Optimal rpm for fuel economy???

Huw Powell audi at mediaone.net
Thu Sep 20 22:09:30 EDT 2001

> Lambda controlled engines are harder to tune, the first thing that needs to
> be done to get real good milage is to get the car out of closed loop without
> activating any enrichments. When the car is in closed loop the AFR will
> cycle from lean to rich and back again all the time, this is a requirement
> of a common catalytic converter. That's far from economic and todays cats
> don't need these large doses of unburt fuel anymore.

hmmm, cats have never "needed" unburnt fuel, in fact it is one thing
that will kill them fast and the reason for OXS/Lambda sensors being
used on cat. equipped cars.  The oscillation is from just barely lean to
just barely rich, the car is actually very close to stoich. the whole

> But let's get back to lambda controlled cis cars again, maybe making a small
> amp for the lambda signal would let the car run a bit leaner. The lambda
> value oscillates around .45 volts, if the signal was oscillating around 0.15
> volts ther would be a bit leaner mixture.

a small voltage source (not referenced to the cars ground or power
supplies of course) placed in line with the OXS signal could be used to
bias it "off center" as you describe.  If it was switched, to choose
"economy," and adjustable for optimum results, it might just help a
little by letting the car run lean perpetually under light loads (ie
highway cruising).

> BTW, CIS is a piece of shit fuel injection system that should never be
> touched while it's working. The Bosch gods will haunt you for the rest of
> your cars lifetime. If you do any modification you will most likely regret
> it, something will break. It does not have to be related but something
> expensive will break...

it's not that bad, a bit Rube Goldberg-ish, but it does work.  And once
you understand the entire system it is not difficult to work on. 
Although modifying it, as you say, can result in far from optimum
results... unless you are really sure of what you are doing.

Huw Powell



More information about the quattro mailing list