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Thread: 5.7 random miss

  1. #1
    Junior Member
    Join Date
    Jan 2013
    Posts
    22

    Default 5.7 random miss

    Hi everybody, I'm new to the tuning bit. I've used my v2 for deleting antitheft, cat delete, and whatnot involved in engine swaps for older vehicles with a gen 3 a few times now, more than paid for what I've needed it for. I'm having an issue with one of my fathers p/u's. It's a 98 l31 5.7 with the black box. I've rebuilt the 5.7 vortec with a balanced bottom end, mildly ported heads, small cam upgrade(unsure the exact specs, so called "rv cam"). New everything on it including the 4l60e behind it. We're having an random missfire. I've been over and over and over this thing trying to find something, bad wires, fuel delivery, something, can't find anything. All the work I had done was prior to receiving my v2, and we had an out of town dyno shop do a tune, due to deleting the cats and different tire sizing. To get to the point, I've done some data logging and found that when the miss happens the rpm jumps wildly up to 7500for one frame, then back to where ever it was at, the injector flow rate jumps to 80%, the spark retards way back, but not much else changes, vss stays consistent, map, o2's, tps, all stay what looks normal. Hopefully somebody can help a bit with this. I'm banging my head against the wall, I know there is more in this engine for tuning, but I need to solve this problem before moving on!

  2. #2
    Senior Member
    Join Date
    Jul 2005
    Posts
    188

    Default

    So many Vortec 350's have random misfires due to the CSFI injection spider. I have also seen them due to cam changes. Do you have a p/n or any specs for that cam. Is it a hydraulic roller cam? STock has specs of 191º/196º 0.412"/0.428" 111º LSA http://www.off-roadweb.com/tech/1012...e_fueling_fix/ At the very least clean those poppets out. http://www.acdelcotechconnect.com/pd...sb_05D-105.pdf peace hog
    1997 rcsb stock L31 longblock, Marine Intake with 28# EV6 injectors, L35 2700 stall TC,Hooker LT's 2.007 60ft

  3. #3
    Junior Member
    Join Date
    Jan 2013
    Posts
    22

    Default

    Yea, I've replaced the spider with the upgraded unit, the cam I'm unsure of, I don't belive it's much more than stock, I should find out exactly though. Like I say its got everything brand new on it. I checked the knock sensor, but the ohms are within spec, I've read a little bit about some frequency could throw that off. But as far as that goes, I'm limited to the blackbox with only the burst knock stuff, I don't know enough about that part though. thanks for the quick response though hog, any suggestions are appreciated.

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