Question about GMC Sierra

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86 gmc high sierra k1500

Recently my truck has started blowing black smoke, idleing rough at stop lights and getting poor gas mileage. What would cause this?

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If the check engine light is on, you would need to check the computer for trouble codes first.
If the engine is fuel injected, it could be a bad injector. If it has a carb, it could be a sticking choke or an internal leak.

Posted on Apr 30, 2013

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SOURCE: 3.9 v6 4x4 check engine light, runs rough

Replace the ECT sensor.
And letme know. If you feel any diference. ok.

Posted on Aug 16, 2008

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SOURCE: 96 gmc suburban 2500 blowing white smoke, bad gas mileage

white smoke indicates a blown head gasket check for milky looking oil on the dipstick

Posted on Feb 13, 2009

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SOURCE: Tailpipe BLACK , exhaust reaks of gas !

garage mans company.
broken plugs.

Posted on Mar 12, 2009

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SOURCE: Black smoke from exhaust,no idle in warm temps-97 Nissan 2WD 2.4L

I had a 1995 nissan pick up with a similar problem, may want to try cleaning out or replacing the EGR valve.

Posted on Jul 23, 2009

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SOURCE: Excessive black exhaust on 2003 GMC Sierra Duramax Diesel.

This is what i would try (cheapest first) redexe/wyyns
injector cleaner,double dose,then i have put 1gal gas in 10gal diesel to increase burn temp (you may encounter a hot start problem temporarilly)then if still smoking, get a compresion check on the engine(this will tell you volumes)
by the way the NATO tanks put in 1/3 gas in diesel to stop it freezing in arctic conditions.any more than 1/3 can result in problems.

Posted on Mar 17, 2010

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This is what i would try (cheapest first) redexe/wyyns
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The blue smoke can be one of two thing.

oil drop from the valve stem (from engine head to cyclinders)
or
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===
I will take a 5-10 minutes high rpm (not redline) ran on the highway.
Pay close attention to the rear view mirror and look for black diesel soot.
=== I will use Diesel Cleen or similar product to condition the fuel. (keep moisture down)
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I can not rule out excessive blown by.
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When was the last valve adjustment?

Please post the actual odometer on the engine and I will follow up on it.

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