2005 4.3 Intermittent Stalling issue

[Chris_Little]

Hope you guys can help me track down an issue Im having with my 05 Tahoe Q4 merc 4.3

Boat typically runs great but has developed a stalling issue. Took the boat out for the first time a few weeks ago and it had developed an issue where it would run for a few seconds and then die. Appeared to be a carb/fuel issue. Replaced the fuel water separator and took it back out with the same issues. Brought it hope and did some research and bypassed the oil pressure safety switch on the muffs and it ran fine for 10 minutes. Installed a new switch, took the boat out, runs great for a 15-20 min ride, we parked and swam for a couple hours, about 5 mins into the ride back to the launch it stumbles and dies, starts right back up and dies. I brought a jumper wire just in case, hooked that up and made the rest of the trip back to the dock without issues.

Oil Pressure on the gauge is consistent and moves with rpm as it has previous.

Think the new quiksilver switch failed, there is a wiring issue, fuel pump going bad?

Diagnosis plans are to, run the engine on the muffs and ohm test the new switch to verify it is opening. Hooking up a mechanical oil pressure gauge to verify its getting oil pressure. Check continuity from oil pressure switch to the fuel pump.

If you have other suggestions Im open to all of them other than leaving the plug out the next time I back it off the trailer, not there yet.

TIA

 

[alldodge]

Don't think its the switch,
Does it die quick like turning the key off, or gasp and die like running out of gas?
Serial number?

 

[tank1949]

Hope you guys can help me track down an issue Im having with my 05 Tahoe Q4 merc 4.3

Boat typically runs great but has developed a stalling issue. Took the boat out for the first time a few weeks ago and it had developed an issue where it would run for a few seconds and then die. Appeared to be a carb/fuel issue. Replaced the fuel water separator and took it back out with the same issues. Brought it hope and did some research and bypassed the oil pressure safety switch on the muffs and it ran fine for 10 minutes. Installed a new switch, took the boat out, runs great for a 15-20 min ride, we parked and swam for a couple hours, about 5 mins into the ride back to the launch it stumbles and dies, starts right back up and dies. I brought a jumper wire just in case, hooked that up and made the rest of the trip back to the dock without issues.

Oil Pressure on the gauge is consistent and moves with rpm as it has previous.

Think the new quiksilver switch failed, there is a wiring issue, fuel pump going bad?

Diagnosis plans are to, run the engine on the muffs and ohm test the new switch to verify it is opening. Hooking up a mechanical oil pressure gauge to verify its getting oil pressure. Check continuity from oil pressure switch to the fuel pump.

If you have other suggestions Im open to all of them other than leaving the plug out the next time I back it off the trailer, not there yet.

TIA

Had an older Alpha that had wiring corrosion. Current went to ground and cut everything off if vibrations were strong enough. If my memory serves me correctly I wiggled wires until I found the bad one.

 

[Chris_Little]

Don't think its the switch,
Does it die quick like turning the key off, or gasp and die like running out of gas?
Serial number?

Gasps like it’s running out of fuel. Can try and save it by pumping the throttle but it coughs and quits.

Ow323446 is the serial.

 

[Rick Stephens]

Running out of fuel, sounds like. You might pull a plug and look, but seems most likely. There are a bunch of things that can cause a fuel loss, of course funk in the fuel is first choice.

Plugged up parts -of which there are several candidates: anti-syphon valve, screen in the fuel tank pickup tube, filters, a fuel line that is falling apart and collapsing interiorly, plugged tank vent and fuel pump, as you already noted.

You might stick an idiot light on the power wire to the fuel pump, see if ya gots an electrical problem.

Might also 'T' the fuel line either before the fuel pump and measure vacuum pulled or after the fuel pump and measure pressure to the carb.

 

[alldodge]

Agree, fuel issue
Need to test your fuel system

 

[Chris_Little]

Agree, fuel issue
Need to test

Running out of fuel, sounds like. You might pull a plug and look, but seems most likely. There are a bunch of things that can cause a fuel loss, of course funk in the fuel is first choice.

Plugged up parts -of which there are several candidates: anti-syphon valve, screen in the fuel tank pickup tube, filters, a fuel line that is falling apart and collapsing interiorly, plugged tank vent and fuel pump, as you already noted.

You might stick an idiot light on the power wire to the fuel pump, see if ya gots an electrical problem.

Might also 'T' the fuel line either before the fuel pump and measure vacuum pulled or after the fuel pump and measure pressure to the carb.

You very well could be correct, but tough for me to ignore the boat working properly when the switch is bypassed.

What’s the spec fuel pressure psi for a carbed engine?

 

[alldodge]

4 to 7 psi

 

[dubs283]

Think the new quiksilver switch failed, there is a wiring issue, fuel pump going bad?

1. not likely
2. most likely
3. possibly

you can test the voltage going to the fuel pump with a back probe while the engine is running, wiggle the wires between the switch and pump, see if voltage drops/goes away

as suggested perform a vacuum and pressure test on the fuel system, no more than 2 in/hg for vacuum

 

[Chris_Little]

1. not likely
2. most likely
3. possibly

you can test the voltage going to the fuel pump with a back probe while the engine is running, wiggle the wires between the switch and pump, see if voltage drops/goes away

as suggested perform a vacuum and pressure test on the fuel system, no more than 2 in/hg for vacuum

Does the switch supply 12v or ground when closed? Im assuming a youtube search will yield how to vacuum test the fuel system, any tips or tricks for a first timer would be appreciated.

 

[dubs283]

switch supply's 12 volts (+) when closed (oil pressure present). fuel pump gets voltage from the starter solenoid primary during cranking

 

[Chris_Little]

Voltage at the connector right above the pump is consistently 13.4x volts, except when its not. The only condition I can get the fuel pump to lose voltage is through holding the female connector on the oil pressure switch towards the front of the boat while it was connected. I pulled the terminals from the connector and sprayed them out and was still able to recreate the issue.

Im assuming the vibrations while under throttle contribute to this issue on the water. Other assumption is that the new switch terminals fit together just enough better for the issue to hide itself for a little while.

When the pump has power the engine runs, so unless you guys have other thoughts, I think the issue is in the connector/terminals. Going to try and tighten up the terminals a little to see if I can make it fail. If it fails, I will get a new connector and terminals.

Anyone have a recommendation on a metripack crimper?

Appreciate all the feedback.

 

[alldodge]

Agree connections and don't forget the ground which is spliced inside the harness

 

[Chris_Little]

After closing down the female terminals in the connector, I tested it on the muffs and couldnt force it to go to 0 volts. A nice day on the lake and no issues.

Thanks for the help. Appears the issue is resolved.