Re: Duty Cycle Meter

[Russ Southerlin <russell.s.southerlin@lmco.com>]

Orin,
Other handy functions of a Duty Cycle Meter:

Since I recently ripped out and replaced almost my entire fuel injection
system I have lately setup a O2 sensor meter inside my car to make sure
I was not running too lean. I have also been playing around with the
Duty Cycle and have found that the DC is real handy for finding vacuum
leaks. As you move and push on the rubber hoses (ISV, Banana Hose,
Injectors etc.) if there is a vacuum leak and you change the amount of
air entering the engine by pushing on the hose you will see a change in
the DC. A meter would give you a good continous health check.

I have also been checking my DC with a oscilliscope and have found that
it is a square wave at a 14 millisecond frequency. This square wave
oscillates about 2 milliseconds (total) back and forth from its set
point. This would be about a 15% change in DC. I think I have heard that
when the O2 sensor gets old this number will increase. With a meter you
could easily tell when to change your O2 sensor. 

I can't tell any difference in the ability of the F/V to keep the O2
sensor at 0.5V with setting the DC from 40-60%. I have found that with a
DC setting of 42% average (the high portion on the scope oscillates from
5-7 mSec. 5/14=35%, 7/14=50%, 42% average) there does seem to be better
throttle response. This is just a seat of the pants observation but it
seems like the turbo boost pressure comes up earlier at low rpm making
for better throttle response.

I am not 100% sure when I talk of 42% DC if it is the same as others.
When observed with a scope I think the high signal (+12V) is when the
F/V is closed and a low (0.0 V) is when the F/V is open. This 42% number
would then mean that the F/V is closed 42% of the time and open 58%. I
do know from 50% DC that you have to turn the 3mm screw CCW to go to
42%.

Russ
87 5KTQ
Littleton, CO