bernd@texas.net wrote:
> Let me rephrase something to make it a bit more detailed...(and yes, you're
> correct on the "not ALWAYS at 140-150" statement. The 140-150 range is a
> general temperature that is required (among other variables) for Closed-Loop.
I disagree with that temp range being a "requirement" for Closed-Loop operation -
mostly because I have watched late-model Dodge vehicles go into closed-loop (from a
cold-start) when outside as well as engine block temperature less than 40 degrees.
It is my understanding that as soon as the PCM can determine that the O2 sensor is
giving a "valid" signal - then it can close the loop and provide as close to a 14.7
to 1 ratio as possible as required by federal emissions. This is why almost all O2
sensors in todays production vehicles are of the self-heating variety - to enable
the PCM to close the loop sooner and thus lower emissions. The way the PCM
determines if the O2 sensor is giving a valid reading is by monitoring the O2 output
voltage for the first time it crosses the 0.45 V threshold. Because our O2 sensors
are heated - this ALWAYS occurs (during cold start) in less than 3 minutes. Ever
wonder why the color/amount of smoke coming out of the tailpipe (during cold start)
changes after about 1-2 minutes?
> The reason for this is that an engine running at 90-100 degrees is still too
> cold for reaching the proper 14.7:1 A/F ratio.
Temperature of an engine (or outside temp) has nothing to do with the A/F ratio
measured at the tailpipe. Think of it from the perspective of a sensor stuck into
the exhaust stream. It is just reading oxygen content and comparing it to the
outside/ambient oxygen content. It will sense an A/F ratio whether or not the truck
is running, hot, cold, under water, etc.
> Remember, colder engines
> require more fuel (basically like a choke on an old Carb).
I agree - and that is why there is a special mode in the PCM for that - warm-up
mode. While warming up (temp less than 140-150) there is an enrichment value
added. Look at the formula at the following URL:
http://www.diy-efi.org/efi332/equations/algorith.htm in the section on Fuel
Enrichments.
The reason I know all this is because I am nearing completion (after 3+ years) of a
custom PCB (Motorola 68332 based) that will provide both fuel and spark delivery to
any gasoline engine (1-8 cylinders). I hope to test it on a 3.0L Nissan V6 in the
very near future.
Latr,
Shane
-- '96 IndyRam-HisIndy-MPI/TB/Pulleys/AccelCoil/MPComp/HookerSuperComps/CompTAs '96 IndyRam-HerIndy-numbered(#142)"Track Truck" '74 Triple-Black Dodge Challenger Rallye 360 home-brew EFI R&D vehicle '68 Black Corvette Convertible 427 (For Sale)
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