EFI and leaded gas

[robert dingli]

Johnny asked,
>  ...
> If there is anyone out there that has figured out how to make the sensors
> behave with lead, I would be really interested in how you did it.
> 
> -j-

FWIW, I have been using a second hand single wire EGO sensor from a 
late '80s Toyota 3SG in my 6 cylinder Jaguar running leaded petrol.
The sensor has worked well for over two years and around 40K km
connected to a voltmeter LED bargraph for display (but not control).

I beleive the initial effects of lead on the zirconia sensor are to
slow the response.  I haven't been able to detect any problems visually,
but closed loop control is another matter.  The intake event to sensor
reading delay (including the sensor delay) is one of the ultimate limits
on conventional control strategies, resulting in a limit cycle around
the set point (usually stoiciometric).  Any extension in the sensor
signal delay will have an adverse effect on closed loop control.

The EGO sensor and gauge is really only useful for detecting lean, rich
or transient AFRs.  I have tuned the engine to run relativley lean
while cruising and slightly rich at higher throttle openings.  I don't 
know how rich or lean these settings amount to, but after a couple of 
years using the gauge with a programmable efi/ignition system, one 
gets a fairly good idea how the system responds to different settings.

If you only wish to use the sensor for display purposes, then I would
recommend trying the sensor with leaded petrol otherwise stick with
unleaded.  An interesting point to note is that 'unleaded' doesn't
necessarily mean zero lead.  It usually means that the fuel has a lower 
lead percentage than the specified legal maximum limit.  New Zealand, 
for example, has a higher percentage of lead in its 'unleaded' than some
countries have in their leaded fuels.  Consequently, some of the cars
destined for that market have different EGO sensors to cope.


Regards,

Robert Dingli
'74 Daimler Sovereign 4.2,  AEMS Wolf Injection + Multi-coil ignition 

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             Robert Dingli           r.dingli at ee.mu.oz.au

Power and Control Systems                 Thermodynamics Research Lab
Electrical Engineering                    Mechanical Engineering
   (+613) 9344 7966                          (+613) 9344 6728
  University of Melbourne, Parkville, 3052, Victoria, AUSTRALIA
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