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Re: Cross counts Posted by SWEDECAR [Email]  (#112)  [Profile/Gallery]
(more from SWEDECAR) on Mon, 3 Jan 2005 09:52:16
In Reply to: Cross counts, Wingerr, Mon, 3 Jan 2005 02:39:18 Members do not see ads below this line. - Help Keep This Site Online - Signup |
Your are right about carb equipped cars, the normal cross count is about 1 per sec.
Cross count is everytime the trace passes over the middle (up or down). You can see a little arrow on my scope that is pointing upwards at this screenshot and the text "rich" in the window. As soon as the trace goes down and the arrow point downwards it changes to "lean" and it is a count.
The only times I have seen another problem messing with the O2 sensor value(instead of the sensor itself) it shows up as that the sensor is stuck (flat lined) on either rich or lean or that it stays at rich or lean peak for a longer time before changing.
As long as the sensor is having a nice curve on either top or bottom, the rest of fuel system is ok.
The O2 sensor can go bad in several ways.
Loosing top or bottom Volt values is one way, reading 0.2-0.6 V instead of 0.1-0.9 as in best scenario.
Being lazy (but good Volt value)is another way and that problem is more visible at idle. At 2500rpm it might very well come to life and look ok to the naked eye but when you have a labscope like mine that registrar cross counts you can usually pick out a bad one since it shows up as maybe only 8-10 in cross count.
With my labscop I can also pick out "flat spots" on the air mass meter.
Sometimes when an AMM goes bad it have a bad spot at a certain Rpm where you feel the car is lagging during acceleration.
By using a special tool to open up the throttle I can dial the rpm in by 100 at the time and look for when the O2 sensor is starting to show either a lazy pattern or go flat lined. That's where the bad spot is on the air mass meter.
Anders
posted by 67.113.8...
, Sun, 2 Jan 2005 10:12:22, Sun, 2 Jan 2005 19:48:35, Mon, 3 Jan 2005 09:52:16 <-- Viewing This Message
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