When manifold vacuum is high (idle), then the absolute air pressure in the manifold is very low, and the electronic control unit provides less fuel. When manifold vacuum is low (throttle wide open), the absolute air pressure in the manifold is high, and. the electronic control unit provides more fuel.
The intake manifold on MPi models is «dry» collector. Because no fuel enters the manifold, fuel is injected at the rear of the intake valve, so fuel cannot enter the intake manifold absolute pressure sensor to foul the diaphragm, and the fuel trap is not used.
Vacuum values of the absolute air pressure sensor in the intake manifold
Note. All units are in mmHg. (mm Nd).
State | Vacuum mm Hg |
Engine off | Zero |
Idle | 435 - 535 |
For heavy loads | Zero |
Acceleration | «560 - 600 |
Manifold absolute pressure sensor type
Internal diaphragm in the electronic control unit
Adjustment
Adjustment of the absolute air pressure sensor in the intake manifold is not possible.
Influence of external factors
- Excess fuel in the fuel trap (if provided by design) or vacuum hose
- Vacuum leak (intake manifold or other vacuum hoses)
- Vacuum leak in intake manifold absolute pressure sensor hose
- Damaged vacuum hose or connection
- Faulty inlet or outlet valve
- Incorrect idle speed
- Incorrect ignition timing
- Faulty spark plugs (large gaps)
Intake manifold absolute pressure sensor checks (integrated with electronic control unit)
1. The performance of the intake manifold absolute pressure sensor can be assessed using a pressure gauge.
2. Connect "T"-shaped adapter to the vacuum hose that connects the intake manifold to the electronic control unit.
3. Using a short piece of hose, connect a pressure gauge to "T"-shaped adapter connected to the vacuum hose.
Note. The vacuum test must be carried out at the junction of the hose to the intake manifold absolute pressure sensor. If the correct values «vacuum» were obtained elsewhere, this does not prove that the vacuum has reached the electronic control unit.
Evaluation of the absolute air pressure sensor in the intake manifold (IDA)
1. Write down the results of the values «vacuum» (engine off) at idle, under heavy loads and braking. Compare the obtained values with the values given in the table.
2. If the values «vacuum» out of order, check:
3. Clogging of the intake manifold channel leads to a decrease «vacuum».
4. Damaged vacuum tube.
5. Leaky diaphragm (inside the electronic control unit).
6. Mechanical failure of the engine, i.e.:
- Vacuum leak.
- Incorrect valve opening or closing timing (timing belt adjustment)
- Worn piston rings.
Checking the diaphragm and vacuum hose of the electronic control unit
1. Disconnect the vacuum hose from the intake manifold. The other end of the hose must be connected to the electronic control box.
2. Connect the vacuum pump to the pressure gauge by attaching the free end of the vacuum hose.
3. Create a vacuum within 400 and 500 mmHg. (mm Hg). The MAP sensor must hold the vacuum for at least two minutes.
4. If the sensor does not hold vacuum, disconnect the hose from the electronic control unit and connect the vacuum pump to the absolute air pressure sensor in the intake manifold.
5. Create a vacuum within 400 and 500 mmHg. The MAP sensor must hold the vacuum for at least two minutes. If the sensor does not hold a vacuum, then this indicates a malfunction of the intake manifold absolute pressure sensor diaphragm. However, if the vacuum is maintained, then this suggests a malfunction of the vacuum hose.
Note. If the diaphragm fails, it cannot be replaced separately. The electronic control unit will need to be replaced.
If special equipment is not available
1. Check for vacuum in the intake manifold.
2. Check the vacuum tube for damage and inspect its connection to the electronic control unit for signs of damage.
3. Check the vacuum tube connection to the ECU for leaks and make sure the diaphragm is holding pressure.