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Check main and fuel pump relays.... (archive)

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Posted by JamesM on January 30, 2001 at 10:21:12:

In Reply to: Random Shutoff on 528e posted by fomanchu on January 30, 2001 at 09:03:26:

The gas smell/shutoff problems are probably unrelated--unless there is a lot of corrosion on your tank and you have water in your fuel system as a result. The cutoff is caused by an intermittant failure of the main or fuel pump relays. Check the Bentley manual for the exact locations. The main relay is probably located on the side of the main fuse box. So are the fuel pump and O2 sensor heater relays. The main relay may be metal or orange plastic. If it cuts off, this kills the Motronic box and fuel pump relay. If the fuel pump relay is bad, this obviously kills the fuel pump (and the engine in turn). The randomness of these orccurences leads me to think that one of these two relays are at fault. They are available from the dealer or any European auto parts store, about $10-20 each. The main relay has 5 prongs, and the fuel relay has 4.

As for the gas smell, check for leaks. The vapor tank and related hoses are pretty sturdy, and it would smell like gas all the time. Since you said it only happens with a full/nearly full tank, look for a bad gasket at the tansfer pump/sender unit. Also check for corrosion behind the right rear wheel. The wheel kicks up dirt and sand that collects at one of the tank brackets. Water and time are all it takes to perforate the tank. You have to remove the rear muffler to drop the tank. If you do drop the tank, now is a good time to replace the fuel filter and all hoses in the area. There is a 2' section of 12mm ID hose from the sender to the fuel pump, and the rest is standard 8mm ID high-pressure hose. You will need new clamps, because BMW loves to use those crappy 1-time-use clamps. Get a dozen so you have spares.

Hope this solves your two problems.

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