Bleeding 4-108

[jimisbell]

No, I am not english, though I sometimes think that would be the right phrase to sum up my frustration.

I have been trying for three days to bleed the air out of my 4-108 using the priming pump.

I replaced the lift pump the engine filter and added a pre filter to the fuel system. Then I started pumping the primer lever. I now have fuel and air coming out all the bleed points. but I cant get the air out even from the first point, the banjo fitting on the top of the engine mounted filter. No mater how long I pump I still get air mixed with the fuel. I tried by passing the new pre filter to eliminate three places where it might be sucking air. I am now down to only the hose connection on the tank and the hose connection on the lift pump input. AND I AM STILL sucking air.

Could the new lift pump be faulty??

How long should you have to pump if the filters are NOT pre filled? I couldnt pre fill them because they are the kind that are open on the bottom and have a cap holding them together by a central bolt. I know I have spent at least 30 minutes pumping the priming lever. I am listening for bubbles in the fuel tank as an indication of air in the return line and I always get several bubbles with each stroke.

I can get fuel mixed with air all thru the system, but cannot get the air out.

[Jesse Holden]

Disconect the pre filter at the tank/inlet side and attach the priming bulb equiped fuel line from an outboard motor fuel tank after meticulessly removing all gasoline. Put diesel in the fuel tank and squeeze the bulb while watching for leaks of air or diesel. When satisfied there are no leaks at the pre filter or lift pump proceed with your usual beeding. Jesse

[Alan Wheeler]

Jim, can you gravity feed fuel into the filters from the tank?? You really need to start by filling those filters first. Otherwise you will continually get a bubble or two through the system.

[Steve Kidson]

I put priming bulbs in the fuel line between the tank and the first filter. Found it to be very sucessful in quickly and painlessly pumping fuel through lines.

Fair winds

Steve

[jimisbell]

Alan:

Cant gravity fill them. They are both above the tank.

Steve:

I have an electric fuel pump that will flow thru when not running. I am going to put it in the line to push the fuel into the system. I can activate it anytime I need to bleed the system and it will give me a backup if the lift pump fails.

Now a question:

It has occured to me that some of this bleeding problem, there I go again, getting english......could be prevented by moving my 'fine' pre filter to the return line and having the engine filter which is somewhat corser at the lift pump output do the removal duty of things harmful to the injector pump. The post filter would "polish" the return fuel of the smaller stuff that gets thru the engine filter (that could clump into larger particles later) as the fuel returned to the tank. This way I would minimise the possibility of leaks on the vacuum side. This would also allow changing the fine filter without bleeding the fuel system.

The question. Is there anything wrong with this idea? What is the symptom of a plugged filter on the return line? Maybe it would need a bypas valve to prevent bursting a line?

[Steve Kidson]

Originally Posted by jimisbell

It has occured to me that some of this bleeding problem, there I go again, getting english......could be prevented by moving my 'fine' pre filter to the return line and having the engine filter which is somewhat corser at the lift pump output do the removal duty of things harmful to the injector pump. The post filter would "polish" the return fuel of the smaller stuff that gets thru the engine filter (that could clump into larger particles later) as the fuel returned to the tank. This way I would minimise the possibility of leaks on the vacuum side. This would also allow changing the fine filter without bleeding the fuel system.

The question. Is there anything wrong with this idea? What is the symptom of a plugged filter on the return line? Maybe it would need a bypas valve to prevent bursting a line?

I do not claim any great expertise in this area, but applying logic to your proposal I would add.......

Positioning of Fine Filter in return line will allow a certain amount of "unfiltered" fuel to reach the injectors. The volume of "unfiltered" fuel will most likely diminish as fuel is consumed and surplus fuel circulated through fine filter on the return line. Re-filling tank will introduce new "unfiltered" fuel to your system.

"unfiltered" meaning fuel that has only been filtered by your coarse engine filter.

Just my thoughts.

[NoTies]

NO, don't shift the secondary filter. It is there to remove the finer contaminants that could damage the injector p/p. Perkins' main weak point is the lift p/p and fitting an electric p/p & switch is a very common solution. Another thing to try is giving the engine 1/2 a turn or so to make sure you have the cam driving the lift p/p lever at its lowest point. You will pump a lot more efficiently this way.

[Alan Wheeler]

Another point missed in comments way above. If anyone fits an electric pump, you need to be able to bypass the mechanical pump. If you get a mechanical lift pump failure due to a hole in the diaphragm, the Electric pump will push fuel through that hole and possibly flood your crankcase with fuel. Oil diluted with fuel is not good. As Pete has said, you need the corse filter, preferably fitted with a water trap, followed by a fine filter. Do not filter the return line. If that has particles in it that can cuaght by a filter, it has already done the damage in the pump. The injectors are what need that fine filter protection anyway. Also you don't want pressure on that return line. It could (although remote) cause problems trying to push through a fine filter.

[jimisbell]

To clarify:

The standard engine mounted filter is ALL there was before I added the pre/post-filter so moving OR removing the new filter will not endanger the engine any more than the orriginal set up which was good enough for the Perkins engineers

The only reason that the NEW filter is finer than the one on the engine is that that is what I had on hand when I decided to ADD a second filter.

So the question is, if I am adding a NEW filter is there any reason not to place it in the return line?

[GordMay]

Originally Posted by jimisbell

... So the question is, if I am adding a NEW filter is there any reason not to place it in the return line?

As previously mentioned (Steve Kidson, pwederell & Alan Wheeler), you don’t want a filtre in the fuel return line.

[DeepFrz]

The standard engine mounted filter is ALL there was before I added the pre/post-filter so moving OR removing the new filter will not endanger the engine any more than the orriginal set up which was good enough for the Perkins engineers

Maybe not. The engineers may have wanted better filtering but the accountants didn't. I've seen that battle before.

The filter on the engine should be thought of as a "filter of last resort". The primary filters should be fitted with a vacuum guage, preferably with a resetable recording needle so you know if they are getting full. You can't do that to an engine mounted filter as the fuel there is under pressure.

If your engine mounted filter ever clogs you have no warning. The engine stops. Why? Hopefully you are docked and not bouncing around in a seaway. The engine and engine mounted filter are also HOT. Try changing that in a seaway.

By the way, the June issue of PassageMaker magazine has an article on fuel polishing. The Sept. 2006 issue of the same magazine has a great article on cleaning your fuel tank and fuel filtering.

I have experienced a clogged fuel line in a seaway. It is not fun. Keep your tanks clean and filter your fuel properly with switchable filters and you should be okay. I also recommend polishing your fuel but it has to be done properly to be worthwhile.

[btrayfors]

I have lived with a 4-108 for 18 years now, and have experienced many types of fuel system difficulties.

My bet is that one or another of your fuel filters -- most likely the one on the engine -- isn't seating properly and is leaking air. This is very easy to do. Check the gaskets carefully (did you replace them with the new filter?) to be sure they're seated properly. Ditto with the auxiliary "fine" filter.

BTW, I use 10 micron Raycor filters before the engine-mounted filter, and am now scrupulous about keeping my fuel clean and filtered.

Most difficult problem I found, and one which sounds a lot like yours, was a pinhole in the copper fuel line running through the bilge in the engine room. The pinhole was ON THE BOTTOM and could not be seen. It was caused by standing water...seawater...sometimes present from leaks in the stuffing box. Finally found this problem by sound.....heard a slight hissing whenever the lever on the fuel lift pump was activated. By feeling along the underside of the fuel line, I found it, and was able to solve yet another great fuel-related mystery with my 4-108.

So...double check, triple check all your connections, gaskets, fuel lines, etc. If you've got bubbles, air is getting in somehow.

Good luck,

Bill

[DeepFrz]

By the way, here is a fact from Caterpillar's Fuel System Division: "the number one cause of fuel system wear is abrasive particles that are smaller than 10 microns".

I don't know this as a fact but apparently particles around 7 microns are the most damaging.

[gonesail]

perhaps you should replace the fuel line from the primary filter to your lift pump. the yanmar has a secondary filter after the lift pump ... and this is a good place to bleed the system before air gets into your high pressure fuel pump. also check the gaskets on the metal fuel lines. the priming bulb previously mentioned is a big help .. you can bleed the entire line with a single squeeze or two.

[By Invitation]

Jimisbell,

I had the same exact thing just happen to me with my 4-108. I found that I had a small air leak from my fuel line going into my new fuel pump. There was no fuel leaking out but after replacing this line I was able to bleed the entire system in about 5 minutes and start her right up. Double check all of your fuel connections and I bet your problem goes away.