Stuck in Open Loop

[Tuck]

At 10:03 AM 10/24/97 -0400, you wrote:
>Is there a FAQ that covers this? What are the most common component
>failures that cause this (other than O2 sensor failure)?
>
>I have two of Mazda's first attempts at production EFI, '84-5 RX-7's.
>One stays in open loop continuously. The other goes rich when it should
>go lean (slight off-throttle or steady cruise), and lean when it should
>go rich (light acceleration in closed loop).
>
>I've only swapped ECU & O2 sensor between the two so far without effect.
>The too rich only had a broken thermostat stuck open, but a new one
>changed nothing.

I had a problem like that on my 87 RX-7 once, for all the years I owned
itit would not go closed loop (which was obvious because the rich/lean idle
mix adjust didn't do anything).  Last year as I was stripping the emissions
crap I happened to remove my EGR valve and found that it was:

1.) Leaking vacuum
2.) Stuck Open
3.) had incredible amounts of carbon in it (like a charcoal briquette had
been hammered in).

As soon as I replaced it with a block plate that I got from Mazdatrix, the
engine started going closed loop at idle.  I suspect that the problem was
that with the EGR stuck open the o2 sensor was so far out of range that
computer couldn't do anything with it.


Justin"Tuck" Cordesman
SOLID BRASS-> Dancing with the devil in the pale moonlight.

Lux in tenebris lucet et tenebrae eam non comprehenderunt.
The Light Shines in the Darkness and the Darkness does not see it.