From: Tony Williams 

Phil Payne wrote:
>> Even cars, come to think of it. If the engine management system
>> goes down most car engines fall back to a "Keep Alive Mode"
>> using hardwired electronics; the engine will keep running, but not
>> at all well.
>
> It's called "limp home mode".

You're quite right. I misremembered the "Keep Alive Memory" we[*]
used to remember engine tuning parameters while the main battery was
changed. Ended up ditching KAM because the dynamic tuning happened fast
enough that it wasn't worth the extra hardware needed to save the results.
The limp-home function is as I described though.

[*]Ford Dunton, programming the EEC IV back in the 80s.

> The Audi rally cars of the early 1980s actually used marine fuel injection
> management.  Maritime law requires a more graceful degradation in the event
> of failure - this is very useful in a rally car because it means a car with
> a "failed" system can get back to service and get it put right.

On the RS 200 we ended up having to use 2 Iveco truck injectors per
cylinder just to get enough fuel into the beast. That was an interesting
engine management strategy.

> There is, IMO, a commercial opportunity in buying up cars of this nature.
> Fix up the limp home issue (sometimes just a cheap temperature sender) and
> sell the car with restored performance.

I wonder how many are driving around now in permanent limp-home mode.
Rotten performance and fuel economy, but they'll keep working. Strictly
speaking, a failed sensor won't put the engine into limp-home though. As we
defined it, limp-home was for a complete failure of the processor module -
as long as the CPU was running it would use fallback engine mappings to
compensate for sensor failure, much as you described for the Audi. Oh the
fun I had testing that on the high-speed track ...

--
Tony

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