FUEL PUMP WOES

[Domsz06]

Hello everyone,

First off hoping to get a hold of Matt or Andrew.

Background:
21IR 2003

Problem:
Fuel Pump wont shut off





Ok everyone yesterday at the lake I noticed a humming noise. After I figured out it was not one of my ballest pumps I called the dealer and we figured out together it is my fuel pump. The weird thing is the pump is pumping, but it will not shut off. And its pumping so much that even when I get the engine started it dies at WOT. So the question is is there a switch or something that needs replaced or is it a whole fuel pump. I really don't want to take my boat up there and have it sit in the hot sun and rain for two to three weeks. Well make a long story short, I finally got my boat off the middle of a lake, and no another boat was not used

well the problem is that it is covered under warrenty, but the dealer is at least two weeks backlogged. Is is possible has everyone heard if I just take the pump off and give it to them can I get another one? Or is it a switch, or how much is a fuel pump? The dealer said it's quite common on these boats Also how hard is it to change the impeller, it's my second year to own it so I figured it's time.

Dom

[Tige M.D.]

seen this on the mercruisers before. fuel pump relay is probably stuck.
there is no switch in the pump or regulator. just a pump nothing more or less, as long as we are talking about a merc. the impeller is pretty easy to change on the marine power gm vortec. its alot harder on the mercruiser. especially in the v-drive models.

[Domsz06]

Does this require a whole new pump or just a relay?

Dom

[Tige M.D.]

just a relay.

[Domsz06]

could you describe it to me where it's located at?

Dom

[Tige M.D.]

i'm a little rusty on the merc engine, i believe it is on top the engine, close to the ecm. there should be two relays, a starter and a fuel pump relay. when you turn on the key you will feel it "click". if the pump never stops running with the key "on" try switching the two relays. they are interchangable. if it shuts off after 2-3 seconds then you have just successfuly trouble shot your fuel system. go to the auto parts store with the bad relay and buy a new one.

[Domsz06]

tige md you rock!!

i'm off to try it.

Dom

[jeffro]

here's another challenge for you MD...

a friend has a 22v '03, with the 350 merc. (same as the 21i above).

he's had this same problem about 7 times now.... the dealer as contact merc and (i'm guessing) not having much luck figuring out why it keeps happening. (the relay messing up).... they even went so far as to replace a wiring harness (i assume the one that encompasses the fuel pump).

any other thoughts as to how to trouble shoot this one?

[Domsz06]

well i swapped out the relays, and the pump worked, then I put the old relay back in and the pump worked, so I guess I'm just gonna carry an extra relay and see what happens.

Off to the store to see if they have one

thanks Tige MD
Dom

[rushin]

I guess it was just stuck, huh?

[Matt Garcia]

dom, as you already know technical questions like this are best handled by Tige MD or lee. Those guys know there stuff.

Changing your impeller is relatively easy especially on a Direct Drive. RZMike wrote an article on how to change your impeller here.

[Tige M.D.]

mr. jeffro,
seven relays! that is unheard of. is he having the same exact problem,
a fuel pump running on?

[jeffro]

yes, same problem.

we're stumped down here....

everytime they replace it, it will work for a few hours, sometimes less, then it will start the continuous running again.

thank god for battery switches.

[Tige M.D.]

you said they replaced the wireharness? are they are going to replace it? i am really not sure what to tell you you got me on this one. if you get me the engine serial # i will submit it and the problem to merc tech support. see what they have to say.
i will need to know when this happened and how long it has been going on.

[walkers2rad]

It might help to add what is called a flashback diode between the coil of the relay and or the fuel pump. Maybe someone with a little bit more electrical knowledge than I can explain this better but I will give it a try. When you apply voltage to a relay to energize it, you are charging a coil that magneticly pulls in the main contacts, the trouble happens when you remove the power to that magnetic field, you basically have a minature version of the coil that fires your spark plugs. Think about it, a ignition coil fires when you remove the voltage to it. It can make a little backwards spike in your electrical system or it could make the relay ring (switch the contacts on and off quickly) and when you are running something with a high current draw like a fuel pump it can weld the contacts together eventually because you are making an arc when you open and close the contacts. Circuts do not like to be broken, that is what the condencer in a points sysem does.
What you would do is hook up a small diode between the two coil leads on the relay. You would point the arrow on the diode so that you do not create a direct short, ie; arrow flowing from neg to pos and blocked. This gives the coil a path to harmlessly collapse into. The same thing can be happening on the other side in fact it may be more likely that when you shut off the fuel pump it also has a magnetic field that needs to go somewhere, otherwise it turns into somewhat of a generator for a split second and becomes a mini welder trying to fuse the contacts together on the relay. I dont know for sure but there is probably a diode in the harness somewhere and it has opened up. You would just do the same thing and put a diode between the two wires going to the fuel pump, just be carefull and put the blocked arrow in the right direction or you create a direct short and wires will suffer.
Let me know if this helps.
Ray