2007 Merc 5.0 TKS stalled at speed, had to be towed

[haglunde]

Well maintained, owned since new. 490 hours. Motor just serviced by marina last fall including new fuel separator filter, plugs & wires. Fuel filter at carb also pulled and inspected, not replaced. Boat ran great for 5 hours this spring and then died while cruising at 2500 rpms. Would not restart or catch regardless of throttle position. I ensured the tether switch was in correct position and main fuse was set. A Good Samaritan had a look and stated he felt it was fuel related. He said he did not see adequate fuel spraying in the carb and the inlet fuel hose to the separator should have fuel coming out when ignition on (?). I've had the boat since new and know that I burn 2 gallons per hour when running easy so my 28ish gallon tank should still have plenty of fuel. Funny thing is, the fuel gauge stopped working as well this spring, shows full even though I know it is not.
So I could throw some gas in and try to start it just in case someone stole gas but that seems unlikely. Is the fuel pump in the tank or is this a suction pump on the motor somewhere? Any ideas on narrowing this issue down would be helpful. I'm capable of simple diagnosis and fixes without special tools. Beyond that, I will pull it and take it to the shop but would prefer to avoid that runaround if possible. Thanks!

 

[alldodge]

The fuel pump is electric and should run when motor is cranking, and continue to run when motor has started.

Below is a block diagram showing how the system works. The purple/yellow wire is what supplies power to the fuel pump.

Remove the fuel filter to see if it's full of fuel and pour gas into clear container to see if there is anything but clean gas

 

[nola mike]

Fill your tank. No way a 5.0 is getting 2 gal/hr.

Edit: was your separator filter dry or have gas in it? As mentioned you have an electric pump after the filter, it shouldn't run unless engine is cranking or running

 

[haglunde]

Believe it or not, I burn 4ish gallons per hour when we are cruising and doing mixed water sports with a light load. And 2 gallons per hour at 1200-1300 rpms booze cruising and pretending to be a pontoon boat. Good suggestion about checking the fuel separator to see if there is fuel in there. I will check that out. So just having the ignition on will not run the fuel pump? Where exactly is the fuel pump? Thanks--

 

[haglunde]

From the diagram, TKS has a "module"? What does that do?

[Edit: I found it iBoats. Cold engine enrichment. I always thought the hissing was from a choke plate. Now I know.]

 

[haglunde]

Ok. Now that the toxic Canadian air has passed, I was able to spend some time on the boat. I was unable to get the water separator filter off. Here in NW Wisconsin, there must be some marina rule that all oil and water separator filters are torqued to the point where you need the jaws of death to take them off. But that's another post. So I moved on the putting another 8 gallons of gas into the tank. And it started up Immediately. Which I thought was odd since every other time in any other vehicle I've run out of gas in it always needed to crank for a bit to recharge the fuel system. So on the lift in the water, it ran perfectly. I let it run from 1500-2000 rpms and it ran like a champ for 2-3 minutes... until it died and the horns went off. Is there a pressure problem somewhere?

 

[Scott Danforth]

You should be pulling the fuel filter every fall and swapping it. A light coat of grease will keep it from sticking

Check your oil pressure. No oil pressure, no fuel pump and you will get alarms

 

[nola mike]

You should be pulling the fuel filter every fall and swapping it. A light coat of grease will keep it from sticking

Check your oil pressure. No oil pressure, no fuel pump and you will get alarms

As will boat stalling with ignition on.

 

[haglunde]

Good thought on oil pressure, I see that is in the path on the diagram alldodge posted. 490 hours, owned since new, oil and filter every fall. Oil pressure gauge shows good pressure, higher than my other V8 vehicles. When I do my own oil and fuel separator, I never have a problem getting them off. It's when the f#n marinas do them, I can't get them off without destroying them. Oil pressure is good.

 

[Scott Danforth]

Good thought on oil pressure, I see that is in the path on the diagram alldodge posted. 490 hours, owned since new, oil and filter every fall. Oil pressure gauge shows good pressure, higher than my other V8 vehicles. When I do my own oil and fuel separator, I never have a problem getting them off. It's when the f#n marinas do them, I can't get them off without destroying them. Oil pressure is good.

Gauge sender is different than switch for fuel pump

 

[Bondo]

Good thought on oil pressure, I see that is in the path on the diagram alldodge posted. 490 hours, owned since new, oil and filter every fall. Oil pressure gauge shows good pressure, higher than my other V8 vehicles. When I do my own oil and fuel separator, I never have a problem getting them off. It's when the f#n marinas do them, I can't get them off without destroying them. Oil pressure is good.

Ayuh,.... Welcome Aboard,...... There should be a fuel pump switch on the portside of the motor's block, aft of center, way down low, just above the oil pan,.....
That oil pressure switch powers the fuel pump, when the motor is runnin',......

When starting, the fuel pump is powered by the outboard side tiny terminal on the starter's solenoid,.....

 

[haglunde]

Thanks for the continued info, I appreciate it. I was able to find only 3 mentions of the oil pressure switch in the Mercruiser Sterndrive manual #31: where it is and what loc-tite and torque to use. No testing or replacement info. Scott and bondo have both mentioned this, it is a common failure point?

 

[Scott Danforth]

It's not a common failure point

 

[haglunde]

So at the marina, the boat ran great. Of course. But like you guys, they also were suspicious of the oil pressure switch. They were also suspicious that Merc had so many of them in stock. So they replaced it. Because of the wildfire pollution, we haven't put in many more hours but so far it's running fine. Is there a way to hot-wire/bypass that sensor? It seem like a simple circuit?

 

[Scott06]

So at the marina, the boat ran great. Of course. But like you guys, they also were suspicious of the oil pressure switch. They were also suspicious that Merc had so many of them in stock. So they replaced it. Because of the wildfire pollution, we haven't put in many more hours but so far it's running fine. Is there a way to hot-wire/bypass that sensor? It seem like a simple circuit?

Take the wiring harness off the switch (down above oil filter) and stick a jumper wire in the harness plug to jump across the two wire terminals. I keep a couple of short sections of wire for just this purpose in my tool kit on the boat.

 

[nola mike]

Purple --> purple/yellow bypasses that switch and lets the FP run.
Looking at the diagram in manual #41 though, there's an additional OP switch that I hadn't noticed before (#26). Appears to let the ICM know if there's no OP, which then presumably kills spark or triggers audio warning (I can't find the warning circuit on the diagram?). Guess it's only present on the TBV. Can @alldodge or anyone else confirm?

 

[haglunde]

Take the wiring harness off the switch (down above oil filter) and stick a jumper wire in the harness plug to jump across the two wire terminals. I keep a couple of short sections of wire for just this purpose in my tool kit on the boat.

Bingo, that's what I was wondering. Thanks Scott.

 

[haglunde]

Purple --> purple/yellow bypasses that switch and lets the FP run.
Looking at the diagram in manual #41 though, there's an additional OP switch that I hadn't noticed before (#26). Appears to let the ICM know if there's no OP, which then presumably kills spark or triggers audio warning (I can't find the warning circuit on the diagram?). Guess it's only present on the TBV. Can @alldodge or anyone else confirm?

That horn is obnoxious. Would love to be able to turn that on and off as well.

 

[haglunde]

And.... we're back. Happened again today. This time just putzing at 13-1400 RPMs. Same as the first time-- dies with very little sputtering and the horn blowing immediately. The marina replaced the oil pressure switch but I'd like to remove it from the equation because I think this may be a process of elimination. I'm going to follow the wires associated with the fuel pump and horn as best I can to see if there is any corrosion or shorting. Mean time, I'm trying to interpret this section in manual #24. I read this as just unplugging the lead to the switch will short the system. Meaning, I read this believing that I don't have to jumper that connector, just unplugging will remove the continuity and fool the system into thinking it has pressure. Right or wrong?

 

[Scott06]

And.... we're back. Happened again today. This time just putzing at 13-1400 RPMs. Same as the first time-- dies with very little sputtering and the horn blowing immediately. The marina replaced the oil pressure switch but I'd like to remove it from the equation because I think this may be a process of elimination. I'm going to follow the wires associated with the fuel pump and horn as best I can to see if there is any corrosion or shorting. Mean time, I'm trying to interpret this section in manual #24. I read this as just unplugging the lead to the switch will short the system. Meaning, I read this believing that I don't have to jumper that connector, just unplugging will remove the continuity and fool the system into thinking it has pressure. Right or wrong?View attachment 388875

Yes the warning alarm switch just disconnect the wire. This switch just creates a connection to ground for the horn.
the fuel pump switch you need to jumper out to bypass