Intermittent Alarm

[FreeBeeTony]

Have twin '95 175 Johnsons, VRO's are intact.
Have an intermittent alarm at idle on port engine, in gear or in neutral. Just 1 short beep, not cyclical....totally intermittent and only at idle, both engines idle ~600-700RPM in gear. Otherwise engine runs great.
Took the hood off and looked behind the air silencer, a small amount of oil/fuel, nothing abnormal.
Did notice a slight sneeze every once in a while. Would a lean condition cause an intermittent alarm?

 

[FreeBeeTony]

Bump...........no input here?

 

[racerone]

Could be the FUEL RESTICTION alarm.----Test run with another ( portable ) tank and hose.

 

[dingbat]

Had a similar issue running off the reserve tank when low on fuel. Seemed to worsen when fuel was sloshing around in the rough.

Changed the fuel lines (tank to fuel pump) and tank selector valve...........problem never came back

 

[FreeBeeTony]

Thanks, maybe I will try running that engine off the aux tank.
BTW.........if it was a fuel restriction issue, would it be more evident at higher RPM's?

 

[dingbat]

Thanks, maybe I will try running that engine off the aux tank.
BTW.........if it was a fuel restriction issue, would it be more evident at higher RPM's?

In my situation, it seemed to manifest as a leak (vacuum) instead of a restriction (blockage).
Don't remember it happening while running. Always trolling which lead to the vacuum leak theory

 

[FreeBeeTony]

How might one check for a vacuum leak?

 

[racerone]

??----If there was a leak it would not trigger a fuel restriction alarm.

 

[dingbat]

How might one check for a vacuum leak?

You need a vacuum tester
For me, it was a good predict to change out the 8 years old fuel lines on the boat. In the process found a suspect oring in the tank selector valve. No problems since

 

[dingbat]

??----If there was a leak it would not trigger a fuel restriction alarm.

I always wondered about that.
What mechanism is used to detect a restriction?

System would need to monitor flow, vacuum or the lack there of.

 

[FreeBeeTony]

Think I may rent this over the w/e....how much vacuum should I pull? Guessing I should start at the engine and work my way towards the tank...
https://www.autozone.com/loan-a-too...emtools-vacuum-pump-and-gauge-tester/2080_0_0

 

[racerone]

There is a switch between the fuel pump and fuel tank.------When fuel is restricted it sounds the alarm.

 

[Terrapin]

You can test the fuel restriction alarm by simply putting a kink in your fuel line. This will give you a continuous alarm until you release the kink.

 

[dingbat]

There is a switch between the fuel pump and fuel tank.------When fuel is restricted it sounds the alarm.

Found what I was looking for....
1-4 hg. (0.49 to 1.9 psi) Is normal operation.
Switch alarms at 5.5 hg. (2.7 psi)

my reserve tank
15’ of 3/8” fuel line = ~1.5 psi
16” head (empty) = ~0.4
Racor separator filter, clean = 0.6 psi
Clean system drop = 2.5 psi

Not much room to play with. A dirty filter or a “sticky” anti-siphon value could put you over the edge

 

[FreeBeeTony]

Would the switch be #26 in the diagram below?

 

[dingbat]

Would the switch be #26 in the diagram below?

View attachment 339392

When was the last time you change separator filter

 

[racerone]

Correct ,--- item #26 is the switch.