Is my fuel pump dead?

[kylef]

Hi all,
I have a 4.3 Mercruiser AlphaOne in my Stingray 190RS. We had it down at the lake today and had trouble with it. We got it off the trailer, rode it for about 5 minutes to the middle of the lake, then shut it off, had a bite to eat and then my son got his skis on. When he was ready, I gave it 3/4 throttle, he just got up and then the engine died. I had to give two pumps of the throttle to get it started again. When he was ready, I gave it 3/4 throttle again and the same happened, and again 4 more times until I got him back on the boat and we decided to get the boat back on the trailer. I had to continuously do this same routine (pump the throttle, get her started, ride for 5 seconds, engine die, pump the throttle, get her started, ride for 5 seconds die, etc) until I eventually got the boat on the trailer. I brought it home, got the flush muffs on, started and it ran for a little while before cutting out again - did this four times, then shut it off and put the cover on.

I am in no way mechanically minded but what makes sense to me is happening is that when I crank it, the fuel pump sucks fuel, the engine starts, then the fuel pump appears to not suck anymore fuel, so it runs on what it sucked in from cranking it and then has no more fuel so it dies. I imagine the fuel pump would make a sound/noise when I switch the ignition on, but I hear absolutely nothing.

As I mentioned, I don't know the ins and outs but if there is something anybody can suggest that I check, I'll do so.

Thanks for your help.

 

[MarcelSydney]

I had the same problem with my 1999 4.3L, carby version with electric fuel pump. Not sure what year yours is.
On mine it was the oil pressure switch. Could be the same thing.
Apparently the starter motor runs the electric fuel pump while cranking and gives enough fuel to start and run for a bit, after that the oil pressure switch takes over running the fuel pump.
I replaced the oil pressure switch and works fine. It was a super easy fix.
You could test on the muffs by finding the two wires on the oil pressure switch. Disconnect them, start the boat up then jump the two wires to bypass the oil pressure switch. See if it keeps running. If it runs for a while, disconnect the wires you jumped. If the motor turns off (may take a few minutes to run out of fuel) then it could be your problem.
Remember to disconnect the jumper wires though if you stop running the boat. Fuel pump may keep running.
Im not a mechanic though, just what I found out from reading forums here!

 

[kylef]

I had the same problem with my 1999 4.3L, carby version with electric fuel pump. Not sure what year yours is.
On mine it was the oil pressure switch. Could be the same thing.
Apparently the starter motor runs the electric fuel pump while cranking and gives enough fuel to start and run for a bit, after that the oil pressure switch takes over running the fuel pump.
I replaced the oil pressure switch and works fine. It was a super easy fix.
You could test on the muffs by finding the two wires on the oil pressure switch. Disconnect them, start the boat up then jump the two wires to bypass the oil pressure switch. See if it keeps running. If it runs for a while, disconnect the wires you jumped. If the motor turns off (may take a few minutes to run out of fuel) then it could be your problem.
Remember to disconnect the jumper wires though if you stop running the boat. Fuel pump may keep running.
Im not a mechanic though, just what I found out from reading forums here!

Thank you so much for your reply. I am not 100% certain what year mine is, but I know that the boat is a 1999.
Would you happen to have a photo of where I can find this oil pressure switch? And when you say 'jump the wires', do you mean connect the two wires to each other?

 

[todhunter]

Could be the anti-siphon valve on the fuel tank or a clogged fuel tank vent. After running it on muffs and having it stall, remove the gas cap. Is there a whoosh of air? Leave the gas cap off and start the engine back up. Will it run without stalling with the gas cap removed?

 

[QBhoy]

Could be a few things. Oil pressure sensor (that activate fuel pump), choke sticking on or a restriction in the fuel line. Usually around the check valve.

 

[Scott06]

Thank you so much for your reply. I am not 100% certain what year mine is, but I know that the boat is a 1999.
Would you happen to have a photo of where I can find this oil pressure switch? And when you say 'jump the wires', do you mean connect the two wires to each other?

Oil pressure switch is usually on a 1/8” pipe T down by oil filter . One side of T has the oil pressure switch (two wires going to it) and the snder for pressure gauge ( single wire bigger dia sensor).
take the wire harness plug off the switch put a jumper wire across the two wire connections. This effectively bypasses the switch.

 

[kylef]

Could be the anti-siphon valve on the fuel tank or a clogged fuel tank vent. After running it on muffs and having it stall, remove the gas cap. Is there a whoosh of air? Leave the gas cap off and start the engine back up. Will it run without stalling with the gas cap removed?

I did try opening the gas cap - no whoosh of air and didn't help keep it running. Thanks for your reply.

 

[kylef]

Oil pressure switch is usually on a 1/8” pipe T down by oil filter . One side of T has the oil pressure switch (two wires going to it) and the snder for pressure gauge ( single wire bigger dia sensor).
take the wire harness plug off the switch put a jumper wire across the two wire connections. This effectively bypasses the switch.

Thank you for your reply. I will give this a try in a few hours. Am I putting the jumper wire across the two connections on the wire harness plug or on the switch itself?

 

[Scott06]

Thank you for your reply. I will give this a try in a few hours. Am I putting the jumper wire across the two connections on the wire harness plug or on the switch itself?

Harness plug. This is just for testing switch needs to be wired up for safe boating

 

[MarcelSydney]

Thank you so much for your reply. I am not 100% certain what year mine is, but I know that the boat is a 1999.
Would you happen to have a photo of where I can find this oil pressure switch? And when you say 'jump the wires', do you mean connect the two wires to each other?

Hey, like Scott06 said, down near the oil filter. Port side on my engine.
Here is a picture of the one I replaced. Might help you locate it (you can see it was pretty rusty).
The oil pressure switch is the one with two wires. If you join those wires, it bypasses the switch.

 

[achris]

Corroded terminals on that switch is a VERY common problem... Your symptoms fit exactly. Pull the connectors and link them with a bit of wire. If that fixes it, then either try to clean up the corrosion or replace the switch.

Chris...

 

[H20Rat]

I went through the same thing this spring. It sounds very much like a bad oil pressure switch. You can temporarily bypass it with a couple inches of wire with flat spade connectors on each end. The replacement for it is a newer design that presumably won't fail as easy.

 

[kylef]

Thank you all for your replies. I disconnected the wires from the switch, the terminals were covered in a blue kinda copper corrosion. Cleaned them up and she ran beautifully, my son and I both got up on skis behind the boat for four hours with no issues.