How to Move the Fuel Filter to the Engine Bay
By Rob Robinette
It's an incredible pain in the butt to change the fuel filter so I
relocated it to the engine bay. I inserted the filter and fuel pressure gauge (see photo
below) in the engine compartment between the brake master cylinder and the engine.
Note: Moving the fuel filter to the engine compartment may allow fuel vapor to
develop in the fuel filter due to the high heat it is exposed to. Vapor lock
might occur - it hasn't happened to me but it is probably the reason Mazda
placed the filter where they did.
What You Need
The easy way-get a fuel injection rated in-line
fuel filter with 5/16" hose fittings from Summit Racing, an 18 inch
length of 5/16 inch fuel injection hose (to replace the stock filter) and two 5/16"
The way I did it-I used a K&N miniature billet
10 micron fuel injection fuel filter ($70). It comes apart for easy cleaning. Get the
following parts from Summit: AN-6 to 1/4" NPT straight adapter ($5); AN-6 to
1/4" NPT 90 degree adapter ($9); three foot long AN-4 steel braided fuel pressure
gauge line ($30). For an electric fuel pressure gauge you can attach the sender in place
of the steel braided fuel line.
Get the following from an auto parts store: two 5/16" hose to
1/4" NPT adapters; one female to female 1/4" NPT adapter; one three way female
1/4" NPT adapter; two 5/16" hose clamps; 18" length of 5/16" fuel
injection hose (to replace the stock filter).
Details of fuel filter & fuel
Put the parts together like the top picture. Use Teflon
tape on the NPT threads but don't use it on the AN connections. Be careful how you tighten
the AN connections on the filter - you have to hold the filter with a thin wrench while you
tighten the AN nut.
Release the fuel pressure before you cut the fuel line,
see the Release Fuel
Pressure how to. It's important to remove the gas cap while
you do this to minimize fuel spillage, the less gas you have in the tank the better.
The line you want to tap in to
Tap into the fuel line nearest the dip stick. The fuel
line has an insulating wrap around it. Cover the line with a rag when you cut it to keep
any fuel from spurting out. Put the hose clamps on the lines, then insert the filter (or
filter and gauge line assembly) and tighten the clamps. You may have to trim the
insulating wrap to make room for the filter. It was easier for me to work on the lower
hose connection by getting under the car just behind the left front wheel.
K&N Billet Fuel Filter below
the brake master cylinder
Securing the gauge line and gauge
Attach your fuel pressure gauge and secure the
line/gauge by putting an insulated hose clamp around the fuel line and secure it to one of
the 10mm bolt holes in on the fender (see photo above). Using the 3 foot long fuel line
you lets you tape the gauge to your windshield for engine tuning.
Remove the stock fuel filter (see the Fuel Filter Replace how to) and replace it with an 18" length of fuel injection hose, this
is a real pain in the butt but you only have to do it once versus doing it every 30,000
After installing the filter/gauge and tightening the
clamps you need to prime the fuel system. See the Release Fuel Pressure How-To for instructions. Make sure there isn't any pooled fuel anywhere
before you start the engine. Take a good look for fuel leaks in the engine compartment and
at the stock fuel filter location before you start the engine. Enjoy.