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  1. #1
    Sr. Apprentice AZ_Kid's Avatar
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    Ft. Mohave, AZ
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    Default Excessive Sute (Black stuff)

    Just got back from a 2900 mile road trip. I noticed a lot of sute (black stuff) around the lower rear panel where the exhaust exits. I got the truck used, i know it's got a flowmaster just not sure how far they went back with it. What would be the cause of the excessive black stuff?
    03 Suburban:
    6" CST lift, 17" Mountain Crusher Rims, 35" Toyo MT tires, Fox 2.0 shocks and a Flowmaster exhaust

  2. #2

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    What you're referring to is "soot," and it's made when either 1) you drive a diesel, or 2) you're running too rich. How fast do you normally cruise on the highway? Fast enough to work the crap out of the engine? It will run a little bit rich at high load, but probably not rich enough to cover a body panel with soot. Normally, you only see that with high-powered forced induction vehicles, running VERY rich, down in the 11:1 AFR range.

    I think you've got a fuel metering issue. Do you know what your kinda mileage you're getting?

  3. #3
    Legend cascott325's Avatar
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    Default

    good posting mateospeed. though 2900 miles is a long haul, i would almost expect to see some black. no much, but some. do you burn any oil? do you have a tune installed?
    2000 silverado with a 5.3l v8, shorty headers, upgraded plugs, 10 mil wires, magnaflow high flow cats, flowmaster 80 series muffler(2 in 2 out) w/ 18 inch stainless silverline tips. i have a k&n CIA. its a 4x4 z71 offroad package. Ls model.
    extended cab 160k miles, truxedo low profile bed cover, diablo sport predator tuner.
    reman tranny @ 130k miles
    Chris

  4. #4
    Sr. Apprentice AZ_Kid's Avatar
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    Default

    Speed ranged from 60-75 mph and i averaged between 12-13 mpg. I have made this trip with two other vehicles and it didn't have the soot. The other two were stock though.

    Not burning any oil and no i don't have a tune
    03 Suburban:
    6" CST lift, 17" Mountain Crusher Rims, 35" Toyo MT tires, Fox 2.0 shocks and a Flowmaster exhaust

  5. #5
    Legend cascott325's Avatar
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    Default

    hmmmm... mow many miles are on your vehicle. you most likely running lean, but you could do a tune up. new plugs and wires, cap and rotor if you have them, seafoam, etc
    2000 silverado with a 5.3l v8, shorty headers, upgraded plugs, 10 mil wires, magnaflow high flow cats, flowmaster 80 series muffler(2 in 2 out) w/ 18 inch stainless silverline tips. i have a k&n CIA. its a 4x4 z71 offroad package. Ls model.
    extended cab 160k miles, truxedo low profile bed cover, diablo sport predator tuner.
    reman tranny @ 130k miles
    Chris

  6. #6

    Default

    yeah good idea cascott a good tuneup and sea foam or similar product will help out your intake is probably carboned up pretty good and just needs a good cleaning up

  7. #7
    Jr. Mechanic bd1326's Avatar
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    Default

    what year is the vehicle, is it burning oil?
    bd1326

    2005 Chevy Silverado 6.0 Vortec 4X4
    K&N Air Filter: Stock Replacement
    E3 Spark Plugs
    Magnaflow Single Exit Exhaust
    Rough Country Leveling Kit
    Skyjacker Add-a-Leaf
    Much More To Come


    "Understeer is hitting the wall with the front of your car. Oversteer is hitting it with the rear."
    - NASCAR driver "Fireball" Roberts.

  8. #8
    Sr. Apprentice AZ_Kid's Avatar
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    Default

    Bought the truck with like 86,000Got 90,000 and some change on it now. I have noticed driving around the last couple days it seems to have a little more get up and go now though.

    It's an 03 and no it's not burning oil
    03 Suburban:
    6" CST lift, 17" Mountain Crusher Rims, 35" Toyo MT tires, Fox 2.0 shocks and a Flowmaster exhaust

  9. #9

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    I'm with mateospeed on this one: excessive soot is usually an indication of air/fuel mixture problems. The PCM's primary purpose is to control fuel mixture, so the first thing I'd probably do would be to put a scanner on it and see if there are any trouble codes (or pending codes). I'd probably also put a fuel pressure gauge on it and see if fuel delivery is running where it should. Assuming your '03 has the same "continuously recirculatiing" fuel system like my '98, the regulators sometimes develop a leak that will let unmetered fuel into the intake which makes it run rich.
    '98 K1500 Suburban LS 5.7 L 4L60E NV246 ARB
    '92 Ford Explorer XLT 4x4 4.0 L A4LD BW13-54 Trac-loc rear
    "My toys were the greasy cogs and springs and pistons that lay around all over the place, and these, I can promise you, were far more fun to play with than most of the plastic rubbish children are given nowadays." Danny in Roald Dahl's Danny The Champion of the World

  10. #10

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    Quote Originally Posted by cascott325 View Post
    hmmmm... mow many miles are on your vehicle. you most likely running lean, but you could do a tune up. new plugs and wires, cap and rotor if you have them, seafoam, etc
    In my opinion, this is backwards. Soot is an indication of a rich condition (unburned fuel in the exhuast collect on the first solid surface it sees: the bumper), not a lean condition. A lean-running engine can produce very hot exhaust, potentially leading to a MELTED bumped, but not a black one. Unless that's actually what's happening, and it's black because it's melted. check it out for us.




    Quote Originally Posted by AZ_Kid
    i averaged between 12-13 mpg
    This does seem a little low. A tune up is in order, although you don't have a distributor, so cap and rotor (the most commonly replaced items) are out. Plug wires are probably fine if you're not getting any misfiring. I might try an engine cleaner, but get the actual GM engine cleaning chemicals, not the sea foam junk. Check the plugs to see if they're discolored or black; that'll give you another indication if it's running richer-than-normal.

    I hope this is helpful.

    -Matt

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