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  • #1

    Bad Miss

    Ok I'm sort of perplexed here. Last week the car starts missing badly. I've heard of people having issue with Taylor wires so I figured that might be the issue. Over the weekend I changed out the wires with a new set of MSD's. I had a new coil sitting on the shelf so I put that in too. So I get the car down off the jacks drive for about 10 minutes and everything is perfect. Then I get in the car to go to work this morning and it's missing like hell again. I drive to the gas station about 3 block away fill up start the car back up and the miss is gone. During my 45 min drive to work the miss comes back and goes a couple times. Ok so here's the deal, new plug wires, new opti and plugs 10k ago, new coil, the opti harness and ICM are old. I'm leaning toward the ICM. Unfortunately I don't have anyway to do a real time scan at the moment.

    Thoughts?
    Tracy, 97 Formula, pretty much stock.
    Tags: None
  • #2
    Could be a short or intermittant break in the ignition harness. Do a wire shake test. Start the car, manually check each portion of the harness by wiggling every wire and harness connection.

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    • #3
      I forgot to mention the only code it's throwing is a P0300. Thanks Joe, I did a visual inspection of the harnesses and they looked good, but that doesn't mean they are. Please correct me if I'm wrong but the opti harness shouldn't cause a miss, that would be more of a timing control issue and should throw some kind of opti related code?
      Tracy, 97 Formula, pretty much stock.

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      • #4
        Looking at the wiring will do little. Moving the wiring while the engine is running should reproduce the fault if it's due to a bad contact or pinched wire.

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        • #5
          If you have access to an OBD-II scanner with "GM enhanced parameters", you can access the misfire count by individual cylinder. That will tell you if its truly a "random" misfire, or if its specific to one or more cylinders. That might get you pointed in the right diretction, and be a lot cheaper than randomly replacing parts, hoping you pick the right one.
          Fred

          381ci all-forged stroker - 10.8:1 - CNC LT4 heads/intake - CC solid roller - MoTeC engine management - 8 LS1 coils - 58mm TB - 78# injectors - 300-shot dry nitrous - TH400 - Gear Vendor O/D - Strange 12-bolt - 4.11's - AS&M headers - duals - Corbeau seat - AutoMeter gauges - roll bar - Spohn suspension - QA1 shocks - a few other odds 'n ends. 800HP/800lb-ft at the flywheel, on a 300-shot. 11.5 @ 117MPH straight motor

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          • #6
            Dang...you're describing my exact problem. I'm trying to diagnose mine as well...haven't had any luck yet.

            If I find it, I'll let you know. Right now, I'm leaning towards the Opti.
            Al 96 Ram Air T/A
            Mods: Build # 784 * Hotchkis STB * SFCs * Borla cat back w/QTP cut-out * AS&M/RK Sports Mid-length headers w/single CAT * Koni SA shocks on lower perch w/ lowered rear * Strano Hollow front & rear antisway bars * 1LE front/rear springs * 1LE aluminum driveshaft * Strange 4.10 gears w/ Zexel Torsen diff. * ARP bearing cap studs & aluminum diff cover* J&M Hotpart poly/poly rear LCAs and poly/poly panhard bar * RAM Powergrip clutch w/ LT4 PP and RAM billet Al flywheel * C5 Z06 brakes * C6 Z06 wheels * Spohn T/A * Spohn DS Loop * fully custom interior w/ custom audio

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            • #7
              Originally posted by Injuneer
              If you have access to an OBD-II scanner with "GM enhanced parameters", you can access the misfire count by individual cylinder. That will tell you if its truly a "random" misfire, or if its specific to one or more cylinders. That might get you pointed in the right diretction, and be a lot cheaper than randomly replacing parts, hoping you pick the right one.
              Yea just randomly throwing parts at a problem wouldn't be my first choice either. I do have access to an enhanced scanner but I have to travel a bit to get to it and haven't had time to make the trip. P0300 only tells me what I already know. The wires and coil did greatly improve the problem. I'm trying to only throw parts at it that I know need to be replaced anyway. The coil was original, the ICM is original. But most of what I've read about bad ICM's seem to be more severe issues? I've ordered new harnesses for the ICM and coil. Some of my harnesses showed signs of severe aging, on visual inspection those look ok, but as Joe points out, that doesn't always tell the whole tale. $20.00 seems like a good investment to rule out the problem and prevent future problems.

              Dang...you're describing my exact problem. I'm trying to diagnose mine as well...haven't had any luck yet.

              If I find it, I'll let you know. Right now, I'm leaning towards the Opti.
              My opti only has 10k on it so I'm pretty sure it's ok.

              Thanks for everyone's input.
              Tracy, 97 Formula, pretty much stock.

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              • #8
                Just a thought

                In the few days before I shot a plug out of the head while on a major interchange I was getting a lot of misses. I hadn't taken the time yet that week to have it scanned to try to narrow it down to what cylinder and all. The only sign I had was the feeling of the miss, it would only come out when the car started getting warm and while warm, not when it was cold.

                After the pain and suffering of doing a heli-coil completely blind on my own the car ran and still runs great.

                Apparently when I changed the plugs and wires from the oem I must have taken some threads out with the old. Funny thing was it wasn't like I replaced the plugs and then shortly after this happened, it was thousands of miles after. Those aluminum heads seem so soft. Maybe just check to see if the plugs are seated well, or the plug for the correct cylinder that is having the problem if you get it advanced scanned.

                DJ
                95 Formula LT1 6 Spd

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                • #9
                  Yea I checked the plug seating when I changed the wires last weekend and reapplied dielectric grease to each one. I was hoping it would be something that simple Thanks
                  Tracy, 97 Formula, pretty much stock.

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