| Fuel/coolant temp PRVR mode is controlled by bit 7 at ROM address 0xFFD3. The default is 1 (fuel temp sensor), setting bit 7 to 0 will switch to coolant temp mode. There are a number of other programmable parameters for PRVR in the ROM: 0xFFC2 - PRVR max RPM
0xFFC3 - PRVR max TP (engine load)
0xFF76 - PRVR min temp for timer #1 at engine start (75C)
0xFF77 - PRVR min temp for timer #2 at engine start (75C)
0xFF78 - PRVR timer #1 (30 seconds from engine start)
0xFF79 - PRVR timer #2 (30 seconds from engine start) From the factory, the PRVR system only uses the first timer. If fuel temp is > 75C at engine start, then the PRVR is activated for 30 seconds.
The second timer allows for a different PRVR activation duration dependent on temperature. There is also a hard-coded hysteresis of 500rpm and 16 TP for the RPM/TP activation points. This is to prevent rapid on/off power cycling of the solenoid when operating close to these points. To change the hysteresis, you'll need to modify source code (i.e. not just a ROM editor) as the ROM address changes between ECU firmware revisions for any hard-coded values. I'll leave disabling the fuel-temp sensor fault-code as an exercise for the reader. ;-)
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22:58:52 06/18/14
