What EMAP tells you
An EMAP sensor measures pressure in the exhaust manifold, upstream of the turbine. Compare it with intake manifold pressure and you learn a lot about your turbo setup. If exhaust pressure is running far above boost, the turbine or housing is choking the engine, which costs power and adds heat. A close ratio usually means the turbo is sized well for the engine. That makes EMAP useful for checking turbine and housing choices and for tuning strategies that use both MAP and EMAP.
Like a normal MAP sensor, it's a three-wire powered sensor: 5V+ supply, a signal back to the Elite and a signal ground.
Installing it so it lasts
The sensor itself can't live on the manifold. Exhaust gas temperature will destroy it. Instead, the pressure is carried to a remotely mounted sensor through a line, and that line is where most failures happen.
- Use a metal tube for the first section off the manifold, long enough to shed heat before any soft line.
- Add a coil or loop in the tube to give it more length to cool and to absorb vibration.
- Mount the sensor away from the turbo and exhaust, higher than the tap if possible, so condensation drains back toward the manifold.
- Keep the line away from anything that will melt or chafe it. A damaged line reads low or not at all.
Wiring tab
Exhaust Manifold Pressure Input is the pin the sensor signal is wired to. For an external sensor, choose an AVI (analog voltage input).
Calibration tab
Pick the calibration that matches your sensor. ESP ships with a list of common ones. If yours isn't in the list, create a custom calibration from the manufacturer's voltage vs pressure data and save it for next time. With the engine off, EMAP should read about the same as your MAP and barometric pressure. If it doesn't, check the calibration before anything else. Make sure the sensor's range comfortably exceeds the highest exhaust pressure you expect, since exhaust pressure is often higher than boost on a turbo engine. EMAP sensors are usually high-range MAP style sensors, so something in the class of the 5 Bar TI or 7 Bar TI MAP sensor is the kind of range to look at. Confirm the calibration is available in ESP before you buy.
Display tab
| Setting | What it does | Our advice |
|---|---|---|
| Warning Maximum | Any EMAP gauge in ESP flashes red above this pressure | Set just above the highest EMAP you see on a healthy pull |
| Display Minimum | Lowest value an EMAP gauge will show | Display only. It doesn't change the sensor reading |
| Display Maximum | Highest value an EMAP gauge will show | Match it to your sensor's range so the gauge is readable |
Diagnostics tab
These checks spot either a wiring or sensor fault or an exhaust pressure condition that could hurt the engine. Each is off by default, and when Engine Protection is active you can give each one a DTC severity.
| Check | Trips when | DTC | Used for |
|---|---|---|---|
| Raw Min | Signal voltage is below your set value | P0470 | Shorted or open wiring |
| Raw Max | Signal voltage is above your set value | P0471 | Shorted or open wiring |
| Operating Min | EMAP is below your set pressure | P0472 | Unexpectedly low exhaust pressure |
| Operating Max | EMAP is above your set pressure | P0473 | Excessive exhaust back pressure |
Raw Min and Raw Max are only offered when the input is set up as an analog voltage input, which it will be with an AVI.
Worked example
Say you log a few full-boost pulls and see EMAP peak a little above boost pressure. We'd set:
- Raw Min and Raw Max just outside the voltage the sensor actually produces, so they only catch wiring faults.
- Warning Maximum a small margin above that peak, so you notice when something changes.
- Operating Max a bit higher again, as a warning-level DTC first. If it ever trips, look for a stuck wastegate, a boost control fault or a blocked exhaust.
Only move to protective actions that cut power once you're confident the limits don't trip in normal driving.
Troubleshooting
| Symptom | Usually |
|---|---|
| EMAP doesn't match MAP with the engine off | Wrong calibration or sensor range |
| Reading slow or much lower than expected | Leaking, kinked or melted pressure line |
| Reading erratic or drops out | Sensor overheating or a loose connection |
| P0470 or P0471 set | Open or shorted signal, 5V supply or ground |
FAQ
Do I need an EMAP sensor?
Not to run the engine, but it's one of the most useful sensors you can add to a turbo build, especially when choosing or comparing turbine housings.
What's a good exhaust to intake pressure ratio?
It depends on the engine and turbo. Rather than chasing a number, log it across your setup changes and see which one makes the most power for the pressure it creates. If you want a second opinion on your logs, book a free consultation.
Running a Nexus? The NSP version is covered in Exhaust Manifold Pressure for Nexus. Related Elite sensors include boost pressure and exhaust gas temperature.
