Join Date: Nov 2009
Location: Fairfax, VA USA
My Ride: 330CiC, M5, X5
Save yourself up to $200 and some headaches - Electric Fuel Pump PM
Fuel Pump Failure Epidemic 2012
So I have been around this forum and many of the other BMW forums and what seems to be a reoccurring theme is after about 7 years is most of the E38, E39, E46 and other similar vintage BMW's not newer than 2006 are have failing fuel pumps at a very high rate. Probably a rate of about 100%, as I say its not if, but when!
So a word to the VERY wise, if you have a spare $150 or so and a couple of hours, order yourself a replacement fuel pump, new fuel pump relay and fuel filter and replace them as a PM item.
There are really 2 typical fuel pump related problems.
One is much easier to diagnose than the other. The first situation is where the fuel pump hard fails and does not provide any fuel to the engine at all. This is a pretty cut & dry situation where the problem is rather obvious. A quick and inexpensive way to determine if you are have fuel supply problems is to purchase a $3 can of starting fluid, remove the air filter and give a good, solid, 2 second shot of starting fluid into the intake path/MAF inlet. Then try to start the engine, if the engine starts then almost immediately dies, then you could repeat the starting fluid process, but more than likely the starting fluid test has confirmed you have fuel supply problem. This will most likely be due to a hard failed fuel pump, but it is worth checking the fuses and possibly switch the horn and fuel pump relay just to rule these out as causes of your no start problem.
The seconds failure mode is a soft fail fuel pump that fails to put out enough pressure and/or fuel volume. These are far harder to identify and symptoms may appear to be intermittent or very minor. In some instances the problems may not even seem fuel related. Surging, poor acceleration, possible lean codes, extended cranking when starting, running out of fuel when the gas gauge shows 1/4 of a tank. Soft fail fuel pumps are not really worth diagnosing in my opinion. For the price of the pump and how easy it is to install, I would just plan on replacing your pump if it is more than 7 years old and you have unidentified driveability problems.
In addition to the pump being a problem, fuel filters are very often neglected and over looked and can cause similar issues to a soft failed fuel pump. Please carefully read the following information on fuel filters below.
SPECIAL NOTE ON FUEL FILTERS - since the early 80's fuel filters have much finer filter elements and will catch far smaller particles to protect the fuel injectors. Although many cars have large fuel filters and manufactures claim the filters can be changed every 50-60k miles, based upon field observations, I would HIGHLY suggest replacing your fuel filter every 30k miles. If you open up any of these filters after 25k miles, they are caked with a very fine black film. This black film builds up and starts to restrict fuel volume and pressure and can cause unusual engine performance issues.
While checking and replacing the fuel filter, also carefully check and replace the fuel pressure regulator vacuum hoses and the "F" fitting in the lower intake boot as any vacuum leaks in these hoses and fittings can also cause fuel pressure issues or lean conditions possibly leading to the CEL lighting for unknown reasons.
What seems to be happening a lot lately is folks are not replacing their fuel pumps as a PM item, they are getting stranded, requiring tow jobs and/or dealer or rush fuel pumps to be purchased of up to $400+. Some even have to pay for the install as they do not have the tools on hand or the time.
These pumps are very easy to replace, only need a few basic tools and you do not even need to get under the car. Even if you buy the pump and do not get it installed, keep it in the trunk with the tools to change it and a copy of a DIY until you get around to actually installing it.
It is almost as easy as changing a tire!
So these fuel pumps are kind of like death, taxes and the cooling system.
As the Nike commercial says, "Just Do It!"
Your wife, kids, girl, buddies, employer, wallet and your schedule will all appreciate a PM fuel pump job.
www.bmaparts.com seems to have the best pricing on the fuel pump, not sure about the relay and filter?
I think there is also an online discount code that may still be good, something like SpecE30?? If I find it, I will edit this post with the discount code, but I do not guarantee it will work.
UPDATE: The BMA online discount code is SpecE30. Reports are the replacement pump is under $108 with free shipping. NOTE: As of Aug 2012 it appears the pump prices may have increased slightly to closer to $120??
Note about soft failures on the fuel pump
Some of the fuel pumps are soft failing. This means they work and you do not have issues starting your car, but they can cause intermittent hesitation, misfiring, stalling as well as problems running out of fuel when the tank is about 1/4 full. This is due to low pressure and/or volume causing the siphon or suction jet pump that transfers fuel from one side of the tank to the pump side to not transfer fuel correctly. What happens is you still have fuel in the non electric pump side, but the electric pump side runs out of fuel. This usually happens with 1/4 of fuel showing on the gauge. The hesitation, misfiring and stalling is usually again to low pressure and/or volume from a weak fuel pump. Many have recently replaced their fuel pump & filter as preventative and found that they have crisper throttle response and better overall acceleration, which was not noticed until the pump and filter were replaced. So there may in fact be some hidden benefits to preventatively replacing your fuel pump and filter.
Fuel Pressure & Volume Testing
From the Bentley manual, following are fuel pressure and volume specs for anyone that happens to have a fuel pressure gauge handy and wants to test either the fuel pressure and/or volume. I have not tried this trick, but some have stated that you can use a regular tire pressure gauge to measure fuel pressure in a pinch. BE CAREFUL DUE TO FUEL SPRAY AND FIRE/BURN HAZZARD!!!
Note on most E46 except the M3 the fuel pressure tap or test point (Schraeder valve) is located on the front of the fuel rail under the upper fuel rail/engine cover. This upper fuel rail/engine cover will need to be removed to access this fuel pressure tap or test point.
On the E46 M3, the fuel pressure tap or test point (Schraeder valve) is located on the fuel pressure regulator block, under the drivers side floor board near the fuel filter.
On SULEV vehicles, I have not done a thorough investigation, however, expect the unexpected with these cars. These cars have the stainless steel fuel tank with the sealed fuel pump. This pump actually has 15 year/150k mile warranty and cannot be serviced without replacing the entire fuel tank assembly which I have heard is in excess of $6000!!! Note to self, if you have a SULEV car sell it before 14 years / 140k miles.
Fuel Pressure Specs
All engines except the S54 3.2L M3 - Fuel pressure 3.5 +/- 0.2 bar or 50.76 +/- 2.9 PSI
Residual fuel pressure after 20 minutes - Fuel pressure >3 bar or >43.51 PSI
S54 3.2L M3 - Fuel pressure 5.0 +/- 0.2 bar or 72.5 +/- 2.9 PSI
Residual fuel pressure after 20 minutes - Fuel pressure >4.5 bar or >62.2 PSI
Fuel Volume Specs
All engines 1.12 liter (1.16 qt) for 30 seconds at 12 Volts or while crank
If your car dies on you with 1/4 of fuel, you can sometimes get it started again by adding a few gallons of fuel. But beware you will again likely run out again once the gauge shows 1/4 tank. This may get you going if you are stranded and buy you a bit of time so you can shop your parts and DIY the pump. If you access the Hidden OBC menu (see my signature below for a link regarding the Hidden OBC Menu) you will be able to check the fuel levels in each side of the fuel tank. Note that most all BMW's have a kidney shaped fuel tank with 2 separate fuel level sensors and 2 fuel pumps, siphon/passive pump the drivers side (Left side), which rarely fails, and the primary electric pump on the the passenger side (Right side).
The way these BMW kidney shaped fuel tanks function with the 2 fuel pumps is as follows:
The electric fuel pump on the right side of the tank is constantly running and excess fuel is returned from the fuel filter/regulator back to the left side of the fuel tank. When the fuel enters the left side of the fuel tank if passes through the passive siphon pump and transfers fuel from the left side to the right side of the fuel tank. Once the fuel level drops below about 1/2 tank the left side of the tank quickly drains and all the fuel is kept in the right side of the tank. If you access the Hidden OBC menu you will be able to see the fuel transfer behavior and if you see the fuel level in the left side of the tank higher than the right side of the tank once stabilized, it is likely indicating a soft fail fuel pump. But also note there are also fuel level sending unit failures that can also show similar behaviors. Best to get to know your cars total average range using the trip odometer and then use this along with fuel level to determine when you may have to refuel and/or have a potential problem cropping up.
As for actual fuel pump failures, there are many myths and ideas as to why and how the pumps fail. Also suggestions that the pumps are overheating due to running the tank low on fuel for extended times and possibly the pump drawing air from time to time. But I can say most of these suggestions are mostly myths. The fuel pump is a DC brush motor that is constantly running and circulating cool fuel. The failures of these pumps really have nothing to do with overheating but simple brush and commutator wear just like a starter motor for an engine. What is typically happening is the brush fail to make proper connection with commutator and fail to start. Most of the fuel pump failures tend to happen after the car is shut down, there appears to be a very low percentage of failures while driving.
Also a few helpful hints on fuel pump replacement -
1. Wiring Connector
Many people new to BMW's or German cars may not understand how to release the wiring from the fuel senders. The connectors have a slide release that is a bit tricky but will be clear once you study it for a moment.
See attached pictures of the wiring connector up close both "latched" and "unlatched"
Pictures courtesy of Frank_E46
2. Make sure you install the gasket on the fuel tank opening lip and not the sending unit. When you remove the sending unit, the round gasket may come out stuck on the sending unit or you may partially pull the gasket out of the tank when removing the sending unit/fuel pump assembly, however, you need to install the gasket on the fuel tank lip before reinstalling the sending unit/fuel pump assembly, there is a small grove in the side of the gasket that goes around the inside lip of the fuel tank opening. What I actually do is install the sender with the gasket loose on the sender, then once the float is inside the tank, I then put the gasket on the tank lip before seating the sending unit. Also be VERY careful to install the gasket the gasket in the correct orientation when you install it on the edge of the fuel tank. This gasket is asymmetrical and should only be installed in the proper orientation. I believe there is the word "TOP or UP" embossed in the fuel sender gasket. If you install the gasket upside down you will have a fuel leak. Fuel leaks will only likely occur at 3/4 tank or higher. Once below 3/4 tank, you will likely not have any leakage.
If this gasket is not installed properly you may have also have Evap codes triggering as well as anything from a large fuel leak, to just a heavy odor of gasoline.
So be warned, make sure you note the orientation of the fuel sender gasket when you remove the sending unit/fuel pump assembly and reinstall the gasket in the correct orientation and make sure the gasket is fitted inside the tank opening and groove in the side of the gasket is installed on the edge of the fuel tank opening.
3. Fuel level can be an issue. If you are 3/4 tank or below you are in pretty good shape, but if you just filled up and need to change the fuel pump, you will have a problem with fuel spilling out of the tank onto the top of the tank and the driveway or asphalt below. Remember gasoline is not only flammable, it can soften asphalt and be an issue if you happen to be indoors. It is apparently very hard if not impossible to siphon fuel from the tank via the fill pipe, so be forewarned and this may be another good reason to proactively replace your pump on your schedule and not the cars schedule!
4. Be careful about residual fuel pressure in the fuel line before changing the fuel pump or filter. If your pump failed and your car will not start, you likely will not need worry about residual fuel pressure, however, if the car still runs and you plan on changing either the fuel pump or fuel filter, it is wise to remove the fuel pump fuse, start the car and let it idle until it dies. If you plan on removing the fuel pump, you can disconnect the wiring connector to the right side fuel sender and start the engine and let it run until it dies. NOTE, if yo disconnect the fuel sender, you may end up with some trouble codes for the fuel sender and you fuel level and mileage figures may be WAY off until you fill the fuel tank. The trouble codes will not likely show up with a standard ODB scanner, however, INPA, SSS or BMW Scanner may read these errors. Just make a note if you do run the engine with the fuel sender disconnected in case you see any codes, you likely forced them to be triggered. This is way you can pull the fuel filter or pump without a high pressure spray of gasoline. You will still likely get some fuel leakage, but hopefully not under pressure. It might also be wise to remove the fuel filler cap to also release any residual pressure in the fuel tank, but suggest you reinstall the cap before removing the fuel sender/pump combo.
Additionally I have no hard data, but it appears the 2002 and newer cars may have more of an issue with the pump life as compared to the very early E46's? Also case in point, many of the newer turbo BMW 3 series have had a series of fuel pump failures while most of these cars were still under warranty. So just making the comment that the pump design can possibly influence life expectancy.
Do not say you have not been warned!
Denial is not an option, as you will get a rude dose of reality.
Last edited by jfoj; 12-04-2012 at 07:05 PM.