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Thread: 3800SC Manual Transmission - Low RPM, Low Boost, AFR Tuning

  1. #1
    Potential Tuner
    Join Date
    Dec 2014

    Question 3800SC Manual Transmission - Low RPM, Low Boost, AFR Tuning

    Hi All,

    Vehicle is a Fiero with 3800SC swapped in with manual transmission. Engine has a 3.4 pulley, 1.9 rockers, headers, 180 t-stat, cold air intake 3.5" piping with K&N, Autolite 104's, tuned the MAF with wideband.

    Is there a way to control PE mode by kPa in the HPT 3800 software? With a manual transmission I think this additional control would be great. Or do we fall back on remapping the O/L AFR Adder table?

    Here's the scenario:
    With the manual and smaller pulley I'm into boost at low rpm under medium load in the higher gears. In 4th or 5th at 20% TPS she can hit 118kPa in certain situations, 123kPa at 25% TPS and 135kPa at 30% TPS. These are somewhat common passing situations in a manual. Yes, I did see KR when in these low TPS and >100kPa scenarios. Could see 4* KR at 2000rpm, 25% TPS and 120kPa type situations. This is no good. Don't want the KR and I think this could create a bad situation going from here to WOT since I'm starting out lean, building heat and then trying to catch up with everything.

    As option 1 my plan was:
    Set the PE to come in early (20% from 1,600rpm and up)
    Remap the AFR TPS Adder table and RPM Adder tables to ramp the AFR in from 14.7 to 13.0 to 12.5 to 12.0 ..... to 11.0 as TPS% increases

    Setting it this way at TPS above 20% out of boost this means she will be slightly rich (13.0) when at medium throttle under light load and <100kPa.

    FYI, most around town and highway cruising happens at <10% TPS. Highway looks like 4-8% TPS at 60-70mph. So fuel mileage should still be fine.

    As option 2 my plan was:
    Set the PE to come in early (20% TPS, but keep 14.7 AFR (via the adders) up to 30 or 35% TPS)
    Leave PE AFR TPS Adder and RPM Adder tables alone
    Remap the O/L AFR Adder table to decrease the AFR in the higher Cylinder Airmass cells in the mid-range rpm's so that it would then only add fuel when >100kPa at 20% TPS and not add fuel when below that
    PCM would select lower of the two AFR's in this case, correct? O/L tables versus PE tables

    I haven't looked at correlating the cylinder airmass table to boost and TPS yet. Seems like it should work, but also may not work at all. Still have to study there. I did look at a manual transmission 3800 Firebird stock tune and the O/L AFR Adder table is mapped in just this way. It drops the AFR in all the upper cylinder airmass cells. Drops it a lot in the low rpm, high cyl airmass cells. Since I'm only in the low boost regions, maybe it's similar to a NA motor? Definitely don't want to assume it is without more studying or one of the advanced guys here sharing their knowledge on this.

    All auto tranny stuff and torque management is disabled.

    Any advice, info, feedback would be great.

    Last edited by FieroMan; 5 Days Ago at 10:43 AM.