What the air bleed is for
The Intake Air Bleed function is built for turbocharged drag cars. A solenoid-controlled valve sits in the intake tract after the turbo. When it opens, it lets some pressurized air escape, so the manifold sees less pressure than the compressor is making. With less resistance on the compressor, the turbo can spin faster while the car is held on the line, and you leave with more shaft speed ready to go.
If a mass air flow sensor is used for fuel or ignition, route the bleed back into the intake after the MAF, not to atmosphere. Air the MAF measured and you then dump overboard never reaches the cylinders, so the ECU thinks the engine is breathing more than it is. It fuels rich and calculates timing from a load figure that's wrong.
Setting it up in ESP
| Setting | What it does | Our advice |
|---|---|---|
| Intake Air Bleed (Wiring tab) | The output that drives the valve | Use a DPO |
| Active State | Low: 0% duty is closed, 100% is open. High reverses that | Default is Low. Change it only if your valve works the opposite way |
| Output Frequency (Settings tab) | How fast the duty signal switches | Default is 23 Hz; the usable range is typically 10 to 1000 Hz. Match the valve maker's spec |
Frequency matters more than people expect. At a low frequency, the valve slams open and shut slowly enough that manifold pressure visibly pulses. Higher frequencies smooth that out, as long as the valve can keep up. For wiring details, see air bleed wiring.
The Intake Air Bleed table
This table, found in the ECU Navigator, sets the duty the valve runs at, which decides how far it opens and how much boost it lets out. You can change its input axis to any channel by selecting the table and pressing F3.
Two axis choices cover most cars:
- Race Time (the default): shape the bleed across the first part of the run.
- Launch Control Output State: the axis only has two values, 0 for off and 1 for on. Put 0% in the off column and 100% in the on column, and the valve opens fully only while launch control is active.
The launch control version is the simplest place to start. It's easy to understand, and the valve can't open by accident once the car is moving. From there, logs of manifold pressure on the line tell you whether you want partial duty or a time-based taper instead. More on the table itself in intake air bleed table.
Troubleshooting
| Symptom | Usually |
|---|---|
| Valve open when it should be closed | Active State set the wrong way for the valve |
| Manifold pressure pulses on the line | Output frequency too low |
| Rich on the line with a MAF car | Bleed venting to atmosphere after the MAF has measured the air |
