Become a ltxtech.com member, Click here to register!
BP-Automotive

Page 1 of 2 12 LastLast
Results 1 to 10 of 20

Thread: Missfiring

  1. #1
    Lurker


    Status
    Offline
    Join Date
    Nov 2015
    Name
    T
    Vehicle
    97 TA
    Posts
    14

    Default Missfiring

    97 LT1 T56. Seems to be runing ok at first but starts missfiring under load and sometimes without a load while revving. I need to double check if it's the same in open/closed loop. Always smells like the car runs rich. Pulled the spark plugs and all 4 of the driver side bank plugs were black and wet. Passenger side plugs all look good.

    Cats are gone, opti & icm replaced. Fuel pressure is a little low at 38lbs at idle and 46 at wot and with the vacuum line pulled on the fpr. Injector harness terminals all read the same on both banks with ignition on and off, as do the resistance in all the injectors. Best as I can tell, there's no vacuum or exhaust leaks. Checked in the dark and don't see spark escaping from the wires.

    Where should I look next?

  2. #2
    Xtreme Member


    Status
    Offline
    Join Date
    Mar 2015
    Name
    Mike Storm "Stormy"
    Vehicle
    1995 Trans Am
    Location
    Washington
    Posts
    1,020
    Blog Entries
    1

    Default

    Vacuum leak? Driver's side? Wonky o2?

    It's not how fast you mow. It's how you mow fast.



    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.
    2008 C6 Corvette LS3 Snake charmer Ram Air intake. 6 Speed Switchable mild to wild exhaust.
    2002 Silverado LT Extd Cab Z71 5.3 A4 Composite Bed Stock

  3. #3
    LTx Guru


    Status
    Offline
    Join Date
    Apr 2013
    Name
    Fred
    Vehicle
    1994 Formula - SOLD
    Location
    Central NJ
    Posts
    2,279

    Default

    Your fuel pressure is fine - actually a little high, but within the GM specs (41-47 PSI with no vacuum). When you reattach the vacuum compensation line to the fuel pressure regulator at idle, its completely normal for the fuel pressure to drop 6 to 8 PSI below the "no vacuum" reading. That is the purpose of the vacuum compensation line - to keep the DIFFERENTIAL pressure between the fuel rail and the intake manifold constant.

    Is the misfire setting any misfire codes? Does the SES light flash when it’s misfiring? Any codes at all? Any engine modifications besides deleting the cats?
    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. #4
    Lurker


    Status
    Offline
    Join Date
    Nov 2015
    Name
    T
    Vehicle
    97 TA
    Posts
    14

    Default

    There were iron heads on the vehicle when I purchased it years ago from a used car lot that are still on it. I removed the AIR system over 10 years ago. I just pulled the fuel rail to remove the egr system and sealed the holes with plates & rtv. Disconnected battery for 30 minutes. No tune. After installing it all back together it now fires up and is idling around 2000rpms, where it wasnt before. Tried checking for possible vacuum leaks with propane, but found nothing. Going to try carb cleaner later to see if I can track down a leak. Exhaust is rich enough with unburnt fuel to burn my eyes quickly. Still has a missfire. No codes & no flashing SES light as of yet.

  5. #5
    LTx Guru


    Status
    Offline
    Join Date
    Apr 2013
    Name
    Fred
    Vehicle
    1994 Formula - SOLD
    Location
    Central NJ
    Posts
    2,279

    Default

    When you reinstalled the rails, did you make sure the o-rings were still on the injectors when you pushed the bottom of the injectors into the manifold? Did you reconnect the vacuum lines?
    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.

  6. #6
    Lurker


    Status
    Offline
    Join Date
    Nov 2015
    Name
    T
    Vehicle
    97 TA
    Posts
    14

    Default

    Checked for vacuum leaks with carb/choke cleaner & no luck. Motor still idles at 2000rpms. An odd finding, the passenger side exhaust manifold started to glow towards the rear cylinder/s after running for approximately 5-10 minutes (as I was doing this after sunset outside). I did swap the plugs from the drivers side to passenger side after I first pulled them out. But I was thinking that's a sign of either runing lean or an exhaust restriction. Only code I got was P0160 for that run time.

  7. #7
    Lurker


    Status
    Offline
    Join Date
    Nov 2015
    Name
    T
    Vehicle
    97 TA
    Posts
    14

    Default

    Yes, lubed all the injector orings and checked vacuum lines.

  8. #8
    Xtreme Member


    Status
    Offline
    Join Date
    Apr 2012
    Name
    Cameron
    Vehicle
    1994 Formula
    Location
    Dover, De
    Posts
    2,076

    Default

    If the headers are glowing it sounds like a timing issue. Are you able to log to see if your pulling timing due to knock retard or another issue. I saw you replaced the opti. What brand?
    2012 Sierra - 5.3, Summit "Stage 1" Truck Cam
    1994 Jimmy - LS? LT? 4wd? AWD? Time? Money?
    1994 Formula - 5.3, Terminator X, Billet VS7875, "Best Cam", T56, QP 9"
    Formula Build Thread


  9. #9
    Lurker


    Status
    Offline
    Join Date
    Jan 2018
    Name
    steven rogers
    Vehicle
    1994 camaro z28 383 eagle crank,k/b performance piston bored 30 over,comp cam,ported heads
    Posts
    13

    Default

    believe it or not but i had some issues like yours and i put a coolant sensor on mine and it fixed mine my car wouldnt even run because the coolant sensor was bad but just a cheap idea may fix it

  10. #10
    Lurker


    Status
    Offline
    Join Date
    Nov 2015
    Name
    T
    Vehicle
    97 TA
    Posts
    14

    Default

    After being stupid busy, I had about an hour to jump back on the car again. After pulling the fuel rail off and replacing a fuel injector o-ring that wasn't seating properly, I spent another 15 minutes or so looking for a vacuum leak that didn't exist. Then I ran across my high idle culprit. The IAC was unplugged. Now it's back to normal rpms, but I suspect it's still running pig rich on the driver side bank as the exhaust was still rich with unburnt fuel that burned my eyes, and it wasn't revving smoothly. Still no codes for the short duration it was running.

Page 1 of 2 12 LastLast

Tags for this Thread

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •