Fuel Filter Replacement – 2005 Mercury Mountaineer

Most people know they need to change their oil and filter and perhaps even their air filter, but there are a number of “forgotten filters” on cars and trucks these days that are often neglected. We’ll be focusing on the fuel filter today. Fuel filters should be replaced every few years or about 40-50k miles (more if you work and fill up in dirty/dusty environments). If your check engine light comes on and the boys at Advance/Auto Zone/Oreilly/etc. get a P0171 and/or P0174 “lean” code you could have a restricted fuel filter. “Lean” means that the engine is getting too much air or not enough fuel. It could be caused by a host of other things, but replacing your fuel filter is good, cheap maintenance and it can usually be done by your average DIYer in a driveway without too much trouble.


The first step is to locate the filter. This one hides behind a plastic shield. Your owner’s manual (you do still have that right??) may tell you where it is, or you could get a Chilton, Haynes, or Clymer manual to point you in the right direction. Honestly, in the shop, I often get faster results off Google that I do from all of our service information software if I’m dealing with a simple thing like a fuel filter.


Once you’re confident you can get to the thing and replace it, you need to relieve the fuel pressure so you don’t have pressurized fuel squirting everywhere. Modern vehicles keep the fuel system pressurized at all times to facilitate quick a quick start-up time when you’re running late for work in the morning, so you need to run the vehicle without the fuel pump operating for a few seconds. Remove the fuel cap to relieve tank pressure and locate the fuel pump fuse or relay and remove it. Again, the owner’s manual helps here. Start the vehicle and let it run until it stalls (usually a few seconds). Sometimes the vehicle won’t start and that’s ok; just crank the engine for about 5 seconds to make sure the fuel pressure is relieved.


The days of using a flat head screwdriver to loosen old-school worm drive clamps are over! For modern vehicles (like this 2005 Mountaineer) you will need a special tool to disconnect the fuel line from the filter.


I got this set from Lisle Tools which has worked for just about every fuel, transmission, and A/C fitting I have ever removed. You can buy most of these tools individually, but I like to have them all in one set. If you do much work with these types of fittings, this set is almost a necessity.


To remove the line, position the tool as shown and push the fuel line in toward the filter and tool. This will relieve the pressure on the springs or fingers holding the fuel line on. While pushing the line in, push the tool into the fuel line (away from the filter), relieving the tension on the springs. Pull the tool and the fuel line away from the filter and it should slide right off. This takes some practice so don’t give up if you can’t get it the first time or two.


The other side of the fuel filter on this vehicle didn’t require a special tool. I simply had to release the clip at the bottom and push it up, releasing the line from the filter.

*Be careful when you remove these lines as fuel will pour out even though the pressure is relieved* I hope you don’t smoke anyway, but it should go without saying that you should leave anything with open flame or embers in the house for this job.


With the filter off, take a white paper towel or tee shirt and empty the filter from the inlet side to see all the junk the filter has trapped over the years. There is an arrow on the side of the filter indicating the direction of fuel flow, so pour from the inline side, not the outlet side.


Yikes! This was the original filter from 2005 and it shows! This vehicle wasn’t running poorly because of the fuel filter, but it obviously needed to be replaced.

Installation of the filter is as simple as firmly reconnecting the lines until they snap back in place. Sometimes the filter body is held on to the frame by a strap or bracket, so keep that in mind as well.

Every vehicle doesn’t have a replaceable fuel filter (my ’98 Cherokee filter is built in the pump, for instance), but if your car has one, it’s a good idea to replace it from time to time. Hope this helps and happy wrenching!

All photos were taken with my iPhone 5C.


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