Hi all! So my 1989 328 just shut off while on a "spirited" driving... Turned out the fuel pump was done. However, when I got the car to a shop, it turns out that there is a grounding/shorting issue on the electrical line coming in to fuel pump. Now, they did test the relays, fuses, fuse board. Seems like there is no issue from battery to fuse box, from one side of the fuse box to the other is also testing fine, all the way to Relays is also fine. We did change relays just in case. They are saying that the grounding issue is between the actual pump and relay. Basically the actual wire in the harness might be melted somewhere. Wanted to get your opinion on this, as I've never heard an issue like that before, where the wire just melted somewhere random like that? Because now they would like to get some of the interior out and try to trace this wire down, which of course will be pretty costly. Thank you!
That would be very unusual. You might also let the shop know that the same +12V wire that goes to the fuel pump also goes to the AAV heater and the WUR heater (except on CH version 1989 328 that don't have a WUR). Easy enough to just unplug them and inspect their wiring to rule them in or out of the problem (and they would have to be unplugged to make a meaningful resistance measurement between the +12V wire going to the fuel pump and ground). What version 1989 328 do you have -- US, Standard (euro), or CH (as, on the US version, that +12V wire also goes to the Protection Relay, and it would also need to be unplugged to make a meaningful resistance measurement)?
It's never random, although I'm sure you didn't mean it literally. Wires melt because too much current flows through them, causing them to overheat and melt. Too much current usually results from a short to ground, but can also result from a failing component that is drawing too much current. The melt occurs in a tiny fraction of a second. To illustrate, take a wrench and touch it to positive and negative terminals on your battery and watch what happens to your wrench. There'll be a massive spark and a melted portion of the wrench. When a wire melts, it can start a car fire if it's anywhere near fuel or fuel vapors. Melted copper is hot enough to ignite anything flammable. And, if the wire is housed inside a harness with other wires, usually they all melt. The main wiring harness in my 911 melted (about a dozen wires) due to a short that occurred momentarily in the ignition switch while I was driving. The entire harness melted. This is why we have fuses in our cars and circuit breakers in our homes. Their purpose is to melt (or trip) when an overcurrent situation exists, thus protecting all the wiring on the circuit from melting and the components from being fried. But in most cars there are often some circuits that are not fuse-protected. The fuel pump circuit is protected, so if the fuse didn't melt then it is unlikely any of the wiring did.
