BMW E30 Main Fuel Pump Replacement

My Robert Bentley E30 Service Manual told me that 1984-1987 cars have an under car (main) fuel pump and an in tank (transfer) fuel pump. If you have a 1988 or later car, then you just have one pump, which is located inside the gas tank. Replacement of that pump is identical to replacing the fuel transfer pump on 1984-1987 E30s.

Rather than wait until the main fuel pump failed and stranded me somewhere, I decided to replace it. Armed with my Robert Bentley E30 Service Manual, called Charlie at Foreign Motors West BMW and he told me that with the BMW CCA discount, the mail fuel pump was $140 (list price was $175). I also picked up two hose clamps (28 cents each), as it is my experience that when hose clamps are under a car for 12 or 13 years, they tend to be semi functional once they are removed.

I still had the Special Tool that I made for the fuel transfer pump replacement. The fuel pumps don't run when there is sufficient pressure in the system, so in order to run the pumps you need to bypass the fuel pump relay so the fuel pumps will run continuously. The Special Tool is two short pieces of wire to a 15 amp fuse. I wrapped the exposed ends of the fuse with electrical tape. I crimped spade connectors to the ends of the wires.

The fuel pump relay is the middle of 3 relays which are on a block mounted near the left shock tower. Remove the cover over the top of all three relays. Remove the relay and connect the fused jumper between terminals 30 and 87. The main fuel pump noise will be audible if you did this right. If you didn't do this right you either did nothing harmful or you just blew a fuse rather than frying your car's electrical system.

Main Fuel Pump Replacement

If you look under the car just forward of the left rear tire you will see the main fuel pump. It is held in place with four rubber mounts. Each rubber cylindrical mount has bolts coming out of either end. The bolts are attached to the pump bracket and to the car's body.

I tried to remove the nuts for these bolts but they were rusted solidly to the bolts. I didn't want to try the usual trick of putting a propane torch on the nuts to loosen them up. My favorite rust eater, PB Blaster, didn't seem to help all that much. I got impatient and ended up twisting the rubber mounts apart, then drilling out the bolts.

Carefully pry the rubber boots off of the two electrical connections. Remove the electrical connections. The electrical terminals are different sizes so you won't be able to mix them up later.

The fuel pump gets fuel from the transfer pump, located under the back seat, and sends the fuel under high pressure to the fuel filter, which is located in the engine compartment. Remove the two hoses from the fuel pump, but be careful and wear eye protection. About cup of gas will spill out of the hoses when you remove them.

There is a small can located between the output side of the fuel pump and the tube which delivers fuel to the fuel filter. The intention of this device is to absorb pulses created by the fuel pump. This small can started leaking on me about two months before I replaced the main fuel pump. The E30 Service Manual didn't mention this part.

I asked a mechanic friend of mine about this part's function. He told me that it wasn't needed, and so I removed it. I replaced the two short lengths of fuel hose which were left with one piece which was about 9 inches long. You can buy a length of fuel hose from your neighborhood auto parts store. Take one of the short pieces with you so that you can get approximately the same inside diameter. Remember to only buy high pressure hose which is intended for fuel injection applications.

Replacement of the pump is easy. Since I neglected to purchase the rubber mounts, I decided just to use long bolts with a 10mm head. I took four short sections of high pressure fuel hose to isolate the pump bracket from the body. I was willing to sacrifice some noise isolation for the ability to remove the nuts at some future time.

Replace the electrical connections, making sure the nuts are tight and you use the lockwashers, but don't overtighten them. Replace the rubber boots, making sure that they completely seal the electrical connections from the ravages of water, dirt, and salt under the car. Replace the hoses, making sure to use new hose clamps. Mount the pump using the hardware of your choice.

Using the Special Tool, run the fuel pumps for about 60 seconds to verify that the pump operates properly and that there are no leaks.

Fuel Filter Replacement

I took this opportunity to also replace the fuel filter, which is located in the engine compartment. The fuel filter on my car hadn't been replaced in about 80,000 miles, so it seemed like it was time.

On 1984-1987 E30s, the fuel filter is large silver can located in the engine compartment underneath and just to the rear of the air filter housing. 1988-1990 E30s have the fuel filter located in front of the left rear wheel, where the main fuel pump is on 1984-1988 cars, and replacement is very easy.

To replace the fuel filter on the 1984-1988 E30s, you will want to remove the air horn and loosen the air filter housing. Loosen, but don't remove, the two nuts which attach the air filter housing to the wheel well. The two halves of the air filter housing are held together with spring clips. Unlatch these clips, remove the air filter element, and remove the front portion of the air filter housing.

Now you should be able to get access to the top part of the fuel filter. The fuel filter is held to a bracket with a long hose clamp. Note the vertical position of the fuel filter so you can put the new fuel filter in about the same vertical position. By reaching under the air filter housing you should be able to loosen this hose clamp with a nutdriver. You should be able to move the fuel filter up and down.

Loosen the hose clamp at the top of the fuel filter with a nutdriver. Some fuel will leak out when you remove the hose from the top of the fuel filter.

Working from under the car with eye protection, remove the lower fuel filter hose clamp. Fuel will spill out when you remove the lower hose clamp. Slide the fuel filter down and out of the engine compartment.

The fuel filter is marked with an arrow which indicates the direction of fuel flow. The arrow should point up when you install the fuel filter. Slide the fuel filter inside the large hose clamp. Make sure that the large hose clamp is still engaging the bracket. Attach the upper hose and lower hose to the fuel filter. Tighten the lower hose clamp.

Working again from the engine compartment, tighten the upper hose's clamp. Position the fuel filter so that it is about in the same position as the previous fuel filter. Tighten the big hose clamp which attaches the fuel filter to the bracket. Don't overtighten this clamp or you will damage the fuel filter. Using the Special Tool, run the fuel pumps for about 60 seconds to verify that there are no leaks at the new fuel filter.

Replace the air horn, the front half of the air filter housing and the air filter element. Take special care to put the air filter element in the same position as it was before. If you put the "dirty" side of the air filter element towards the engine, all sorts of dirt will be sucked into your engine. Tighten up the nuts which attach the air filter housing to the wheel well.