What an EMAP sensor tells you
Your MAP sensor reads pressure in the intake manifold. An exhaust manifold pressure sensor, or EMAP, reads it on the other side of the engine, before the turbine. The two numbers together are very useful:
- Turbine efficiency. If exhaust pressure climbs far above boost, the turbine or wastegate may be a restriction, and that often costs power and adds heat.
- Tuning. On Nexus, enabling EMAP unlocks the Engine Pressure Ratio tuning method, which uses both pressures to model how well the engine is filling its cylinders.
Electrically an EMAP sensor is simple: a powered pressure sensor with three wires, 5V supply, signal to the ECU and signal ground.
Installing it without cooking it
The exhaust manifold gets hot enough to destroy a pressure sensor mounted directly to it. The usual approach, and the one we use, is to tap the manifold, run a length of tube away from the heat, and mount the sensor somewhere cooler. The tube itself has to survive those temperatures too, so use metal line near the manifold and route it clear of anything that can melt. Pressure pulses in the exhaust are harsh, which is also why filtering matters below.
Setting it up in NSP
| Node | What it does | Our advice |
|---|---|---|
| Configuration | Holds the sensor calibration. Load a Haltech sensor's calibration with Load from File, or type one in; Save to File keeps a copy | Use the manufacturer's data for a third-party sensor, and save it |
| Filter | How much the signal is smoothed | Exhaust pulses make the raw reading noisy; a filter around 100 ms may be needed |
| Display | Warning Maximum, Display Minimum and Display Maximum | Set the display range to cover what your sensor can read |
| Diagnostics | High and low voltage DTCs, plus minimum and maximum pressure DTCs | Turn on the voltage checks at least |
| Wiring | Assigns the input | Any free AVI; pull-up disabled |
Filtering
Filtering is a trade-off. More filtering makes the value steadier but slower to react, because the ECU is effectively averaging over a longer window. Less filtering reacts faster but lets noise through. Exhaust pressure pulses with every cylinder firing, so EMAP usually needs more smoothing than intake MAP, often in the region of 100 ms. Start there, log it, and reduce it only if the value lags in a way that matters.
Display limits matter more than you'd think
Display Minimum and Display Maximum set where gauges and bars begin and end, and they also set the lowest and highest pressure you'll be allowed to use in settings and tables. Set them too narrow and you'll find your table axes won't go high enough. Warning Maximum is the pressure where EMAP gauges and number displays switch to their warning state.
Diagnostics and protection
Each voltage and pressure diagnostic can be given a DTC severity. That ties it into engine protection, so a sensor fault, or real exhaust pressure getting dangerously high, can trigger a safer tune automatically.
Troubleshooting
| Symptom | Usually |
|---|---|
| Reading jumps around wildly | Not enough filtering |
| Reading lags behind boost changes | Filter set higher than needed |
| Stuck at the top or bottom of range | Wiring fault, or pull-up left enabled |
| Can't enter a high enough value in a table | Display Maximum set too low |
| Sensor failed after a short time | Mounted too close to the manifold; move it further away on a longer line |
FAQ
Do I need EMAP to tune a turbo car?
No, most turbo cars are tuned without one. It's a valuable diagnostic tool, and it's required if you want to use the Engine Pressure Ratio method.
Can I use the same kind of sensor as my MAP sensor?
Many builders do, as long as its range covers the exhaust pressure you expect, which is often higher than boost. Choose the range with some headroom. For more on the intake side, see our manifold pressure and barometric pressure articles.
