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Stumble

This is a discussion on Stumble within the General Help forums, part of the LSx Technical Help Section category; When my car is cold and idling up to warm up it stumbles doesn't stall but acts like it's runnig ...

  1. #1
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    Stumble

    When my car is cold and idling up to warm up it stumbles doesn't stall but acts like it's runnig out of fuel. The deco pump is fairly new what's up with that??

  2. #2
    None Shall Pass Knight's Avatar
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    Check the fuel pressure at the rail, you should see 58 psi. You could also try cleaning the MAF, as that could be a possible cause as well. I take it you aren't getting a SES light?

  3. #3
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    No trouble code When it warms it's fine. 58lbs for lt or ls mine is lt. If pump is bad it's under warranty would you recommend a racetronic??

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    None Shall Pass Knight's Avatar
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    My mistake, I didn't catch you were a LT1. With the vacuum line disconnected from the regulator and plugged, you should see around 41-47 psi. With the vacuum line attached, it will vary. I'd expect around 35 psi or so. If you can monitor the pressure while driving, you should see nothing less than 40 psi.

    I've heard Racetronics are good, as well as Walbro.

  5. #5
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    Ran it today but let it warm up first. I got on it hard and it did fine. Reckon why it only cuts out when cold. By the way the opti- spark is gone I've got a msd distributor.

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    None Shall Pass Knight's Avatar
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    Hmm.....wonder if it's not an O2 sensor problem if it's only while cold. Strange you aren't throwing a code, although you could have it scanned to see if one is pending.

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    Scan it while it's cold??

  8. #8
    None Shall Pass Knight's Avatar
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    Cold or warm. Sometimes there will be a code pending that won't throw a SES light.

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    Senior Member Too Fast's Avatar
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    Quote Originally Posted by Knight View Post
    Hmm.....wonder if it's not an O2 sensor problem if it's only while cold. Strange you aren't throwing a code, although you could have it scanned to see if one is pending.
    Remember the PCM mostly ignores 02 sensors until the engine is warm.

    OP, have you ever had your injectors cleaned? The engine is supposed to run fat (rich) until over aprox. 160*. If they are partially dirty, that may show up like this. Also, deposits on you intake valves can cause this.

  10. #10
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    Quote Originally Posted by Too Fast View Post
    Remember the PCM mostly ignores 02 sensors until the engine is warm.

    OP, have you ever had your injectors cleaned? The engine is supposed to run fat (rich) until over aprox. 160*. If they are partially dirty, that may show up like this. Also, deposits on you intake valves can cause this.
    I would expect the problem to present itself even when warm, under a full load/WOT condition. It's something to look into though.

  11. #11
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    Also, its almost 20 years old. How is that fuel filter?

  12. #12
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    Fuel filter is pretty new but after it warms up it's fine. Wot no prob idle no prob cruising no prob. Just when cold and idled up

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