Low fuel pressure

[SKYCHENEY]

I need some thoughts/information on the original fuel system. After the re-power, we hooked up 1/2" fuel hoses to the original copper and plumbed to a dual Racor 1000, then to the Cat fuel/water separator, and then to the engine. At higher rpm, I'm getting a low fuel pressure warning. The Cat service guys are saying that I need to take out the Racors and just run with the Cat spin on as the primary (secondary is on the engine). I don't like not having the 30 micron Racors before that 10 micron Cat filter though.

Apparently these common rail engines pass a large volume of fuel. I understand that to cool fuel that you just pressurized to 20,000psi, that you probably need a pretty good volume but I'm told that the 1/2" lines should be sufficient.

So, other ideas are that all of the bends and turns and selector valves are causing some restriction. Could/should I run all new lines from the tanks? Anybody ever run into this? Could the returns be part of the problem? Just looking for all ideas at this point before tearing it all apart.

[carolinacoast]

Maybe bypass for the test? If that solves it, perhaps valve the racors with a 2 micron filter as a polisher to run at the dock.

[Pascal]

I can’t imagine not having racors and only relying on the secondaries. Never seen any boat without primaries.

The engines installation guide should have specs for everything from exhaust hose diameter to fuel supply and return. Another possibility would be a restriction at the fuel pick up in the tanks.

When I repowered we replaced all the fuel lines and valves just to be safe. I thought about pulling the pick ups but didn’t want to mile a can of worm

[cww]

After 20 years of having large boats I would never run without oil/water separating primary filters. They have saved my bacon a number of times, I would have just trashed an engine a few months ago when I had a failed fuel cooler. That's a very common problem in saltwater but may not be a concern for you in fresh. It's a big risk for a $500 problem to become a $50k problem. Not to mention injector pumps and injectors if you pick up a tank of fuel with algae or particulates in it. I am not enthusiastic about the "just remove them" idea, and Detroits are way more forgiving about bad fuel than those CATs you have now.

To eliminate the racors as a possibility, just remove the filter elements from the racors and try running the engines. If the warning stops you have your answer.

[bostonhatteras]

Do you have vacuum and pressure gauges after the primary and before secondary respectively to get an idea what is going on normally? perhaps vacuum on both 30 and 10 micron units? I'd think that would be a good start to locate restrictions.

[Steve Mannshardt]

I need some thoughts/information on the original fuel system. After the re-power, we hooked up 1/2" fuel hoses to the original copper and plumbed to a dual Racor 1000, then to the Cat fuel/water separator, and then to the engine. At higher rpm, I'm getting a low fuel pressure warning. The Cat service guys are saying that I need to take out the Racors and just run with the Cat spin on as the primary (secondary is on the engine). I don't like not having the 30 micron Racors before that 10 micron Cat filter though.

Apparently these common rail engines pass a large volume of fuel. I understand that to cool fuel that you just pressurized to 20,000psi, that you probably need a pretty good volume but I'm told that the 1/2" lines should be sufficient.

So, other ideas are that all of the bends and turns and selector valves are causing some restriction. Could/should I run all new lines from the tanks? Anybody ever run into this? Could the returns be part of the problem? Just looking for all ideas at this point before tearing it all apart.

Having been through multiple exercises with the Caterpillar Industrial Engine process, application, load rating, duty cycle, and related audits on surface drill rigs, what Cat wanted, Cat got. Any deviation and it was a case of not our problem, warranty or otherwise. Doing what required was the only way to work through the problems that they formally owned

[warrenw]

Sky,

Just sent you an e-mail with an attachment that may be a reference data point. It is a summary of a 47 Commander repower (not mine) where the guy ended up replacing all of the original copper tubing with larger ID hose to reduce restrictions to meet the requirements for the new 6.7QSBs.

[jim rosenthal]

You might look at the large Fleetguard fuel filtration units from Seaboard Marine. They are rated for Cummins QSM11s at 700+ hp. Running new and bigger fuel lines might also be a good idea, if only because Cat might decline to sign off on the install if you don't.

[Bob Quinn]

I would guess the 2 old plus 2 new filters would create most of your restriction.

Just thinking out loud it seems like filters are a large flow restriction and piping would be a low restriction.

So if 95% of restriction is from filters, you could probably go to double the line size and still have the same level of restriction. Just thoughts - so I would guess to much filtering.
This is all on the vacuum side of things (I think) so that restriction would starve the pump?

[SKYCHENEY]

A fluid engineer friend looked at this setup and tells me that the 1/2" lines should be able to supply over 240gph. That is most likely not the problem. I'll be looking closer at the Racors. I want to keep them even though the Cat primary is a water separator. I'll post results of a few different configurations we are going to test out next week. Thanks for the replies and suggestions.