Yet another O2 sensor fakeout trick

[James Seabolt]

"Mark Romans" <romans at pacbell.net> wrote:

>>Hi James:  With a GM ecm (Unless it is some strange app) the ecm ignores the
02 sensor when at more than 70% throttle anyway. It goes into PE (Power
Enrichment) and goes to a richer commanded afr.  So making the 02 "Read"
lean won't change the pw.<<<

The throttle position switch on my L-jetronic system has only two contacts.
They are either opened or closed. One detects idle and the other wide open
throttle. So the FI system never goes into power mode unless it is actually
under wide open throttle.

I checked the TPS switch the other day (had my mom actually hold the
accelerator to the floor) and the switch closed so I know that's working.

Since I can reach 5 pounds of boost without evening been under wide open
throttle while going up a hill, the FI system never goes into power mode so
the O2 sensor tells the computer to cut back on the pulse rate when it sees
all this extra fuel from the 5th injector and extra fuel pressure.

I beleive that by simply breaking the circuit between the O2 sensor and
computer as soon as I enter the boost zone, this helps get fuel into the
motor quicker which cools the combustion chamber down and prevents detonation.

I have been thinking about something. Since the O2 sensor will never give
an output of more than .9 volts my trick may not work. If I drop the
voltage between the O2 sensor and computer from .9 volts to say .3 volts,
this might cause the computer to pulse the injectors to the point where it
floods the engine. 

I imagine that if the computer is trying to shoot for a specific mixture
(such as 13:1 or .9 volts under wide open throttle) because the output of
the O2 sensor maxxes out at .9 volts, simply dropping the voltage to .3
volts is as far as it will go.

So the computer might increase the pulse rate trying to shoot for a richer
mixture but because it will never see .9 volts, it overshoots.

There is one way to find out, which is to just try it. I will try using a
diode like one guy mentioned and see what happens.





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James Seabolt -----> mailto:jseabolt at intermediatn.net
Webpage: http://users.intermediatn.net/jseabolt/
ICQ # : 7344463

United States

1980 FIAT 2000 TURBO Spider injected (John Deere aspirated)
1981 FIAT 2000 Spider (Rest in Pieces)
1981 FIAT X 1/9 (Injected)
1994 JEEP Wrangler (2.5l )
1976 Chevrolet Pickup (454 Big block/7.3 liter) 
     
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