[Gmecm] Crazy 7730 problem - random numbers for TPS & ECMverywarm...

[David Allen]

And the answer is......

...a bad MEMCAL!

I don't know how it caused this, but changing to another MEMCAL (with the same program in it) cured the problem.

I erased and re-programmed that MEMCAL and again it did the same thing no matter what program I install in it. 

That one goes in the trash.

Later,
David
  ----- Original Message ----- 
  From: David Allen 
  To: terry ; gmecm at diy-efi.org 
  Sent: Sunday, March 17, 2013 8:46 AM
  Subject: Re: [Gmecm] Crazy 7730 problem - random numbers for TPS & ECMverywarm...


  It's a 1987 car, with a newer model ECM, possibly an early 90's ECM. 

  I'm going to check some things this morning and will see what the grounds look like.

  Thanks!
  David
    ----- Original Message ----- 
    From: terry 
    To: gmecm at diy-efi.org 
    Sent: Saturday, March 16, 2013 10:51 PM
    Subject: Re: [Gmecm] Crazy 7730 problem - random numbers for TPS & ECM verywarm...


    David,
    What year Buick are you working on? I have had issues with ground circuits on that ecm where the terminals become loose 
    cause skewed the data.
    Terry


    From: David Allen <davida1 at hiwaay.net>
    To: GM-ECM <gmecm at diy-efi.org> 
    Sent: Saturday, March 16, 2013 11:35 PM
    Subject: [Gmecm] Crazy 7730 problem - random numbers for TPS & ECM very warm...


    Hello guys, I've got a stumper of a problem.

    Just finished re-pinning a MAF ECM (old 3.8 Buick, has the 2 connectors) for 
    a 7730.

    I powered it up to see the data on the computer, and I get some strange 
    things.
    The fuel pump prime function and Check Engine light function as normal.

    When first powered up, the TPS shows a seemingly normal voltage. The TPS 
    reading will move with the pedal position. Then, gradually, it starts to 
    read a bogus higher and higher voltage, eventually stopping about 3V, with 
    no change when the pedal is moved.  Verifying with a meter, the TPS voltage 
    is stable at 0.5V and does operate normally with the throttle.

    The second thing is, the MAP reading is fixed at approx. 60 kPa. The MAP 
    sensor voltage is correct (measured with meter) and does fluctuate with 
    vacuum.

    Then, the ECM gets warm, after 3 or 4 minutes. This is without starting the 
    engine or activating anything.

    I have disconnected everything from the ECM other than the "A/B" connector, 
    and powered it up. The scan data does the same thing, TPS starts at low, and 
    after a few minutes it climbs.

    The TPS issue will return to normal (for a few moments) if I power off the 
    ECM and power on again. The MAP never reads other than approx 60 at any 
    time.

    The sensor +5V reference and sensor ground are correct and never fluctuate 
    even as the readings drift.

    I thought the ECM was damaged, so I tried another one. It did the same 
    thing. I know both these ECM's have worked correctly before.

    I'm running Code59 V.23 exactly the same as another identical engine which 
    runs fine.

    I've used the same diagram for 2 other conversions, and they both worked 
    fine. I am at a loss.

    Thanks for any insight!
    Sincerely,
    David 

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