cold starting

[eric schumacher]

Hi ric
Obviously you are not getting enough of the right kind of fuel.  By that I
mean not atomized enough.  There is a curve in one of the bosch books on how
much fuel it takes to start a cold engine.  It is unbelievable the large
amount required. A lot of the fuel is wasted of course because of poor
atomization.  Bosch discusses this as a design feature of their cold start
injectors. An interesting and related point is the VW experience with Warm
engines. 
On CIS engines they of course have a cold start injector that squirts when
the engine is cold and the engine is cranking. Worked great when the engine
was cold, But when the car was driven a short distance like a mile or two
and left to sit for a half hour the things would not start no way.  This
condition was most frequently encountered in cars that were a year or so
old. The factorys solution,after ignoring the problem for a few years, was
to add a "cold start pulse relay"  In addition to the previous stuff this
relay gives the cold start injector one quick goose every time the starter
engages, regardless of temp.  Presto mo more problem.  On my DIY EFI based
on Bosch stuff the cold start algorithm I use is when air is flowing into
the engine and the cylinder heads (air cooled engine) are cold I squirt fuel
into the manifold. The squirting is duty cycle modulated at a fixed rate
with the duration determined by a pot and cylinder head temp. The pot
setting is empirically determined
Lotsa Luck Eric
85 GTI with VR6 power