CO Emissions

[Seth Allen]

> 
> Steve, thanks for the reply.  I stated the problem wrong yesterday.  Here is the
> actual situation:  HC 455/450 loaded-fail, 459/450 idle-fail
>                    CO 1.05/3.75 loaded-pass, 0.74/5.00 idle-pass
> I changed my O2 trigger level from .57 to .60 for the idle and loaded areas 
> which resulted in todays readings:
>                    HC 393/450 loaded-pass, 486/450 idle-fail
>                    CO 1.51/3.75 loaded-pass, 0.85/5.00 idle-pass
> This change corrected the loaded readings as expected and the idle CO as well, 
> but did not effect the idle HC as expected.  What are causes for ignition 
> misfire?  After checking the obvious, wire, plugs, vacuum leaks, what adjustment
> do you think I can make to the FI and ignition that might improve the idle HC.  
> I can change the idle O2 trigger voltage separately and I can adjust the 
> ignition timing over the whole range.  Since this is a closed loop system any 
> changes to the fuel map are nulified by the O2 sensor loop.  I'm currently 
> running 10 degrees of advance at idle.  Thanks, me.
> >

I have a couple of suggestions.  I don't know what the engine is, but 
this might help.  First, the o2 sender might cool offtoo much to work at 
idle unless it is stuffed right  up close to an exhaust port.  Even 3 
wire heated EGOs (O2) sensors cann cool quite a bit.  A fix can be to 
crank up the idle to the max allowed.  This heats the o2 sensor up a 
little and can help.  Too lean at idle will cause a misfire.  Sounds like 
a richer idle will smooth out misfires.  The CO is low indicating no lack 
of oxygen, so it's probably a lean misfire at idle.  If you can cut the 
EGO out at idle and default slightly rich at idle , the CO will rise 
slighly, but the reduction in misfire will drastically reduce the HC.  I 
would also run as much ignition timing as i could, without pinging.  10 
sounds low, but i don't know what the motor is or the exact gasoline.  I 
am used to super unleaded at 92 (RON+MON)/2 with a small bore.  I am used 
to 12-14 degrees advance static, but again it all depends.

Just my $0.02  

Seth Allen 


student,

Vehicle Research Institute