What are the downsides to disabling the A, B, C elevation tables?

[thunder550]

I live at 7400 ft and I'm trying to figure out the best way to get a DSP5 tune set up to work here. The issue that I'm up against is that the barometer here at my elevation reads about 11.2-11.3 psi, which would put me into the A tables for boost and B tables for timing. Since the DSP switching only happens in the C tables, essentially this means that even with a standard DSP tune, I'll never run in any of the tables other than A regardless of switch position.

The only potential solution that I have read about that would allow me to actually have DSP switching functionality here at elevation is to lower the barometer values in B2203 and B0907 so that the ECM always uses the C tables regardless of what elevation I'm running at.

What kind of problems would I run into setting up a tune like this?

[LB72004]

you may have too much timing if you drive down to a lower elevation, but you can have one of your DSP tune set up for that. you just have to remember to switch it

[THEFERMANATOR]

I've only been up to around 6000 feet, but noticed no real drawbacks to running just the one set of tables. Just go into the baro tables and set them to a low value so it stays in the C table.

[thunder550]

Thanks guys. I made the changes to the baro tables, everything seems good so far.

[killerbee]

It is a VGT aid. Before 04-05, it was not necessary because the wastegate (LB7) serves to put a hard limit on the turbine shaft. With no wastegate (LLY), the tables you mention protect the turbocharger as we climb through them. Note the stepdown in performance level as elevation increases on the stock tune. If there were only one set of parameters, the turbo would experience harder working conditions at higher elevation, increasing the failure rate.

[DURAtotheMAX]

For the past year I lived in Jackson Hole (wyoming), IIRC its about 6500' MSL. Because my defuel interface for my ESC/TCS (electronic stability control/traction control...IE, stabilitrak) retrofit used the baro sensor input to control defuel during TCS/ESC events (it was the easiest way to translate torque reduction requests from the ABS module to the ECM, without having to reverse engineer J1939 CAN), whenever the truck was driving normally (IE, in control/not sliding and TCS/ESC inactive), my little interface module would just send the ECM a sea-level reading on the baro sensor input. And then when torque-reduction was requested from the ABS module during an ESC or TCS event, my translator module would send the ECM a faked signal that represented anywhere from 10psi baro pressure (maximum defuel) to 13psi (minimum defuel) based on how much torque reduction is requested by the ABS module. I then tuned the "max injected fuel quantity vs. baro pressure" table accordingly to reproduce a variable defuel input that works perfectly in sync with the ABS module.

But anyway. What that meant was, when I was living in Wyoming (and the truck wasnt fishtailing/ESC active), the actual barometric pressure was probably 11psi or so, but the ECM thought it was 14.7psi because my ABS translator module was feeding the ECM a "no defuel requested" command.

I never noticed any issues, other than I had to retune the "C" (sea level) vane position tables a bit so the ECM would add a bit more vane position down low to help spool up at altitude.

I just moved back to connecticut a couple weeks ago, so now Im just going to retune the tables back to "actual" sea level values.

Ben

[thunder550]

Yeah I just disabled my Baro tables by setting them to always run in the C tables. I haven't had any issues yet, and now the DSP5 is working as it should.