How To Disable the EGR Valve
By Rob Robinette
A few years ago scientists discovered they could reduce the formation of nitrogen
oxides (NOx) during combustion by keeping combustion temperatures below about 2500 degrees
F. They did this by injecting an inert (non burning) gas into the air/fuel mixture of the
engine. The inert gas helps cool the combustion event to below the threshold where NOx are
formed. It turned out that exhaust gas works well as an inert gas. The EGR valve allows a
metered amount of exhaust to enter the intake of the RX-7's engine. An ECU
controlled solenoid controls vacuum to the EGR. The valve is closed with no
vacuum, open with vacuum.
The chart on page F-125 of the Mazda 3rg gen Workshop
Manual shows that the EGR valve only opens under relatively light loads between 1050
and 3850 rpm. It is closed at idle, deceleration, rpm above 3850, and heavy load. So it
seems that there would be little benefit in disabling the system. The emission book,
"Understanding Automotive Emissions Control," states that an engine may need
it's timing retarded and/or the air/fuel mixture richened to prevent detonation but since
the RX-7's valve is closed under wide open throttle we don't need our mixture richened.
I've heard from several list members that have disabled the valve with no apparent change
in engine operation.
The EGR valve
How to Disable the EGR Valve
This mod is for off road use (racing) only, it is not legal for
public highway use vehicles. The Exhaust Gas Recirculation valve can be easily disabled on
93 non-California spec cars by simply plugging or removing its vacuum line. I decided to
disable mine in the hopes of prolonging its life so it won't stick open (bad) and cause
problems. If it's needed in the future to pass emissions I'll reinstall the vacuum hose.
California spec cars and cars manufactured in 1994 have an electrical sensor on the EGR valve
that reports the valve's position to the ECU that will cause the Check Engine light to
illuminate if you disable it. To get around this you have to remove the valve and
and fabricate a blocking plate to place between the EGR valve and its mounting
hole on the lower intake manifold. This allows the valve to open and
close but not inject any exhaust gas into the intake. Just buy a sheet of
aluminum from a hardware store and cut the plate using tin snips. Use the EGR
valve itself as the template. See the Replace
For cars without the EGR electrical connector (like mine, see picture
above), the EGR valve is very easy to disable. The valve is located just above the
down-pipe on the lower intake manifold. To get to
the valve you'll have to remove the black plastic crossover tube that runs from the Y-pipe
to the intercooler. With the crossover tube off you'll be able to remove and plug it's
vacuum line. You could also just pinch it shut with a heavy duty paper clip. I chose to
remove the vacuum line and cap the ends (see photo).