Fuel line leak 4.3 Mercruiser

[tcarden]

I have a 1997 4.3 Mercruiser. I replaced the fuel pump last year due to failure and boat ran fine. It solved the hard start problem that I was having. However, during winteriztion a few weeks ago I noticed that my fuel line that goes from the water seperating fuel filter to the fuel pump was leaking at the fuel pump. I was careful to not overturn the fitting on the pump itself but I couldn't seem to get the proper seal on the compression fitting into the pump. I would tighten it up, run the engine for a minute, shut down and it would take maybe 15 - 30 seconds to start leaking. I suppose that was due to pressure. I may have bent the line slightly, as it is a metal fuel line and it was a bugger to get on, when I installed it.

Any tricks to getting it to seal? What am I doing wrong? The leak looks like it is coming from the compression nut fitting going into the fuel pump and not the nut that is actually attached to the pump.

I lossened and tightened several times and thought I had it stopped but was in the garage last night and, out of curiousity, just checked and it had leaked some.

Thanks,

 

[Fishermark]

Re: Fuel line leak 4.3 Mercruiser

You say it is a compression fitting. Do you really mean that? Or is it a flare fitting?

 

[Fishermark]

Re: Fuel line leak 4.3 Mercruiser

Here is a picture of a fuel pump. (Not necessarily likes yours). This one has an adapter to go from a pipe thread to a flare fitting. Do you have something like that? The pipe fitting side can use some thread sealant - but not the flare fitting side. That you simply tighten. If it still leaks you may have a defect in the flare.

It you truly have a compression fitting, then you may need to cut the line and add a new compression ring. But again - no sealant on that either.

 

[Don S]

Re: Fuel line leak 4.3 Mercruiser

Those connections are on the suction side of the pump, and the leak would not be seen while running, as it would be sucking air. Check the fittings that go into the pump and make sure it's not damaged. If cross threaded, you may need to replace the fittings. Are you sure you don't have a gasket on the pump fitting leaking (item 10 below)

http://forums.iboats.com/attachment.php?attachmentid=21155&stc=1&d=1229362135

 

[Don S]

Re: Fuel line leak 4.3 Mercruiser

Those connections are on the suction side of the pump, and the leak would not be seen while running, as it would be sucking air. Check the fittings that go into the pump and make sure it's not damaged. If cross threaded, you may need to replace the fittings. Are you sure you don't have a gasket on the pump fitting leaking (item 10 below)

 

[Don S]

Re: Fuel line leak 4.3 Mercruiser

Those connections are on the suction side of the pump, and the leak would not be seen while running, as it would be sucking air. Check the fittings that go into the pump and make sure it's not damaged. If cross threaded, you may need to replace the fittings. Are you sure you don't have a gasket on the pump fitting leaking.

 

[tcarden]

Re: Fuel line leak 4.3 Mercruiser

Fishermark,

Sorry, it is a flare fitting. I wonder if I have tightened it too far and dmaged the flare, either on the line or in the pump?

Thanks,

 

[Silvertip]

Re: Fuel line leak 4.3 Mercruiser

You asked that as a question but since we can't see the interior of the fitting on the pump or the flare it will be up to you to determine what's wrong. It is one or the other or both. Check the flare for a crack running from the center of the tube outward. Regardless how insignificant a crack may seem, it will leak. Check the fitting in the pump. Crossed threads are obvious and the flare mating surface must not have any scoring or it won't seal. The fix will be to replace the line, cut and flare it again, and replace the fitting on the pump.

 

[Fishermark]

Re: Fuel line leak 4.3 Mercruiser

Actually I was speaking in very general terms, and in fact, I over looked the part where you mentioned it was from the water separation filter to the pump. As Don S points out - that is the suction side. He also gives a more specific diagram of your particular set up. (Three times to make sure! ) Check the gasket as indicated.

 

[tcarden]

Re: Fuel line leak 4.3 Mercruiser

Excellent replies guys. Thanks!

Great diagram, Don. I will check the gasket on the pump fitting. It is not cross threaded, seems to tighten up quite well and I have payed real close attention to where the leaks was actually coming from. I didn't think it was from that gasket as it seemed to be dry there (touching pump and nut), as best I could tell and just a little lower (not touching pump but touching where line runs into nut that tightens on flare) at the flare it was wet.

Thanks, I will check and post results.

 

[tcarden]

Re: Fuel line leak 4.3 Mercruiser

Hey guys,

I removed the pump tonight and the gasket #10 above is there but the fitting it is on screws all the way in and bottoms out like brass to brass feeling instead of a tight rubberized kind of feeling. Its hard to tell if that was the leaking area but the other fittings seemed fine. Any idea where to get an o-ring to replace it? Auto parts store? It has been leaking without pressure over the winter so it is probably sucking air as well.

Oh well, I will search for an o-ring and report back.

 

[180shabah]

Re: Fuel line leak 4.3 Mercruiser

O-rings are not hard to find. Take the old one to an auto parts store or a place that works on hydraulics, or........

Just match it up to a new one.

 

[tcarden]

Re: Fuel line leak 4.3 Mercruiser

Thanks Shabah,

I found one at Lowes in the Plumbing section. #10 vs. #35 the difference is that it is a smaller in diameter but a bit larger in size if that makes sense. I installed the fitting last night onto the pump and it fit much better, did not bottom out. I am soaking one of the o-rings in gas overnight to see if it will be affected since I got it from the plumbing section and I guess they are actually faucet o-rings. I just want ot be extra careful due to the potential for safety issues if not done properly.

I'm gonna try and get it back together this week and I really won't know until I summerize in a few weeks/month/cant' get here soon enough.

 

[180shabah]

Re: Fuel line leak 4.3 Mercruiser

It is better than the one that was leaking. At least for now. What material is the oring made of? If it was viton, then you are good to go.