4.3 Mercruiser Fires but will not run

[Jgrimm1983]

New to boating. Bought a 1996 regal 182 last week took it out once and had to be towed back.

Model - MCM 4.3 LX Gen+
Engine Serial - 0F823523
2 barrel carb

First time out everything started fine but after anchoring for an hour boat would not turn over. Ended up replacing starter.
Now after 3 pumps turns over fine and fires right away but will not run. Maybe runs for 1/2 second but nothing. Seems like not getting gas and also cannot hear fuel pump prime when turn key on. After researching some I thought it was fuel pump. Removed it and put 12volts to it and pumped fine so put it back in. Next I went to oil pressure switch removed both wires and jumped the purple wire to purple and yellow wire with a jumper wire (as instructed by another forum to rule out pressure switch) and pump would not pump. The solid purple wire has constant 12 volts to it with key on but when jumped to p/y wire nothing. I then jumped from battery to p/y wire and pump turns on. I am not an electrician by any means but just cannot understand why using the 12volt purple wire is any different from jumping from battery?

Seems weird to have 2 problems at the exact same time and I have read the starter has something to do with fuel pump. So maybe thinking I was given the wrong starter or possibly hooked it up wrong but I took pics and 99.9% sure all wires are in correct spot or at least the spot they came off old starter. Starter I was given from dealership was a Sierra 18-5913-1.

Any help would be appreciated

 

[alldodge]

The solid purple wire has constant 12 volts to it with key on but when jumped to p/y wire nothing.

This is the issue, its showing there is a bad connection or corrosion.

You have an electrical issue and not a fuel issue. The carb will be full of fuel and motor would run until it ran out for some time at idle. The 12V is reduced to a level that the motor will not run.

Check voltage at the coil it should stay at 12V

 

[Bt Doctur]

the fuel pump does not do that with a carb`d motor

 

[Rick Stephens]

Jgrimm, you done pretty good figuring this out. And you do have some sort of electrical issue. Maybe ignition switch, I'd start there. That purple wire gets its power from the ignition switch. Might just be dirty connectors - I'd start looking for that at the battery and work forward.

Purple wire power goes to the oil pressure switch which directly powers the pump when oil pressure and ignition power is present. Also, the outside small lug on the starter supplies power directly to the pump when you are cranking as a primer.

 

[isaacs]

Are you sure it's not the lanyard safety switch? See if it will run if you keep the key in the start position with the starter grinding.

 

[nola mike]

Are you sure it's not the lanyard safety switch? See if it will run if you keep the key in the start position with the starter grinding.

It won't catch at all if this was the issue

 

[Jgrimm1983]

Thank you for help. I will try these solutions and let you know. Thanks again.

 

[isaacs]

It won't catch at all if this was the issue

If my lanyard switch is turned off, my boat will definitely run in the start position. At this point, the coil receives voltage directly from the starter 'till I release the switch. I think it has do do with defeating the oil pressure cutoff switch until the oil pressure builds up.

 

[Rick Stephens]

If my lanyard switch is turned off, my boat will definitely run in the start position. At this point, the coil receives voltage directly from the starter 'till I release the switch. I think it has do do with defeating the oil pressure cutoff switch until the oil pressure builds up.

What? Don’t think you’re wired right. I can see how it could back power the coil from the starter prime wire purple/yel, but should not be that way.

 

[isaacs]

What? Don’t think you’re wired right. I can see how it could back power the coil from the starter prime wire purple/yel, but should not be that way.

It's been this way since I bought it new. BTW, when I said "release the switch" I was referring to the ignition switch springing back to the run position, not the lanyard safety switch.

 

[isaacs]

[No message]

 

[Rick Stephens]

Ok, I see where the pur/yel going to the fuel pump would cross over and power the coil during cranking. Even works correctly to kill the motor should one fall overboard. Good call on checking it.

 

[Jgrimm1983]

Update: So I have 12.9 volts at pur/yellow wire connected to coil on starter with engine cranking and I unplugged the black plug to fuel pump and have 12.9 volts there when engine is cranking. I am I suppose to have voltage to black plug on fuel pump when key is in the on position (I don't only when cranking).

Not sure if I fouled plugs or what now because it will not fire up for that 1/2 second anymore. Even tried starting fluid and no fire.

Any advise is appreciated.

 

[nola mike]

isaacs

My mistake, I was thinking neutral switch

 

[nola mike]

Update: So I have 12.9 volts at pur/yellow wire connected to coil on starter with engine cranking and I unplugged the black plug to fuel pump and have 12.9 volts there when engine is cranking. I am I suppose to have voltage to black plug on fuel pump when key is in the on position (I don't only when cranking).

Not sure if I fouled plugs or what now because it will not fire up for that 1/2 second anymore. Even tried starting fluid and no fire.

Any advise is appreciated.

i don't know your exact wiring, but you should have a switch to the fuel pump. During cranking the yellow wire supplies voltage to the switch. When running, the power to the pump is supplied via the ignition (purple wire). The switch contacts are closed by oil pressure. So check for 12v at the purple wire at the switch. If it's there with ignition on, you have a bad switch.

 

[Jgrimm1983]

With key on I have power to my purple wire that is connected to oil sensor and when I turn the engine over it connects power to the purple/yellow wire so to me that sounds like the oil pressure switch is working. I keep hearing about the fuel pump priming when the key is turned to on. What all is involved with the priming? Mine fuel pump does not prime.

 

[nola mike]

With key on I have power to my purple wire that is connected to oil sensor and when I turn the engine over it connects power to the purple/yellow wire so to me that sounds like the oil pressure switch is working. I keep hearing about the fuel pump priming when the key is turned to on. What all is involved with the priming? Mine fuel pump does not prime.

No, the switch isn't working. The switch runs on the power from the purple wire once oil pressure is up and the ignition switch is in the run position. It's initially supplied by the wire from the starter. The 12v should still be in the purple/yellow wire after the key is released from the start position and the motor catches. The pump doesn't prime in a carb engine.

 

[Jgrimm1983]

Not sure I am following. So when the key is on I have power to the purple wire only then when I crank the engine I have power to both purple and purple/yellow wires but the engine does not catch at all anymore like it did before so when I release key I lose power to purple/yellow wire. Are you saying I should keep power to purple/yellow wire even though the engine is not running?

Thanks again and sorry but very new to boats.

 

[alldodge]

Just forget about looking for power at the fuel pump, this is not your problem

Check for 12V on the + (positive) side of the ignition coil. Not the one on the starter but the one on the coil

The reason it fires and dies when the key is released is because voltage is breaking. I'm thinking its the key switch or the kill switch

 

[Jgrimm1983]

OK. When should I have power and when should I not have power at the coil? I see there are 2 wires attached to it.