No spark 4.3 Mercruiser

[nola mike]

It should have 3 wires

No, that looks correct on his motor.
You should get 12 v from p/y while cranking, starter powers it. When oil pressure rises and you're in the run position, starter no longer supplies voltage. At that point the switch closes and 12v is supplied by purple through the switch to p/y. P/y supplies the fuel pump. So next step is check for 12v at purple at the switch with ignition on. If you have 12v then the switch is bad.

 

[Wayneg13]

No, that looks correct on his motor.
You should get 12 v from p/y while cranking, starter powers it. When oil pressure rises and you're in the run position, starter no longer supplies voltage. At that point the switch closes and 12v is supplied by purple through the switch to p/y. P/y supplies the fuel pump. So next step is check for 12v at purple at the switch with ignition on. If you have 12v then the switch is bad.

Yes, the purple yellow that powers the pump starts at the starter. I checked power there and it turns off when it stops cranking at the starter. So I guess I gotta buy a new starter. I got it to run wiring power strait from the ignition switch on the empty prong, that prong powers on when in Run position.

 

[nola mike]

Mine only has two - so there are switches that have purple on one side and pur/yel on the other.

Wayne, you need to test the oil pressure switch. First, when the key is on run position, the purple wire should be hot. When the motor has oil pressure - and it only needs about 5 PSI - the other side (pur/yel) of the switch should be hot. SInce you say the motor doesn't continue running, the test is to connect both sides of the switch together and see if the motor keeps running. You are connecting the purple to the pur/yel. If this fixes the problem you need a new oil pressure switch.

Yes, the purple yellow that powers the pump starts at the starter. I checked power there and it turns off when it stops cranking at the starter. So I guess I gotta buy a new starter.

No, that's what it should be doing. Test either how I said or how Rick said. Actually, do mine first to make sure you're getting 12v at the switch.

 

[Rick Stephens]

Yes, the purple yellow that powers the pump starts at the starter. I checked power there and it turns off when it stops cranking at the starter. So I guess I gotta buy a new starter. I got it to run wiring power strait from the ignition switch on the empty prong, that prong powers on when in Run position.

NO NO NO!!!!

The pur/yel coming from the starter is ONLY to supply pump power during cranking! That is how it works. Your starter is perfect.

Once you stop cranking that source goes dead.

At that point, the oil pressure should come up and the oil pressure switch takes over powering the pump.

 

[nola mike]

NO NO NO!!!!

The pur/yel coming from the starter is ONLY to supply pump power during cranking! That is how it works. Your starter is perfect.

Once you stop cranking that source goes dead.

At that point, the oil pressure should come up and the oil pressure switch takes over powering the pump.

I'mma stop posting now until Rick goes to bed.

 

[Rick Stephens]

The whole reason for the pump needing oil pressure to run is that a leak in a boat creates a bomb. If the fuel pump runs whenever the key is on and there is a leak, that fuel goes into the bilge. Unlike a car where it would just dribble out on the ground. The oil pressure switch is a safety measure. A hugely important one.

 

[Rick Stephens]

I'mma stop posting now until Rick goes to bed.

Don't do that...... we lost internet for the last 24 hours due to wind storms here. I'm just getting back into things :^)

 

[nola mike]

Don't do that...... we lost internet for the last 24 hours due to wind storms here. I'm just getting back into things :^)

Then stop copying me

 

[Wayneg13]

NO NO NO!!!!

The pur/yel coming from the starter is ONLY to supply pump power during cranking! That is how it works. Your starter is perfect.

Once you stop cranking that source goes dead.

At that point, the oil pressure should come up and the oil pressure switch takes over powering the pump.

Lol ok sorry I was confused and didn’t realize the switch takes over. The purple yellow on the switch shuts off when you stop cranking. Purple wire powers on and stays on while running. Also the switch is dumping oil out the yellow/purple wire connection while it’s running.

 

[Scott06]

Lol ok sorry I was confused and didn’t realize the switch takes over. The purple yellow on the switch shuts off when you stop cranking. Purple wire powers on and stays on while running. Also the switch is dumping oil out the yellow/purple wire connection while it’s running.

Sounds like your switch is bad if oil is coming out of it. Temporarily you can put a jumper wire in the connection to bypass it If need be.

 

[Wayneg13]

NO NO NO!!!!

The pur/yel coming from the starter is ONLY to supply pump power during cranking! That is how it works. Your starter is perfect.

Once you stop cranking that source goes dead.

At that point, the oil pressure should come up and the oil pressure switch takes over powering the pump.

I was just curious which wire from the oil switch powers the pump. There’s a purple/yellow running to the pump. Also there’s a purple/yellow at that switch so I assumed there’s where it got power from.

 

[Rick Stephens]

Then stop copying me

Post slower !!

 

[Rick Stephens]

I was just curious which wire from the oil switch powers the pump. There’s a purple/yellow running to the pump. Also there’s a purple/yellow at that switch so I assumed there’s where it got power from.

Purple should be the power source at the oil pressure switch - coming from ignition switch.

Purple yellow from the starter should be connected to the same lug as the purple yellow going to the pump.


Edit: Purple yellow from the switch and from the starter both go to power the pump. They come together somewhere - not necessarily at the pressure switch. I misread your post as stating you had purple yellow on both sides of the oil pressure switch. Sorry.

 

[Scott06]

Look at the wiring diagram black is always ground, or the negative side of a 12 v system.
the fuel pump gets the positive 12 v from the purple yellow wire from two different ways

off the starter during cranking

when 12 v positive is supplied to the oil pressure (ignition switch is in run once engine is started) the oil pressure switch closes at 5 psi to make sure the ignition isn’t inadvertently left on or engine dies out... the down stream side of the oil pressure switch is the also a leg of the purple yellow wire as they are spliced together in the harness. If the oil pressure switch doesn’t work fuel pump will run while starter cranks but then stop when keys is switched to run ...

 

[nola mike]

I was just curious which wire from the oil switch powers the pump. There’s a purple/yellow running to the pump. Also there’s a purple/yellow at that switch so I assumed there’s where it got power from.

That's what the switch does; when it has oil pressure the switch closes and connects the power from the purple wire to the p/y wire.

 

[Wayneg13]

That's what the switch does; when it has oil pressure the switch closes and connects the power from the purple wire to the p/y wire.

I’m gonna buy that oil switch and replace it. That has to be the issue.

 

[Scott06]

I’m gonna buy that oil switch and replace it. That has to be the issue.

if there is no power on the purple supplying the switch you won’t get anything downstream of it...
you can test it two ways, not that it’s an expensive part-
put a jumper wire across the two terminals in the wiring harness.
use an ohm meter to see if there is continuity when the engine is running and there is more than 5 psi oil pressure.
but if this were the case the engine would start run for a bit until the carb emptied of fuel then die out

 

[Wayneg13]

if there is no power on the purple supplying the switch you won’t get anything downstream of it...
you can test it two ways, not that it’s an expensive part-
put a jumper wire across the two terminals in the wiring harness.
use an ohm meter to see if there is continuity when the engine is running and there is more than 5 psi oil pressure.
but if this were the case the engine would start run for a bit until the carb emptied of fuel then die out

That’s exactly what happens, it runs for about 1 minute and dies out. The purple wire has power and the purple/yellow that goes to the pump only gets power while cranking then never lights up again. The oil switch is leaking a lot of oil, what’s strange is the oil gauge still seems to work

 

[Scott06]

That’s exactly what happens, it runs for about 1 minute and dies out. The purple wire has power and the purple/yellow that goes to the pump only gets power while cranking then never lights up again. The oil switch is leaking a lot of oil, what’s strange is the oil gauge still seems to work

Ok must have missed that in the thread , jumper it out it should run

guage and switch are off different sources. there is a round sender often on a t with the switch has a single wire on it this is what sends the signal to the gauge