Ragnarok <yum@yermom.org> wrote:
: For those who didn't see the posts or don't remember, I heard about a
: technique to bypass the cat: splice a resistor of the appropriate size
: into the black wire coming from your downstream O2 sensor, and the
: altered readings will make the computer think the cat is still there.
: Most feedback I got didn't seem to think it would work. Well, my good
: buddy Jason tried it on his Neon, and it worked beautifully, so I gave
: it a try for the hell of it. And what do you know, it works! The Dak
: starts easier, runs smoother, especially cold, and idles smoother. Power
: and MPG are unchanged, as they were when I first took out the cat. 1
: weird thing: just taking out the cat, no check engine light. install the
: resistor, truck runs better, check engine light comes on and stays on.
: *shrug*
William,
This isn't a flame, so I sincerely hope you don't take it as such,
I'm just looking for some clarification... :-) Based on your post, it
sounds like after you used the resistor to alter the downstream O2 sensor
signal, you got a check engine light? The main reason most folks are
looking to simulate the downstream signal is to eliminate the check engine
light, rather than to change engine operation, thus most folks would
probably suggest that this method doesn't work. As far as the improved
operation goes, I've seen many cases of the "placebo effect" when doing
mods, is there any chance this could be what is happening?
Just to interject a theory here...
Based on what I have read, the downstream O2 sensor isn't *supposed* to
have an effect on engine operation, its basically there to tell the
driver when its time to buy a new cat. However, I have seen posts from
people who are convinced it actually does have an effect on engine
operation, so perhaps it does.
Anyway, on to the theory. In order for this to make sense, we have to
assume two things:
1- That the downstream O2 sensor has an effect on engine operation
2- Since you were getting no check engine light before, the computer was
operating under the assumption that your cat and downstream O2 sensor
were operational. (Otherwise, it would have turned on the check
engine light.)
My theory would be that the computer was adjusting the operation of the
engine based on bad data from the downstream O2 sensor, causing the
engine difficulties. When you inserted the resistor, the computer
either detected that the sensor was bad or the data from the sensor was
far enough out of whack to cause the computer to assume either the
sensor or the cat is bad. In either case, the computer would now ignore
the data coming from the downstream O2 sensor, and cease to (mis)adjust
the engine based upon that data. If that's the case, I suspect the
same engine improvements could be had by simply disconnecting the sensor.
---Jon-
.---- Jon Steiger ------ jon@dakota-truck.net or jon@jonsteiger.com -----. | I'm the: AOPA, DoD, EAA, NMA, NRA, SPA, USUA. Rec & UL Pilot - SEL | | '70 Barracuda, '92 Ram 4x4, '96 Dakota, '96 Intruder 1400, '96 FireFly | `----------------------------------------- http://www.jonsteiger.com ----'
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