1995 k2500 running 97 5.7 vortec w/ tbi. Multiple codes, won't idle under 1k rpm, i'm at a loss

Discussion in 'Feedback, Help and Suggestions' started by jalatl, Aug 5, 2017.

  1. jalatl

    jalatl Newbie

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    Hello all,

    I've been following the board for quite a while but this is my first post.

    I've got a 1995 k2500 and two weeks ago I swapped in a 5.7 vortec from a 97 gmc yukon. I'm running the tbi off the old engine with an aftermarket dual plane intake and a carb spacer with tbi adapter plate. All sensors and accessories from the '95. Everything went well with the swap and I have put a couple hundred miles on it since then, but a few days ago it started stumbling off the line. It almost seemed like it wasn't getting fuel but if i let off of it and hit it again it would come back to life. the first day it only did it twice within 10 mins of starting. I was very low on gas so I filled up and it ran fine the rest of the day. The second day it happened a couple more times and seemed to have a slight random misfire. I checked timing and it seemed to be good but on the 3rd day i drove off to work and 5 mins down the road i noticed it wasn't taking pedal. I had to be very light on the pedal to accelerate, which worried me enough to turn around and take it back home. I bought a new fuel pump (a TPI unit for a '91 camaro) and did the swap today. I got the new pump in and now I'm at a loss. I turned the key and primed the pump and it seems to be working fine. I cranked it and it started right up and then died after a few seconds. Started it again and same thing. If i barely touch the gas it will idle around 1100 but as soon as i let off it dies.

    I checked all the vacuum lines ( all new when I did the swap) and everything is tight and connected properly as far as I can tell.
    I unplugged the MAP and it idles fine. Revs up fine with map unplugged as well but its running rich of course.
    I unplugged the temp sensor at the thermostat with the map plugged back in and it will idle but runs rough.
    I unplugged the TPS and it idles roughly.
    Unplugged the IAC and it idles high.
    I replaced all the sensors except the knock sensor when i did the swap as well so they are all new (actually, i did the IAC 6 mos ago).
    New distributor, New coil, new plugs and wires
    Vac gauge reads steady 20 at idle with map unplugged.
    Replaced the regulator spring with higher psi spring a few months ago (can't recall if it was 15 or 18 psi spring).
    All grounds are intact and have good contacts.
    I have MULTIPLE codes: iac, map, cts, tps, o2 (currently unplugged, had to order one and it won't be here until later this week but it's been like that since the swap), egr (deleted the egr doing the swap), etc. Injectors look like they are spraying a good pattern but heavy with map unplugged.
    I reset the iac with the aldl and no change.
    I cleaned the ecm ground wire and made sure the contact was good.
    Oil pressure is 50+.
    New fuel filter a few months ago and fuel tank looked very clean inside today.
    Fuel pump runs fine and continuous
    Battery cables tight and clean
    New Alt, new water pump, timing set, etc
    It had started hard 1-2 shift a few days after the swap, found vacuum leak and sealed it up and it shifted better but still very slightly harder than I am used to. I assumed it was ecm related at the time since I had not had it programmed to the new engine.
    I timed it with a vacuum gauge since I can't see timing marks... but it was performing well until now.

    I'm at a loss here. I'm starting to think the ECM or wiring is the issue since everything else is new. I know the TPI pump puts out more flow but the regulator should be limiting it as far as I understand. And it runs fine with the MAP unplugged so... I don't know. It's a stock ecm, I haven't gotten around to getting a custom tune yet but it's the last thing on my list of things to do... well, it was until all of this started happening lol.

    Btw, it was running GREAT for the last couple of weeks. Def more power that the old tbi engine! I was very happy with the swap until this problem came up!

    Sorry for being so long winded, I'm trying to be as thorough as possible so I don't waste your time. Any help would be greatly appreciated!! I'm usually pretty good with troublshooting but this one's got me stumped. Hoping there's someone out there that's seen this somewhere along the line. I've done a lot of research and I feel like I've covered the basics but I def may have missed some stuff! This is a great board so I'm thinking if anyone can help me I'll find them here.
     
  2. jalatl

    jalatl Newbie

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