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  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).
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  3. #3
    Colorado_Baja's Avatar
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    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 09:03 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
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    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
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    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
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    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
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    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 09:45 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
    cheftyler's Avatar
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    Diggin the updates!
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  19. #19
    Colorado_Baja's Avatar
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    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
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    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

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    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

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    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.

  28. #28
    VICTORY!!! (mostly) If "Victory" means working half-assed- then I am WINNING like a BOSS.

    https://youtu.be/k9SWTDB1L1s


    Got the correct computer- 2003 Express Van- does both DBW and DBC.
    Installed computer- started, idled, revved it, and it "hung" at 3K rpms and wouldn't idle down- arghhh!
    Shut it off- started, idled, and then crept up and hung at 3K rpms- (insert colorful metaphors here)
    Unplugged IAC- no change
    Shut it off- key on, then off
    Unplugged IAC- started and idled, revved, etc. as normal.

    After MUCH Sherlock Holmes detective work- 2 of the 4 wires on the IAC were wired backwards... Did I mention that next time I am doing my OWN harness work? Thankfully, my new neighbor has a super whammy scanner computer thing that does detailed Live Data stuff. Told us that the computer was trying to SHUT the IAC, and the engine acted as if it was opening...

    Rewired the IAC and it runs great!

    Getting a TCC code for the torque converter control that is not in use- might have to check that. And a knock sensor code. Super quiet, super smooth, and overall- pretty darned happy with it!

    I'll see if I can struggle bus it though posting pictures later today.
    Last edited by PovertyByJeep; May 31st, 2018 at 09:53 AM.

  29. #29
    I only got one image to upload- and it is a poser shot.

    Man am I dumb at this...



    Anyway- this is the car. It looks better in the picture than in person- and is a tangible example that I am NOT a body and paint professional.

  30. #30
    I am ON IT NOW!!! (I hope)

    Here is how the harness arrived in the box. I am not sure what I "should" have expected, but this is what I got. Removing 40 miles of brittle plastic loom was a real treat!



    I had the intake off already to try and clean it up and make it look nicer- so I just set it back on the motor and started laying out the wires. HOLY SMOKES there are a bunch of them! I plugged each one in and then identified the extra ones. Any wires that were not needed were removed at the computer plug and eliminated from the harness. My fingernails still hurt from prying up those little tabs!

    Removed the throttle control computer, transmission control harness, EGR, etc.



    Then we put the motor in the car, and started routing them how we wanted them. I knew I did not want the harness running up over the intake. My wife wasn't too keen on wadding them up on the windshield either. Note the magnetic trouble light blinding the camera- it blinded me most of the project.



    Finally, we fabbed up a sheetmetal computer mount and started finalizing the wire routing... I bet BruckerBrothers are jealous of my wicked fab skillz.



    And then my powers of picture uploading petered out...

    Anyway- thanks for all the advice. I am sure I'll have more questions.

    The plan is to put more trans fluid in (removal of the TV cable at the trans for replacement resulted in an awesome ATF fountain), and drive it tomorrow and see what happens.

    I better make sure our AAA is paid up.

  31. #31
    Colorado_Baja's Avatar
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    Quote Originally Posted by PovertyByJeep View Post

    The plan is to put more trans fluid in (removal of the TV cable at the trans for replacement resulted in an awesome ATF fountain), and drive it tomorrow and see what happens.

    I better make sure our AAA is paid up.
    What happened!?

  32. #32
    Thanks for asking! It is running really good! It doesn't pull as hard as the 400 I built and took out- but it is silky smooth, and actually sounds pretty stout through the flowmasters.

    I have a low idle issue (never dies- but idles at 400-500 in gear). I don't know what the "target idle" the computer is looking for, but I am reading it might be due to no VSS. Computer is constantly trying to lower the idle due to the next problem-

    I also keep getting a "higher idle than expected" code- since no VSS, the computer thinks the car is not moving, and doesn't understand a high idle when coasting. Dakota digital has a VSS sender that goes in line with the speedo cable. Might look into that.

    I also had some fuel delivery issues due to pump mounting- which were due to bad mechanic (me). Pump supplied 13psi to the pro-jection no problem, but couldn't muster 58psi when under half a tank of gas. Moved it lower than the tank, and problem solved (I hope). I ordered the Walbro pump everyone raves about and will keep it in the car just in case.

    Oh yeah- BRAKES. In 1958, Chevrolet did not have auto-adjusters on the brakes. I know that I already "knew" that- but apparently filed that in the way back... Pedal was smushy and travelled to the floor occasionally (like when I really needed to stop) Anyway, adjusted them up, and have better pedal feel, and it stops MUCH better.

    Next thing is to get the VSS code and TCC codes handled. The TCC can be tricked with a light bulb for now- then off to J&S for dyno tune! I can't wait to see my hooptie next to a CTS-V or Corvette up there.

  33. #33
    Well, fuel pump is still crap. Will not pull fuel... especially in traffic, when it is hot as bejeezus, in Pueblo this past weekend. Yuck.

    I checked the part number on Orielly and they have a note now that says, "An additional low pressure feed pump may be required." Crud. It literally has to pull it through 8" of fuel line through the outlet (in the sender) to the pump (now mounted below the tank). Can't do it.

    SO- Since I had the new Walbro pump- I thought, "I'll throw this on in the campground".

    It did not come with fittings... (the ones the instructions say to use)
    The fittings are metric...
    And require a copper/brass washer to seal...

    Home Depot doesn't have those. Neither does Autozone. After which I quick looking.

    Ordered the Walbro "install kit" and hope to have it soon.

  34. #34
    update-

    VSS installed (Dakota Digital SEN-01-4160)- it has 2 wires- I put one to the low VSS pin and the other to the high VSS pin. PRESTO- low idle GONE. Seriously- this made a HUGE difference. It also cruises better around town- off idle response is much smoother.

    Tricked TCC with a light bulb- no change in drivability- but it should hopefully take care of the CEL.

    Fuel pump is still problematic- new Walbro does not like to pull fuel when under 1/2 tank either. Fittings/internal tank lines look good (they are fairly new), no obvious holes or cracks.
    For now we keep it above 1/2 tank and all is well.

    Drug it to Idaho and Montana and put all sorts of miles on it sightseeing there. Drove it out to the Warbirds Auto Classic this past weekend.

    Downtown Bozeman over the 4th of July-



    And after the Warbirds Auto Classic- the ball bearing wheel bearings were growling- I think I figured out why-



    $300 worth of new ball bearings and back to silky smooth again!
    Last edited by PovertyByJeep; July 31st, 2018 at 04:44 PM.

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