EGR Code 71 resolved--non-conventional and surprising

Discussion in '80-Series Tech' started by monteburns, Feb 17, 2009.

  1. monteburns

    monteburns

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    Over the past few YEARS I've been battling that blasted code 71. I've foolishly replaced every part in the system in an effort to solve this problem.

    Ater reading multiple threads again and again, I went through the FSM tests and everything tested out as they should, including vacuum levels. When driving, my EGR simply acted as if it were always off. My gas mileage was terrible (worse than normal), I had engine ping even after tearing down the engine and scrubbing the carbon off and the CEL would come on immediately after two drive cycles.

    So I read a post by Chris Wilcox explaining that the VSV, when hot, would simply not work, even though it would pass the FSM tests. Remember, when the VSV is not functioning, it cancels the EGR system by opening up the vacuum and eliminating the "suck" from the the modulator.

    Anyway, so I simply plugged the line to the VSV, essentially making it so the EGR is on all the time. After doing this, I neglected to reset the light before taking off. As I was driving, the light went off by itself and has not come on for over two months! So now my EGR is on all the time, but the ECU likes what it sees. My only concern is that my emissions may be crappy at low RPMs and may not pass.

    This of course, won't work on 1995 and newer (ODBII) as you'll throw a 402 code, but nonetheless, my gas mileage went back to normal and the pinging disappeared.

    Who'd a thunk?
     
    Last edited: Feb 17, 2009
  2. super90

    super90

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    So you were getting pinging?

    I had recently replaced my vacuum modulator with a factory new unit with the blue sticker on it. Next thing I know, truck is pinging. I took it to my indy to troubleshoot and he says "vacuum modulator is bad". I tell him it's about a year old and should be fine. He orders a new one and proves it to me. Yes, the part was new, but it didn't operate correctly. It passed all the tests per the FSM, but when installed it didn't open the EGR valve all the way and threw off things making the engine ping. I watched all this with old part, then watched him put in another new EGR modulator and the problem disappeared immediately.

    Might be your problem too.

    FYI, I had also replace all EGR components a few years ago, just because, and all new vacuum lines. I had the intake off and figured it good PM.
     
  3. monteburns

    monteburns

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    I was getting fairly significant pinging when the EGR wasn't able to switch "on" because of the VSV canceling the modulator. Once I got the VSV out of the way, the pinging disappeared.
     
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