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

[David Allen]

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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