Yet another O2 sensor fakeout trick

[CLsnyder]

----- Original Message -----
From: James Seabolt <jseabolt at intermediatn.net>
To: <diy_efi at efi332.eng.ohio-state.edu>
Sent: Sunday, May 16, 1999 7:46 AM
Subject: Re: Yet another O2 sensor fakeout trick


> "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.
>

MUCH simpler method - install a boost detection switch - preferably
adjustable (make one from a vacuum retard diaphragm and a microswitch if
necessary) and connect it with the WOT switch in the TPS. If the WOT switch
closes at WOT, put the switch in parallel. If it opens, put it in series.
This way EITHER WOT or boost will put the system in PE mode.
>
>
>
>
> ----------------------------------------------------------
>
> 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)
>
> ----------------------------------------------------------
>
>