Sep 172012

Last month I wrote about performing a DIY tune-up on my E36 M3. In that post I talked about replacing spark plugs and the air filter. This weekend I finished the main components of a tune-up by replacing the fuel filter and cleaning the Mass Air Flow (MAF) sensor.

The fuel filter is a very easy item to overlook. The suggested interval on the E36 M3 is every 60,000 miles, so my car is right there with 57,000. The process is very straightforward, and the replacement filter is less than $40.

I did a lot of online research prior to replacing. The job looked easy, but opening up the fuel line is not something to take lightly. In addition to some of the usual forums, I was greatly assisted by Doug Vetter’s Doug’s Domain web site, which includes an extremely thorough description of the E36 fuel filter replacement. This site is a big resource for any DIYer, with multiple descriptions of DIY jobs for both the E36 and E46 BMW models.

It’s very important to depressurize your fuel system by pulling fuse #18 before accessing the filter. (Note — the exact procedure and filter location is different for early model E36s.) This prevents gasoline under pressure spewing out when you remove the hoses from the filter.

As predicted, I encountered very little gas leakage, just the amount that was in the old filter. I also purchased a kit from BMW that contained a replacement section of hose for the rear of the filter, and two new clamps. It was part #13311703490 for anyone considering this replacement.

I bought it primarily as a precaution in case I damaged the hose disconnecting it from the filter. I did not, but since I had the kit I replaced the piece of hose anyway. The old clamps were in good shape so I left those on. Thanks to my friends at Hollin Hall Automotive, I had access to a lift that made the project much easier.

Here are some pics, click to enlarge:

Filter is located front left under driver seat, protected by metal plate

Plate removed

Closeup of old filter – note hoses fore and aft

Rear hose disengaged — this is the section I replaced

All done

Cleaning the MAF sensor is a very simple process. The MAF sensor measures air flow and sends a signal to the car’s engine control unit (ECU). This reading regulates the air to fuel ratio of the engine’s combustion.

The sensor is a wire inside a plastic tube, and over time it can get dirty and become less accurate. You can prevent this from happening by spraying cleaning solution on the sensor.

All you do is open the hood and remove the middle part of the air intake tube. You release two clips right behind the filter, loosen the clamp behind the sensor and remove the unit. Then you spray the heck out of it with MAF cleaning spray, making sure nothing but the spray touches the actual sensor. Allow some time to dry before reinserting and driving the car.

MAF unit in middle, with clips in front and clamp in back

Shot of MAF, you can see actual sensor inside

Cleaner widely available at auto parts stores

Preventative maintenance like this requires no specialized mechanical knowledge, and is tailor made for DIYing. Doing this myself saves me a lot of money and that is of course a big plus. I wouldn’t want to own two older M cars otherwise.

Beyond the savings, I feel that doing some of your own work enriches the BMW ownership experience. The latest BMWs are increasingly reliant on software and limit the ability of owners to be anything but spectators when it comes to maintenance. The E36 M3 and E39 M5 are performance cars that are still more mechanical than computer.

I’ll never be a mechanic, and I have no problem taking the big jobs to my independent. But doing the basic stuff myself makes me appreciate my two M cars all the more, and will help keep them in top condition for years to come.

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