I know this may sound dumb, but I could not tell from your above post, Have you tried putting like 5 more gallons of fuel in the tank ?
Chris

yes ^^^^ that's why you use a remote fuel tank to make sure where your problem is the boat side or the engine side.

Process of elimination a lot of times working on boats is the key. A crack fuel pick up tube or broken off in the fuel tank is the thought here - but that does not take out of the mix a collapsing rubber fuel line from the fuel tank or a bad anti siphon valve and so on.

A. Remote small outboard fuel tank with primer bulb and new fuel line is a great tool to have. Plus very usable for boat / engine winterizations. one the best 60 bucks you will ever spend. and of course the cost of fresh fuel to fill it. .

ON THE SCAN and fault codes ---- What is your available power showing percentage wise ? if it shows 100 percent you are not in guardian mode.

Next as Mark aka MUC said to change the breaker for the fuel pump actually I would change that and the breaker for the fuel injectors. You have 4 breakers on top under the engine hood - so pull the engine hood off. and you will see the 4 breakers.

I just fixed one that ran as an engine miss and kept getting worse --- then stalled completely and would not restart - It was the fuel injector breaker. Like I said there is 4 of those breakers on the top of the engine under engine hood / cover.

BUP The scan at the time said 100% Power availability. Looks like my fuel gauges are reading that I still have fuel when in fact the tanks were empty!! After I filled the tanks and put it in the water before I ran the scan at the beginning of this thread, I had tried to start it about five times and I think the reason it wouldn't run is that the fuel didn't have enough time to prime the fuel pump or rail. I had never run my boat very much less then a 1/4 tank and always try to keep it above 1/4 at the end of a day of boating.

After seeing just air in the fuel rail when I was testing it in the shop, and then the fuel pump finally primed the system, I put it in the water today and it ran. It started up and ran a little rough for about 3 seconds then smoothed out. Got it up to temp and it rev fine and sounded normal. Cleared faults and everything was clear.

I agree on changing the relays, are they Mercury specific, as I don't want to buy a cheap part?
Also should I install a fuel pressure gauge on the engine?. Where would I plug into the rail?
One last question, while running at 3,000 and running out of fuel, could that do damage as far a lean condition?
I can't thank you guys enough for the help, I feel bad as I could have figured it out on my own, but being out of gas was not what I thought. I really though it was worse then that. Thanks BUP and all the other members help!!

Oh, BUP I forgot to ask this, my tach will read some times 200 to 1000 rpm higher at times, not all the time just intermittently when it happens but it has been doing since I bought it three years ago. Any idea on where to start?

Remember that your fuel tanks are "V" shaped at the bottom. Your fuel gauges only register linearly; and when it get's down toward the bottom it's not a true reading. If you are below 1/4 of a tank; you might as well be empty.

Fuel gauges on boats are never right, 1/2 tank means fill up or be stranded.

again that's why one uses a remote 3 or 6 gallon fuel tank with a PRIMER bulb inline with the fuel line. Just like what small outboard boats use. The primer bulb, using it is the way to prime the fuel system plus used for testing -- separating the complete boat side fuel system. . And again a great tool for engine / fuel system lay ups / winterizations. . 60 to 90 bucks the best under a 100 bucks tool a boat owner can buy.

Do not buy cheap primer bulbs thou - that will bite you.

I would not install a fuel gauge on your 496 rail. When driving your not going to see it anyways plus its another leak and or air point in the fuel system. U have a inline shrader valve - a simple laymens TEST is to unscrew the cap and depress the valve - if fuel sprays out (watch out for that and cool engine NOT HOT - you can shield it ) then you know YOU HAVE FUEL UP to the injectors. Again just a simple laymens test . It comes in handy out on the water and NO start.

My thoughts:
1/2 tank means you better know where your next fuel stop is.
1/4 tank means you better have it in direct sight

Old waterman's rule:
Full tanks measured in thirds:
1/3 to get there
1/3 to get back
1/3 in reserve

My thoughts on fuel sending units.
When ordering a new one or adjusting a replacement one.
Dont measure the depth of the tank like the instructions tell you to, measure the length of the fuel withdrawal tube and use that dimension instead.
I have worked on more than a few boats that the end of the dip tube was 4-5" from the bottom of the tank.

a lot of the parts on your engine are manufactured by someone other than Mercury, so yes you can can get the same part from other suppliers.

BUT, let me tell you about one of the Mercury Marine factory classes I attended many years ago.
We were discussing impellers and one of the other students asked why he should buy Mercury impellers instead of Sierra brand as he had heard from Sierra that they got them from the same supplier. One of the other students spoke up and identified himself as a MerCruiser engineer who was sitting in on the class as a refresher. He told us that at that time Sierra did indeed buy the exact same impellers as Mercury Marine. BUT that as part of Mercury's Q/A testing of parts they receive from outside vendors they were currently rejecting 30% of those impellers. He asked us did we think the vender was scrapping those thousands of impellers or selling them to a low cost supplier like Sierra?

This is one of the reasons that genuine MerCruiser parts seem so expensive.

Are there times that you should consider aftermarket parts? Oh ya. But remember it's now your job to do the Q and A.

There are some people in this business that have spent a lot of time on this (BUP is one of them), they have their own parts manufactured or source them from the OEM vender and do their own Q/A.

I mostly just go to the local dealer and get what I need because in the long run it really doesn't add that much to the cost of boating. But in some situations, like MCM spark plug wires for a 496 ci. I just can't justify that $$$$$ to my friends and family.

My fault for breaking my 1/4 tank rule that day, We just went way up town and then had to drive up river into the wind to the furthest launch that I put in at. BUP I thought the same thing with just pressing the valve to check on fuel pressure in the fuel rail if this ever happened again. I do have the portable tank set that you spoke of and that is because of reading your posts over the years. I have had about three other fuel problems on boats and have learned from each, one bad pump, one way valve pulled, and the best one was this..
I had a 2 year old boat and went on a week vacation and the second day in to the trip the boat just dies.I tracked it down to a electric fuel pump. Found one an hour away and installed it, still no fuel. So I think that the fuel pickup, plugged line, or line problem some where and work in the hot sun for four hours and have the tank access hole open and I can hear bubbles, what ?? so I remove the pump and the NEW pump from Mercury is wired backwards and was pumping air in the tank!!!! WTF
SO I cut the wires and reversed them and I"m back on the lake. Replace but inspect....

Anybody know why my tach would read higher rpm sometimes? Would it be the tach or the crank angle sensor?