The boat is a 2000 Fountain with staggered 500 EFI engines. I bought it recently. It was a repo, so I have little maintenance history. When I changed the spin on fuel filters, the engines would not start. I removed a filter and it had NO gas in it. I carefully filled it and put it back on. The engine started and ran fine. The other day while running at about 3500 rpms, the port engine backfired twice and quit. It had about 1/8 tank on the gas gauge. It was not empty, but I may have sucked some air. I switched to a full tank and it would not start. I removed the spin on filter and it was half empty. The fuel line was also empty. I could hear the electric fuel pump run, but it sounded like it was not under load. I filled the filter and line with gas and it started. I shut it off after a few minutes and turned on the key. The fuel pump now sounded like it was under a load. It restarted fine. The boat has no secondary fuel pumps that I can find.

Is this normal for EFI engines? If not, is there a cure? I did a search before starting this thread and one writer reffered to an EFI fuel system upgrade, but I could not find any more info.

First of all, any Fountain reading below 1/2 tank usually needs to be parked at a gas station or it is going to run out, you got lucky I guess. You should have mechanical fuel pumps mounted to the water pumps, these are what draw fuel to the electric fuel pump. If the engine doesn't spin some they will not pull fuel.

I agree. It's nice that you know that you can run it down to an 1/8th tank, but I never really let mine get much blow a 1/2 tank. I don't own a fountain, but few gas tank sending units read properly, regardless of manufacturer. Regardless of how the manufacturer mounts the tanks the gas gauge really cannot read accurately.

The manufacturer could mount the tanks level at idle and then they would read wrong on plane, or mount them level on plane and they would read wrong at idle (I don't really think that any manufacturer does this, I'm just pointing out that they're damned either way). Either way you're screwed and your gauge really isn't going to read right.

I would put a 1/2 tank in each tank and see if you still get this problem. If you still have the same problem you likely need to rebuild your fuel pumps.

Your issue is" head height". The stock fuel pump on the 500efi does not like lifting fuel from deep in the tank and pulling it to the filter mounted high up on the motors. If you run out of fuel, the line and filter ar full of air. Vane rotor high pressure pumps SUCK at sucking. The push real well, thats why the pump is in the gas tank of your tow vehicle.

An easy solution is a small 2 or 3 gallon pony tank rigged to a low pressure pump that can PULL fuel.

I use a holley black pump to draw from the tanks and feed my pony tank which is mounted slightly higher than the efi pump. It feed the HP pump at 3psi.

An added bonus is you can use the LP pump to drain the tanks when its storage time.

Ted G, No secondary fuel pumps. I had only the water pump mounted fuel pumps on my Formula and they worked fine by themselves. I could estimate the fuel within 10 gallons in that boat and I never had a fuel problem in twelve years.

W J B, I think the rebuild/replace might be right. By the way, I grew up in G.P.P.

Airpacker, I like your idea, but I was hoping I could remain with stock plumbing. If not, that sounds like a " better than stock " solution. I for sure do not want to carry around 800 or 1000 lbs. of fuel just to make sure I do not suck air into the lines.

One other piece of info that may be helpful..............I always have to purge the air from my fuel system after I change the fuel filters or my 502 MPI's won't start. I use the hose from my pressure test gauge kit with the gauge removed, screw it onto the shrader valve, and put the open end into an empty plastic bottle. Have to cycle the key at least a half dozen times per engine and let the pumps go thru the priming cycle to get all the air out. Like someone else said..............those pumps do not like to pull, much better at pushing. That's why late model EFI vehicles have the pumps in the bottom of the tank submerged in fuel.

I agree with Ted G...1/4 tanks, no less and it's about empty. If I come off plane that low I sometimes stall a motor.
Idling into the harbor and watched the gauge drop like a rock.

REPO??? Did you check for sugar in the fuel tanks??

The early 500 EFI's did not have the seawater pump driven mechanical fuel pumps, just the electric pumps. In warmer climates, they had problems with vapor lock. Mercury made an upgrade kit with the mechanical fuel pumps for the early 500 EFI's. The later 500 EFI's had the additional mechanical pumps from the factory. Once you have been around the 500 EFI's for a while, you can spot the "later generation" 500 EFI's rather quickly as they had a couple of other hardware changes made at the same time that makes them easy to spot with just a quick glance. For instance, the early 500 EFI's had a straight rubber hose connector between the header and the tailpipe whereas the later (version 2) had a "U" shaped connector between the header and tailpipe. It is much more simple to remove the "U" connector than it was to remove the straight connector - you had to take the bolts out of the header and then wiggle it to get the connector loose at the same time. With the "U" shaped connector, you removed the connector and then had both hands free to deal only with removing the header, carefully. The oil dipstick on the early 500 EFI's has a curled end whereas the later 500 EFI's had the round ball on the end of the dipstick, although I have seen a few early ones that had the ball ends, but the header connector was still the straight piece. This is not a hard-fast rule, but a general observation that seems to be rather accurate.

funny I can run my 05 29 to e on fuel without concern . Have done it several times ...