Fuel Pump/Cooler Relay

[bobbysky]

2002 23v - Mercruiser 350mpi

A few weeks ago I noticed when I turn my key off that the mercruiser cool fuel and fuel pump would stay running. Traced the wiring back to a relay that sits atop the engine. When I flick the relay with my finger it turns off the pumps. It didn't happen every single time, but maybe 50-75% of the time. So I figured the relay was bad, so I bought a new one. It worked great for about a week then started doing the same thing as the old one.

I talked to a buddy that used to rebuild engines, and he said that a lot of the new relays are Chinese made and 40% are defective from the get go. The only other thing he could think was that the connections to either the pump or the cooler were corroded and are pulling to much juice causing the relay to stay open.

I'm going to check and clean the connections but was wondering if you guys have any other ideas of what would be causing this issue?

[Ewok]

I had my kill switch fail on my old boat and 3 BRAND NEW kill switches straight from the box were bad too. It very well could have been a bad relay out of the box.

[boatwakes]

You are correct, it's just a bad relay. We've been seeing quite a few problems this last year with new faulty relays as well.

[chpthril]

it's very simple to diagnose a stuck relay. With a test light or volt meter, there should not be both + and - at the same time on the coil side of the relay. These are probably labeled 85 and 86. Once the key, or what ever is turned off, either power of ground is removed from one side of the coil and the relay contacts open and the device powered by the relay shuts off. When the relay "sticks" and fuel pump keeps running, test the contacts.

The fact that you can tap the relay and the pump shuts off sounds like just a bad relay, but too much current draw can "weld" the contacts and cause them to stick.

[bobbysky]

What would cause to much amp draw from the fuel pump (failing, corrosion, etc).

[boatwakes]

Too much amperage draw is from a hi-load situation like: frozen FP motor, short in the system, corrosion, etc...but the wiring for that relay has an inline breaker for the fuel pump which would trip if there was too much current draw. Most engines have these as circuit breakers and others, very few, have waterproof fusing inline. There is continuous power supplied to the relay when the keyswitch is off but the relay is controlled by keyswitch activation. The MEFI 1 and 2 systems utilize an ignition relay in front of the fuel pump relay but that is superceded in the MEFI3 systems on most of the post 1998 boats by just using the FP relay.
Hopefully that helps, good luck.