A year ago I had problems with the engine on my 82 BMW 320i cutting out/stalling. I was told to change the ceramic fuse for the fuel pump. I did; it seemed to work for awhile and then the problem redeveloped. Changed the fuse again, worked okay for awhile, and the problem has once again returned. There must be a problem in the electrical system that would cause fuses to fail so frequently. Any ideas or solutions? Thanks.
One thing to check for on the fuse block is the temperature of the fuse ends and connector clips. After the engine has been running a while, touch the ends of the fuse where the metal cap sits in the fuse block clips. If an end is excessively hot (uncomfortable to touch), your problem is there. The excessive heat will eventual melt or crystalize the solder of the fuseable element to the end cap causing the fuse to open. Usually the fuse amperage is higher than the current flowing through the circuit so measure that. If the current measured is close to the rating of the fuse, look at the current specification for the fuel pump circuit. You might have a marginal fuel pump that overcurrents intermittantly. If the amperage draw is correct, look at the connections to the fuse clip that is running hot to see it there is a resistive connection. Sometimes the rivet that connects the fuse clip to the terminal lug behind gets loose and corroded causing a resistive connection.
Hope these ideas help with your problem.
Your car is equipped with CIS fuel injection and the fuel pump (even when new and with a clean fuel filter) draws a lot of electrical current. With age and/or a partially clogged filter the current draw will go up even higher and this could be what is leading to the fuse failure.
By replacing the fuse you’re only curing the symptom, not the cause. An inductive ammeter could be used to check the fuel pump current draw.
High current draw from CIS fuel pumps was also responsible for a lot of electrical problems in the old VW Rabbits, Sciroccos, Dashers, etc. In the case of the VWs an in-line wire connector behind the fuse block would burn, and depending on the severity and length of time involved, even the fuse block connectors and the fuse block itself would burn out.
This was a common problem with the VWs and your BMW uses the same system.