Help Tracking Down a Fuel Issue

[crayiii]

I'm pretty sure the issue I'm having with our generator is a fuel starvation issue but I'm a novice so. Not sure.

There are fuel and return lines running from each tank I'm the stern forward 20 feet forward and 3 feet up to valves that to allows tank selection. After the valves, a Facet Cube fuel pump rated at 1-1.5 psi and 7gph pumps the fuel another 10 feet forward and 6 feet up to a racor filter then it goes into the 9kw generator with a full load fuel consider rate of 1 gph.

There was a much larger and louder pump that failed and I replaced. The symptoms were very similar to what I have now but a bit worse.

At load the generator would stumble and lose RPM for a couple seconds before getting back to 3600. It would do this about every 5 minutes.

After I replaced the large fuel pump with the Facet pump (also did all the filters), everything ran perfectly for the last 10 hours of run time. Now it's starting to have the issue again.

I'm not somewhere I can easily hire a pro so I'm left trying to figure this out. Is this to far and to much head for this pump? If so, what specs do I need? Is the pump located I'm the wrong spot? Should it be at the tank(s)? At the generator?

Could this be air getting in the system? If so, where is the likely spot?

Besides fuel, what else should I be looking at?

[Cheechako]

If starving for fuel they will often go up in rpm, then back. So it may be air. It sounds like a complex fuel feed system, so not sure ....but that also indicates plenty of possibilities for an air bubble in the system I suppose. I would try bleeding the high points if you can. If a filter is handy remove the top and make sure it's full of fuel, if not fill it up by hand.

[Compass790]

My guess is your pump is a little low psi. A 3 to 5psi pump would be better as 1 psi is about 27" of water head from memory. But you could have air too! *#!*&kn fuel/air problems can sometimes be difficult.
A higher pressure pump is indicated tho.

[Lepke]

Most pumps would handle the distance. Does the generator have it's own lift pump or is the new pump supplying all the lift and distance needs? 7gph doesn't sound right, usually the small electric pumps do 25-35gph. And now you've had 2 pumps with the same problem. Does the loss in rpm happen when some electrical appliance cycles on line? Like the AC or reefer? What is the electrical load when this happens?
A 3600 rpm generator engine is marginal, by 9kw the engine is usually more powerful and runs at 1800 for quieter operation and longer engine life. At full load your generators engine would probably cause it to slow when something with a high amp draw comes on line.

[Compass790]

Originally Posted by Lepke

Most pumps would handle the distance. Does the generator have it's own lift pump or is the new pump supplying all the lift and distance needs? 7gph doesn't sound right, usually the small electric pumps do 25-35gph. And now you've had 2 pumps with the same problem. Does the loss in rpm happen when some electrical appliance cycles on line? Like the AC or reefer? What is the electrical load when this happens?
A 3600 rpm generator engine is marginal, by 9kw the engine is usually more powerful and runs at 1800 for quieter operation and longer engine life. At full load your generators engine would probably cause it to slow when something with a high amp draw comes on line.

Yea good point this Lepke, his problem could be electrical, not my area of knowledge, but inrush current from motor starting could easy cause it to stumble if he was heavily loaded.
Still think he doesn't have enough psi when he says he has 6ft head tho. Could be both.

[Wotname]

Originally Posted by crayiii

.........

I'm not somewhere I can easily hire a pro so I'm left trying to figure this out. Is this to far and to much head for this pump? If so, what specs do I need? Is the pump located I'm the wrong spot? Should it be at the tank(s)? At the generator?

Could this be air getting in the system? If so, where is the likely spot?

........

If it IS air, then it is more likely to be on the suction side of the pump. If it was on the delivery (push) side then you should see fuel weeping out rather than air getting sucked in.

However as others have noted, the pump seems a little small for this job although it has worked OK for the first ten hours.

As a generalisation, pumps push better than suck.

[crayiii]

This is the pump. Also, it stumbles regardless of whether it's loaded to 80% or 30%.

I don't notice the amps changing when it stinks so I don't think it's from load changes.

[Compass790]

Yr pump specs say min lift 40" You are saying it needs 72" in your first post so I'd have that as a minimum.
However as Wotname noted strange it worked for first 10 hrs but maybe it got hot???

[sainted]

I like and use Facet pumps all the time. However, the cube is not right for your application. It doesn't have the lift capability.

Facets 40222 does, though: https://www.aircraftspruce.com/catal...statepump2.php

Get one of these babies and you won't have to worry about the pump being a problem. You may have other problems, but it won't be the pump.

[Cadence]

Originally Posted by crayiii

I'm pretty sure the issue I'm having with our generator is a fuel starvation issue but I'm a novice so. Not sure.

There are fuel and return lines running from each tank I'm the stern forward 20 feet forward and 3 feet up to valves that to allows tank selection. After the valves, a Facet Cube fuel pump rated at 1-1.5 psi and 7gph pumps the fuel another 10 feet forward and 6 feet up to a racor filter then it goes into the 9kw generator with a full load fuel consider rate of 1 gph.

There was a much larger and louder pump that failed and I replaced. The symptoms were very similar to what I have now but a bit worse.

At load the generator would stumble and lose RPM for a couple seconds before getting back to 3600. It would do this about every 5 minutes.

After I replaced the large fuel pump with the Facet pump (also did all the filters), everything ran perfectly for the last 10 hours of run time. Now it's starting to have the issue again.

I'm not somewhere I can easily hire a pro so I'm left trying to figure this out. Is this to far and to much head for this pump? If so, what specs do I need? Is the pump located I'm the wrong spot? Should it be at the tank(s)? At the generator?

Could this be air getting in the system? If so, where is the likely spot?

Besides fuel, what else should I be looking at?

If it ran great for ten hours I would look at vibration allowing a fuel fitting to suck air. Or possibly you have a screen at the tank pickup giving you the problem.

[sailormed]

Intermittant fuel starvation can be caused by the accumulation of crud from the fuel in the tank on the mesh of the pickup tube. Check if you have one and remove it to be sure. Don’t ask me how I know this

[crayiii]

Originally Posted by sainted

I like and use Facet pumps all the time. However, the cube is not right for your application. It doesn't have the lift capability.

This one does, though: https://www.pegasusautoracing.com/pr...gaAgo1EALw_wcB

Get one of these babies and you won't have to worry about the pump being a problem. You may have other problems, but it won't be the pump.

That one might be a little too high of pressure for the Racor.

[crayiii]

Originally Posted by sailormed

Intermittant fuel starvation can be caused by the accumulation of crud from the fuel in the tank on the mesh of the pickup tube. Check if you have one and remove it to be sure. Don’t ask me how I know this

I'll switch to the other tank and give it a shot.

[Cheechako]

I dont know about zeroing in on the pump. A small $20 NAPA fuel pump worked fine for the 80 HP Mercedes in my 47 footer. There wasn't more than 18" of lift though I would guess.

[KadeyKrogen38]

How clean is your secondary fuel filter. If dirty this could also be causing your issue.