Fuel not priming after filter change

[terah]

I've just changed the CAV 296 prefilter and main fuel filter on our Yanmar 4JH3-TE and cannot get the fuel bled through.

I've tried topping up the primary filter, topping up the fuel hose between the two filters, and can draw fuel (with vacuum pump) from the top of the fuel hose that feeds the main filter and out of the bleed screw at the main filter.

No amount of pumping the manual pump on the main filter works. The engine starts but struggles after ~1 minute and cuts out after ~ 5 mins.

Have changed the main filter again, opened up the 296 and checked the seals and they all seem fine, but still nothing through.

I managed to run the engine out of fuel a few weeks ago and it primed pretty quickly after that (2 - 3 mins) just using the manual pump.

I'm guessing an air lock or small air leak somewhere but not sure what to try next.

[steve77]

Originally Posted by terah

I've just changed the CAV 296 prefilter and main fuel filter on our Yanmar 4JH3-TE and cannot get the fuel bled through.

I've tried topping up the primary filter, topping up the fuel hose between the two filters, and can draw fuel (with vacuum pump) from the top of the fuel hose that feeds the main filter and out of the bleed screw at the main filter.

No amount of pumping the manual pump on the main filter works. The engine starts but struggles after ~1 minute and cuts out after ~ 5 mins.

Have changed the main filter again, opened up the 296 and checked the seals and they all seem fine, but still nothing through.

I managed to run the engine out of fuel a few weeks ago and it primed pretty quickly after that (2 - 3 mins) just using the manual pump.

I'm guessing an air lock or small air leak somewhere but not sure what to try next.

Let me make sure I understand your description. Does your Yanmar have a mushroom-shaped piece of metal mounted on top of the engine-mounted fuel filter that you push on to manually pump fuel? If so, then you should be able to open the bleed screw on the side of the pump housing and pump fuel until the filter is filled and air has been expelled.

Are you saying that this pump is working, or not working? Or that it worked a few weeks ago, but does not work now?

Steve

[terah]

Originally Posted by steve77

Let me make sure I understand your description. Does your Yanmar have a mushroom-shaped piece of metal mounted on top of the engine-mounted fuel filter that you push on to manually pump fuel? If so, then you should be able to open the bleed screw on the side of the pump housing and pump fuel until the filter is filled and air has been expelled.

Are you saying that this pump is working, or not working? Or that it worked a few weeks ago, but does not work now?

Steve

Hi Steve. Yes - we have the 'mushroom' style manual pump on the top of the housing that the main filter screws into. It worked a few weeks ago after running out of fuel, but not now after changing both the main and pre-filters.

I completely removed the bleed screw and can draw fuel out by attaching a vacuum pump to the hole the bleed screw goes in.

[steve77]

Originally Posted by terah

Hi Steve. Yes - we have the 'mushroom' style manual pump on the top of the housing that the main filter screws into. It worked a few weeks ago after running out of fuel, but not now after changing both the main and pre-filters.

I completely removed the bleed screw and can draw fuel out by attaching a vacuum pump to the hole the bleed screw goes in.

Okay, now I understand. It's a possibility that the diaphragm in the Yanmar mushroom pump has failed. I don't think this unit can be serviced, on our Yanmar 4JH3-HTE it looks like one piece and no way to disassemble it.

If the diaphragm has failed, perhaps you are drawing air into the engine-mounted filter at that point. One way to check would be to remove the inlet and outlet hoses from the filter and join them together with a barbed fitting. This would bypass the filter. This leaves you with only the CAV filter, however. The CAV is a good filter, but it's up to you whether you feel comfortable running the engine for ten minutes or so using it as your only filter. If the engine runs good for that time, then I would say the Yanmar filter is the source of your air leak.

Alternatively, can you temporarily install a different filter in place of the Yanmar unit to replace it, just for the time it takes to test the engine? Maybe you or a friend has a Racor or something you are not using, or you can buy something at the auto parts store. You should be able to fill it with fuel using your vacuum pump. This way you have two filters in series for the test, and are unlikely to have any problems with anything getting to the injection pump. With the replacement filter (I think the Yanmar filter is ten micron, so get the same element for you test filter) installed, you can run your engine as long as need be to make sure you have solved the problem.

This will at least confirm or eliminate the Yanmar filter pump as the source of trouble.

Best of luck!

Steve

[Greg Mason]

Terah, you mentioned changing the CAV filter, and the seals look good. Did you for sure get the old one out first? 2 seals aren't better than 1, guaranteed!

[aquafacts]

I'd go right back to the primary C.A.V. filter housing ! They have square profile o-rings and if not put in squarely will suck air and / or leak. The package has many o-rings of sllghtly different sizes - be sure you get the correct one for each location. Use a sharpe pick to get up into the slot on the upper aluminum housing to dig old o-ring out. Check someone else hasn't left another one up there ! There is also a o-ring on the bolt and another on the spigot facing down on the aluminum top housing. Change them all !
That should solve your problem - NOTE - If it was running o.k. before - don't over think this - 95% chance - its something you did with the filter(s)

[Capt Y Knot]

I had the same problem a few years ago...air was the problem.

The secondary filter container would fill with diesel after pumping the diaphragm pump. The engine would start and run until the fuel in the secondary filter ran out. Did this several times and no luck. Very frustrating!

The following solved the problem. No trouble after 3 years.

I would first disconnect the fuel line that enters the manual fuel pump from the primary filter.

Attach a tapered fitting that comes with a manual bellows for an inflatable boat ( the bellows will blow air backwards to the primary filter) on the end of the hose. Close the fuel shut off valve.

Pump a few strokes of air and closely observe the fittings, primary filter seals, hose, and fuel line for any bubbles. Look close, it only takes a small amount of air to loose the fuel prime. Spray some soapy water if need to see leaks.

My leak was a "new" off the shelf fuel shut off valve. Replaced it with a new Racor valve and the problem was solved. Good luck

[River Cruiser]

A friend had the same problem on a 4-107 Perkins. The he had the wrong seal on top of the filter and it blocked the holes where fuel flowed through into the engine mounted filter.

[OBT]

Before you go to far (and someone might have already written about this) try rotating the engine 1/4 turn to get the pump off the cam so that it can do its job. The telling sign is if the manual priming lever doesn't feel any resistence when trying to prime.

[terah]

@Greg Mason - Yes, fished out the old one and put a new one in. Changed out the small seals too. Also tried pulling apart and putting back together just to be sure.

@aquafacts - Made sure we had old ones out and pulled new ones out again to make sure I hadn't got the large ones the wrong way round. No problems there. Was also pretty sure to start with it must have been something I had done.

@Capt Y Knot - Yes, we did the same thing. Must have tried half a dozen variations each time refilling the filter and running the engine until it ran out. Sometimes the engine would immediately struggle, sometimes it would purr on for 5 minutes giving false hope!

@River Cruiser - Was that having the two big seals the wrong way round? Checked that too.

@OBT - Tried that too! (but very useful to know)

Many many thanks to @steve77 who turned out to be in the same marina as us and came over with his working main filter and assembly. I'd been focusing mostly on the filters as I knew the manual pump had worked recently and it seemed most likely something I had done, but it turned out it was actually the manual pump. Took it off and there's definitely something loose inside. Unfortunately not serviceable so another one ordered and a car hired to go and collect it.

Thank you all for the suggestions.

[coastalexplorer]

CAV is part of the Lucas group of companies, specialising in fuel injection systems.
Actually the initials of Charles A Vandervell.
Read more at CAV Filters - Education please