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Thread: Tuning help needed - '91 TBI 383 w/ Vortec heads

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    Carb and Points!
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    Apr 2017
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    Tuning help needed - '91 TBI 383 w/ Vortec heads

    Hi all, could use some tuning advice.

    I've built and installed a vortec-head 383 in my '91 squarebody suburban. 3/4 ton, 4wd, 4L80e tranny. 16147060 PCM, using $85 mask. Here's my intro thread for some more info:

    http://www.gearhead-efi.com/Fuel-Inj...ortec-head-383

    Considering my complete lack of experience with tuning, it's running decent. I know it's running rich and I'm continuing to play with the BLM table using my log files and an adjustment spreadsheet that @Dave W provided me. But other than that, I'm unsure of where to go next with tuning, e.g. spark, IAC, choke, etc. My two biggest concerns (other than still a bit rich) are,

    1. Significant surging during compression braking. I can hear it out the tailpipe, see it in the tach (300-400 rpm surge range, cycle time is about 1 second) and feel it in the seat of the pants. It might be doing the same thing, but very slightly, during steady, low speed cruise, too. But going down hills with foot off throttle and brakes, it's pretty bad.

    2. High idle at cold startup. 1200-1300 rpm, doesn't match target idle in .BIN. Takes several minutes before it will even come down to below 1000.

    Do these issues sound like they're related? Vacuum leak? I've attached all the files I'm using in TunerPro, including my two latest log files and my latest modified .bin file - just in case anyone has the desire to take a look.

    Oh, and EGR has been deleted via RPM limits (Dave W helped with that on initial .BIN creation) and no EGR valve physically installed. EGR is complicated on Vortecs - need to route exhaust gas from DS exhaust manifold to intake manifold.

    Thanks much!
    Attached Files Attached Files

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