Detroit Diesel (DD671N) Questions
 

Eisboch wrote:
"Wayne.B" wrote in message
...

On Wed, 25 Jan 2006 00:31:55 +0100, "Steve Lusardi"
wrote:


I think you should identify symtoms,
if you want meaningful help.

It's a 1981 Johnson & Towers marine conversion, supposedly rebuilt
within the last 1,000 hours or so by the previous owner.

My port side engine is taking longer to cold start than it used to,
sometimes needing 8 to 12 seconds of cranking. It used to start on
the first or second turn even when stone cold, and the starboard
engine still does. If it has been run within a day or two it still
starts very quickly. There is very little exhaust smoke at startup
even when cold, and what little there is goes away quickly. The
engine is running well and making full power as far as I can
determine.



There's a guy at our marina who had a somewhat similar problem for a couple
of years. Turns out he had a very small air leak in the fuel supply line
for one engine. It would run fine after starting, (I assume because the
leak was overcome by fuel, but that is pure speculation), but was hard
starting.

Ain't boats fun?

Eisboch (grandkid #5 is a girl!)



Hi again, you say it's making full revs??? a fixed pitch prop is an
excellent dynomometer so if it were seriously down on compression I
think you'd see it in the top end max revs performance.

I think before you go too much further you might check the fuel supply
especially as you say it starts easier after a day, but by then it's
well cold so any mechanical defect in the compression etc would still be
there.

Seems granddad Eisboch is on the trail here (he's having a good
day???:-)), fuel filters are a good source of air leaks also. It might
be slowly allowing the fuel to go back down the lines & air in.

These engines as with many Cummins, don't have an injector pump in the
commonly known sense, they have a moderately pressurised fuel rail not
unlike the one in your petrol car. Along this rail (they call it a fuel
manifold in the manual) the unit injectors are sited. There is a
restriction in the fuel rail outlet to maintain feed pressure to the
unit injectors, if the fuel rail isn't properly pressurised by the gear
pump supply it won't start ......... easily. The injectors are driven by
the camshaft & rocker arms the same as the valves are & do the final
pressure increase & injection all in the one movement (pump injector
combination).

You can imagine if your fuel system, the gear fuel rail pressure pump as
mentioned (which is also the lift pump usually), the fuel rails & the
unit injectors themselves, get any air in there it will need a few turns
to pump it through & clear it. Once started they can live with a tiny
airleak becasue it just goes straight through the system & out the
return line.


K

Detroit Diesel (DD671N) Questions
 

"K. Smith" wrote in message
...
Eisboch wrote:
"Wayne.B" wrote in message
...

On Wed, 25 Jan 2006 00:31:55 +0100, "Steve Lusardi"
wrote:


I think you should identify symtoms,
if you want meaningful help.

It's a 1981 Johnson & Towers marine conversion, supposedly rebuilt
within the last 1,000 hours or so by the previous owner.

My port side engine is taking longer to cold start than it used to,
sometimes needing 8 to 12 seconds of cranking. It used to start on
the first or second turn even when stone cold, and the starboard
engine still does. If it has been run within a day or two it still
starts very quickly. There is very little exhaust smoke at startup
even when cold, and what little there is goes away quickly. The
engine is running well and making full power as far as I can
determine.



There's a guy at our marina who had a somewhat similar problem for a
couple of years. Turns out he had a very small air leak in the fuel
supply line for one engine. It would run fine after starting, (I assume
because the leak was overcome by fuel, but that is pure speculation), but
was hard starting.

Ain't boats fun?

Eisboch (grandkid #5 is a girl!)



Hi again, you say it's making full revs??? a fixed pitch prop is an
excellent dynomometer so if it were seriously down on compression I think
you'd see it in the top end max revs performance.

I think before you go too much further you might check the fuel supply
especially as you say it starts easier after a day, but by then it's well
cold so any mechanical defect in the compression etc would still be there.

Seems granddad Eisboch is on the trail here (he's having a good
day???:-)), fuel filters are a good source of air leaks also. It might be
slowly allowing the fuel to go back down the lines & air in.

These engines as with many Cummins, don't have an injector pump in the
commonly known sense, they have a moderately pressurised fuel rail not
unlike the one in your petrol car. Along this rail (they call it a fuel
manifold in the manual) the unit injectors are sited. There is a
restriction in the fuel rail outlet to maintain feed pressure to the unit
injectors, if the fuel rail isn't properly pressurised by the gear pump
supply it won't start ......... easily. The injectors are driven by the
camshaft & rocker arms the same as the valves are & do the final pressure
increase & injection all in the one movement (pump injector combination).

You can imagine if your fuel system, the gear fuel rail pressure pump as
mentioned (which is also the lift pump usually), the fuel rails & the unit
injectors themselves, get any air in there it will need a few turns to
pump it through & clear it. Once started they can live with a tiny
airleak becasue it just goes straight through the system & out the return
line.


K

I think some people put pressure guages before and after the fuel filter.
You would know what the pressure is when starting and if the fuel filter is
getting clogged.

Detroit Diesel (DD671N) Questions
 

Wayne,
This is simple. You have fuel feed leakdown on that engine. On the detroits,
you have a gearpump that draws fuel from the tank and pushes the fuel
through a strainer and then a filter. From the filter it enters the Cylinder
head where it passes through a cast feed log. Unused fuel is turned around
and again passed through the return log in the head. From there it is
returns heated to the tank. Fuel pressure at the out side of the pump should
be about 45 lbs. Your problem is that the feed line to the inlet of the pump
is draining back to the tank. Probably a very small leak in that line.
Steve


"Wayne.B" wrote in message
...
On Wed, 25 Jan 2006 00:31:55 +0100, "Steve Lusardi"
wrote:

I think you should identify symtoms,
if you want meaningful help.

It's a 1981 Johnson & Towers marine conversion, supposedly rebuilt
within the last 1,000 hours or so by the previous owner.

My port side engine is taking longer to cold start than it used to,
sometimes needing 8 to 12 seconds of cranking. It used to start on
the first or second turn even when stone cold, and the starboard
engine still does. If it has been run within a day or two it still
starts very quickly. There is very little exhaust smoke at startup
even when cold, and what little there is goes away quickly. The
engine is running well and making full power as far as I can
determine.

Detroit Diesel (DD671N) Questions
 

"Steve Lusardi" wrote in message
...

Wayne,
This is simple. You have fuel feed leakdown on that engine. On the
detroits, you have a gearpump that draws fuel from the tank and pushes the
fuel through a strainer and then a filter. From the filter it enters the
Cylinder head where it passes through a cast feed log. Unused fuel is
turned around and again passed through the return log in the head. From
there it is returns heated to the tank. Fuel pressure at the out side of
the pump should be about 45 lbs. Your problem is that the feed line to the
inlet of the pump is draining back to the tank. Probably a very small leak
in that line.
Steve



Wayne, I might add that the guy with the similar problem that I mentioned
before also had DD671s, FWIW

Eisboch

Detroit Diesel (DD671N) Questions
 

On Thu, 26 Jan 2006 10:00:09 +0100, "Steve Lusardi"
wrote:

This is simple. You have fuel feed leakdown on that engine. On the detroits,
you have a gearpump that draws fuel from the tank and pushes the fuel
through a strainer and then a filter. From the filter it enters the Cylinder
head where it passes through a cast feed log. Unused fuel is turned around
and again passed through the return log in the head. From there it is
returns heated to the tank. Fuel pressure at the out side of the pump should
be about 45 lbs. Your problem is that the feed line to the inlet of the pump
is draining back to the tank. Probably a very small leak in that line.
Steve

Thanks, good description. I think I'll start by replacing the engine
mounted fuel filters and gaskets since there seems to be a consensus
that the problem is somewhere in that area. The fuel tanks are 75%
full right now which puts the fuel level above the engines, so that
should rule out an issue with the Racors if I understand this
correctly.

Detroit Diesel (DD671N) Questions
 

On Thu, 26 Jan 2006 04:50:08 -0500, "Eisboch" wrote:

Wayne, I might add that the guy with the similar problem that I mentioned
before also had DD671s, FWIW

Thanks, do you happen to know how he located the leak?

Detroit Diesel (DD671N) Questions
 

"Wayne.B" wrote in message
...
On Thu, 26 Jan 2006 04:50:08 -0500, "Eisboch" wrote:

Wayne, I might add that the guy with the similar problem that I mentioned
before also had DD671s, FWIW

Thanks, do you happen to know how he located the leak?


I don't. Next time I go down to check the boat, I'll ask.

Eisboch

Detroit Diesel (DD671N) Questions
 

On Thu, 26 Jan 2006 06:38:42 GMT, "Calif Bill"
wrote:

I think some people put pressure guages before and after the fuel filter.
You would know what the pressure is when starting and if the fuel filter is
getting clogged.

I have vacuum guages on the suction side of my Racors to provide a
warning if they are starting to load up.

Everything looks normal there.

Detroit Diesel (DD671N) Questions
 

Wayne, when the engine is in the "hard to start condition", and then it
finally starts, does it do so on all cylinders, or does it go thru a
period where only 1, 2, 3, etc cylinders are firing for a while before
all 6 finally kick in? This could indicate a very slow leak between the
injection pump and the injectors.

bob


Wayne.B wrote:
On Thu, 26 Jan 2006 06:38:42 GMT, "Calif Bill"
wrote:


I think some people put pressure guages before and after the fuel filter.
You would know what the pressure is when starting and if the fuel filter is
getting clogged.


I have vacuum guages on the suction side of my Racors to provide a
warning if they are starting to load up.

Everything looks normal there.

Detroit Diesel (DD671N) Questions
 

On Thu, 26 Jan 2006 15:16:07 -0800, RW Salnick
wrote:

Wayne, when the engine is in the "hard to start condition", and then it
finally starts, does it do so on all cylinders, or does it go thru a
period where only 1, 2, 3, etc cylinders are firing for a while before
all 6 finally kick in? This could indicate a very slow leak between the
injection pump and the injectors.

Usually you can hear one or two kick a couple of times and then they
all light up a second or two later.

On a DD671 there is no central injection pump. Each cylinder has its
own driven by the cam as I understand it.