Elec and mechanical fuel pumps
 

Anyone running elec pumps to back-up their mechanicals?
I'm wanting to do this and I'm curious how it should be configured.

need to know more about what you have and why you want to do this. I have run 1200 hp engines on nothing but a mechanical pump with no problems. I did have an electric as a backup but never needed it.

I personally don't care for it. In todays market, we have pumps to suit the needs whether it be a single electric or single mechanical.

I was up against the same decision 4-5 years ago after my 557 build and considered mech/elec combo. Decided it was too much BS and went with a mechanical marine CV products on the advice of someone with experience with the CV. Bolted right up to the sea pump and works just fine. Simple and affective, can't beat that.

I agree. I heard the argument on having a electric as a backup in case you lose the mechanical, but, I think that's a bit over cautious. Might as well keep a spare starter, distributor, camshaft, water pump, and ignition switch on board then too lol

Hey watch it mister, I'm the over kill type....I keep a tow line in the boat and always bring my cell phone !!

Ha, I know some guys who keep a spare bravo in their pickup bed at all times!

Bravo failure to me = switch over to my spare... 12 ft Mirrocraft with scream'n 9.9 Johnson on the back and a couple of fishing rods.

My concern is if I loose some fuel press on an extended high speed run, eng would go lean and I might not know until the damage was already done. It's happened once to this boat (before I bought it) and I don't want it to happen again.

It's not for capacity per se, but more for an automatic back-up.

compedgemarine : was your elec pump set to automatically come on, or did it require user action to activate? How was it plumbed into the sys?

I hear what you guys are saying abt carrying around spare parts and I agree, especially with the Fountain where storage space is limited.

Here's a crude drawing of what I have in mind. System would run on mechanical pump normally, but if fuel press dropped while eng still had oil press, the elec pump would come on automatically. I would add a warning light at the helm to indicate I had switched over to elec. Could also add a push button LOP bypass switch to prime carbs if needed.
I know the diagram looks busy but don't think it would look so bad once installed.


[ATTACH=CONFIG]502256[/ATTACH]

HOLY FUK man. Let start with the basics. For starters, what are you running for power? My guess, is a 29 Fever, its nothing that's gonna require something as involved as that drawing.

A quality mechanical pump, like a six valve style with 1/2 NPT in/out, will support 800HP without breaking a sweat. Key is proper fuel line size, and pickup size in tank, etc. Many times fuel delivery issues aren't the pump itself, but the plumbing. Keep it simple bro.

Only when I go to the Ozarks !!!!! :angry-smiley-038:

Eng had a 6 valve 130 GPM pump with 1/2" lines from tank to carbs on it when it went lean. Suspect something got into the check valves inside the pump and it dropped the fuel press.

I'm running full roller 454's making ~500hp, but like I said before, it's not for capacity. The mech pump should have been 2x what the eng needed, but it went lean anyway.

it was in a race boat so it ran for an hour at a time at WOT and never had a problem. the electric was on a switch but was just there as a backup as you hate to lose a race because a pump failed with a lap to go. we never needed the electric pumps and they basically were just used to prime the system when the engines were changed. the electrics were Weldons so they could handle it just fine if needed.

I have some switches that trigger at 4PSI. If psi falls below 4psi, switch makes contact, triggers my alarm and LED on dash. I know what you're thinking of doing, to save your engines, and its a good idea, but I think you'll be fine with the right pump and lines, as long as your not running some crazy 1200-1500HP boosted engine.

Well, theres certain things you cant avoid. A piece of crud getting stuck in a needle and seat can do the same, no pump can fix that. Mercury used those 6 valve pumps on the 800SC, 900sc and 1000sc. How much power you making?

I originally was just going to install the low press switches, LEDs and alarm, then I decided to take it one step further. .Then came working out the details and this is what I came up with. With this set-up you can still stay out on the water running the elec and deal with the mech pump later.

I'm still having fuel press issues with these pumps as we speak. One min they are at 8.5 psi, next min they are at 4.5 psi. The pumps are 10 years old and I'll be ordering rebuild kits ASAP. That will probably resolve the unstable fuel press issue, but some insurance wouldn't hurt.

Ya after 10 years might be time for a kit. Also make sure no air leaks on inlet side of pump and lines. Been there

zz28zz - I can certainly understand your concerns. Back up was one reason I was considering going with a mech/elec combo. That plus making sure my 557 was being fed adequately. However in doing some research I had found that electric fuel pumps should be mounted as close to possible to the bottom of the fuel tank. In my case that means at or close to the bottom of the bilge and I was concerned about any bilge water possibly getting to the pump, or pump wiring. That, plus plumbing a return line from the elec pump, wiring, etc. I'm a believer in keeping things as simple as possible. Hence my decision to go with a reliable mechanical pump only. Which btw is rebuildable if/when necessary. That said, I do not at all think your plan/idea is real overkill, and allot of fuel systems are run with the combo. Like I said, I just decided to keep it simple.

It is an interesting question. I have a 20' Cigarette and like most of the early model Cigarette's they were equipped with backup electric fuel pumps. I have retained the setup that has a on/off switch on the panel. They were equipped with SW pumps and work great. I also use the pump to prime the fuel before starting and always run the pump when running hard. I recently re-plumbed the original fittings and hoses. Like many that have commented, i like simplicity. I added a stainless fuel log that mounts on the fuel pump that cleans up the lines. If anyone is interested I can post a photo. My feeling is, if a backup electric fuel pump gives you piece of mind and the expense and effort is not a problem, always error on he side of caution.

I'm interested in seeing how Cig incorporated the elec pump into system (i.e. where it draws from and where it discharges to, where pump mounts, etc).
I'd much rather copy a design that's known to work than try and re-invent the wheel!

I have taken a photo of my pump setup but having issues posting. If you want me to send please provide your email.

The set-up that i have is: fuel line from tank to fuel separator, 2 lines coming out of fuel separator, 1 line to mechanical fuel pump, other to electric fuel pump. Outlet side of mechanical fuel pump combines with the electric fuel pump and goes to the carb,
.
I hope this is not too confusing. The photo will clear up the description. Please let me know if you have any questions.

PM sent..

Thx for the pic goin70 and all the responses from the group!

After speaking to the manuf of my mechanical pumps, and the responses I have received here, I think I'm going to shelve the elec back-up pump idea for now.
I'm having the mech pumps rebuilt. When they come back I'll keep a close eye on them. First hint of low fuel press though; I'll be revisiting the elec back-up idea again.

So what your saying is that you want it to come on automaticly if the mech pump pressure drops below a certain point? Now your getting into pressure switches in the fuel line between the pump and carb and elec pump would need to be plumbed in after the mech pump so it doesn't have to push thru the now broken mech pump.
Sounds like a nightmare to me and some serious overkill. Install some fuel pressure guges if your that worried about it and be done with it. How about an elc oil pump in case you have a drop in oil pressure?

Fuel press indicators are definitely on the list. Just wish someone made one with alarm capability,, kinda like a depth finder that has alarms for water depth being too shallow.

If oil press drops, chances are you got more problems than just a bad oil pump..

check out fwmurphy.com they make guages and alarms. might be someone close by, they do lot of ag/oil industry.

Hook a pro light or similar up and mount in dash so that when fuel pressure drops below set pressure it blinds you (figure of speech, but you definitely can't miss it). We used to run 2 in our boat, one for oil pressure and one for exhaust temp. Should have had one for fuel as in the end the mech pump gave up mid race and melted pistons and sent the metal through turbos. Never knew it was the mech pump until it went on dyno after rebuild and couldn't get fuel pressure up!

Why don't you just use a fuel pressure switch? When fuel pressure drops below 4psi it removes 12v from the ignition and shuts down the engine. When it removes the 12v it then turns on an idiot light on your dash using a normally closed 12v relay. Below 4psi and your ignition will be off and the bowls will dry up with the spark gone. $30 in parts.

Thx for the link. I checked it out and it looks like quality stuff. Unfortunately the lowest press switchgauge they offer is a 0-80 psi. Might work good with F.I. but not so good with a low press fuel sys. They did mention offering special switchgauges but would require a min order.

Sorry to hear abt the meltdown. One of my engs suffered a similar fate. Lucky for me it belonged to the prev owner when it happened.

While researching this subject I can across a few posts where this idea was presented. Some good points were brought up for not having the switch shut eng down automatically. Among them, the fear of eng shutting down at the worst possible moment, like trying to get out of the way of someone haul'in a$$, while turning into a big wave, in the middle of a aggressive high speed turn, maneuvering up close to some high-end equip, etc

I planning on going with a low press switch but it will just be for aural/visual alerts.