5.7L TBI stalling and low idle help

Discussion in 'Engine Performance + Maintenance' started by James Archer, Jul 22, 2020.

Car Parts
  1. James Archer

    James Archer Newbie

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    Praying that someone can help me diagnose this issue I'm having. At slow speeds and under load the oil pressure drops to 5ish and stalls out. Also while driving down the road it'll cut in and out for a few seconds. The motor seems very weak to me vs what it should be. It's a 89 k1500 5.7L TBI

    Here's a list of what I've done so far.
    - Replaced the TBI base gasket.
    - New fuel pump and fuel filter.
    - All rubber fuel lines. I did have to patch the old lines into the new lines at the pump.
    - Oil and filter 10W30
    - 2 1/2 X 10 air filter
    - New MAP sensor and IAC sensor
    - 2 new vacuum lines
    - Changed the timing from 14 to 8 ( which helped the throttle response before the truck got to fill temp. Them the "hiccupping" got worse)
    - visually checked the injectors. Loaded it in the driveway and had it checked by a friend.
    - New plugs and wires. Checked the firing order also

    From the discussion I had with someone he's mentioned the EGR being clogged and to delete that, torque converter, distributor.

    The butterflies on the throttle body are a little pitted up but I don't think it would cause that big of an issue. It's got the stock exhaust manifold and cat but it fell off after that so there's no muffler for back pressure. Which im in the process of custom designing a system for it. Just trying to get the truck to run a little more stable.

    Any suggestions or places to start to figure out this issue? I'm tired of just throwing parts at it and wasting money at this point.

    93E3CE13-E2F5-4982-9FC6-61D444DC9C87.jpeg
     
  2. mtl111

    mtl111 Newbie

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    Check the fuel.pressure regulator, it has a spring inside...they break. It's located at the back of the throttle body so remove the throttle body from the intake, easier to mess with


    Sent from my SAMSUNG-SM-G930A using Tapatalk
     
  3. PlayingWithTBI

    PlayingWithTBI Desert Old Guy

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    How did you do that? It should be set @ 0* with the EST wire disconnected. What is you fuel pressure? Is your CTS sender working properly? After checking your timing, you really need a scanner to see what's going on with it.
     
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  4. thinger2

    thinger2 I'm Awesome

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    You need to reset your base timing to 0
    disconnect the distributor reference wire which is a tan wire with a black stripe located under a plastic cover on the passenger side firewall.
    Since you disconnected the idle air control valve, that needs a reset to.
    Dont do anything else untill youve done this first no matter what anybody tells you.
    Base timing at zero. reset iac.
    go from there.
    Lots of youtube vids and forum posts on how to do this so look it up but a tbi needs to be at zero with iac functioning before you can do anything to it.
    Pay close attention to the iac reset. the pintle that sticks out of the end of it needs to be very carefully pushed back in or it will break when you put power back to it.
     
    Last edited: Jul 23, 2020
  5. James Archer

    James Archer Newbie

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    I reset the base timing to 0 with the plug unplugged last night but when I plugged it back in the timing was at 14-15. From what I understood from the internet it should be around 4. So I redid the timing and went past 0 with it unplugged and plugged it back in, checked it and now its around 8-9.
     
  6. James Archer

    James Archer Newbie

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    Just got done and still having an issue. I reset the timing unplugged to 0 replugged it and it's around 14 ( off of the timing marker ) took out the IAC and reset the pin. Unplugged the battery for 5 minutes. Put a wire in-between the A and B connectors. Let that sit for 5 minutes. Disconnected that started it drove it down the road and still no luck
     
  7. PlayingWithTBI

    PlayingWithTBI Desert Old Guy

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    No, 14 - 15 is fine. You set a 7.4L to 4* BTDC with the EST wire disconnected. I have my 5.7L running at ~20* FWIW.

    Here's how to calibrate your throttle body's IAC and TPS

    How-to-Tune-a-GM-EFI-System.pdf
     
  8. evilunclegrimace

    evilunclegrimace Does not always play well with others

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    This is not correct! 3 of my trucks run some where around 20+ degrees with the computer controlling the timing.

    Set your timing to zero degrees with the EST bypass wire disconnected, then reconnect the EST by pass wire. Then set your base idle speed.
    Ground ALDL terminals A to B KOEO and disconnect the IAC. Start the truck and see if you have the correct idle speed (425 plus or minus 25 RPM in drive and in Open loop. THEN see what you controlled timing is. Another thing to check is the TPS and make sure that it is not out of spec.
     
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  9. PlayingWithTBI

    PlayingWithTBI Desert Old Guy

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    :lol: That's another way to put it! :cheers:
     
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  10. thinger2

    thinger2 I'm Awesome

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    I think thats kinda the moral of the story.
    You really cant diagnose a TBI without the base timing correct.
    Too many people get wrapped up in looking at controlled timing without understanding all of the variables that can affect controlled timing. So they get frustrated and start twisting the distributor all over the place in an attempt to chase a number that doesnt mean shit untill everything else is working.
     

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