[Diy_efi] O2 Sensor or Computer

[Peter Foote]

> > After that, the block learn values all began to drop
> > to 125, which is the min. value I allowed. The O2 sensor was constantly
> > reading high and causing the computer to "de-tune" the motor so lean it
> > wouldn't run right. It's done this cycle a few times and really has me
> > puzzled.
>
> Nothing wrong with even 110s, so long as the car seems about right.   As
> long as you in the neighborhood, your fine.   If you want 128s, you'll
have
> to run Open Loop, but then your tune has to be spot on.

But the car doesn't run right. I had thought I made that clear when I said
it de-tuned lean. It starts stumbling really badly. I tried a minimum of 125
in a failed attempt to try and keep it from going lean so I could
troubleshoot this problem without killing the motor.

> > Anyone ever see an O2 sensor intermittently work?
>
> Yes,
> and I've seen that from the exhaust gases being too cold to keep the O2
hot
> enough to function.

Have you specifically seen an unheated O2 sensor work fine and then start
reading rich and not work again? I drove it for an hour with it working
fine,except at idle, the whole time.

> > Can the computer back drive the O2 sensor?
>
> The O2 is basically a battery that needs heat and oxygen to generate a
> voltage.

That didn't answer the question but unless my computer is bad, it puts about
0.4V onto the O2 wire. Is it supposed to?

> I'd recommend first finding a 3 wire O2 and trying that.
> Bruce

I didn't want to buy a 3-wire until I knew the O2 was the problem. I did
some testing though so read-on.

I borrowed a IR temperature meter. The steel pipe was reaching at least 530
degees F (it basically maxed out the IR temp probe) at the O2 location,
right after the header collector while running at about 1500rpm. The O2
sensor would go rich to lean if I varied the computer O2 input between 0V
and 1V. During this testing, it seemed to work fine. Also, it was working
well before the pipe reached it's maximum temperature so it wasn't maginally
hot enough.

After this test, I found the pipe temperature drops off to about 350 degrees
F at idle so I know I will have to put a 3-wire in it to get it to read
properly when idling. As it idled the O2 began reading rich even when I
drove the O2 computer input to 1V and made it heavily lean.

I then pushed the motor back up to 1500rpm and the O2 kept reading rich. I
couldn't get it to read lean again. I think I have a bad O2 since if it was
hot enough to work in the first test then it should get hot enough to start
working again during this test. I've never heard of an intermittent rich O2
failure before though, anyone else? I always understood they failed lean and
then the motor begins running rich trying to compensate.

For everyone's information, the ceramic headers were about 150 degrees F
lower in temp ( around 375-400 degrees F) at the collector than right after
the collector, on the steel pipe, when I had the motor running at 1500rpm.
This really demonstrated to me how well they hold the heat in.

Peter


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