuner for my Vehicle

What I’m seeing / questioning:

It seems like I’m running into a combination of:

• Injector nonlinearity at low pulsewidth (DW550s at idle)
• Deadtime dominating total pulsewidth
• Possibly airflow modeling issues at low load (supercharger bypass / reversion affecting MAF signal?)
• Because of this:

• The ECU can achieve stoich via closed-loop correction
• But the base fueling model appears significantly biased rich at idle
• AFM Fuel adjustments don’t meaningfully move trims in this region

Constraints (KTuner / platform):

• No direct injector scaling (cc/min) adjustment available
• No Speed Density Maps
• Only real injector control is via:

• Deadtime table
• AFM Fuel table

What I’m trying to determine:

• Is this behavior expected with:

• Large injectors (DW550)
• Returnless Honda system
• Low pulsewidth idle region

• At what point should I stop chasing trims at idle and accept some (massive) correction?
• Is it more appropriate to:

• Continue refining deadtime
• Raise idle airflow / idle speed to move out of low PW region
• Or revisit injector sizing entirely? (Had same problem with 410cc Injectors)

• Has anyone seen MAF signal distortion at idle on Sprintex setups due to bypass/reversion, especially with aftermarket intake placement?
• Goal:

  Not necessarily perfect trims, but:

• Stable idle
• Reasonable correction (not pegged)
• Predictable behavior transitioning into load
• AFR Tracking CMD well when driving, +-5-10% Trims overall

Any insight from people familiar with Honda MAF systems, KTuner limitations, or PD supercharger behavior would be appreciated.