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My fuel pump on my daily driver '80 528i is randomly cutting off, but only while driving on the interstates. It does it when I'm not on the gas pedal very much at all. When it shuts off, the car dies and I hold up traffic for about 1-2 minutes. I open the hood, mess with the fuses, and it goes again like nothing's happened.

I've cleaned and replaced the fuses on position 1 and don't see any corrosion there. I've bent in the prongs slightly to have a tighter grip on the fuse.

The Multipurpose/Combo relay is original (170k). The fuel pump itself is less than 2 months old. This did occur once several months ago with the old fuel pump. It's also been really wet here in GA so I'm not sure if moisture has something to do with it.

This doesn't occur when I'm on main roads/side streets. Only while driving on the interstate. Also I'm not sure if messing with the fuses actually solves anything. It could be the movement of opening and closing the hood.

If it's not the fuses, could it be an issue with the AFM flap? Is WD40 ok to lube that flap?

Any other suggestions about what might be causing the issue?

How do you know it's the pump? Can you hear it stop working?
If the problem is the same as before, then it appears that the fuel pump is not the culprit.
And if we will correlate the "interstate" versus slower traffic as a symptoms, it may appear that it may be a fuel supply issues which may point at the fuel filter or the fuel pressure regulator.
The combo-relay can play games too. And there is a throttle position sensor that may be sending bad signals. But that won't kill the engine.
Don't dismiss the ignition system. Bad coils can cut out when they get hot. Wait a bit, they cool and they work again, which may also explain the interstate versus city streets observation.
To check the AFM, move the flap by hand. Does it catch or has a lot of resistance to open and close? If so, a little WD40 will not work. You will need to replace it. They are available rebuilt, not very expensive either, but I doubt it's you AFM.
Let us know what you find.

Just placed an order for a new Combo-relay, getting delivered tomorrow. Amazon had it available.

If it still dies after replacing the combo relay there could be an old alarm system waking up and killing the engine. It happened to me.

wmmag wrote:If it still dies after replacing the combo relay there could be an old alarm system waking up and killing the engine. It happened to me.

Wow, I never would have thought about that. There is an old alarm system with they keyhole to activate near the trunk button. I do have the key. How do I bypass that?

My alarm was key activated too, via a lock on the front fender.

I had a mechanic disable it, so I don't know how it was done. Maybe follow the wires from the switch and see if they lead to a brain somewhere.

One week after swapping Combo relays and all is well. I took apart the old relay and some of the solder points looked a little cracked. I'm guessing the cold enlarged them. I did find the brain to my alarm system but haven't done anything about it yet.