| Automotive diagnostic strategies: | | | | know how much exhaust gas is being recirculated into |
| Barometric pressure, manifold pressure, intake air | | | | the cylinders to effectively know the real weight of the |
| temperature, volumetric efficiency and exhaust gas | | | | air in the chamber. This action performed by the EGR |
| recirculation these items are all involved along with | | | | system actually cools the cylinders to reduce NOX |
| modifiers like battery voltage, coolant temperature and | | | | emissions and engine ping. Modifiers tweak the |
| throttle position. Of course you have to look at trim, | | | | calculated values to compensate for operating |
| short term fuel trim and the adaptive strategy being | | | | conditions that always change. I recommend a good |
| long term fuel trim. The most important input to the | | | | emissions shop for any repair EGR related. |
| PCM needs for most any calculation is engine speed. | | | | -Battery voltage, the PCM looks at battery voltage as |
| This input comes from a sensor that is located in the | | | | an input to modify parameters, which is important to all |
| distributor. The PCM must see what the engineer | | | | systems and will maintain fuel efficiency and catalyst. |
| designed it to see of the vehicle won't run. | | | | Therefore a good battery in is crucial to all operating |
| -Barometric pressure, when the key is first turned to | | | | systems! |
| the on position, the PCM reads the BARO sensor to | | | | -Coolant temperature, when cold the engine coolant |
| determine the altitude the vehicle will be operating at. | | | | temperature or (ECT) will cause the PCM to add time |
| Higher altitudes have less dense air and less molecules | | | | to the base pulse width or (BPW) to compensate for |
| of oxygen in a given volume of air. | | | | lack & fuel vaporization. The PCM will never subtract |
| -Manifold absolute pressure or (MAP) is the | | | | time for BPW, it will only add. The ECT is the main |
| measurement of potential air. This measurement tells | | | | control sensor when the engine is cold or in closed |
| the PCM how much air is ready to enter the | | | | loop. When the engine warms up, it remains in closed |
| combustion chamber when the intake valve opens. | | | | loop and the o2 or oxygen sensor takes charge. |
| -Intake air temperature or (IAT) hot air is less dense | | | | -Throttle position sensor or (TPS) affect the BPW in |
| than cold air. Volumetric efficiency, this value is stored | | | | two ways. The PCM looks at throttle position to |
| in the PROM. It is a value measured by the engineer | | | | determine which strategy to use (idle, cruise or wide |
| when the vehicle was developed that represents the | | | | open throttle). The PCM looks for rate of change from |
| amount of air that has the ability to enter the cylinder | | | | the TPS to effect BPW and cause either and |
| on the intake stroke at a given rpm.- | | | | accelerator pump effect or a fuel cut effect. |
| -Exhaust gas recirculation or (EGR) the PCM needs to | | | | |