Re: 3.9k Ohm Diagnostic mode on a P4.

["Bruce Plecan" <nacelp@bright.net>]

> >Bruce Plecan wrote:
> >> Then for a while this was the mode that when done on the assembly line,
that
> >> the EPA demanded that the car be recorded in.  What the policy is now
for
> >> the new car recordings is now I haven't a clue.
> >That's strange!  AFAIK, only GM has an analog limp home mode.

> I'm still a little confused by this term above "analog limp home
> mode". Is there infact some analog fueling and INJ firing taking
> place, or is this mode simply a way for the ecm to revert to analog
> defaults if it's *sensor* base goes awry? Reason I'm asking is that
> some previous posts suggested that fueling would still continue even
> if the memory storing the ecm code had failed. I'm puzzled as to how
> this would be possible, since the ecm fires the INJs, both timing-wise
> *and* driver-wise.

If the processor fails, there is what's called a Redundant Fuel Devise.
It's set by the network resistors.   On the P-4 memcals it's on the memcal
itself, and on the C-3s it may be soldered in or socketed.

> I guess what I'm asking is: what is the extent to which the ECM is
> able to fail and still have the INJs fire. Mind you, I'm OK with and
> presume that the IGN would continue on without ecm intervention/EST,
> via it's own autonimous module; but I'm unclear as to where the INJ
> timing/firing is going to come from, if the ECM fails to the point
> where it can't execute code anymore. This currently dudn't make sense
> to me.

I don't know who well they would start without any prom in them, but once
running you can do about anything and the engine will run, thou not very
well.  I've run a 747 with nothing but the injectors power and grounds.
While not at all a stock engine, I think I got 25 MPH out of it, so I could
at least drive.
Bruce
>
> TIA,
> Gar
>
>
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