Fuel problem on 1986 3870 175hp hinos-gctid387187

[Guest]

It's time to ask to pros so here I am. I am experiencing a problem of losing rpms on the starboard engine after cruising at 2800 for about 10 minutes. I pulled the throttle back and kept the engine running, after a equalizing the rpms at about 1300 I could throttle back up but problem would repeat in a very short time. We first thought of the fuel filters so we replaced those. After reading a thread created back in early March (if memory serves me correctly) we thought about a clogged screen on the fuel pick up out of the tank. Before ruling out the clogged pick up we replaced the fuel lines. During a test run to see if the new fuel lined helped the problem reoccured. We opened the bleeder on the fuel line and there was significant air in the line. When the air was allowed to escape and we had full fuel flow the engine powered right back up. I was fortunate enough when I bought the 3870 it included a spare engine with only 450 hours on it. Our thoughts at the moment is to put the primer pump from the spare engine on and see if that solves the problem. Any input or suggestions would be greatly appreciated. Steve

[dmcb]

Blow air back through the line to the tank. That should clear the screen if that is the problem.

It might come back but it should let you know if the screen was plugged.

Did you change both filters?

Doug

[Guest]

We replaced the Racor filters on both engines. Maybe I'm missing something but I'm only aware of one filter on the the engine. We did blow back through the fuel line back to the tank. We are thinking that we are picking up air into the fuel line. The fact that the engine runs perfectly when the line is bled of air makes us think that the fuel pick up is not the problem. I don't know where to start in determining where air is entering. We are thinking that replacing the primer pump is a logical starting point.

[mmichellich]

HAPPY wrote:
We replaced the Racor filters on both engines. Maybe I'm missing something but I'm only aware of one filter on the the engine. We did blow back through the fuel line back to the tank. We are thinking that we are picking up air into the fuel line. The fact that the engine runs perfectly when the line is bled of air makes us think that the fuel pick up is not the problem. I don't know where to start in determining where air is entering. We are thinking that replacing the primer pump is a logical starting point.

There is a Hino fuel filter on the engine. As i recall on the 175s it is a water sep only filter. Check it.

[Guest]

The filter you are refering to I believe only has a screen in it not a replaceable element according to my buddy who is helping me. By the way he does have alot of diesel experience. I wonder if air could be entering the system at that point?

[mmichellich]

HAPPY wrote:
The filter you are refering to I believe only has a screen in it not a replaceable element according to my buddy who is helping me. By the way he does have alot of diesel experience. I wonder if air could be entering the system at that point?

That is why I suggested you check it. What color is the donut in the bottom of it? If I recall it changes color with water in it, but I am sure your mechanic knows that. Heck I may have confused the 175 with another engine.

[LTCret]

The normal setup from the tank includes an off engine filter which on my 1988 was a RACOR 26S. On the engine you normally have both a water separator and a second fuel filter.

On mine the fuel filter on the engine is a cylinder with a bolt through it from the bottom to the top.This filter takes a internal paper cartridge.

The water separator is mounted on the engine next to the engine mounted fuel filter, it has a clear lower section with a thin donut visible in the bottom. The donut starts to rise toward the top of the clear section if there is water present.

Any of these components could be leaking a small amount of air. There is a bleeder valve on top of one of the components on the engine. I think on top of the fuel filter, but I am not sure about that.

Be sure all components are tightened and try again.

Good Luck

[mmichellich]

From the descriptions so far, I would vote for a leak on the vacuum side of the engine pump, that includes all filters, all fuel lines, fittings on the tank, etc. If you have not checked the screen in the bottom of the fuel tank sucking tube do it, may have been removed by a prior owner. Can't remember if you can run both engines off a single tank but this would be a way to eliminate some of the plumbing upstream of the valves including the tank sucking tube.

[capt._ron]

If I remember right the supply pump pulls fuel from the tank thru the primary filter & pushes it thru the water separator & the secondary filter mounted on the port side of the hino. Get some clear line & add a 6" length to the line from the Racor to the pump. Watch it while running if you see bubbles in the clear section it is sucking air down stream from there. Check that your valves are fully open before you start. I would change the secondary & drain the separator 1st, it may be partially plugged & restricting fuel flow. Good Luck

[Guest]

Thanks guys. Looks like my work is cut out for me tomorrow. First thing will be a test run pulling fuel only from the port side. Then we will go from there. I appreciate your input. I'll post the results as soon as I know them

[Guest]

I just solved a similar problem - engine would run about 5 minutes and quit - no prime. Turned out to be an air leak where the fuel tank dip tube screws into the hose fitting. Cleaned the threads, applied a little pipe compound, and tightened her up. No more air. BTW, there is no screen on the end of the pickup tube.

Mike

[Guest]

I think the screens should be cut off the pickup tubes and accept the racors as primary screens. The screens plug in rough seas when muck gets stirred up and are far tougher to service than the racors while at sea. Isolation valves on either side of the racors also make changes underway easier too. or you could have the tanks cleaned ....

dstorey

[outaport]

check the housing on your racor 26s there is a plug on top plastik and in side of it there is a ball if there is sludge in there it will allow fuel to drain back could eventually cause a no start and the problems that you described

[Guest]

Day two of repair attempt. We checked the cartridge on the engine mounted fuel filter that filters the return fuel going to the Feed pump. Couldn't get one today so left it out. We replaced and double clamped all of the fuel lines from the tank to the water fuel separator. Tried it and still lost power. Then we replaced the Feed pump and tried it and still lost power. Each time the engine ran fine at the dock but under load the problem showed up. Then we tried running just off the port tank. By doing this we "infected" the port engine and it experienced the same problem air in the fuel system. We bled the port engine and it returned to operating normally.

On Tuesday, the next day we can work on it, we are going to take two 5 gallon containers of diesel. We will draw fuel directly from the container to the Racor if the problem still exists we can rule out the tank pickup. Then we will run from the container to the water fuel separator if the problem still exists then we can rule out the filter and the fuel lines. At that point we will know that it is something mounted on the engine. Sound like a good approach? - Steve

[mmichellich]

When you hooked up the stbd engine by valving to the port tank, I hope you had the stbd tank valve off. If so, then you have clearly tied your issues down to the plumbing between port tank valves and the port tank. Could be valve issue, hose on valve issue, bad hose to tank from valve, or plumbing issue at tank including the pickup tube inside tank. All this assumes the port tank has fuel at a level above the pickup tube.