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.

 

[Avenger]

Not saying your guy is wrong, but while revamping my fuel system I've been doing some research, and there are a lot of factors like friction vs hose length and 90° elbows that add a surprising amount of restrictions. As stated previously I would bypass the Racors and use a vacuum gauge or the engine's sensors to verify, but you may need to upsize the fuel system or change the style of fittings to overcome the length of the runs and inherent restrictions in the configuration.

My previous system configuration, even though significantly oversized (on paper) for the engine's specs, still resulted in high vacuum even with spotless filters. It didn't take much contamination to quickly result a significant performance drop.

 

[SKYCHENEY]

Not saying your guy is wrong, but while revamping my fuel system I've been doing some research, and there are a lot of factors like friction vs hose length and 90° elbows that add a surprising amount of restrictions. As stated previously I would bypass the Racors and use a vacuum gauge or the engine's sensors to verify, but you may need to upsize the fuel system or change the style of fittings to overcome the length of the runs and inherent restrictions in the configuration.

My previous system configuration, even though significantly oversized (on paper) for the engine's specs, still resulted in high vacuum even with spotless filters. It didn't take much contamination to quickly result a significant performance drop.

All valid points. We'll see what the gauges show as we play around with it. I may indeed need to upsize if I want to keep the Racors, which I do.

 

[Bob Quinn]

This should be interesting to see the relative resistance of the different elements in the sytem!

 

[SKYCHENEY]

Update: So the warning message wasn't really "low fuel pressure, pre-filter" as it says but high vacuum readings. I really couldn't test this until I got the right transmissions installed. Now she handles and runs as she should without being grossly overpropped. So, I plumbed the Racors and the Cat filters back in together and test ran with one 30 micron in one Racor and no filter in the other.

I started out with readings on the Cat screen of 3 inches of vacuum on the stbd and 0 on the port. Once underway, the port jumped to 13 and stayed there while the stbd ran 3-4 the whole time and once read 5 and this was on either the 30 micron or the Racor with no filter; same reading.

So now I assume that the port engine has a bad sensor. To confirm, I just had a 15ft fuel hose made up to connect the port engine to the stbd supply after all of the filters on that side. Once I can prove the issue is not with my part of the fuel system, then I can call out Cat Service.

 

[cww]

Was 21 knots top end or cruise? Either way, crazy fast for a 53.

 

[SKYCHENEY]

Was 21 knots top end or cruise? Either way, crazy fast for a 53.

Top end but I'm still a little under propped and I need more tabs. Its fine for this season but next winter I'll be tweeking those props and adding new trim tabs.

 

[jim rosenthal]

What was your load percentage at WOT? Just curious.

 

[SKYCHENEY]

What was your load percentage at WOT? Just curious.

Ha!! I forgot to look. Too many things to check out. At 2200rpm, I was at 19kts and 70% load. She topped out a little over 2400 and I was told that max loaded should be 2320-2350. So, I can obviously use a little more prop.

 

[Bob Quinn]

Don't expect any of us to catch you in a game of chase LOL! That's cookin along pretty fast!

 

[carolinacoast]

That boat is really a Cheney 53 custom. I bet it sells for 7 figures one day after we are all gone. Nicely done.
Is the waterline higher too, with less weight?