CAT 3126 - does this system have lift pumps between the tanks and the RACORs?

markrinker

markrinker

New Member
Jul 19, 2011
325
Lake Union - Seattle, WA
Boat Info
2000 410DA
Engines
Caterpillar 3126
2000 CAT 3126 375hp - does anyone here know if there is a lift pump between the tank and the RACORs, or does the injector pump work on suction?

Reason I am interested: My 'sync weirdness' (see other thread) is actually only at or near WOT, and increases under fuel/water/gear/people load. It also happens on BOTH port and starboard sides, which tend to rule out the syncronizer, as it only matches starboard RPMs to port.

I ran ~7hrs this holiday week at 2200rpm cruise without as much as a flinch in the sync. Increase the 'go-lever' to WOT and the intermittant port or starboard slow dance would start.

My theory at this point is that under high fuel draw conditions, the system is momentarily drawing air past an o-ring, fitting, or a bubble gets pulled out of the fuel itself. Postive fuel pressure between the tank and the primary filter will often solve these problems as it pushes the fuel through the filters, rather than the injector pump sucking it through. I have added lift pumps to GM work trucks in the past that were not originally fitted with them, and solved high load fuel starve problems.

Thinking that if my boat doesn't already have them, I'll mount them near the RACORs and wire them to be powered directly off their respective port/starboard alternator battery charge lead with an appropriate fuse for overload or short protection. This way, the only way the pump is pumping is with a running engine...

Thoughts? Comments?
 
I have no idea what your problem is. are you slowing down or are your tachs jumping around?
 
With synchronizer off, what is your WOT on each engine? Your issue sounds like there may be a big difference between port and starboard and the synch can't keep up.
 
Your boat does not need lift pumps. You need to find and fix the problem instead of patching around it.

If both engines are now fluctuating, then My first guess is that you have clogged secondary filters....because 1.) high rpm rpm fluctuation is the first sign of a clogged secondary, and 2.) its a cheap fix ($30), 3.)The Racors trap particle sizes at 5, 10 or 30 microns, depending upon what element you are using; the Cat high efficiency filters trap at 2 microns, so your Racors are passing debris that the secondaries are catching, therefore, the Racors may be working, but the secondaries could be clogged.

If the the Racors were leaking air.......air will go in a hole where diesel fuel cannot come out.......then the fuel level in the Racors would gradually go down to where they are 1/2 full then the engines would stall at any speed where you applied some power.

One test you can do is to install a clear hose on the return to the tanks and see if there are air bubbles in it.........if there are, you are looking for an air leak.

From here, you probably need to get a Cat technician out to the boat to evaluate the problem.

Good luck with it............
 
Agree completely with fixing the root problem...however that is what eludes me!

1) They are actually running slow intermittantly - you can feel and hear the 100-200 RPM drop. Usually it lasts just a few seconds. (If its on the port side, of course then the starboard trys to match it if they are sync'd.)

2) Fuel filters are all fresh - ~15hrs on the secondaries, maybe 25hrs on the RACORs I'd estimate. Changed the engine filters on the run from storage to the slip this spring. The RACORs were swapped out 3x as I got all the algae worked out of the system last summer during 700+ miles of cruising. RACORs were removed, disassembled and cleaned every nut, bolt and o-ring. They look great so far this season. My experience with a clogging filter (primary or secondary) is once it goes slow, it stays slow. My problem now is more intermittant. Like a govenor kicking in, then releasing. Weird!

3) I'll probably swap out all fresh filters just to make sure, after I've gotten three big fills on all the fuel that wintered over, with treated diesel. I am not in a rush to throw parts at this thing. The lift pump addition is just an idea that never hurts a diesel fuel system overall.
 
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Sea Gull said:
With synchronizer off, what is your WOT on each engine? Your issue sounds like there may be a big difference between port and starboard and the synch can't keep up.
Click to expand...

~15hrs ago when I brought the boat around from storage I tested this and was able to make 2800 port and starboard no problem. I actually changed the engine filters at this time, before doing the tests. RACORs had been done 3x last season, with fresh filters after the units were disassembled and bucket cleaned every nut, bolt, and o-ring to remove the last traces of algae, which was more significant on the starboard side than the port.

With fuel, water, waste, gear, people on board this weekend I was only able to make 2650 rpm with sync off and throttles wide open. The intermittant slow running still happened without the syncronizer - which is what points me to fuel starve issues. There is not a big difference between port and starboard when using manual throttle control.

Agreed that NEW FILTERS regardless of hours and what I think may be happening is a cheap next step. I won't be back to the boat for a few weeks, but that will be the next thing I do - both RACORs and secondaries at the engines. I will then consider all data to be accurate.
 
One last observation...repeated. If you run the boat at max RPM of 2300, you would never even know there was an issue at all. That is basically what I do all weekend, and the fuel consumption has been great at an average of 17gph.

I have a new speed sensor in hand, so as soon as its installed I will start recording mileage again and then I'll get overall MPG numbers but I know its well north of 1mpg...maybe even as high as 1.4 based on the distances covered and my rough estimate of miles...so the engines are running sweet at 2200 cruise speeds and the oil is still translucent side to side and no smoke at idle, just a bit of soot around the water exits on each side. Overall very very happy with these CATS!!! :)

Also...also... water temp even at 165f and oil pressure at 50psi side to side at 2300rpm. Very consistant side to side from startup through manevers back to cooldown. Never more that a needle width of difference between port and starboard when it comes to water temp or oil pressure readings and thats probably sender/gauge variations.
 
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You obviously have some experience with diesel engines/fuel systems. There is one minor difference with a Sea Ray diesel system that does affect how an engine runs with a plugged filter.......all the lines are tight, all are double wall braided lines with swedged on fittings. If ....big IF.....the Racor is leak free, a plugged or partially plugged secondary will create a vacuum in the lines and that affects flow rates. IT begins where you cannot reach 2800 rpm, then the max rpms gradually decreases to the point where you can't even cruise. As that point approaches, rpms will fluctuate some.

Since you are going to change Racors, check the new flat o-ring as you install it...it is easy to roll one 1/2 around as you straighten it out and slip it into the groove on the lid. The small red o-ring on the t-handle is also very east to cut as you roll it down the threads on the t-bolt.

I hope this is as easy as new filters........and I've seen it take a case of Racors and 6 secondaries to clean up a dose of bad fuel....just hope you can do that one while tied to a pole somewhere instead of bouncing around in a sloppy sea somewhere.
 
I am operating under the assumption that the relatively new secondaries are in fact plugging and they will be changed about two running hours after a fresh set of RACORs go in - next visit to the boat. Why not start from there.

Again, thanks for everyones input - its funny how sitting down, typing, and reading can lead to a solution that you can't come to while underway. Same thing learned over many years on www.thedieselpage.com where I am a moderator for the Duramax forum.
 
fwebster said:
>>>There is one minor difference with a Sea Ray diesel system that does affect how an engine runs with a plugged filter.......all the lines are tight, all are double wall braided lines with swedged on fittings. If ....big IF.....the Racor is leak free, a plugged or partially plugged secondary will create a vacuum in the lines and that affects flow rates. >>>
Click to expand...

This entire description makes the case for adding lift pumps between the tanks and the primaries. The point is to provide about 4# of positive fuel pressure to help the system NOT go into a 'vaccuum' or fuel starved mode, pulling air bubbles out of the fuel and/or finding the weak point in the system to suck in air.

I will* swap out filters next, but the lift pumps will be installed - near the RACORs - before we go on our two week Lake Superior journey in August!!!
 
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I don't follow your logic at all......if the Racors are plugged then trying to push fuel thru them is fruitless. Having a vacuum because the Cat/Sea Ray fuel system is tight causes the engines to slow down which gives you an early warning that you have a fiiter problem and that beats the heck out of forcing fuel and air thru the clogged up Racor, which the lift pump will do, until you reach the head pressure of the pump design anyway. Have you ever had to purge a 3116/3126?...........well slowing down and getting to a dock to change the filters is a lot better than having to purge one.

Finally, you will have one of a kind 410DA when you add your lift pumps...........no one else I've ever heard of has ever found the need to add them to what may be the simplest and most dependable fuel system installed on pleasure boats.
 
First off there is no 'forcing' the fuel at 4psi. Its simply positive pressure on the tank side to help create a constant fuel supply. The terms 'plugged' or 'clogged' are inaccurate. What happens over time in any filter media is 'restriction'. 100% restriction would be 'plugged'. I have only seen one 'plugged' filter in my life, and that was one that was full of water AND frozen solid. All the rest - well they are restricted to some degree.

Restriction causes the fuel to flow more slowly, and under high power demand, the injection pump becomes fuel starved and starts pulling air out of suspension in the fuel.

Suspended air in a fuel system and injectors are NOT friends. Imagine what the fuel flow looks like as the injector closes - when the fuel behind it is full of air. Ever heard the pipes rattle in a house with hot water circulation, when the flow valve closes??? On the old mechanical systems, its not as problematic. One the new common rail 25K# psi system like the Isuzu Duramax, air can cause premature injector wear. This is where adding a lift pump to a diesel supply system comes into play.


As for having a unique SeaRay, that is completely my goal. :)
 
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I'm with Frank, I'm confused why a lift pump would do anything. Don't our CATs run at like 10psi fuel pressure? That's more than enough fuel if everything is functioning correctly. So much fuel is delivered to the injectors that they have a fuel return for what's not used, which is a lot. To starve an injector, you have to have something going on and a lift pump won't cure it.
 
Turtlesboat said:
I'm with Frank, I'm confused why a lift pump would do anything. Don't our CATs run at like 10psi fuel pressure? That's more than enough fuel if everything is functioning correctly. So much fuel is delivered to the injectors that they have a fuel return for what's not used, which is a lot. To starve an injector, you have to have something going on and a lift pump won't cure it.
Click to expand...

Obviously its not necessary, or the CAT engineers that know alot more than me would have already built them into the system.

My goal is to reduce or avoid a suction on the feed side of the injector pump. Maybe it extends injector pump life, maybe it doesn't. We'll never prove that definitively here. It is* clear from common experience here that as filters restrict, engines run slow and I personally don't want my IP sucking for fuel and potentially sending pressurized air with fuel through the injectors.

2001-2003 GM Duramaxes were the only years that would 'run slow' as a fuel filter restricted. Early year LB7s also had by far the highest rate of injector failures. Whether these two observations are related, I cannot say or prove. In subseqent years, GM has programmed an ECM 'limp' mode and illuminates the SES light on the dash to alert the operator of a restricted fuel filter. They do not want the truck to be operated under high restriction, as this puts extra stress on the IP and injectors.

GM does not have a lift pump on their Duramax series trucks. Many people add one between the tank and the filter - especially if they add additional filtration and/or turn up fuel rates. It is also thought to aid the IP and injectors over the long haul, by keeping suspended air to a minimum.

Plumbing in a test port for monitoring restriction is also planned...that way you don't wait for the engine to start running slow, you change filters as they hit a predetermined restriction. http://www.kennedydiesel.com/detail.cfm?ID=289
 
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Take a look at Parker Filtration Parts and you might find that you don't need to engineer in a test port because they have already done that. Dual Racors come with vacuum gauges, but I believe the 410DA just has a single 500MA Racor. Parker has a replacement T-handle where you mount the vacuum gauge in the top of the Racor lid. You might find that a smarter investment than lift pumps is to change the 500MA filters to 900MA's which increases your filtration capacity from 60gph to 180gph.

On the lift pump thing, we obviously are not communicating. Lift pump or not, once the Racor gets plugged up the engines are going to slow down to the point that the engines are only getting what the Racor processes. These are not Duramax's and automotive mechanical logic doesn't always translate. My experience has been that these engines will not suck air from a plugged fuel filter..........oh, they might if you keep running without reducing the power and force them to eventually shut down from fuel starvation.
 
Mine has a telltale hand on it, but I think they have just plain vacuum gauges........but would be almost useless to me.

You should use 30 microns in the primaries. The Cat high efficiency filters are 2 micron........and be sure you use nothing but Caterpillar filters.
 
markrinker said:
http://www.defender.com/product.jsp?path=-1|311|302335|107095|699530&id=1716464


Spendy...would you run the 2micron or 10micron filters with these? I wonder if the restriction gauge holds the highest reading, or do they expect you to read the gauge while underway at WOT? That would be a problem with my filter location...
Click to expand...


I don't believe the entire new setup is what Frank was talking about. He had posted about a vacuum gauge previously that I am very interested in. frank, do you have more information on the upgrade to the existing Racor?
 
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