![]() ![]() You can read the fuel pressure without having to hook up a fuel pressure gauge to the line. On some models, you’ll even find a fuel rail pressure sensor (FRP), this sensor is reading fuel rail pressure just as it would be with an external gauge. The temperature is another reading the PCM will use to determine if and when it is appropriate to run the EVAP monitor. A fuel temperature sensor does as the name implies. The PCM has a preset calculation for the amount of bleed down time it will look for to determine the actual fuel tank pressure.įuel temperature sensors are quite popular now too. It’s a small amount of pressure that is applied (.25 psi or more) but it’s enough to run the EVAP monitor. These systems are called “return-less systems” (no fuel travels back to the tank) and are widely used on most of the today’s modern cars. A small reed valve allows the air only to go in one direction which allows the internal pressure to rise in the fuel tank system. The LDP (leak detection pump) uses vacuum to pull a small diaphragm up and down, then releases the vacuum to make its opposing chamber draw in ambient air and force that air into the fuel tank system. On vehicles that use pressure to perform the EVAP monitor test, a small vacuum operated air pressure pump is used. Since the job of the EVAP system is to reduce emissions, it stands to reason if there are any emission related codes stored in the PCM the eventual outcome of the EVAP test would be inaccurate. The last, but most important, thing is there cannot be any other fault codes stored in the PCM. Most of the systems are set up to only run the test with the vehicle under 35 mph so tank slosh is kept to a minimum. Hg on most GM vehicles (8,000 to 10,000 feet above sea level). The barometric pressure must fall between 22 in. The air temperature in the tank will affect the fuel vapors. The ambient air temperature needs to be between 40 and 100 degrees for most vehicles and the fuel level needs to be near a half a full tank. There are a lot of factors that have to be correct for the PCM to carry out the EVAP monitor. Chrysler, most European and a few Asian products use pressure to run the monitors. Ford, GM and some Asian imports use a vacuum to run the monitor. These EVAP monitors can be run in two different ways. When the PCM receives a signal from the FTP that there is excessive tank pressure or vacuum the PCM will then send a signal to the EVAP purge solenoid to correct the fuel tank pressure level. The FTP (fuel tank pressure) sensor is used to measure the pressure during the EVAP monitor test. Most vehicles today will have a fuel tank pressure sensor, or in some cases it will be called an EVAP pressure/vacuum sensor. A smoke machine works well in these cases. DTC P0442 for a small leak can be hard to find. If it fails, the PCM will attempt to run the monitor at least three times before setting the code again. The calculated change in fuel tank vacuum is compared to a calibrated value preset in the PCM for a leak as small as. If the leak is taken care of and the target vacuum has obtained the change in the fuel tank, vacuum (bleed-up) will be calculated for a calibrated period. The EVAP running loss system monitor will abort and not continue with the leak check portion of its test. A secondary code is usually associated with it (DTC P1450 Unable to bleed-up fuel tank vacuum). If a P0455 is set the EVAP monitoring system will shut down and not run its self-test. ![]() ![]() P0457 is the more direct code for the fuel cap not installed correctly, but either code means a large leak. “Gross,” meaning large, leak can be an indication of a leak or more than likely an operator error (forgetting to put the gas cap back on correctly). It’s almost impossible to talk about fuel systems without getting into EVAP systems as well. ![]()
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |