Changing Fuel Filter: 16v c900

[euromobile900]

Replacing the fuel filter is considered a piece of routine maintenance. The Bentley manual recommends this job once every 30,000 miles, but our fuel filters are very large and many cars go a very long time without ever having it done, with few ill effects. Still, it's a job worth doing on a car you don't know. Some say it's helped them with idle, but the real symptom of a bad fuel filter is poor acceleration and top-end (in other words, when you are using fuel the most, and flow can't keep up pressure through the blocked filter).

First-timers should know that replacing a fuel filter is more difficult than replacing the oil or air filter. I can't count the stories I've heard of people jumping into this job with too little time, and ending up with undrivable cars and a huge job on their hands because the old fuel filter is so firmly stuck in place. Be prepared for brittle nylon lines, frozen banjo bolts, an old fuel filter that crushes under your wrenches, and a mount that disintegrates with rust. Scope the job out, go slow, and try not to be destructive.

The most important thing about this job is to know how banjo bolts and fittings work. Here is a photo showing the basic principle:



The basic idea is that the banjo bolt screws into the end of the fuel filter, and is hollow, allowing fuel through and into the banjo fitting on the end of the plastic fuel line. Our sealing-washers are not copper, but work on the same principle of being squeezed and thus sealing. So it's very simple to get these fittings off. There's no sealing tape or rusty pipe threads, because all the threads are immersed within the fuel filter. There's no nylon fuel line splicing involved. All you need to do to disconnect a banjo bolt is unscrew it! You'll still need the right wrenches and a few hours on your hands to tackle this job, but it's pretty easy once you know what you're getting yourself into

Difficulty: 1.5/5

Tools Required:
-17mm wrench
-19mm wrench (3/4" works too)
-22mm wrench (7/8" works too and was what I used)
-3/8" wrench (weird huh, but my filter strap bolt would fit no metric sizes)
-Big adjustable wrench (optional but recommended)
-Jack and jackstands (optional but recommended)

Parts Required:
-Fuel filter
-Sealing washers

The fuel filter is located right above the rear axle, on the right side. It is mounted to the unibody via a metal strap. For ease of work, I recommend raising the car and removing the right rear wheel. You can opt not to do this if you wish, but it gives you lots more wiggle room and cuts the amount of under-car squirming down by half at least.

Cleanliness is paramount in jobs like these. You don't want to introduce flakes of rust or dirt into the fuel line, especially if it is the "to-engine" fuel line, because this gas is supposed to be clean! I recommend knocking off the loose dirt and rust with a wire brush. Don't attack the nylon line with it, but clean around the banjo bolt and fitting a bit before disassembly.

You should also probably have a catch-pan for all the fuel that drains out of the system (about two cups I'd say) when you remove the filter. Some say to rid the fuel system of pressure up in the engine bay at the fuel rail, but I say, why bother if you're just going to loosen a bolt and do the same thing down by the filter? Save yourself the work and just don't get sprayed with fuel while you're under the car. You know how to take care of yourself, right?

The fuel filter gets inlet and outlet through two different-sized banjo bolts, the larger one on the line coming from the fuel tank and the smaller one going to the delivery fuel line. After you've gotten rid of the rust, your first job is to loosen these. You can do whichever one first. I did the small (closest to wheel) one. You may have to knock off some rust cakes with the wrench-flats before you can get your wrench on the rusty banjo bolt. Be careful not to round off the banjo bolt! You get only so many tries with this! I recommend box-end wrenches.



Just crack the bolt loose. Try not to look directly at it without eye protection. It will spray fuel with the remains of the pressure in the fuel lines when you loosen the bolt. Once you've got the bolt cracked and caught what fuel did spill out, leave it. Better to leave it on there so it only drips than to let all the fuel drain everywhere just yet.

Then, do the other side! I had a big adjustable wrench for this, but if you don't, you can probably get away with the 22mm on the opposite side holding the filter steady while you loosen the banjo bolt. Remember, only crack it loose, then stop!

Once you're done with this, it's time to un-mount the filter from the car. The reason you crack the banjo bolts first is because doing that on a filter that's flopping all over the place on nylon lines is not fun at all. Undo the 3/8" (that's what it was on my car; no metric wrench would fit) bolt that holds the fuel filter strap to the car, and set the strap and bolt aside.



Finish removing both banjo bolts. Position catch-pan below filter to catch fuel that drips/sprays out. Drop filter into catch-pan.

As they say, installation is the reverse of removal! The fuel filter is marked with a direction of flow. This direction should be left-to-right, but the banjo fittings and bolts are different sizes, making it very difficult to put the filter on backwards. Make sure there are no rust particles inside the after-filter line (probably keep 'em out of the into-filter line too for safe measure) and you should be all set. Torque the banjos pretty tight, but be careful not to drag the banjo fittings around, kink their nylon lines, or strip the threads (remember they are aluminum).

Now turn the key and start the car, or cycle the fuel pump using a jumper (see Bentley manual for how to do this). It may take a few seconds cranking the starter to get all the air out of the system, so don't be surprised if your car is hard to start the first time after this repair. Probably not one to do in very cold weather.

Have fun, and enjoy!

[Saabhat93]

Great writeup. Very descriptive and accurate of how it should be done. I've done it a few times with much less finesse and found it to be extremely easy. I basically just found some wrenches, put the car on ramps and figured out what went where by looking, so having a guide like this would've saved time and gas all over the place. The most challenging part of this job for me was finding out what to do with the old gas that came out of the line (still no idea wtf to do with it). Loosen those bolts SLOWLY. It does spray if you just yank it off, but if you slowly undo it you can relieve the pressure in the line without catching a face full of gas.

[euromobile900]

I've done it a few times with much less finesse...

I think it's funny that you think I did it with finesse.
While I was under there, I got rust in my eyes twice, knocked a bump-stop off (guess that needed replacing), and discovered a sticky caliper, cracked brake hoses, and a bad rear wheel bearing. I forgot to disassemble the bump-stop base and unknowingly lost the brake pad anti-rattle clip in the gravel, only to remember its removal at 2am on a rainy night, so I went outside in pajamas in the rain with a flashlight to find it.

[Shazam]

only to remember its removal at 2am on a rainy night, so I went outside in pajamas in the rain with a flashlight to find it.

When a note to yourself for the morning just wouldn't suffice

[euromobile900]

When a note to yourself for the morning just wouldn't suffice

The suspense of wondering whether I'd find it or not would likely have kept me from sleeping.

[SmaartAasSaabr]

Oh I hate this job so much

But I think I can add pictures from my own experience to add colour (rust colour!) to your thread :p





I like how the Bosch plastic sticker label seems to be made of tougher stuff than the actual filter. Why not just make the whole filter out of that plastic it would be easier

Cycling the key won't do anything as the pump doesn't run unless the engine spins first. I never bothered much and just cranked the engine until it started, it isn't very long.

[euromobile900]

Oh I hate this job so much

But I think I can add pictures from my own experience to add colour (rust colour!) to your thread :p

Cycling the key won't do anything as the pump doesn't run unless the engine spins first. I never bothered much and just cranked the engine until it started, it isn't very long.

Thanks for that! The key cycling was just an educated guess, something I was going to look up but never got around to. I've amended the tutorial to reflect the true information.

[s900t8v]

The early K Jet 8 valve 900's have a function that cycles the fuel pump when you turn the key to ignition on. I don't know maybe it's just non lambda K jet (Aus never had lambda) but my 84 900T and my Mums 85 900i (8valve K jet no lambda) both do it when you turn the key.

To prove it was happening I got someone else to turn the key while I had my hand on the pump, no mistaking it, it humms for 1-2 seconds.

[Eddy]

The next time you replace your fuel filter, buy a mountain bike tube. Cut it across so that it is no longer a circle. Then split the tube length wise with a razor. Wrap your new fuel filter with it. No more rust and a much easier change the next time......

[roberto]

Hi, I have just read your post on changing a fuel filter and the benefits of doing so. I currently am experiencing problems when accelerating. It seems that when accelerating hard my turbo is not giving its all, it is as if something is holding the car back, it drives fine if you build up speed slowly but its when you need the power that the problem is apparent. The car is a 1988 900t, does it have a filter as you describe and could this be the problem. Robert.