Stuck in Open Loop

[Mark Fabiny]

Don't know Mazda's very well, but my thoughts apply to EFI in general:

Felix Miata 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.

A bad engine coolant temp sensor will do this.  Also, a bad MAP (or MAF)
sensor could be the culprit (I would think the check engine light would
flag MAP/MAF faults).

>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).

The transient compenation is usually tied to TPS, MAP/MAF, and RPM.  I
don't know how good RX-7's were about this.  As for steady cruise, you
should see switching back and forth between rich and lean.  Again, the
main sensors are ECT, MAP/MAF, and TPS. 

> I've only swapped ECU & O2 sensor between the two so far without effect.

Could both O2 sensors be bad - or maybe just lazy?  Unheated O2 sensors
can cool off at idle or light loads and not respond appropriately.

> The too rich only had a broken thermostat stuck open, but a new one
> changed nothing.
> --
> "It cannot be emphasized too strongly or too often that this great
> nation was founded, not by religionists, but by Christians, not on
> religions, but on the gospel of Jesus Christ! For this very reason
> peoples of other faiths have been afforded asylum, prosperity, and
> freedom of worship here."  Patrick Henry

I see you are using an old history book for this quote.  Why don't let
the liberal police exchange it for one of their "new and improved"
versions.  After all, we wouldn't want to let our thinking be confused
by the facts, would we?

> Team OS/2
> FIXx ADDRESSs TOo REPLYy.
> Felix Miata

P.S. I also saw your email complaining about "Rad and Coolant" thread. 
You mean this isn't the DO IT YOURSELF ANTIFREEZE list?

Mark Fabiny