348 Fuel pump earths/grounds

It seems odd that the earth will be far from the pumps, especially if it is not shared with any other systems. Having said that, the F355 pump/s use an earth which is shared by numerous systems, some of which are nowhere near the pumps.


Are you having problems with the pumps?

 

are you able to do a resistance check from the wiring to the metal framework of the car to see if the grounding point isnt optimal?

 

Are you getting a significantly different resistance reading from the earth pin on the Left pump harness to, say, the engine earth (than you are with the Right pump)? As Josh implies, wherever the earth is, it's probably a good bet that it's using the chassis as a return path.

It's normal for pump relays to be fairly warm, but letting them get too warm can lead to melted relay panels. I think the chances are that it's a pump about to expire.

Not sure I follow you. Unless I'm looking at the wrong diagram, the pump relays feed the pumps and the O2 probe heaters. On the 2.5, they feed the aux air valves, too.

 

You can do a simple check of the fuel pumps - unplug both relays and plug in two lengths of wire with spade terminals at one of their ends into the relay sockets 30 and 87 (see pic). Then, connect an ammeter (set at at least 10A range, better 20A) to the wires and read the current draw. You don't need to have the ignition on for this test. If the "hot relay" pump draws considerably higher Amps than the other pump, then it is faulty and you need to replace it. If its current draw is similar or not much higher than the other pump, you can tie the two wires together just before starting the engine (put back the other "cool" relay) and see if the bank runs fine then.
Image Unavailable, Please Login

 

Miro, would the pump pull any more amps at higher engine rpms? I can't imagine that the fuel pumps would have to work any harder (if the fuel injectors are open longer). There would be less back pressure on the pump.

 

I don't think the electric current through the pump motor varies much between idle and high rpm as the pump runs, more or less, at constant pressure. These pumps are a positive displacement type so their motor current draw is largely proportional to the pumping pressure. There could be slightly higher current draw during acceleration (low intake vacuum) when the pressure regulator increases somewhat the fuel pressure.

 

The problem you had is not uncommon. When the contacts between the spades and the sockets of the relays and fuses corrode somewhat, they develop resistance and start heating up. The heat causes some burning of the contacts and the things get worse - more resistance and more heat. You just need to clean the spades of the relays and the fuses and pull them out and push back in a few times every, say, 6 months. If you still have somewhat excessive heat on one of them, you will probably need to open-up the relay panel and inspect/clean the female sockets for the offending relay or fuse.

I recently had a failure of one of the radiator fans on my 348; found out that the relay socket had melted and the relay spade 87 and its female connector in the panel badly burnt. I had to replace the relay panel with another good (used) one. I am planning to repair the damaged panel, probably by inserting sockets for relays which have larger spades for the pins 30 and 87 for the two radiator fan relays, and keep it as spare.

 

See my earlier post as to how to disassemble the fuse/relay board: https://www.ferrarichat.com/forum/threads/348-fuse-box-repair.557448/#post-145503419

 

I’m not sure what you are trying to do but here’s a rough understanding of the system.


Cars electrical is an independent and isolated system. Hence, the work earth, ground and the three dash symbol in the drawing are misused. This is a completely different subject altogether for a another power system. A car chassis and all conductive parts share a common which is the negative side of the power system, the negative side of the battery. That’s not to say every conductive part(metal) in a 355 is a potential negative ties to the negative side of the battery post. The three dash line symbol in the drawing indicates the common, the negative side of the electrical system. It can be anywhere, likely everywhere; the engine block, the frame that holds the engine. In the engine bay somewhere a large negative wire from the battery bonds to the metal frame. That’s the common. Alternately, find the alternator and trace the negative wire to a point. That’s where the common is.


In 5 years of ownership, I’ve never bisect or take it apart so I don’t know where everything is so I can not give a location. If possibly please elaborate on what it is you are trying to do.

P.S. I don’t look at manufacturers diagrams as they not standard electrical logic. It is useless in my opinion.

 

Good to hear. I usually don’t read the whole thread only a few posts at the beginning.