UPDATED
I have a 97 JDM HDJ81V 1HD-FT. I deleted the EGR system some time ago, and now installed a PDI FMIC and 18 PSI spring in the Mamba turbo, so I am using this opportunity to clean up and simplify the vacuum system.
My stock configuration was as follows, without the additional BACS valve in the L/EGR box
Translated into a simpler diagram, it looks like this:
What is the function of the EVRV (25819)?
Here is what I understand so far:
1. The EVRV receives engine vacuum through the blue line and then, through the Emission Control ECU regulates the vacuum (negative) pressure through to orange port.
2. The BACS VSV is on by default, which means it pulls the boost compensator diaphram down, further increasing fuel. When the truck reaches a specific altitude, the BACS VSV shuts off, thus reducing fuel. What controls the BACS VSV?
3. The EGR system controls the two EGR VSVs, which use vacuum from the EVRV to turn on EGR valves.
4. The blue VSV simply switches what the TPS measures - vacuum or boost. When there is no voltage on it, ports 2 and 3 are bridged, so the TPS measures vacuum that is supplied through the EVRV. When 12V is applied to it, ports 1 and 2 are bridged, so the TPS measures boost.
This means that the EGR ECU regulates the degree of vacuum that the EVRV lets through to the BACS and whether or not the BACS VSV is on. On the JDM non-EGR configuations (L/EGR box on the first diagram), the BACS is controled through an altitude compensator valve, which unfortunately is out of production and I haven't found one. Even without it, people seem to be connecting vacuum directly to BACS, bypassing the BACS VSV, and if there is too much smoke, increasing the tension on the boost compensator spring. Basically, the following configuration:
To avoid the EGR throwing an error code, the EGR ECU is disabled by disconnecting the following pins on the ECU harness:
I have a 97 JDM HDJ81V 1HD-FT. I deleted the EGR system some time ago, and now installed a PDI FMIC and 18 PSI spring in the Mamba turbo, so I am using this opportunity to clean up and simplify the vacuum system.
My stock configuration was as follows, without the additional BACS valve in the L/EGR box
Translated into a simpler diagram, it looks like this:
What is the function of the EVRV (25819)?
Here is what I understand so far:
1. The EVRV receives engine vacuum through the blue line and then, through the Emission Control ECU regulates the vacuum (negative) pressure through to orange port.
2. The BACS VSV is on by default, which means it pulls the boost compensator diaphram down, further increasing fuel. When the truck reaches a specific altitude, the BACS VSV shuts off, thus reducing fuel. What controls the BACS VSV?
3. The EGR system controls the two EGR VSVs, which use vacuum from the EVRV to turn on EGR valves.
4. The blue VSV simply switches what the TPS measures - vacuum or boost. When there is no voltage on it, ports 2 and 3 are bridged, so the TPS measures vacuum that is supplied through the EVRV. When 12V is applied to it, ports 1 and 2 are bridged, so the TPS measures boost.
This means that the EGR ECU regulates the degree of vacuum that the EVRV lets through to the BACS and whether or not the BACS VSV is on. On the JDM non-EGR configuations (L/EGR box on the first diagram), the BACS is controled through an altitude compensator valve, which unfortunately is out of production and I haven't found one. Even without it, people seem to be connecting vacuum directly to BACS, bypassing the BACS VSV, and if there is too much smoke, increasing the tension on the boost compensator spring. Basically, the following configuration:
To avoid the EGR throwing an error code, the EGR ECU is disabled by disconnecting the following pins on the ECU harness:
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