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Thread: Fresh TBI Swap - No Start

  1. #1
    Electronic Ignition!
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    Fresh TBI Swap - No Start

    Pulling my hair out here. Just finished a TBI swap in my 86 K20. ECM is wired to 12v constant, and 12v on key/crank. Engine will crank, injectors pulse, distributor sparks, but will not fire. Doesn't even try. No spit, no sputter, just cranks. Advancing and retarding the distributor a few degrees changes nothing. If I hold my foot to the floor while cranking, it will sputter a bit and occasionally backfire through the TB and at least try to start. Seems like dist is 180 out, but I've checked four times, and I'm reasonably certain I'm on the money.

    For sake of argument, this is how I checked for TDC/distributor position: Pulled plug #1 (drivers side front), finger over the hole, bumped starter until compression was felt, crawled under truck and rotated flexplate until timing mark and balancer were aligned at 0. Rotor on distributor was pointing at cyl #1. Rotated dist until rotor was aligned with plug #1 on dist cap. Harness and coil inputs are facing the firewall, slightly towards the driver's side. Reinstalled cap and double checked plug wire routing.

    One thing I'm not certain on; the HEI dist had one pink wire providing 12v to the coil. I used that wire to power the TBI coil. However, on the modular plug for the coil, there is a pink wire and a white wire. My understanding is the white wire is only used for a tach signal and is not needed for anything else. Am I correct?

    Really frustrated. Hoping someone has some insight.

  2. #2
    Super Moderator dave w's Avatar
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    There are two connector plugs to the TBI Coil:

    Usually one of the TBI coil connectors is a 12 AWG pink wire with a 16 AWG white wire. The 12 AWG pink wire needs 20 amp power from the ignition switch in both Run & Start.

    The other TBI coil wiring usually has two wires (16 AWG Pink & 16 AWG White) that will send the Run & Start power from the TBI Coil to the HEI ignition Module on the distributor.

    One of the jobs of the ignition module is to send a Distributor Reference Pulse (DRP) to the ECM (sometimes called RPM Reference Pulse).

    If the ECM Does Not get a DRP signal from the Distributor Ignition Module, the engine will NOT START.

    dave w

  3. #3
    Electronic Ignition!
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    I'm using the stock/existing 12awg pink to provide 12v power the coil, which is the same wire that previously powered the HEI coil when the truck was carb'd. The other white lead on the grey connector is currently unused.

    The 16 awg pink and white "mini harness" runs from the black connector attached to the coil, over to the ignition module on the distributor.

    Do I need to connect anything to the white "incoming" wire that is typically paired with the 12 awg pink? My understanding is this is just a tachometer lead.

  4. #4
    Electronic Ignition!
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    Think I got it figured out. I believe the IAC was a little wonky. It was fully seated, not letting any air in to ignite the fuel. I held the throttle open 1/4 way and she lit off. I had to keep feathering the throttle until the IAC could get calibration from the ECM. She fires right up and idles real smooth now.

    I let her warm up, disconnected the timing advance and set the base timing at 0.

    Now to get that 700r4 TV cable dialed in and take her for a test drive.

  5. #5
    Fuel Injected! PlayingWithTBI's Avatar
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    Quote Originally Posted by JCampbell View Post
    Think I got it figured out. I believe the IAC was a little wonky. It was fully seated, not letting any air in to ignite the fuel. I held the throttle open 1/4 way and she lit off. I had to keep feathering the throttle until the IAC could get calibration from the ECM. She fires right up and idles real smooth now.

    I let her warm up, disconnected the timing advance and set the base timing at 0.

    Now to get that 700r4 TV cable dialed in and take her for a test drive.
    Good to hear you got it going. I don't know if you have seen this, it explains a lot...

    http://www.tvmadeez.com/article/index.php

  6. #6
    Electronic Ignition!
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    Yep. I'm using Bowtie Overdrive's TV Made EZ kit for the TBI.

    Screenshot_20190610-101406_Instagram.jpg

  7. #7
    Fuel Injected!
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    Key on engine off, IAC should go to ~145. Perhaps IAC is wired wrong. You make no mention of using BBC throttle body but your pic w lack of ridge at the bore opening suggest that. Pay attention to IAC wiring here: http://www.gearhead-efi.com/Fuel-Inj...o-7-4-tbi-swap

    Went back and read your older post saw that you have ultimate mods hence lack of ridge mention. Nonetheless, might want to check iac wiring if slammed shut key on.
    Last edited by stew86MCSS396; 06-12-2019 at 12:39 AM.

  8. #8
    Fuel Injected!
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    a lower cost option to adapt a 700r4 to a BB tbi is to cut the bell crank off a SB tbi and weld it onto the BB throttle shaft. make sure your TV cable is tight @ WOT. i do this by attaching a smal pair of vise grips onto the little stop at the end of the TV cable. I adjust 1 click at a time until i have about 1/16" of TV cable "free play" while holding the bell crank at WOT. you dont want it so tight that it strains the cable. DO NOT rely on the self ractheting mechanism and "call it good" especially if you have an aftermarket shift kit install (transgo, etc). Also, a pressure guage is HIGHLY recommended to confirm pressure and more importantly instant pressure rise. What i mean: as you begin moving the throttle with a properly setup tv cable, the needle on your guage should immediately beging to build pressure.

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