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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" hose clamps.
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).
Fuel filter & gauge hose

Details of fuel filter & fuel gauge install

Close-up of filter


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.
fuel_gauge.gif (6086 bytes)

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.
fuel_filter2.gif (71525 bytes)

K&N Billet Fuel Filter below the brake master cylinder

fuel_gauge_line.gif (54030 bytes)

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 miles.
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.
Rob Robinette

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