2003 Chevy Venture 3.4 with insufficient EGR flow

Discussion in 'Domestics' started by Mobile Dan, May 20, 2008.

  1. Mobile Dan

    Mobile Dan wrench

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    This van runs fine, but sometimes the CEL comes on for a P0401 code. I haven't taken anything apart yet. Please give me an opinion as to what you think is the most likely cause.

    A. Passage between egr and intake is partially plugged. Can I clean it with a piece of wire about 5 inches long?

    B. Passage between egr and exhaust manifold is partially plugged.

    C. The egr is gunky and sticks sometimes.

    D. The egr has an intermittent electrical problem.

    This van has the very common 3.4 V6 and is totally stock. About 100,000 miles.
    Dan
     
  2. Gus

    Gus wrench

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    You pretty much have it covered....

    Inspect for the following conditions:

    • A vacuum restriction to the MAP sensor--A skewed MAP sensor reading can cause the PCM to read incorrect MAP changes during the EGR flow test.

    • An engine that is running poorly due to a mechanical condition such as worn piston rings, worn camshaft, etc.--These types of conditions can cause low engine vacuum and thus can cause a less than expected MAP changes during the flow test.

    • Excessive back pressure in the exhaust system may cause this DTC to set. This condition can cause low engine vacuum and thus can cause a less than expected MAP changes during the EGR flow test. Possible causes of this could be a restriction in the exhaust system or non original equipment manufacture (OEM) exhaust parts.

    • Exhaust system leaks can cause an insufficient amount of EGR flow through the EGR valve. This condition can cause a less than expected MAP changes due to insufficient exhaust back pressure. possible causes of this could be a leaking exhaust system, a leaking EGR pipe or non original equipment manufacture (OEM) exhaust parts.

    • A restriction in the intake manifold such as carbon deposits and casting flash
     
  3. Mobile Dan

    Mobile Dan wrench

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    Gus, thank you for the very descriptive info on what conditions might set the p0401 code.

    Maybe I should have asked more direct questions...

    What would be considered the most likely cause?

    Can I clean out the intake with a short piece of stiff wire without removing the intake? (I'm trying to give this customer a labor cost estimate.)

    Thank you,
    Dan
     
  4. MoparFan

    MoparFan Sr. Member

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    Dan, stiff wire could work, but I've found it better to use the frayed end of a speedometer cable or brake cable so it acts as a "brush" to clean out the passage. Whatever you do, make sure you don't leave any particles behind, as they can get caught in the EGR valve pintle.
     
  5. Mobile Dan

    Mobile Dan wrench

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    Thanks, Moparfan. I'll try to find something better than plain stiff wire if I have to clean out the passage.

    Is a plugged intake a common problem on this engine?

    Dan
     
  6. Gus

    Gus wrench

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    The plenum doesn't have to be plugged.....all it needs is a slight restriction, due to dirt/oil accumulating on the flashing in the passageway....the restriction is enough so that the slight opening of the EGR is not picked up by the MAP...
     
  7. Mobile Dan

    Mobile Dan wrench

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    Is a restricted EGR passage a common problem on the GM 3.4 V6?

    Can I clean it without removing the manifold? Just the EGR valve, and maybe the throttle body?

    Thank you for your help and patience,
    Dan
     
  8. Gus

    Gus wrench

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    Seen it happen more on 3.1's that 3.4's....

    Have seen people run a wire throughthe plenum and it worked.....here's the problem....you run the risk of breaking off a chunk of gunk or flashing, that can be sucked into the engine, and though remote, could get stuck under a valve, creating another problem....chances of this happening are rare, but it could happen.....

    The recommended method is to remove the upper plenum, and acid bath the passageway....

    But I have seen others take the shortcut and it works out fine....to quote Harry Callahan, "Do you feel lucky, Punk?"
     
  9. Mobile Dan

    Mobile Dan wrench

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    If I have to clean it, I will block open the throttle and use a shop-vac to blow air into the intake during the cleaning process. Hopefully, any chunks that come loose will be blown out of the passage instead of falling into the manifold.

    Thanks for your help,
    Dan
     

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