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  1. #1
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    ANDREW
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    Default 93 corvette--poor idle/running rich/surging/bucking running out of ideas

    Car in question is a 93 6 speed with 68k miles. It sits for weeks to months at a time, and has only had about 2k miles put on it over the last 8 years. Car has been running terrible the past 8 years and has been to 2 dealerships and Guldstrand Performance in an attempt to fix the problem, which both places have failed to do so.

    The car will usually run decently when cold, but the idle quality is poor (you can hear it popping and breaking up at idle). Driveability is poor as well whether cold or hot, but it is intermittent. It will buck and surge when in high gear on the freeway, but if you downshift and get into higher RPMs, it runs better, but doesn't pull well. No DTCs are showing up either. Here's what's been replaced so far:

    -New EGR
    -New injectors from Fuel injector connection (bosch 3's)
    -New TPS
    -New set of Plugs last week
    -New MAP sensor
    -O2 sensors have been replaced twice, most current set is about 6 years old
    -Intake manifold has been re-sealed (just finished yesterday) as there was a vacuum leak (sprayed carb cleaner around the intake and idle changed)
    -New ignition module (yesterday)
    -New ignition coil (yesterday)
    -Plug wires are about 8 years old
    -New Magnaflow cats (previous set were original and broken elements inside), replaced 6 months ago
    -New fuel pressure regulator
    -MSD optispark (8 years old)
    -New water pump put in at the same time as the opti
    -New fuel filter (3 months ago)

    Car smells like a lot of fuel at idle, when using an IR thermometer on each port of the exhaust manifold, temps are much hotter on passenger side bank (450 degrees) and driver's side bank is between 200-300 degrees. Fuel pressure is good at the schraeder valve on the rail--45 psi. Fuel pump is original from 93.

    I was really hoping that resealing the intake manifold would help out a lot, in combination with the new coil and ignition module. First drive was fantastic, car ran great, then after a few hours, drove it again, and it's cranking over for 4-5 seconds before firing up, and driveability is back to what it was before. Drove it again just now, same issue, hard cranking and poor driveability.

    No one around here wants to touch lt1 cars (including the dealership). It's not my car, it belongs to my mom and I really want to get it running great again. I've run datalogs and it confirms the car is running really rich, and o2 sensor voltage between banks is not even. I've swapped o2 sensors from side to side with no change.

    Wiring appears fine all around the intake manifold, but I"m not sure what else to check at this point. Really running out of ideas and it's pointless to keep throwing parts at it.

    Please point me in the right direction!
    Last edited by HellaciousA; 01-21-2018 at 09:39 PM.

  2. #2
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    Default

    Quote Originally Posted by HellaciousA View Post
    MSD optispark (8 years old)
    Almost positive this may be part of your issue. MSD has a horrible reputation with Opti's. New and even rebuilt units are garbage.

    Also, please change your font color.
    2012 Sierra - 5.3, Summit "Stage 1" Truck Cam
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    1994 Formula - 5.3, Terminator X, Billet VS7875, "Best Cam", T56, QP 9"
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  3. #3
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    Default

    What software are you using for the data logs? Do you have the data logs in a .csv format? I'd be glad to look them over. I've been doing it for many years. Interestingly, in the past year I was able to solve an epidemic of erratic idle problems caused by a faulty optical module in the MSD Opti. Unfortunately that specific rash of problems was common to units produced in the last couple years, not from 8 years ago.

    But as noted by Cameron in the post above, the MSD units have suffered a series of serious problems over the years since they sold their first unit. Solve one problem, and one or two new ones show up.
    SOLD - GONE TO A (VERY) GOOD HOME ! - 94 Formula A3+1: 381ci forged stroker - Callies Stealth, Oliver 5.85 billet rods, BME nitrous pistons / CNC LT4 heads / CC solid roller / TH400+GearVendors OD / 4.11 Strange 12-bolt / 300-shot N2O / Spohn Suspension / roll bar / MoTeC M48 Pro engine management system /a few other odds 'n ends.

  4. The Following User Says Thank You to Injuneer For This Post:


  5. #4
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    Mike Storm "Stormy"
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    Default

    Did you do a Fuel Pressure leak down test? Hook a Gage to the Schrader valve key on . Don't start then off and see if pressure drops right off. Might have a clogged injector. I'm just saying cause it can happen.

    Sent from my HP Pro Slate 8 using Tapatalk



    1995 Trans Am - CAI - TB coolant bypass - Headers & Performance Muffler - Poly mounts - stock LT1/A4 - 13.3 1/4 - 1.9 60 foot , driven daily.
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  6. #5
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    Default

    Quote Originally Posted by Injuneer View Post
    What software are you using for the data logs? Do you have the data logs in a .csv format? I'd be glad to look them over. I've been doing it for many years. Interestingly, in the past year I was able to solve an epidemic of erratic idle problems caused by a faulty optical module in the MSD Opti. Unfortunately that specific rash of problems was common to units produced in the last couple years, not from 8 years ago.

    But as noted by Cameron in the post above, the MSD units have suffered a series of serious problems over the years since they sold their first unit. Solve one problem, and one or two new ones show up.
    I just did a fresh data log 10 mins ago, its scan9495. I have an csv file but it won't let me attach it to this post--can I email it to you? Bank 1 o2 sensor voltage is much higher than bank 2. I'm also getting a tremendous amount of knock at idle and while driving. It's running poorly both in closed and open loop. In addition to that, the coolant temperature reading was fluctuating a bunch and occassionally would display "SYS" on the cluster.

  7. #6
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    You can email the file to

    InjuneerZZ@aol.com

    Just put "data log - HellaciousA" in the topic.

    No codes? If you have DTC 43 for the knock sensor, the ECM will provide default knock retard, up to 15°, based on MAP and RPM.
    SOLD - GONE TO A (VERY) GOOD HOME ! - 94 Formula A3+1: 381ci forged stroker - Callies Stealth, Oliver 5.85 billet rods, BME nitrous pistons / CNC LT4 heads / CC solid roller / TH400+GearVendors OD / 4.11 Strange 12-bolt / 300-shot N2O / Spohn Suspension / roll bar / MoTeC M48 Pro engine management system /a few other odds 'n ends.

  8. #7
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    Quote Originally Posted by HellaciousA View Post
    I just did a fresh data log 10 mins ago, its scan9495.
    Wow, I didn't think my software would work well for any Corvette, but maybe just for a 93(?). Does your 93 have a CCM?

    1998 Trans Am - LS1/A4 - all stock and almost all original - one owner - driven daily.
    Author of Scan9495, free pc apps 93-95 LT1,94/95 L32: http://ltxtech.com/forums/showthread...light=scan9495

  9. #8
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    @GaryDoug

    I took a quick look at his log. Appears to have indexing problems, randomly shifting data over a few columns in a single record. Also relatively slow scan 1 or 2 frames per second. Left O2 sensor appears to be stuck at 1.032 volts. Right sensor behaving more normally.

    I can send you the scan if you want.
    SOLD - GONE TO A (VERY) GOOD HOME ! - 94 Formula A3+1: 381ci forged stroker - Callies Stealth, Oliver 5.85 billet rods, BME nitrous pistons / CNC LT4 heads / CC solid roller / TH400+GearVendors OD / 4.11 Strange 12-bolt / 300-shot N2O / Spohn Suspension / roll bar / MoTeC M48 Pro engine management system /a few other odds 'n ends.

  10. #9
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    Default

    Quote Originally Posted by Injuneer View Post
    @GaryDoug

    I took a quick look at his log. Appears to have indexing problems, randomly shifting data over a few columns in a single record. Also relatively slow scan 1 or 2 frames per second. Left O2 sensor appears to be stuck at 1.032 volts. Right sensor behaving more normally.

    I can send you the scan if you want.
    Sure, do that to scan9495@gmail.com.
    I have a feeling this app wont work well for a Y-car after all.

    1998 Trans Am - LS1/A4 - all stock and almost all original - one owner - driven daily.
    Author of Scan9495, free pc apps 93-95 LT1,94/95 L32: http://ltxtech.com/forums/showthread...light=scan9495

  11. #10
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    Default

    He used version 2.5.1

    I have the 92-93 Corvette ECM diagrams. Looks like the same 4-connector setup as the 93 F-Body ECM, same terminals for most sensors, actuators, with a few extra pins added for the interfaces with the myriad of additional controllers - has skip-shift, interfaces to DERM, CCM, Selective Ride, Tire Pressure modules,
    SOLD - GONE TO A (VERY) GOOD HOME ! - 94 Formula A3+1: 381ci forged stroker - Callies Stealth, Oliver 5.85 billet rods, BME nitrous pistons / CNC LT4 heads / CC solid roller / TH400+GearVendors OD / 4.11 Strange 12-bolt / 300-shot N2O / Spohn Suspension / roll bar / MoTeC M48 Pro engine management system /a few other odds 'n ends.

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