If that's the case, I'm good. I do the same to a 60amp continuous duty relay. Thanks, Smitty.

I'm not one to speculate on the fuel pump ruining drivers, but most any electric motor when spun by another power source is a generator. Perhaps any residual pressure on the pressure side of the pump, that is not past a check valve will turn the pump over backwards as it "depressurizes" on key off, thus causing some voltage generation, opposite of the pumps intended polarity. Not sure, just a thought.

Sounds plausible,and by simply installing a independent 25$ relay this (if true) would become a non-issue. I quit trying to run my fuel pump off my Mefi harness 8 years ago and instead use the keyed fuel pump power FROM the Mefi to trigger a heavy duty relay with 10 gauge power wires from the power source because of running a larger fuel pump then the Mefi system was ever meant to support. Anyone that has a 900+ hp motor will obviously be running a bigger fuel pump then stock and will also have a higher amperage load and SHOULD configure their pump this way too, Smitty

These are Whipple 525 kits..... right? I was under the impression that the fuel pumps were already powered through a relay that was part of the kit. There is a green wire from the ECM that controls the relay. I just replaced the relay on one of my engines.

According to Whipple, the pumps that come with the kit are only good to 900hp. I just bought mine..... I wonder if my kits are different.

On my boat the fuel is returned to the water separator which is between the tank and pump. That's what Whipple recommended. Do you feel that this is an issue? Why would returning fuel to the tank be a better option?

All Merc wiring harnesses have a relay for the fuel pump. It is triggered by a small gray wire. There are 2 relays as part of the harness. One turns on the ecm and the other turns on the fuel pump. On my harnesses, we use 10 gauge wires both in and out of the fuel pump relay. However, we are easily able to put the larger wires in the harness when we build it.The wires in the stock Merc efi harness are 16 or 18 gauge. They work fine for the smaller stock pump, but on larger pumps, I prefer the larger gauge wire. The relay is large enough, but making a 6+ ft run with 18 gauge wire could cause a problem. The other option is to let the stock relay with the smaller wires trigger another relay with heavier gauge wires.
Returning the fuel to the tank is always the best option. In pretty much every case, there is at least one way or another to get it back to the tank. Depending on the boat and how the fuel system is run, you could have vapor lock issues as well as aerating the fuel. Look at the Merc 502 Mags. They were famous for vapor locking and they returned the fuel to the tank and that pump was much smaller. The larger the pump, the more fuel it moves, the hotter that fuel gets, the more potential for problems. It's pretty much always easier to return the fuel to the filter head or inlet of the pump, but that doesn't make it the best bet.
Eddie

Eddie, does this boat have the Superflow fuel valves or the originals? I was under the impression that once you return to the tank that you have to the special valve so that you are not filling a tank that you are not pulling from.

Do you have 4 tanks or 2?

It seems that returning to the water separator causes inconsistant fuel pressure. Do you have gauges? Have you compared them to mechanical?

There are 2 tanks. I just installed electric gauges on the dash and mechanical ones at the regulator. I only made 1 short run after installing them, but when I checked at idle and at 3500 they were about the same. I'll pay attention to them to see if the pressure stays consistent. I'm not sure how difficult it would be to return the fuel to the tank. I'm guessing that's why Whipple put a fuel cooler on the return line.

http://www.hardin-marine.com/c-1376-...k-returns.aspx

If there are no spare bungs on the tank, this is the easiest way. Split the fuel fill hose and return there.

I put the Imco 6 port electric fuel switching valves on mine and plumed it so it returns to the tank it is sucked from , cut the filler necks and made my own tees , with the Imco valves the fuel guages follow the tanks its pulled from and you can switch tanks right from the dash , the factory switching valves I think are very restrictive and dont look to appealing .