4-108 Fuel Shutoff

[lonesomewander]

I have just rebuilt a 4-108. Rebuilt pump, injectors, etc. I bought the boat after the engine was flooded so don't have any experience with it running yet. I have a couple of questions. First, I'm not sure which way the fuel shutoff solenoid should be wired. Applying juice to it pulls the lever on the pump towards the back of the engine. Should power be applied to it any time it is running or does applying power to it kill the engine? I obviously need to get this right before I can bleed the thing. I tried bleeding it both ways but couldn't get fuel at the injectors. I decided it would be better to figure out which way is correct before cranking the engine any more. I was able to get clean fuel out of pump side vent. I'm also curious about the fuel return line at the top of the CAV filter. If I pump the lift pump manually, fuel eventually comes out this line. What controls the pressure built up in this part of the system? Should I temporarily block this off while trying to bleed it? Any advice would be very welcome. Thanks.

[svHyLyte]

The shut-off solenoid is normally in the extended position (at rest) which allows fuel to flow into the injection pump. It is activated by a momentary switch normally on the panel--the shut-off or "Kill" switch/button-which causes the plunger to retract, blocking the flow of fuel to the high pressure side of the pump.

There should be a bleed-screw on the injection pump itself. Once you've got clean fuel without bubbles coming from that, you crack the injectors, one-by-one until you get clear fuel without bubbles coming from each. You can "blip" the engine over for this with the starter but close your raw water intake to prevent flooding the muffler and the consequences.

FWIW...

[billwa]

"I'm also curious about the fuel return line at the top of the CAV filter. If I pump the lift pump manually, fuel eventually comes out this line. What controls the pressure built up in this part of the system?"
The pressure here is controlled by the height of hose back to your tank. It is simply an on demand style circuit. The lift pump is exactly that, a pump to lift the fuel from a low tank. If your tank is higher than the motor, you dont need the lift pump.

As you will by now be aware this makes bleeding the perkins tricky as cracking the injectors nut feeds fuel back from the cav filter rather than through from the injection pump side. You need to bleed at the injector pump.

Another warning, once you get your engine started, it needs electrical power to actuate the solonoid and shut it down. If you loose battery power, you loose the ability to kill the motor. Learn how to do this manually.

[gjordan]

A side note about Perkins engine. They seem to be more sensitive to air in the fuel system than other diesels. If you dont do a perfect job of getting the air out on a filter change, they will start and run for a minute or so and go dead as a stone. You then have to do a very careful full bleeding sequence to get them running again. In contrast, I had a Mercedes diesel in a previous boat that seemed to take almost anything in stride. If a filter change wasnt perfect it would sputter and fart, but keep running until the air worked itself out of the system. I ran it out of fuel once(that I will admit to) and switched tanks and it started up, ran rough for a minute or two and then smoothed out. It seemed to be much more forgiving of air in the system. It must be the design of the injection pump. Perkins are great engines, they are just a little fussy. ___My 2 cents worth.____Grant.

[Cheechako]

Interesting, I had just the opposite impression about the 4-108.... I couldnt get mine NOT to run. Filter changes, injectors out and back in etc. It always started before I could even get the bleeding done!

[SimonV]

First thing I noticed is you said this engine had been flooded, I take this to mean it has been under water. If it was salt chuck and replace any electrical item, its just not worth the worry if it was salt it will fail soon. fresh well that can be a little different.

[lonesomewander]

Thanks all for the help. Just what I needed. Interesting about the lift pump; there is an electric fuel pump just down stream of the Racor filters in this boat. Sounds like I don't need both. I've seen several threads about this subject. Not sure yet whether I'll eliminate the lift pump. Got to get it running first!

[Cheechako]

Originally Posted by SimonV

First thing I noticed is you said this engine had been flooded, I take this to mean it has been under water. If it was salt chuck and replace any electrical item, its just not worth the worry if it was salt it will fail soon. fresh well that can be a little different.

I thnk he said the engine has been rebuilt....

[phorvati]

Fuel solenoid should be powerd off the 12 V ignition that powers the instruments. When energized, it retracts and keeps the fuel valve open. When you cut off 12V supply, it releases the solenoid, the lever goes back to original position and pushes the shutoff valve, shuts off the fuel supply. That puzzled me for awhile this spring.
I wish I had the CAV DPA pump with port for fuel shutoff. Then you would not need the mechanical shutoff, like a pull cable or this solenoind that pulls the lever for you. It was a pain in the a.. to install as there is absolutely no room down there on westerbeke 40.

[Jesse]

The elecric fuel pump is there to make bleeding the air from the system easier. Simply switch it on and then go through the process following the exact sequence outlined in the manuel, and it should start if the timing and compression are right.

[Blue Stocking]

#2 and #9 contradict each other.
There is a Perkins generic wiring diagram in the shop manuals file here

[SimonV]

Lonesomewanderer, did you replace all the electrics on your rebuild?

[lonesomewander]

Hi everyone. I'm still a little confused about this. As noted, I've gotten two different answers on the shutoff position for running. Is the shutoff solenoid engaged always when running or not? The wiring diagram in the manuals section shows two connections on the stop switch but only one wire permanently to ground. No wire is shown to the shutoff solenoid either from the ignition switch or stop switch.

The engine was flooded and has been rebuilt. All new electrics. I'm testing it in the shop before putting it back in to make sure all is good. I have had to rig up a few things and am not using the boat's systems thus my need to understand how things work.

On the subject of the electric fuel pump, once the system is bleed, will fuel flow through it if it's not turned on? It sounds like it would be helpful to have if I don't have to leave it running all the time. Thanks again.

[Blue Stocking]

I recently re-wired a 4-236 Perkins that was set up to run with the solenoid powered up to allow fuel to flow.
I wired in a n/o relay, powered the solenoid circuit from seperate source, actuated by the ignition switch.
Shut off the key, relay drops out, solenoid is de-powered, engine stops.

[Acushla]

Fuel Shut-off solenoid
Generic design generally requires that the solenoid is energised to shut off the fuel supply. Therefore it only sees voltage when you turn the key to the shut down position.

Electric Fuel Pumps
These pumps supply a small positive head and run all the time the engine is running..

Acushla