From: Wally Plumley [wplumley@bellsouth.net]
Sent: Tuesday, November 07, 2000 5:11 PM
To: res062vo
Cc: 928@list.928oc.org
Subject: Re: [928OC Public] Engine Performance... or not.
At 04:25 AM 11/7/00, you wrote:

  Wally, thanks... 89 S4 
    ----- Original Message ----- 
    From: Wally Plumley 
    To: res062vo 
    Sent: Monday, November 06, 2000 7:08 AM 
    Subject: Re: [928OC Public] Engine Performance... or not.


    At 02:51 AM 11/6/00, you wrote:
      I'm having an engine performance problem.  I read a short article in 928 
      International, that said if you're having trouble in achieving a smooth 
      idle, it may be indication of a "brain" problem.  Since I purchased I've 
      never been able to achieve a perfectly smooth idle, even after a new 
      timing belt and tuneup.  At idle, every few seconds it's like theres a 
      little studder. My real concern though is twice I have experienced an 
      engine "cutout." I'm not sure how to describe it?  It's like someone 
      flipped a switch to cutout 4 of the 8 cylinders, almost no excelleration 
      - very rough.


That may be an exact description of what is happening. The '89 and up 928s have 
an ignition circuit temperature sensor system. This system has a temperature 
sensor on each sid of the engine that monitors exhaust temperatures. If one side 
has a lower temp, the system kills the fuel injection for those four cylinders. 
This prevents pumping unburned fuel into the cat, which prevents overheating and 
a possible fire.

This is one of those situations where you need to catch the malfunction as it is
happening. Perhaps the best way of doing that is to remove the carpeted cover from 
the ECU units on the passenger's kick panel. Look at the rear of the visible ECU 
- you should find a clear relay package, about the size of a cigarette pack. Inside 
the relay will be two LEDs - one red, one green. If the temp sensor senses low exhaust temp from cylinders 1, 7, 6, 4 (right ignition coil) the system will illuminate the red LED and shut down Injection Circuit I that feeds those cylinders. If the other sensor senses low temps from cylinders 5. 8. 3. 2 (left ignition coil) the system will illuminate the green LED and shut down Injection Circuit II that feeds those cylinders.

This means that you need to leave the cover off and keep an eye on the red/green 
LEDs. If either of the LEDs illuminates, the problem is probably with one of the 
exhaust temp sensors. The sensors are located in the bottom of the exhaust 
manifolds, and are replaced from beneath the car. Occasionally, the sensor can 
be removed and turned, and will then work for some time.
 
Wally Plumley
928 Specialists
www.928gt.com




        Common themes (conincidental or not); both times cutout occurred minutes 
        after cold start with outdoor temperatures around 45-50 degrees F, both 
        times after slowing from around 40 mph to a standing stop then cutout 
        occurred when attempting to accelerate... this could be extremely 
        dangerous... both times I pulled over, shutdown the car, waited a 
        minute, restarted and it idled and performed normally again.  99.9% 
        of the time the car runs great.  Confused! Does this sound extremely 
        familiar to anyone? Is all this inconsistency "brain" related?  Can 
        someone with experience expand on this before my 928 leaves me powerless 
        in the middle of a intersection in front of a semi truck?????



  Impossible to answer without knowing the year model of your 928.


  Wally