Fuel pump issues are not a common problem on BMWs, especially E36s. As these cars age however and rack up miles you are bound to have a failing component eventually. E36 fuel pumps typically last well over 100,000 miles, and they usually won’t have trouble until around the 150k mark.
In this article, I will discuss symptoms of a bad BMW E36 fuel pump, how to test the fuel pump, and how to replace the fuel pump.
BMW E36 fuel pump diagnosis is easy, and replacement is a walk in the park. Whether you are a full-blown BMW mechanic or just trying to save a few bucks on labor, fuel pump replacement should not take longer than thirty minutes or so.
How is fuel pump replacement so easy? Primarily because the fuel pump on an E36 is extremely accessible. No dropping the fuel tank, or removing lots of parts to get to the E36 fuel pump. You can access it in a matter of seconds by simply pulling up on your backseat.
I made a video on diagnosing BMW E36 fuel issues, the video is located at the bottom of this article.
You can check out an inexpensive new BMW E36 fuel pump here.
Symptoms of a bad BMW E36 fuel pump
Well, the most obvious symptom of a bad fuel pump is a no-start. Typically when fuel pumps fail they die in an all of a sudden manner instead of a slow burn. This means that you usually won’t have too many symptoms until you’re stuck in a parking lot on the wrong side of town (happened to my baby brother).
If you do have a failing fuel pump you may notice:
- An electronic motor whine sound coming from the rear passenger side area while you are driving. This is the most common symptom I see and it means that your fuel pump is on its last leg.
- The car doesn’t want to start when the engine is warm but sometimes it will start when the engine is cold.
- The vehicle starts, but dies when the system is put under a heavier load, such as driving the car.
When my brother’s fuel pump went out on his E36, it went out in a DVD store parking lot. I diagnosed it as the fuel pump after noticing that the fuel pump fuse was blown. I replaced the fuel pump fuse and the car started right up. At that point I prayed that the car would make it a half-mile to the house. It did not make it half a block before the fuse blew again, the car died and I got stuck in the very next parking lot down the street.
Causes of BMW E36 premature fuel pump failure
I said previously that BMW fuel pumps are extremely resilient. However, I have also seen quite a few that rolled over significantly sooner than they should have. Here are some common causes for an E36 fuel pump to go bad prematurely.
Running the car with a very low fuel level.
At this point, E36s are usually going to be at least twenty years old. Twenty years is plenty of time for some mineral deposits to be created and fall to the bottom of the tank. Even on new cars, it is never recommended to wait until your vehicle is flashing a red low fuel light to fill up the tank. Gasoline acts as a lubricant for the fuel pump in the tank. If the tank is being run dry frequently you will eventually cause the fuel pump to overheat. Another good reason, and one to specifically worry about with older vehicles, is that your fuel pump may pick up some of that crap at the bottom of the tank. If it does, there’s a good chance it will clog your fuel pump.
Take a look whenever you remove the fuel pump out of a car with 50,000 or more miles on it, you will see plenty of debris floating at the bottom of the tank.
Car sits for an extended period of time (think six months or more).
The filters on the fuel pump are pretty flimsy. If the car is left sitting for a long time with little fuel in the tank, then the sock filter will more than likely dry out and probably fall off. At that point, your fuel pump more than likely won’t work. I have removed fuel pumps from BMWs after the vehicle had been sitting for months, and the “sock” filter was laying at the bottom of the tank along with several fragments of plastic. Rust can also develop in the fuel pump overtime, and ethanol mixed gas only lasts around three months until it is no longer usable.
Different grades of gasoline will not make a difference
I know plenty of people that say putting 93 instead of 87 will help out the fuel system and the fuel pump will last longer. They believe that 93 has some sort of additional cleaners that are good for the fuel pump. This is not true, 93 will not do anything for your fuel pump to make it last longer. The only difference between the two is the octane rating.
Fuel quality is well regulated in the United States, however, it is worth it to stay away from gas pumps or gas stations that appear poorly maintained. If there is water in the gas you are buying it can damage your fuel pump.
How to Diagnose
I want to mention that I believe it’s best to replace a fuel pump as part of your preventive maintenance between 125 – 150k miles. After that, your pump is at risk of failure, and once it fails the car isn’t going to move again until you change it. As I mentioned above, I have been left stranded more than once in a parking lot because a fuel pump went bad. Each time I did the car was well past the 100,000-mile mark.
You can perform a fuel pressure test with a fuel pressure gauge. You can rent one from your local autoparts store, I have never seen one that did not keep a rental in stock. Depending on what year your E36 is you may have a schrader valve at the end of your fuel rail. My 1995 318i did not have one, but all of my family’s E36s 96+ had a schrader valve to attach a fuel pressure gauge to.
When testing the fuel pressure you will first need to determine how much fuel pressure you should be getting to the rail. If the fuel pressure fluctuates or it is significantly lower than it should be, you will likely need a new pump.
Lift your back seat, and turn your key to the second position. You should hear a motor whirring sound coming from the passenger area. This is the fuel pump priming. If your fuel pump is completely fried you won’t hear any noise.
Check your fuel pump fuse, if the fuse is blown you can change it. If it blows again when you try and drive, your fuel pump is gone.
BMW E36 fuel pump replacement procedure
Luckily the fuel pump on your vehicle is very easy to replace and well within the scope of most DIY’ers. Most auto parts stores should be able to get a hold of the fuel pump or they can be purchased online.
First things first, you’re going to be working around gasoline and should be in a well-ventilated area. Either work on your car outside or have plenty of ventilation in your garage.
Second, cell phones, flashlights, and any other electronics or sources of heat should be kept well away from your work area while you perform this job.
Third, your tank should be at half a tank or less, preferably less. Any more and the pump will splash gasoline everywhere upon removal and installation. Do not attempt this if you have a full tank of gas, as the tank itself is tilted and will spill into the rear seat. You will have to siphon some fuel out if your tank if it is full.
Fourth, disconnect your battery. Eliminate the risk of any accidental sparks from an electrical connection.
BMW E36 fuel pump removal
Move the front seats forward as much as possible so you have plenty of working room.
The seat bottoms are fastened in with two large metal clips on either end of the seat. Wedge your fingers into the bottom and simply pull up and forward to release the seat.
There’s a black lining with an access slit cut out on the passenger’s side, this is where the fuel pump is located. Open up the access slit to gain access to the top of the fuel pump.
The metal cover is held in with four Philips head screws, remove these and pull it out of the way.
Remove the fuel pump wires. One is for the fuel pump and one is for the sending unit.
You’ll probably notice that there is a lot of debris on top of the fuel pump and in the area surrounding the fuel pump. Use a vacuum to get rid of all that debris, as you wouldn’t want it falling into your tank.
BMW fuel pumps are held in with a locking ring, after many years they usually take some convincing to remove. I use a screwdriver and a small mallet to remove the ring. BMW actually makes a special tool to remove the locking ring, but you don’t need it.
Don’t bang the ring really hard or you will risk damaging it. A series of light taps will get the ring moving, and eventually it will loosen enough to where you can loosen it with your hand.
Depending on the E36 you own you may have only one hose going to the fuel pump or you may have two. My brother’s early E36 318i had one hose to the fuel pump, and the second nozzle was capped off. My 328i fuel pump had two hoses running to it.
Original fuel pumps should have the crimp style fuel pump clamps holding the fuel hoses in place. If it has been replaced before, it probably has regular clamps.
If the fuel pump hoses do have the crimp style clamps either use a diagonal cutter or a flathead screwdriver. I did not have a diagonal cutter. I was able to release the crimp with the flathead and remove the hoses.
The plastic nipples inside the hoses break down over time so you need to take special care in removing the fuel hoses once you have removed the clamps. You can use a pick tool or try and twist the end of the hose a bit to break the bond.
If you were recently running your vehicle, the hose may still have some pressure in it. Take care in removing it, as it may shoot some fuel out. My vehicle hadn’t been running for a day or two so the fuel pressure was at a minimal.
Remove the locking ring and set it aside. Take note of how the tank seal is pressed into the tank, re-install the same way. If you bought a new tank seal that’s great, if not it’s not a big deal.
Installing your new E36 fuel pump
The fuel pump and sending unit must be oriented correctly or it won’t install. Luckily, BMW was friendly in putting small notches on the sending unit and on the tank to help with the correct installation. Line up the notches, and push the pump into the tank. You’ll notice that the sender will initially hit the bottom and then float up.
Before re-installing the locking ring, it’s a good idea to spritz the threads a little bit with WD-40. Be careful with this so as not to get too much into the gas tank. The lock ring often requires excessive force if you do not spray the threads first.
Push down the pump while re-installing the locking ring. This will ensure that the locking ring is re-installed correctly. Tighten down the locking ring, and re-install the hoses. I usually have some normal clamps sitting around that I use to re-install the hoses as the crimp style clamps can not be re-used.
If you spilled some gasoline, let it evaporate for a few hours before re-installing the two wires and closing the cover.
Don’t put the seat back on until you’ve test run the vehicle and confirmed that there are no leaks.
At this point, you’re done with your fuel pump replacement, congratulations!
Fuel pump replacement is also a good time to go ahead and replace your inline fuel filter if you haven’t replaced it in a while. Typically they should be replaced every 15,000 miles!
Your vehicle may not start immediately after replacing your fuel pump. That’s okay, as the fuel system needs to pressurize.
Throw in some fuel treatment right after changing your fuel pump if you have at least a quarter tank of gas.
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