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  1. #1

    Default Warm start black smoke

    I've lingered here for a while, but this is my first post. Hopefully someone will have some ideas.

    I have a '99 C2500 Burb with around 80k miles on the 7.4L. A couple of weeks ago I noticed that on warm starts it will crank and crank before it starts up. Sometimes I'll have to pump the gas pedal a couple times. When it finally does start, there is a bit of black smoke that dissipates quickly. On cold starts, it turns over like a champ. No problems what so ever.

    Any suggestions?

    Thanks in advance!

  2. #2

    dwill3015's Avatar
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    Jan 2007
    Yacolt, Washington
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    Welcome to the site! hopefully another member here with knowledge on the 7.4 will jump in and shed some light on your problem.
    Washington State
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  3. #3


    black smoke from a gasser??!!!??

    and by warm start you mean if you were to turn the truck off to order at a drive thru or sometihing?


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  4. #4


    Well, not exactly. It's more pronounced when after the truck has been driven enough to warm up, and then turned off for more than just a couple minutes, even up to a few hours.

  5. #5


    Quote Originally Posted by RussCrypto View Post
    Well, not exactly. It's more pronounced when after the truck has been driven enough to warm up, and then turned off for more than just a couple minutes, even up to a few hours.
    when was the last time the fuel filter was replaced?

  6. #6


    Just over a year and 15k miles ago.
    Last edited by RussCrypto; 12-07-2008 at 08:59 PM.

  7. #7


    One thing you might want to check is your coolant temperature sensor.

    the coolant temp sensor signal acts as a choke on fuel injected engines, when it is cold it puts more gas in the engine (like pulling the choke on your lawnmore when you first start it) and as your coolant temp warms up, it tells the computer to lean out the gas mixture.

    If the sensor is bad and is sending a cold coolant temp to computer, the computer would always be putting too much gas in. When you're starting from cold, that wouldn't be a problem, but when your engine is already warm, the air/fuel mixture would be too rich to start well and you'd need to open the throttle (pump the gas) to get more air in to allow it to start..the extra gas would come out as incomplete combustion and carbon deposits (black smoke)

    New sensor is only $11.99 and can be checked with a ohmeter

    Only thing is usually a bad CTS would cause a CEL code...but maybe it isn't bad enough to throw a code.
    Last edited by Big6ft6; 12-12-2008 at 05:02 PM.

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