Results 1 to 27 of 27
  1. #1

    Question LS SWAP HELP- Starts and dies- no link to scan tool

    Hey there!

    So I bought an LS with a "custom" harness and flashed computer from a seller on craigslist out of state. It is a business and this is what they do... Price was less than I could gather the parts on my own.

    Less than pleased so far. Details later- if it matters.

    Finally got the wiring harness cleaned up to my liking, the computer mounted, engine mounted, etc.

    Tried to fire it today. Fires right off, runs for a second or two and dies- over and over, with deadly consistency.

    2001 Tahoe (I think)
    5.3
    Cable actuated throttle body
    Truck intake

    No MAF at this time (motor was missing quite a few parts- argh)
    No o2 sensors at this time.
    Check engine light was a flakey LED that kept flickering. Volt meter shows it on all the time (does not go out a few seconds after key on- shouldn't it?).
    Scan tool will not link to the Computer- nothing.
    Validated diagnostic port wiring- it is correct- power, grounds, and data wire are all correct.

    My understanding is that the motor should run without MAF and o2- true?
    First thought is VATS- is there anyway to validate if it has been disabled without me buying the full tuning software suite?
    What is the deal with the scan tool not linking?

    Some of these may be basic questions- bear with me- old fart trying to learn new tricks...
    If you cross thread a bolt, there is no need for loctite.

    Run whatcha brung... And hope you brought enough.

  2. #2
    Do you have an IAT on the motor? You mentioned some missing parts... If you don't have a MAF and you don't have an IAT, it's not gonna work real well.

    Do you know if the backup fuel air ratio maps are still in the ECM after being flashed? (Hard to confirm for yourself, but worth asking the company).
    Cages: '08 Dodge 6.7CTD, '08 Nissan Xterra Offroad
    Bikes: '05 GSXR 1000, '98 WR400

  3. #3
    Colorado_Baja's Avatar
    Join Date
    May 2006
    Location
    Coloradical Springs
    Member #
    9500
    I would install the maf and 02 sensors but it should run with out them. Next I would check and double check all your grounds. When I did my 8.1 swap I had one bad ground on the core support that was causing me all kinds of problems.

    To me it sounds like you still have VATS turned on, and the ecu killing it right after start. Not sure why you dont have data link connection but it seems like something is screwy with your harness and ecu.
    197? DJ-5 LHD & 4wd

  4. #4
    Thank you SO MUCH for the suggestions!

    For reference- https://youtu.be/1lpuIiPB2sk?t=218

    I get it- it isn't going to set HP numbers on a dyno, or run perfect without all the goodies- but I thought it would start, idle, and maybe rev a bit... like the video.

    I believe on these- the IAT is part of the MAF.

    My hang-up is that it has taken MONTHS to get the harness and computer. So sending it back to have it "checked" could screw up an entire summer of cruising. Otherwise I would have sent the harness back and asked for a better job. Is there a local company that might check the computer for "cheap"?

    GROUNDS- When I cleaned up the harness, I combined all the grounds. Did I mess that up? Upon further research, some are sensor "low level" grounds that go back to the computer, and some are actual chassis type grounds (I think). Well, they are combined now. BUT- they all went into huge weird splices before- so the only change I made was to bridge the two gigantic ground splices together.
    Last edited by PovertyByJeep; April 30th, 2018 at 08:03 AM.

  5. #5
    Well, the company is pretty sure it is VATS- they were having trouble with the VATS removal on their HP software...

    I see 208 Motorsports and J&S recommended for tuning.

    J&S looks like they are in Arvada which is closer than 208 Motorsports in Idaho.

    Are their any companies in south Denver or even Colorado Springs that do PCM programming?

  6. #6
    Finishline Performance is in Denver and i am pretty sure does programming (720) 201-1834.

    i have heard nothing but good things about 208 motorsports.
    - Professional web wheeler

  7. #7
    Colorado_Baja's Avatar
    Join Date
    May 2006
    Location
    Coloradical Springs
    Member #
    9500
    I did the same with the grounds on my 8.1 swap. the 350 TBI in my 94 had like 8 of them scattered in the harness so I tied them into a couple sets and attached them to the rear of the heads on the 8.1. Sounds like your good there.

    That sucks on the VATS and the tuner being so slow. I used Howell in Michigan, their work was top notch but they were not super speedy either time I delt with them.

    I have never delt with these people personally but their name is always coming up in LS tuning posts and people seem to like their stuff.
    http://www.blackbearperformance.com/

  8. #8
    THANK YOU!!!

    I am hoping I can walk into a shop, drop the thing off and grab it the next day or something. The original company's slowness has really put me in a bind for time. I would rather not ship it somewhere- so I'll check out J&S (they were at the swap meet- and their harness work looks incredible), and Finishline. See if either wants to take pity on me...

    Good news on the grounds! It would be simple enough to chase them down and validate pin locations- but that is more work- more time...

    I did also learn while cleaning up the harness- There is no oil pressure signal to the computer. Surprised me. I figured GM would have a "safety" of no oil pressure, no fuel.

    Thanks again- I'll report back with what the local tuning companies say.

  9. #9
    Colorado_Baja's Avatar
    Join Date
    May 2006
    Location
    Coloradical Springs
    Member #
    9500
    Quote Originally Posted by PovertyByJeep View Post
    Thanks again- I'll report back with what the local tuning companies say.
    Happy to help.
    Please do let us know what you find on local tuners. The tune that Howell did for me is pretty darn good for being done out of state with no logs. I'd like to have it dyno or log tuned by someone local to iron out a couple kinks and see if there is any more power in there.

  10. #10
    J&S looks like they will get my business. Very clear that they know LS Swaps inside and out.

    I'll run the computer up there later this week, and get it back in a few days.

    More money out of my pocket, but the cost of the initial tune counts towards a full tune later if I choose to have them do one. Sounds like pretty good stuff to me.

    I can't say that I am not nervous that the computer will be A-Okay and the screw up will be something I did. But at least I will have confidence that the computer should start the engine!

  11. #11
    Steven's Avatar
    Join Date
    Dec 2004
    Location
    Highlands Ranch, Co
    Member #
    5346
    Talk with JR at j&s hes amazing with all ls engines

  12. #12
    Quote Originally Posted by Steven View Post
    Talk with JR at j&s hes amazing with all ls engines
    Already did.

    And YES- JR is awesome. Very willing to work with me, and he is sure they can get my problem solved. Dropped the Computer off late last week- should be ready early this week.

    Had to wipe the drool off my chin the whole time I was there- good grief they had some wicked cars there! CTS-V's, Corvettes, awesome stuff. Did not feel worthy- that's for sure!

  13. #13
    Good Grief...

    The saga continues.

    The computer and harness are later model fly by wire that have been "converted" to fly by cable. J&S is not super confident all this will work.

    I'll pick up my computer tomorrow with (hopefully) a tune in it that will work. If not- they have graciously offered to cut me a deal on their computer and harness product.

    Trying hard to stay focused that this will be really cool when I get it running!

  14. #14
    Colorado_Baja's Avatar
    Join Date
    May 2006
    Location
    Coloradical Springs
    Member #
    9500
    My 8.1 was converted from DBW to cable. The base tune they used on mine was from a 2wd suburban or something like that that was LS based but cable TB to start.
    Sounds like if anyone can get you sorted its them, I'm holding out hope for you.

    20170204_095556 by colorado_baja, on Flickr

  15. #15
    THAT looks bada$$!

    So J&S Performance for the win!

    Installed the computer, hit the key- IMMEDIATELY fired and idled! I was happy enough that I was almost able to ignore my smoldering anger at the water pump leaking coolant all over the floor when I pressure tested the cooling system...

    I need to get with them today and see about one issue- the computer is setting a code about looking for the throttle control computer. Which is obviously an issue. If it is not fixable with programming, then my check engine light is going to get removed until I can gather the funds to have the harness and computer redone (or I come across a deal and do it myself). It sounds like from Colorado_Baja's post- that it should be fixable. My computer is out of a 2006 Avalanche.

    Next stop is AA Performance to rework the exhaust!

  16. #16
    I was going to put a picture or two here- but there are monkeys and footballs when it comes to me and posting pictures...

    SOOO- here is a video of the thing sounding like a tractor:

    https://youtu.be/ikJvX83J95E

    Oh- and the data port was wired backwards- it is tapered, and was backwards/upside down. Moved all the wires to the right spots and BINGO- links, reads, and even shows live data. AMAZING... ugh. Next time I am reworking the harness myself.
    Last edited by PovertyByJeep; May 14th, 2018 at 08:45 AM.

  17. #17
    Well, it runs like a tractor because the computer does not have the hardware to actuate the IAC... according to my internet research. Oh, and apparently my left leg might fall off soon as a result of this weird rash on my elbow. Gotta love the internet!

    So the original company is going to ship out a new computer "today".

  18. #18
    Camp Cook Geek cheftyler's Avatar
    Join Date
    Feb 2006
    Location
    Arvada, CO
    Member #
    8454
    Images
    1
    Diggin the updates!
    "Blow and Hookers can change the World. - Gags
    Quote Originally Posted by scottycards View Post
    MJ has no lethal dose. You might crawl under your couch and eat M&M's all day if you get too high, but it ain't gonna kill you.

  19. #19
    Colorado_Baja's Avatar
    Join Date
    May 2006
    Location
    Coloradical Springs
    Member #
    9500
    Quote Originally Posted by PovertyByJeep View Post
    Well, it runs like a tractor because the computer does not have the hardware to actuate the IAC... according to my internet research. Oh, and apparently my left leg might fall off soon as a result of this weird rash on my elbow. Gotta love the internet!

    So the original company is going to ship out a new computer "today".
    Hmm so different ECU part numbers?

    Did your original issue end up being VATS killing it on startup?

    Hope the original company comes through for you with a good ECU.

  20. #20
    Yes- basically the blue green harness/computers are mostly drive by wire- with a few being able to do both. There are a few resources on the web that show computer Service and Hardware numbers and whether they can support drive by cable. Mine was on the "not" side on every site... You can apparently also open the thing and look for a little chip that can control IAC.

    This site has been helpful- http://lt1swap.com/cable_conversion.htm
    As has this one- https://www.mrk-motorsports.com/gm-iac-pcms/


    It sounds like Express vans are the most common unicorns that can do both. Some CTS-V's and GTO's apparently could as well.

    VATS was indeed the problem initially.

    I am waiting for a tracking number for the computer that supposedly was shipped yesterday...

  21. #21
    So NOW I have a snazzy red/blue computer to go with my blue/green harness... and radio silence from the other end. Never sent a tracking number- computer just showed up. The WRONG computer...

    Apparently you can modify the O2 wiring on the blue/green harness to work with the red/blue computer, and then GRIND some portion of the green plug to fit the red port on the computer... again based on interwebz research.

    So here I am, hemorrhaging more time and money to try and sort through this mess.

    Maybe a red/blue harness is also on it's way
    Maybe a blue/green computer that will work is on it's way
    Maybe I am SOL- and expected to now figure it out on my own

    Note to self- Communication is KEY to a successful business.

  22. #22
    newracer's Avatar
    Join Date
    Aug 2006
    Location
    Timnath, CO
    Member #
    10010
    Images
    29
    That sucks, hopefully they make it right, quickly.
    Have you ever seen a man eat so much fish?

  23. #23
    I hope so too.

    I would prefer to have the correct computer to match the harness- since I have days of work cleaning up this harness, and installing some cool nylon split loom I bought.

    Second choice would be a "new" red/blue harness to match the most recent computer they sent (J&S felt red/blue was the right way from the start)- but that would require me to redo all the work I have done- or pay for the J&S harness...

    3rd choice would be the modify harness/grind connector route- since it would be a massive hodge podge of parts- and confusing to remember what is what when buying new parts.

  24. #24

    Join Date
    Aug 2001
    Location
    Parker
    Member #
    19
    Images
    8
    So who are these jackwagons that can't get the right parts to you? Hopefully I didn't miss the name already posted.

  25. #25
    Not gonna happen until I either have all the parts in hand and am satisfied, or I am no longer able to get any response from them. They are in Topeka, Kansas- so buyer beware if you are dealing with a company there.

    I would not hesitate to recommend J&S for computer work, though! Good stuff there. Good people- and local.

  26. #26

    Join Date
    Aug 2001
    Location
    Parker
    Member #
    19
    Images
    8
    Completely understandable!

  27. #27
    Returned from the exhaust shop! AA Performance wins again.

    Excellent quality, good price, quick turn around.

    Just gotta get the rest of the mess together.

Posting Permissions

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