Fuel starvation??

[maddog2112]

Well it finally happened. The dreaded problem on the water. First time out for the year. My 06 Q6 5.0 carbureted was out on the water yesterday and gave me some fts. Started up fine, idled thru no wake zone and warmed her up. Gave her the gradual increase she`s runing good. 500 yards later , poof ! She shutters a little and shutsoff. She would start fine but would repeat the same problem over and over. She would run fine at idle and move fine at 2000 rpm or so. Thats how I got her back to the dock. It`s just when I got on her she would come out nice and smooth for several hundred yards and shutdown. All regular maintenance has been done on her as required. Seems like fuel starvation. Ran fine on the cuffs at home before going to the lake. I did put a new mercruiser water seperator onher the day before we went out cause I had remembered that was the one thing I didnt do when winterizing. I`m wondering If I could have put the wrong water seperator on or maybe my fuel pump isnt keeping up?? The guy at the parts desk didnt look up the number he just said the one on the shelf was form my boat Mercruiser 35-802893T. Stabilizer used in tank as required. Any experiences like this out there??

 

[gm280]

Certainly sound like a fuel delivery issue. Also sounds like your fuel pump may need some looking at. If your tank has a vent, make sure it is clean and free of any obstruction as well. And if your fuel line is getting old, may be a get time to replace it as well... The reason you can start it up easily and move in the slower speeds is because your fuel pump is keeping the carb(s) supplies at that fuel demand. But when you ask for more fuel, it can't keep up and dies.... JMHO!

 

[alldodge]

Well it finally happened. The dreaded problem on the water. First time out for the year. My 06 Q6 5.0 carbureted was out on the water yesterday and gave me some fts. Started up fine, idled thru no wake zone and warmed her up. Gave her the gradual increase she`s runing good. 500 yards later , poof ! She shutters a little and shutsoff. She would start fine but would repeat the same problem over and over. She would run fine at idle and move fine at 2000 rpm or so. Thats how I got her back to the dock. It`s just when I got on her she would come out nice and smooth for several hundred yards and shutdown. All regular maintenance has been done on her as required. Seems like fuel starvation. Ran fine on the cuffs at home before going to the lake. I did put a new mercruiser water seperator onher the day before we went out cause I had remembered that was the one thing I didnt do when winterizing. I`m wondering If I could have put the wrong water seperator on or maybe my fuel pump isnt keeping up?? The guy at the parts desk didnt look up the number he just said the one on the shelf was form my boat Mercruiser 35-802893T. Stabilizer used in tank as required. Any experiences like this out there??

This thread should be in a motor section. Your saying iIt's a 2006 Merc 5.0 with a carb, I think you have TBI and the thing that looks like a carb is actually a throttle body, Might be wrong but could sure use your serial number to verify.

Sounds to me like an electrical problem.

 

[maddog2112]

Thanks for the responses. My engine serial number is OW626517

 

[maddog2112]

Gm 280, I was thinking the same thing. It`s a 250.00 part, the fuel pump so I wondr if there is a way to check the fuel pressure before purchasing one? Also I sem to remmeber a paper filter right at the carburetor inlet on old vehicles way back when. I haven`t checked that for clogging yet. I was suspicious of the new fuel water seperator I installed the day before, but it was a merc model for GM V8`s so I`m steering away from that now.

 

[alldodge]

Thanks for the responses. My engine serial number is OW626517

Well your right you have a carb with an electric fuel pump. Could be as GM mentioned, its running out of fuel. After it dies you crank the engine which runs the pump long enough to get it started again. Since you just replaced your fuel filter check the seal. If the seal is not making good contact your pump will be sucking air.

If its easy to get to safely, once the engine dies, keep the key turn off and loosen the filter to see if fuel comes out around the seal. Have a container to catch the overflow. If that is full, then pick up a cheap vacuum/fuel pressure gauge (about $20) from Harbor Freight/Autozone. Put that inline between the carb and pump, should see 4 to 7 psi.

There is a filter screen in the carb inlet item 29 below link
http://www.mercruiserparts.com/Show...11540.png&inbr=11741&bnbr=80&bdesc=Carburetor

 

[GA_Boater]

Moved this to the Mercruiser section, Mad.

Check the fuel tank vent. During a long lay-up bugs like to make a new home in small things like vents. Just something simple to look at.

 

[maddog2112]

Thanks for all the responses. I will work your suggestions this week and update. Nothing better than sharing ones knowledge and information. Thank you !!

 

[Bt Doctur]

run with the tank gas cap open to rule out a clogged vent hose
verify it actually is fuel related and not spark related. check the main engine harness plug for any pin corrosion and make sure the clamp is snug.

 

[UncleWillie]

Is the Fuel pump running when the engine is Running?
With the Key ON, Engine OFF, The Pump may not run.

In many installations....
The fuel pump is powered during cranking via the Starter Power.
The fuel pump is powered during Engine RUN via an Oil Pressure switch.

If the Oil pressure switch is defective, the Fuel system will be momentarily supplied while starting, and then loose supply as the fuel is used up.
Be sure you have correctly identify the real source of the problem before you start blindly throwing money at it.

 

[maddog2112]

Good one uncle willie. I will check that too.

 

[maddog2112]

Uncle Willie, is the oil pressure switch the same source for the oil pressure guage, because the guage was reading normal during operation
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[Eric 3.7LX Alpha 1]

No there is a oil sender for the pressure gauge and an oil switch for the fuel pump, they may be near each other I don't know your engine but should be two separate items.

 

[UncleWillie]

No there is a oil sender for the pressure gauge and an oil switch for the fuel pump, they may be near each other I don't know your engine but should be two separate items.

Correct!

There may be 3 oil pressure sensing devices. Pay attention!

#1 Pressure sender to Oil Pressure Gage.
#2 Pressure switch that closes at < 5 psi to sound Engine Alarm.
#3 Pressure switch that closes at >5 psi to power the Fuel pump.

#2&3 could be a single, multi-connection device or 2 separate devices.

Don't confuse these with the Water Temperature Sender, and Water Temp Alarm Switch that look similar.

 

[maddog2112]

Update on fuel starvation problem. Finally got to check some stuff on my boat in the driveway due to rain since last post. removed and check fuel water separator gasket, no leakage and all looks fine. I blew out my fuel vent hose and felt some restriction at first but wasn`t 100 percent sure anything blew out so I kept troubleshooting. The external vent next to the fuel cap was clear of debris. Cleaned dirty air filter. while I was messing around I noticed something I hadn`t noticed before. With my key switch off, when I turn on my master switch I can hear my electric fuel pump running. I didn`t think this was normal. I removed the connector off the oil pressure switch next to my oil filter housing the pump continued running . I did see the oil pressure sender right next to it. With the oil pressure switch connector off, the pump was still running. I ohmed out the oil pressure switch I found and it showed open with engine off which I believe is correct. My mercruiser manual shows 2 pressure switches but I could only find the one by the oil filter. Does anyone know if the pump running with only the master switch is normal? Or where a second pressure switch can be found. Again, my boat is an 06 tahoe q6 with 5.0 TKS. Thanks for any help.

 

[alldodge]

Update on fuel starvation problem. Finally got to check some stuff on my boat in the driveway due to rain since last post. removed and check fuel water separator gasket, no leakage and all looks fine. I blew out my fuel vent hose and felt some restriction at first but wasn`t 100 percent sure anything blew out so I kept troubleshooting. The external vent next to the fuel cap was clear of debris. Cleaned dirty air filter. while I was messing around I noticed something I hadn`t noticed before. With my key switch off, when I turn on my master switch I can hear my electric fuel pump running. I didn`t think this was normal. I removed the connector off the oil pressure switch next to my oil filter housing the pump continued running . I did see the oil pressure sender right next to it. With the oil pressure switch connector off, the pump was still running. I ohmed out the oil pressure switch I found and it showed open with engine off which I believe is correct. My mercruiser manual shows 2 pressure switches but I could only find the one by the oil filter. Does anyone know if the pump running with only the master switch is normal? Or where a second pressure switch can be found. Again, my boat is an 06 tahoe q6 with 5.0 TKS. Thanks for any help.

The second will be below the distributer, just to the left at the top rear of the engine deck

 

[maddog2112]

All dodge I believe I found the 2nd switch you mentioned right by the distributor. It`s got the type of terminal that just presses on and off. 1 wire. I removed that terminal on the switch and my fuel pump still runs with just the master switch on and key off. That my have nothing to do with my original problem, just something I ran into. While I had my fuel inlet to carburetor line removed I turned the master switch on where I could here my electric fuel pump on and 0 fuel came out of the line. Not sure if thats normal. The engine may have to be cranking before fuel would come out.

 

[alldodge]

All dodge I believe I found the 2nd switch you mentioned right by the distributor. It`s got the type of terminal that just presses on and off. 1 wire. I removed that terminal on the switch and my fuel pump still runs with just the master switch on and key off. That my have nothing to do with my original problem, just something I ran into. While I had my fuel inlet to carburetor line removed I turned the master switch on where I could here my electric fuel pump on and 0 fuel came out of the line. Not sure if thats normal. The engine may have to be cranking before fuel would come out.

Looks like your engine has two oil pressure switches. The one below the distributer may not have anything to do with the fuel pump. There should be a Tee fitting where the oil sender is and may have the switch to control the pump on/off

 

[UncleWillie]

... My seloc mercruiser manual shows 2 oil pressure switches. I could only find the one next to the oil pressure sender next to the oil filter housing. I noticed something I never noticed before. Key off and only the Master switch on , I can hear my electric fuel pump running. I removed the oil pressure switch I could finds` connector and it kept running. removed connector off oil pressure sender and it continued to run. I didn`t think that was normal. ...

The Fuel pump running with the igniton OFF is an issue.
Consider the classical fuel leak scenario that starts a fire as you crank the boat.
The engine isn't running, but the fuel pump continues to supply fuel to the fire by the gallon.
The fuel pump should not start until the starter is engaged. Key ON, Engine OFF, Pump OFF!
It may stop momentarily when the engine starts, and before the oil pressure comes up a second later. Key ON, Engine ON. Pump ON!
The pump running with the Key OFF is a fire hazzard.
If the fuel pump is running Key OFF, Does the Pump Stop when the engine starts???

When you turn the key ON, does your Low Oil Pressure Alarm Sound?
Removing the wire from the Oil Alarm Pressure Switch will silence the alarm and identify that switch.

Something to keep in the back of your Head....
When it absolutely does not make any sense, and it apperas that magic is at play, you have a ground problem!

 

[maddog2112]

Does anyone know which fuse is for the fuel pump? Mine are not labeled and I don't have the q6 owners manual. I could pl that fuse to verify that it is the electric fuel pump I'm actually hearing. I'm pretty sure it is but when I touch the pump you can't feel the vibration.