Crome ECU Injector Offset: Why 1000cc Injectors Won’t Start and How to Fix It

The offset value is everything at cranking

When you swap to much larger injectors on a Crome-tuned Honda and the car refuses to fire — even after pulling plugs, smelling for fuel, and cranking until the battery drops — the injector offset is almost always the problem. Not the fuel map. Not the fuel multiplier. The offset.

What injector dead time actually is

Every fuel injector has a mechanical delay between when the ECU fires its signal and when the pintle physically opens far enough for fuel to flow. That gap is called dead time — also referred to as latency, or just “offset” in Crome’s interface. The ECU compensates by adding extra time to the commanded pulse width, firing the signal early to account for the mechanical delay.

Dead time is not a fixed number. It shrinks as battery voltage rises. A running engine sitting at 14V will see shorter dead times than a cranking engine at 10–11V. That voltage sag during cranking is exactly why the wrong offset causes a complete no-start rather than just a rough idle. Pulse widths at low RPM are already short. If dead time eats most of that window, the injector barely cracks open — or doesn’t open at all. You can crank all day and never smell fuel.

Why jumping from 450cc to 1000cc shifts things dramatically

Larger injectors don’t automatically mean longer dead times — that depends on the specific injector design. But Precision 1000cc units have dead time characteristics that are significantly different from the smaller injectors most Crome tuners encounter first.

After running 450cc injectors with an offset in the 30–60 range without issues, it’s natural to assume the 1000s will land somewhere nearby. They don’t. Those values leave the Precision 1000s effectively closed at cranking voltage. The commanded pulse width minus the actual dead time approaches zero. No amount of fuel multiplier adjustment saves you from that, because the multiplier scales pulse width proportionally — and near-zero scaled up is still near-zero.

The offset range that’s worked for Precision 1000cc units on Crome is in the 110s. That’s a long way from where most people start looking.

The injector selection table — the part that gets missed

Crome has a built-in injector selection table with preconfigured dead time curves for known injectors. The offset field alone is not the whole fix. The injector selection table sets the dead time curve across the battery voltage range; the offset is a coarse trim layered on top of that baseline.

For Precision 1000cc injectors, both have to be correct at the same time. “Precision 1000cc” needs to be selected in the injector table, and the offset needs to be in the 110s. Miss either one and you’re flying blind. The table selection handles the voltage-compensated curve across the RPM and load range; the offset handles the starting point that lets the engine actually fire and hold an idle.

Low impedance injectors on a saturated Honda ECU

Precision 1000cc units are low impedance — around 2 to 2.5 ohms. Honda OBD1 ECUs use saturated injector drivers designed for high-impedance injectors, typically in the 10–16 ohm range. Running low-impedance injectors directly into saturated drivers pushes excessive current through the driver transistors and can destroy them over time.

The common fix is an inline resistor: 10 ohms at 10 watts per injector. This limits current so the saturated driver survives. It works, but the resistor changes the injector’s electrical response and can shift its effective dead time compared to what a proper peak-and-hold driver would produce. A dedicated peak-and-hold driver box is the cleaner long-term solution — it sends a high-current spike to open the injector, then drops to a lower hold current for the rest of the pulse width.

Published dead time specs for a given injector are often tied to one specific driver configuration. The same injector will behave differently through a resistor box than through a peak-and-hold controller. Switch driver methods and expect to revisit dead time settings from scratch.

Finding dead time data when you don’t have a datasheet

Published data for Precision injectors can be hard to track down, especially for older or rebranded units. If you’re starting without specs, bracket it empirically: get the car running with an offset high enough to actually open the injectors, then do a steady light-throttle AFR check once the engine is warm.

Rich at idle and light load but leaning under heavy throttle suggests dead time is set too high. Lean at idle with normal enrichment under load points the other way. Dead time has its biggest proportional effect at low pulse widths — idle and light cruise — and its impact fades as pulse width grows at high load. That pattern makes it relatively straightforward to bracket without a dyno.

Phearable.net maintains a dead time reference table for many common Honda injectors. Fuel Injector Clinic’s Data Match service publishes calibration data for injectors they flow-test. Both are worth checking before dialing in by feel.

Sources

• phearable.net
• hondata.com
• fuelinjectorclinic.com
• hpacademy.com
• akao.co.uk
• hondaswap.com
• d-series.org