Misc ?? EFI

[Scot Sealander]

Bruce Plecan wrote:

> After that interesting post from Scott S. (thanks, by the way), I got
> a couple guestions.

You are welcome, glad you enjoyed it.

 
> The following is in reference to 82-92 gm EFI systems, but if someone 
> has other info., would they comment about the manufacturer.  If true or 
> false for the later, please note the exception.

You can't really make a blanket statement about how this or that GM
system works.  The process is similar, but not identical for different
engine/chassis/years, etc.

 
> WOT, is it only truely correct to call this PE, rather than even 
> mentioning "open loop"?.

When in PE, the process is open loop, i.e., the feedback device is not
being used.  It can be in open loop, and not in PE, like when the
engine is first started.
 

> Is it really closed loop, open loop, and PE?.

Well, PE has to be open loop for the systems mentioned.  When in closed 
loop, it is not in PE.  When in open loop, it may or may not be in PE. 
When in PE, it is open loop. 

Remember that this is just process control.  When a process is open
loop, it is not using feedback.  When it is closed loop, this means that
it is using some feedback to monitor and adjust the process.

As the feedback device used here is the O2 sensor, and it is only 
accurate at 14.7 AFR, it is only used when the commanded AFR is 14.7.

 
> In stock calibrations has anyone seen a EGR Enable that would
> enable other than when in closed loop?.

I think so.  Would have to go look at some stuff to be sure.

 
> Any one have any clues about diagnostics for when flagging/rather
> than coding errors are present?.

If a sensor is out of limits, the process enters "sensor substitution" 
mode as soon as that condition is present.  It continues to use this
mode for the time the sensor is flaged bad.  If the bad condition
is present for the min time required while the associated test 
conditions are also met, it will set an error code.

You may have heard some say that it goes into "limp home" mode.  But this
mode is reserved for a bad processor, PROM or bad A/D.  Bad sensors just 
use substitute values.  The accuracy of these values are up to the coder 
and calibrator.  I feel that the sensor substitution scheme should not be 
so good as to prevent the owner from getting the sensor fixed....

Scot Sealander   Sealand at clarityconnect.com