I would like to thank all the people who offered suggestions on diesel engine
surging. Three causal factors were mentioned. The most common suggestion was
an air leak in a low pressure fuel line or a faulty filter gasket. Also
mentioned was the possibility of a power consuming device, i.e. a generator,
temporarily shutting off, another was slippage in the transmission (I didn't want to
really hear that). On a run today I carefully monitored the engine to document
the symptoms.
Like most watched devices, nothing untoward happened for the first hour. Then
the engine surged for a few seconds, running a bit faster before returned to
normal. I had time to note the ampere dial and saw that the batteries were
still charging. I don't have a speed indicator on my boat but I do have a shaft
speed tachometer. The shaft rpm increased as the engine surged, possibly
eliminating transmission clutch slippage. The fuel line on my boat is only under
negative pressure for a short distance, from the tank to the large primary fuel
filter to the lift pump, a total distance of about 2 feet. From the lift pump
on the line is under positive pressure. If there is a leak, fuel should leak
out rather than air leaking in. I'll check all lines for leaks again and even
replace the secondary fuel filter and gaskets.
I can imagine only two more possibilities, one is a partial blockage in the
fuel return line from the secondary filter to the tank, letting fuel pressure
temporarily build up. The other is something wrong with the governer on the
injection pump.
Paraphrasing Sherlock Holmes, when you eliminate all the probable causes,
what remains, no matter how improbable, is the culprit. It's one of the great
mysteries of the sea.
Larry Z
I would like to thank all the people who offered suggestions on diesel engine
surging. Three causal factors were mentioned. The most common suggestion was
an air leak in a low pressure fuel line or a faulty filter gasket. Also
mentioned was the possibility of a power consuming device, i.e. a generator,
temporarily shutting off, another was slippage in the transmission (I didn't want to
really hear that). On a run today I carefully monitored the engine to document
the symptoms.
Like most watched devices, nothing untoward happened for the first hour. Then
the engine surged for a few seconds, running a bit faster before returned to
normal. I had time to note the ampere dial and saw that the batteries were
still charging. I don't have a speed indicator on my boat but I do have a shaft
speed tachometer. The shaft rpm increased as the engine surged, possibly
eliminating transmission clutch slippage. The fuel line on my boat is only under
negative pressure for a short distance, from the tank to the large primary fuel
filter to the lift pump, a total distance of about 2 feet. From the lift pump
on the line is under positive pressure. If there is a leak, fuel should leak
out rather than air leaking in. I'll check all lines for leaks again and even
replace the secondary fuel filter and gaskets.
I can imagine only two more possibilities, one is a partial blockage in the
fuel return line from the secondary filter to the tank, letting fuel pressure
temporarily build up. The other is something wrong with the governer on the
injection pump.
Paraphrasing Sherlock Holmes, when you eliminate all the probable causes,
what remains, no matter how improbable, is the culprit. It's one of the great
mysteries of the sea.
Larry Z
