Unusual problem with LH 2.2 system

[John Bertram]

>Here is a guess- when you drop the throttle completely, the injectors 
>quit firing  when under decel.  This as a common strategy for efi.  When 
>you lift, but not fully, either a value from the MAF (LH is hot wire, 
>right?) or or the fact that a throttle closed microswitch is not 
>engaged.  This results in the injectors firing, and the resultant black 
>plume.  You were probably going quite rich at full boost to reduce NOX 
>emissions.  Then you have excess fuel and exhaust in a hot fast moving 
>exhaust.  Whn you lift the throttle partially, you have leftover unburned 
>HC in the tailpipe and a suddenly slowly moving exhaust stream.  The 
>result is condensing hydrocarbons and water from the now stoichiometric 
>exhaust gases passing thru the catalyst.  The result is instant turbo smog.
>
>This is just my first guess.  I would bet that everythig is fine.  And 
>that you would never see this transient situation on the LA driving cycle 
>emissions test for Volvo certification ;)


Ok, assuming that this is not a problem, can anyone think of a good way to
eliminate the black smoke?  It doesn't look good.


John Bertram, Technician
Garry Small Saab
(Turbobricks list Admin.)
Volvo Turbo APC project (www.teleport.com/~bertram/volvoapc)
'87 Volvo 740 Turbo Sedan
'70 Toyota Corona Mk.I