Optimal rpm for fuel economy???

Jörgen Karlsson jorgen.m.karlsson at home.se
Fri Sep 21 02:36:29 EDT 2001


The CIS cars without O2 sensors or catalytic converters sometimes start
running lean. This can be achived by raising the control pressure a bit, if
someone want to experiment with this an EGT meter is a very good tool. A
lambda meter helps too but it does not warn for high combustion

The EGT meter can be used to optimize timing and to warn if you are running
too lean.

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.

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.

The voltage from an ordinary lambda sensor changes very quickly from 0.2
volt just above lambda=1 to 0.8volts just below lambda=1. They are often
called switch mode lambda sensors because of this and that is what the ecu
looks for, if it is lean it enriches until the lambda sensor switches from
lean to rich and then the ecu start to lean out the mixture.

But I don't think that modifying the lambda signal will be very successful,
but it is very simple to try it. It can make a differance.

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...

Jörgen Karlsson
Gothenburg, Sweden.

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