6CTA loosing prime

[Pascal]

Had an issue my port engine today, fired it up and it shut down after a couple of minutes. Primed it with the priming pump, then 50 pushes on the mechanical plunger and it fired right up running for a couple of minutes. Switched tank, repeated and same result. If I keep the priming pump on, it runs fine.

So, not a tank pick up problem… that leaves the Racor or the mechanical lift pump. Racors are 6 years old, all fuel lines from tank to engines also replaced 6 years ago along with valves.

No air leak at the racor since the walbro is before the racor and if d see the leak.

I ve never had to mess with a racor internals in all these years, there is a check valve inside, right? Could that be sticking under suction from the lift pump but not under pressure from the walbro?

Both the racor and secondary have low hours but I ll try that first tomorrow

 

[MadHatter53]

Pull the tops of the racors to be sure they are full.

 

[Captain Ralph]

There is a floating ball / check valve in the racor.
It keeps (slows down) fuel from draining back to the fuel tank.
When gunked up, it may stick.
Lack of use and it may stick also.
Draining the filter and a couple of taps should clear it.

However; If you can prime the engine blowing fuel thru the racor. I do not think this is your issue.

You mentioned mechanical priming pump, Engine mounted on the mechanical fuel/lift pump?
There is no electric lift pump way down under the left side of the engine???.

The Achilles Heel of Cummins has been their lift pumps.
The electric pumps are less reliable than a Rule float switch.The priming plunger on the mechanical pump is almost as bad. Then the reed valves in the mechanical pump itself.
Lets find a pressure gauge and install it on the secondary fuel filter.
Watch it as you prime with the Walbro pump, then lift plunger and then when running.

Other thoughts; fuel return valve open?

 

[madhatter1]

Speaking from experience on a truck Cummins look for a cracked injector tube line or a leak at a fitting. Trivial leak going undetected allows air back into the system. I have a very bitter story about a crappy Cummins dealer on that. But still, take a look. Minor leak that evaporates gets worse over time and then easy to smell what is going on.

Also FYI your engines are basically still young and new. The Cummins I installed in 98 on my 34 developed this issue very early on and covered by warranty. The truck was at 250K miles. So an anytime thing. At least a simple fix if this is the issue.

 

[Pascal]

I ve looked around the injector tubes and everywhere else. No leaks.

Ralph, no electric pump just the small mechanical lift pump with the round plunger. From there it goes to the secondary and the injector pump.

When we got back from the autopilot calibration yesterday, I tuned off the priming pump and switched the valves, engine ran fine at 1000 for 10 minutes before I shut it down. This morning it fired right up and stayed running.

I hate intermittent issues

 

[Sonic Boom]

assuming your 6CTA's have the mechanical Bosch P pump, the fuel return line on the injection pump has a check valve (ball and spring) that can get a piece of trash in it and stick open, this will cause the system to seem to have lost prime when it's really a lack of fuel pressure in the pump causing a no start/hard start/low power issue. If your filters are full of fuel I would suspect this. Usually removing the spring and ball and a quick shot of brake clean takes care of this. Sometimes, the debris pass and problem clears up on it's own too

 

[Captain Ralph]

I hate intermittent issues

Brother, you have what,,, 15 hours on your new engines??
Your new hoses, new fittings, new everything??

Sonic may have it; a piece of dust in the wrong place.
A dry plunger/primer seal, or other things.

If your having issues putting hours on your own stuff, I'm here to help.

Still a pressure gauge on that secondary filter should be SOP.

 

[Pascal]

Brother, you have what,,, 15 hours on your new engines??
Your new hoses, new fittings, new everything??

Sonic may have it; a piece of dust in the wrong place.
A dry plunger/primer seal, or other things.

If your having issues putting hours on your own stuff, I'm here to help.

Still a pressure gauge on that secondary filter should be SOP.

No, I have close to 200 hours. Not much but I had a lot of work to do for the first couple of years after the repower so we barely used the boat …

Engine fired right up and run fine today.

 

[Captain Ralph]

No, I have close to 200 hours. Not much but I had a lot of work to do for the first couple of years after the repower so we barely used the boat …

Engine fired right up and run fine today.

Great news.
Lets go water skiing. You go first..