99-04 Mustang Fuel Filter Replacement

My used 99 Mustang GT was having some trouble with warm starts. One possible candidate is the fuel filter. Fortunately 99-04 Mustang fuel filter replacement is pretty easy. Since it’s an old car, even if the fuel filter wasn’t the problem, it’s good preventative maintenance. I went ahead and did the work.

Parts Required

Filter tool and new filter

Filter tool and new filter

Besides a jack and jack stands to lift the car, this job only requires a quick disconnect tool and a new fuel filter:

Depressurize the Fuel System

There's a fuel pump switch in the trunk on the driver's side behind this panel

There’s a fuel pump switch in the trunk on the driver’s side behind this panel

Before you start, you want to depressurize the fuel system. If you don’t, the pressurized gas will spray everywhere when you disconnect the fuel filter. Aside from simply being messy, this is also dangerous, as gas vapor is extremely flammable. Fortunately, the Mustang has an easy way to do this via an inertia switch in the trunk, on the driver’s side.

Remove the panel by undoing this plastic connector

Remove the panel by undoing this plastic connector

Pull back the liner and there is the switch

Pull back the liner and there is the switch

The trim is removed by undoing a plastic connector and pulling back on the cloth liner, as pictured. You can see the inertia switch at this point. It is the black plastic box to the right, with the orange on top. This switch is intended to shut off fuel in the event of a crash, as I understand it, but it is also the approved way to cut off the fuel pump.

With the car running, unplug this plug

With the car running, unplug this plug

Unplugged, the running car will run out of fuel and shut off

Unplugged, the running car will run out of fuel and shut off

Now, with the car running, unplug the inertia switch connector. The car will run for a few seconds and then shut off. Voila, the fuel system is as empty as it’s going to be.

Lift the Car

I like to lift the car with the front wheels on wheel ramps and the back wheels on jack stands, making it level

I like to lift the car with the front wheels on wheel ramps and the back wheels on jack stands, making it level

The first step is to lift the car high enough to get to the fuel filter. It’s located in front of the rear axle, above and to the front of the rear differential. You might be able to get away with only jacking up the rear of the car. To get enough space to crawl under, I ended up putting the front on Rhino Ramps as shown, and then jacking the rear of the car up and putting it on jack stands.

Remove the Old Fuel Filter

The fuel filter is just above the rear diff

The fuel filter is just above the rear diff

With the fuel system depressurized and the car in the air, it’s time to crawl under and remove the old fuel filter. As pictured, it’s directly above the rear differential.

Close up of the filter

Close up of the filter

Here’s a closeup of the filter. The basic steps are to remove the two plastic end covers, undo the screw securing the filter, and then remove the fuel line from both sides with the quick disconnect tool. I’ll go over the steps in more detail below.

Remove the Plastic End Covers

This plastic clip is on the end of the filter connection

This plastic clip is on the end of the filter connection

It pops right off

It pops right off

To start, these little plastic covers are secured to the ends where the fuel line connects to the filter. Simply pull them off by hand. They can simply hang there after being disconnected. The small plastic security line will allow it to dangle from the fuel line.

Second plastic piece

Second plastic piece

Both plastic pieces removed

Both plastic pieces removed

Once you do the same thing to the other side, as shown, you can move on.

Loosen the Filter

Loosen the hose clamp securing the filter to the car

Loosen the hose clamp securing the filter to the car

At this point, you can go ahead and loosen the hose clamp holding the filter. Once the fuel lines are actually disconnected, you’re going to drip gasoline and make a mess. Thus, I prefer to get this part done in advance. That way, I can yank it out as fast as possible ones the lines are off.

It’s not necessary to fully remove the clamp, but that’s up to you. If you get it really loose, it’s easy enough to slide it out through the enormous gap that is left.

Undo the Lines and Finish Removal

Before doing the fuel line removal, make sure you’re wearing gloves and eye protection and have a rag handy to soak up the gasoline. Even with the fuel line depressurized, you’re going to get a decent amount of gas dripping out. Gasoline vapor is extremely flammable, so make sure to not do this part with ANY open flames around, cigarettes, etc.

The fuel line tool has two ends

The fuel line tool has two ends

Clamp and push into fitting

Clamp and push into fitting

Once you’re ready, clip the tool onto the fitting and push it in away from the connector. If you have the same fuel line disconnect tool I linked, you use side F. If not, it was a 5/16″ tool for my car. I have read in forums that the Mustang requires a 5/8″ tool. Your mileage may vary.

In any case, you’ll know if the tool is the right size because it will close around the line. Push it into the connector firmly, which will release two clips inside. Then, pull the filter and line apart. Have a rag handy, as gas will start coming out.

One side removed, both sides are removed the same way

One side removed, both sides are removed the same way

Both sides are removed the same way. Once the fuel lines are removed, you can pull the fuel filter off of the mount and remove it from the car.

Fuel filter spewing gunk after removal

Fuel filter spewing gunk after removal

You probably want something to stick the fuel filter in after it comes out. I didn’t think ahead, and got gas all over my driveway. It came out a pretty nasty brown color as pictured; I’m pretty sure this filter was due for replacement.

Reinstallation

Reinstallation is the reverse of removal

Reinstallation is the reverse of removal

Reinstallation is the reverse of removal. There’s not a whole lot to it. The lines push back on, the filter clips back into its mount, the hose clamp is cinched down firmly but not too tight, and the plastic clips are reinstalled. The one trick is making sure the filter is installed the correct way. The new filter, shown in the picture, has an arrow pointing in the direction of fuel flow. It should go from the passenger side to the driver’s side of the car, as pictured. Also, you can refer to the old filter for orientation.

In all, this is an easy tuneup that can be accomplished at home with little besides a $9 tool and a cheap replacement part. If your car is having fuel supply problems, replacing the fuel filter is a great place to start.

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