Two kinds of correction
Haltech's boost control in NSP has two separate sets of corrections, and knowing which one to reach for saves a lot of head scratching.
- Duty cycle corrections change the solenoid duty the ECU commands. Think of them as adjusting how hard the controller pushes, without changing where it's trying to go.
- Target pressure corrections change the boost the ECU is aiming for. They only exist in closed loop mode, because open loop has no target to adjust.
A simple rule we use: if you want a different amount of boost, correct the target. If boost is already right in one condition but drifts off in another, correct the duty so the controller starts from a better place. If you're unsure how open and closed loop differ, read our boost control setup guide first.
Duty cycle corrections
These adjust the base duty cycle in closed loop, or the duty itself in open loop.
| Correction | Changes duty based on | Table | Our advice |
|---|---|---|---|
| Overall | Nothing; it's a single number | Single value, shown on the right of the page | In closed loop it can only take duty away. In open loop it can go either way. Handy for quick global tweaks |
| Air temp | Intake air temperature | Up to 2D | Hot air generally needs a little more duty to hold the same boost, and cold air a little less |
| Coolant temp | Engine coolant temperature | 2D | Useful if the wastegate or turbo behaves differently when the engine is cold |
| Gear | Current gear | 2D | Load and spool change gear to gear, so a small per-gear trim often smooths things out |
| TPS | Throttle position | 2D | Softens duty at partial throttle |
| Flex fuel composition | Ethanol percentage | 2D | Pairs with an ethanol-based target so the base duty keeps up |
| Generic | Any ECU channel you choose | Up to 3D | Enable it and a new tab appears. The escape hatch for anything not covered above |
Target pressure corrections
These move the closed loop target pressure up or down. Most of them are about safety or drivability, and one is about making more power.
| Correction | Adjusts the target based on | Table | Typical use |
|---|---|---|---|
| Overall | Nothing; a single number | Single value, on the right of the page | Reduces the target across the board |
| Air temp | Intake air temperature | 2D | Pull boost back when intake air gets too hot |
| Coolant temp | Coolant temperature | 2D | Pull boost back when the engine is overheating, or before it's warmed up |
| Gear | Current gear | 2D | Less boost in the low gears to help traction |
| TPS | Throttle position | 2D | Lower targets at small throttle openings, so power follows your foot more predictably |
| Flex fuel composition | Ethanol percentage | 2D | More boost when there's more ethanol in the tank |
| Generic | Any channel, under custom conditions you define | Up to 3D | Enable it to get its own tab |
How we use them on a real car
Here's a typical street car on pump gas and E85 with closed loop boost control:
- Get the base right first. Tune the base duty table so boost lands close to target on its own, in a middle gear, on a normal day. Corrections should be small adjustments, not a rescue.
- Gear target. Lower the target in first and second so the tires can actually use what the engine makes. We refine it from logs of wheel speed and engine speed together.
- Air temp and coolant targets. Leave them at zero through the normal range, then taper boost down once temperatures climb past where you're comfortable. This is cheap engine insurance.
- Flex fuel. If the car has an ethanol sensor, add boost with ethanol content on the target side. If the base duty then lags at high ethanol, add a matching duty correction so closed loop doesn't have to make up the whole difference. See how flex fuel control works.
- TPS target. Only if the car feels abrupt at part throttle. Many cars don't need it.
Stacking many corrections at once makes it hard to see why boost is doing what it's doing. Add one at a time, log boost, target and duty together, and confirm each change before the next.
Troubleshooting
| Symptom | Usually |
|---|---|
| Can't find any target pressure corrections | Boost control is in open loop mode |
| Positive overall duty correction does nothing in closed loop | Expected; in closed loop the overall duty correction only subtracts |
| Boost overshoots in one gear only | Base duty too high for that gear; add a negative gear duty correction |
| Boost drops on hot days even though target is fine | Needs a little more duty with air temp, or check the air temp target correction isn't pulling boost too early |
| Boost is fine on gasoline but slow to reach target on E85 | Target raised with ethanol, but base duty wasn't |
If closed loop still hunts after the corrections are sorted, the PID gains are next. Start with proportional gain and integral gain.
FAQ
Should I correct duty or target for gear?
If you want less boost in low gears, use the target correction. If boost is meant to be the same in every gear but isn't, use the duty correction.
Can I use a channel that isn't listed?
Yes. Both families have a generic correction that can use any ECU channel, with up to 3D mapping.
