Results 1 to 15 of 22

Thread: l29 misfires vortec black box

Hybrid View

Previous Post Previous Post   Next Post Next Post
  1. #1
    Fuel Injected! ralmo94's Avatar
    Join Date
    Feb 2020
    Posts
    774

    l29 misfires vortec black box

    I have a 1998 k2500 7.4 vortec 454 4l80e 3.73.

    A little background,

    I bought the truck with the typical hot start issue.
    Got worse after I got the truck.
    Replaced injectors and FPR.

    That was 2019.

    Thought for a while I had a bad head gasket,
    but turned out to be a bad intake manifold gasket.
    Finally got around to changing it, in 2020.

    First startup and it knocked. Bad.
    Turns out, something had been screwed
    to the firewall at some point in time. Well there was a
    self drilling screw that landed in number 3 cylinder.
    Replaced num 3 piston and rings. What a job. Lol

    New Distributor, ceramic boot plug wires, Blu streak cap and rotor.
    New NGK plugs. Deleted EGR, and cats. Exhaust is true dual 2.5, with
    glass packs in cat locations, flowmasters after that with rear exit.

    I have a missfire at idle.

    No codes. But random missfire code is set to no error reported.
    Thought maybe my truck had been tuned before I got it,
    But reviewing other stock files from HPT respository with the same OS
    Also had no error reported.

    I seen once a YouTube video of a guy that had
    replaced his injectors and had misfires,
    And his injectors were not seated all the way in the hole.

    Has anyone else ever ran across this before?

    Missfire, missfire code, or anything else helpful?

    I know these trucks seem to be like a unicorn, not a lot of info on them with OBD2 454.

    Thanks

  2. #2
    Super Moderator dave w's Avatar
    Join Date
    Feb 2011
    Posts
    6,313
    Often an infrared thermometer ( https://www.homedepot.com/p/Milwauke...s&locale=en-US ) is helpful to measure the exhaust manifold temperatures. Measure the temperate of each exhaust port close the cylinder head. A cylinder that is misfiring will have a slightly lower temperature. Perhaps identifying the cylinder that is misfiring is the next step.

    Perhaps an injector connector or injector wire is causing the misfire.

    dave w

  3. #3
    Fuel Injected! ralmo94's Avatar
    Join Date
    Feb 2020
    Posts
    774
    Quote Originally Posted by dave w View Post
    Often an infrared thermometer ( https://www.homedepot.com/p/Milwauke...s&locale=en-US ) is helpful to measure the exhaust manifold temperatures. Measure the temperate of each exhaust port close the cylinder head. A cylinder that is misfiring will have a slightly lower temperature. Perhaps identifying the cylinder that is misfiring is the next step.

    Perhaps an injector connector or injector wire is causing the misfire.

    dave w
    Seems like I remember trying that before without anything conclusive.
    How much of a difference are we talking, a hundred degrees, or less?
    I'll check again as soon as I get a chance, and record the temps on a paper
    And post them here.

    I don't think I mentioned before, it's not like a constant missfire
    And doesn't seem to be noticable above 1k rpm, but when noticed,
    I can see wideband go rich, then stft seems to lean it out for a second.

    Idle AFR seems to be 14.6, 14.7 when smooth,when missfiring, goes down to 13.9
    then up as high as 16 before settling back out to 14.6, 14.7

    Also I have new denso narrow band sensors and a 180 thermostat with an ⅛" hole drilled in it.

    Thanks

  4. #4
    Fuel Injected! ralmo94's Avatar
    Join Date
    Feb 2020
    Posts
    774
    Temps are
    390. 7
    485. 5
    475. 3
    400. 1


    388. 8
    417. 6
    450. 4
    450. 2

  5. #5
    Super Moderator dave w's Avatar
    Join Date
    Feb 2011
    Posts
    6,313
    Quote Originally Posted by ralmo94 View Post
    Temps are
    390. 7
    485. 5
    475. 3
    400. 1


    388. 8
    417. 6
    450. 4
    450. 2
    I agree, inconclusive data. What are the exhaust manifold temperatures at a steady 1500 RPM's?

    Fuel / Air / Spark are the basics for an engine to run.
    MAF Grams per second flow at idle vs. 1500 RPM's?
    Drive a steady speed for a few miles, then shut off the engine and coast to a stop and look at the spark plugs?
    Flow Rate of each injector before and after being cleaned?

  6. #6
    Fuel Injected! ralmo94's Avatar
    Join Date
    Feb 2020
    Posts
    774
    to keep idle at 1500rpm and
    check temps and record maf flow, and compare to idle, all
    Tables seem to be lb per hour this generation.
    I haven't cleaned injectors, or flow tested them.
    After I got the truck in 2019, I replaced the multecs with brand new
    Bosh injectors. Supposed to be stock replacements from a Ford application
    For the engine cut plug review, I don't know how feasible that is at this time
    I am in a city right now with a 18 ft box trailer in tow.

    I am wondering if I should pull the plenum and inspect the injectors. I'd rather not as
    It can be hard to find a place on the road to do it. Does it sound like it could be a
    fuel caused missfire? Only thing not new in ignition system is module and coil.

    Incase nobody has worked on one of these, the l29 plenum covers the injectors and harness.
    When I had it apart last was when I was replacing the number 3 piston.
    The plastic fuel rail is what holds the injectors in the hole of the lower intake.

Similar Threads

  1. Transmission Hot Mode Vortec Black Box???
    By ralmo94 in forum GM EFI Systems
    Replies: 8
    Last Post: 01-06-2021, 04:55 AM
  2. 1998 Vortec Black Box?
    By scratcholaman in forum Introductions
    Replies: 3
    Last Post: 04-21-2015, 01:16 AM
  3. Replies: 8
    Last Post: 02-12-2014, 06:25 AM
  4. Replies: 11
    Last Post: 04-28-2013, 02:22 AM
  5. Great Article for the Black Box Vortec to 411 PCM
    By EagleMark in forum GM EFI Systems
    Replies: 0
    Last Post: 03-18-2011, 09:15 PM

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
  •