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Thread: 05 grand prix GTP, tune rework

  1. #1
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    05 grand prix GTP, tune rework

    Hey all i got a buddy with a 2005 GTP with stage 1 XS cam, zzp headers, 3.6" pulley, k&n intake, msd wires/coils. He had a tune done online awhile ago and wanted to rework it now he knows i tune, i got the tune file and a quick log yesterday, most seems good but i dont like how the commanded AFR hunts, im used to N/A tuning so just looking for some advice on the boosted aspect. so take a look and throw some feed back at me, i got some stuff i want to readjust but just looking for more insight from the boost vets on here, thanks.dans 06 gtp.hptdans gtp headers 3.6 intake and msd wires coil and cam.hpl

  2. #2
    Tuning Addict 5FDP's Avatar
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    I'd tell him to remove those MSD coils, they are nothing but pure junk. Known for issues later down the line and don't hold up well under high revs.

    As for the tune, it may seem like it AFR hunts because of the way it's set up. It's set for 11 AFR commanded which is good and safe but is TPS is set anywhere from 40-25% depending on RPM, then he has it adding anywhere from 1.5 to .5 on the AFR depending on engine RPM, so it can go up and down quickly. I'm sure whoever tuned the car at first want to make sure it didnt lean out right away as he mashed the gas, then just have it lean back out to 11 AFR commanded once he's past 3500-4000 rpm.
    2016 Silverado CCSB 5.3/6L80e, not as slow but still heavy.

    If you don't post your tune and logs when you have questions you aren't helping yourself.

  3. #3
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    Thanks for the reply 5FDP, yeah i seen the way the afr adder is setup and im not a fan of it, would you recommend zeroing out the closed loop afr adder, set OL afr vs CT to 14.7 at 176/194 instead of 14.3, also what should i set base afr in pe mode for i see its 11 than has the add vs tps set up 1.5 to 40% than 1.2 at 45% than tapers off to .3 at 50% tps, the pe is set at 40% tps as is, so should i zero those tables? i was thinking setting pe afr to 10.7 than lean out to 11.7 progressively after 4500rpm based on the add vs rpm vs time chart, i have not tuned FI 3.8 before only N/A so just seeing where to go, thanks.

  4. #4
    Tuning Addict 5FDP's Avatar
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    I'd just set the PE throttle % to like 50% because 20-40% is what you use just for everyday traffic driving, there isnt a need to be in PE during those situations. The DMW throttle bodys open alot differently than the 97-03 GTP cables throttle bodys. On those years, you could set it at 30-35% without an issue because it was cable opened and didnt need as much throttle opening if that makes any sense. You could do more with less in a way with those cable TB's.


    The only thing I'd zero out is the "ADD vs TPS" table, then leave the Base AFR vs ETC at 11 AFR.

    Adjust the OL table to the fuel you are running, so if you are running E10 fuel set the stoich to 14.1ish and the OL for temps you will run the motor at to the same. And past that you really shouldnt need to adjust much else, the cars going to drop into closed loop as fast as it can, so it's not going to use those tables all the time. You could prolly just leave them stock because it already at 14.2ish at 195? coolant temp.
    2016 Silverado CCSB 5.3/6L80e, not as slow but still heavy.

    If you don't post your tune and logs when you have questions you aren't helping yourself.

  5. #5
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    I have found a very simple approach to get the WOT set to 12.5:1 and LTFT's close to zero. I constantly scan my 03 3800SC GTP PCM and monitor fueling very carefully. I supplement the scans with wideband O2 charting.
    This was my approach.
    The first thing that I did was to zero the TPS air fuel adder. As the throttle opens you do not want to go leaner but have enrichment. (If you add to the A/F ratio it leans out the engine)
    Second I bumped up the VE adder vs time very slightly like .1 per AF number from 2500-6,000 RPM.
    The last thing I did was to adjust the MAF curve ever so slightly. The LTFT numbers in the cruising mode all showed the the PCM was adding fuel. A very slight adjustment to the numbers under 7000 Hz seem to get the LTFT's near zero. I left the numbers above 7,000 HZ stock as we are using the LS1 MAF and its V8 curve.
    Now each engine is different, but I just wanted to make a point that only small changes in the program can make a big difference. I am running a 3.4" pulley on a Gen V supercharger ( with supporting mods) that puts out 11 psi of boost, a ZZ SSIC which proved to be a must a 3" exhaust, 180* stat and Autolite 104 plugs.
    Haven't dyno'd yet but there is a "seat of the pants" difference.