DIY_EFI Digest V4 #577

[William T Wilson]

On Wed, 13 Oct 1999, DIY_EFI Digest wrote:

> My friend has an RX-7 (early '90s pretty much standard equipped I
> believe) which is running fairly rich. I haven't looked at
> it yet but I'm going to help him troubleshoot it later this week.  Does
> mazada use a similar system to GM?  Im thinking it's pretty different ..

I don't know too much about the GM motors, but I can say a (very) little
bit about the Mazda...

The Turbo II ECU is pretty much a modern EFI controller.  There is an
oxygen sensor, which is used at low rpm and part throttle.  At higher
speeds or full throttle, the ECU switches over to fuel maps.  The ECU also
controls the wastegate via (I believe) vacuum activation in order to
regulate boost.  The ECU has fuel maps up to very high boost levels, but
does not use most of them as there is a fuel cut at around 8 psi of boost.

The rotariness of the motor doesn't really affect the ECU very much.

If the engine is running rich only at idle, there are a number of simple
adjustments to correct that.  If the engine is running rich at full
throttle, it's probably supposed to - the turbo models do run fairly rich
in order to prevent knock.  The rich running at other conditions is very
possibly a bad O2 sensor, or it could be something else.  but it probably
isn't the ECU failing as they are quite sturdy.

How do you know the engine is running rich?  It could be, for example, a
plugged catalytic converter, which can cause similar symptoms...