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Thread: Idle Stumble

  1. #1

    Default Idle Stumble

    My 1990 305 1500 runs great..... just put in new timing gear set and distributor along with fresh valve grind.
    Everything is whiz bang until I reconnect the timing bypass wire, then it stumbles and stalls out if left to just idle.
    Any input?
    Last edited by kcfocus1; 08-10-2011 at 12:30 AM.

  2. #2
    Sr. Mechanic Ethan's Avatar
    Join Date
    Sep 2009
    Location
    Cedar Park, TX
    Posts
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    Default

    Did you time the engine correctly? Make sure your crank position sensor was working?
    1994 Chevy Silverado 1500 Ext Cab 350 cuin TBI in dark Chevy blue
    160,000+ miles
    Original paint
    Original interior
    Original engine and tranny
    wrecked twice stolen once
    Diamond Plate bed rails
    Power windows
    Original Alloy wheels
    Original fancy smancy cup holder
    Tow package
    Original plastic bed liner
    K&N Cone Air Intake
    Dual MagnaFlow exhaust(not true dual) with chrome tips
    MSD Street Fire Performance Ignition coil

  3. #3

    Default

    1990 no crank sensor and yes timing is correct.

  4. #4
    Sr. Mechanic Ethan's Avatar
    Join Date
    Sep 2009
    Location
    Cedar Park, TX
    Posts
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    Default

    If it has a PCM it has a crank position sensor, you just got to look for the thing, it's the only real explanation of why it stalls out when you bypass the...timing bypass wire? Why do you have to bypass that? Now I don't get what you are doing...

    Ok, so the truck runs great, until you bypass the timing wire...which is connected to the crank sensor to determine the actual timing of the truck..well of course it would die if you bypass it, if the PCM no longer has the crank sensor position, it doesn't know when to inject fuel and when to tell the ignition coil to fire.

    Idk, that's my best guess, unless you did something wrong.
    1994 Chevy Silverado 1500 Ext Cab 350 cuin TBI in dark Chevy blue
    160,000+ miles
    Original paint
    Original interior
    Original engine and tranny
    wrecked twice stolen once
    Diamond Plate bed rails
    Power windows
    Original Alloy wheels
    Original fancy smancy cup holder
    Tow package
    Original plastic bed liner
    K&N Cone Air Intake
    Dual MagnaFlow exhaust(not true dual) with chrome tips
    MSD Street Fire Performance Ignition coil

  5. #5

    Default

    My truck is a 1990 Chevy 305 aren't crank sensors included in OBD 2? My truck is OBD 1. Also truck runs grear with bypass disconnected..
    as soon as I connect it the idle starts to stumble and it will stall out. I see fuel being sprayed during reconnect and intill it stalls. Thanks
    for any input. Am driving it for five days with bypass discoed cause I hate using the starter motor at each red light.

  6. #6

    Default

    Does anyone have any input I may exercise on this stumbler?

  7. #7
    Sr. Mechanic Ethan's Avatar
    Join Date
    Sep 2009
    Location
    Cedar Park, TX
    Posts
    150

    Default

    Quote Originally Posted by kcfocus1 View Post
    My truck is a 1990 Chevy 305 aren't crank sensors included in OBD 2? My truck is OBD 1. Also truck runs grear with bypass disconnected..
    as soon as I connect it the idle starts to stumble and it will stall out. I see fuel being sprayed during reconnect and intill it stalls. Thanks
    for any input. Am driving it for five days with bypass discoed cause I hate using the starter motor at each red light.
    OBD 1 still uses a crank sensor, how else would you and your PCM read RPMs? Sounds like you messed something up electronic wise, might not the be crank sensor, but I don't know anymore, I'd just take it to a shop, or ask this question in the powertrain sub forum.
    1994 Chevy Silverado 1500 Ext Cab 350 cuin TBI in dark Chevy blue
    160,000+ miles
    Original paint
    Original interior
    Original engine and tranny
    wrecked twice stolen once
    Diamond Plate bed rails
    Power windows
    Original Alloy wheels
    Original fancy smancy cup holder
    Tow package
    Original plastic bed liner
    K&N Cone Air Intake
    Dual MagnaFlow exhaust(not true dual) with chrome tips
    MSD Street Fire Performance Ignition coil

  8. #8

    Default

    OBD-1 has no crank position sensor, it uses the pickup coil in the distributor

  9. #9

    Default

    Now that we have established that Any suggestions to the cause ?

  10. #10

    Default

    Double check to make sure your not off a tooth when you stabbed your distributor.

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