PDQH2O

My injected Gen VI 2006 Mag 496 starts perfectly cold, runs well. After sitting for a couple of hours, it turns over fine but seems like it's flooded. It finally fires after about 15 to 20 cycles, then runs great after that. Fuel pumps are new, and there are no other known problems of any kind. The engine has only about 250 hours total time on it.

I've heard that it may be the fuel pressure regulator, but others say that would be rare. Some even suggest changing the plugs but that seems a little out of line at this point.

What say the 496 experts?

PDQH2O

Nothing? Is there additional information needed to help diagnose the problem?

The fuel pressure is consistently above 40psi at the rail so fuel does not seem to be the problem. Air is good as is spark. The combustion trifecta is there, yet the problem exists. One other symptom is that at WOT from take off, it sometimes hesitates for a second, then picks right up and is fine after that and runs well.

Blueabyss

How old are the plugs and what brand are they. How old is the fuel and the fuel watter seperator.

BUP

iTrader: (9)

Post your engine serial #

I take it your cool fuel is the GEN II set with the spin fuel filter on the front starboard side of engine ? Gen III cool fuel systems for Merc right around 2006 came into play and does not have a spin on fuel filter. All filters are in the fuel cooler for GEN III cool fuel set ups. They are totally different fuel system set ups hence the need to know what you have for a fuel system set up and engine serial #.

Next is did you scan the engine ??? - this is where I would check first - Next is when your engine is hard to start have you checked fuel pressure with key on and then when cranking engine and then at engine running thru out all rpms ? What are the fuel pressure readings during these fuel pressure tests ?

PDQH2O

Thanks for the reply. Here's what I know:
Yes, the cool fuel unit is on the starboard side of the engine, though I believe that the filter is internal. There is no mention of servicing the fuel system anywhere in the manual nor is there a spin-on separation filter, other than oil filter, on the engine. Seems kind of strange to me, but I know very little about marine systems.

My engine serial is 0W618453. Engine has not been scanned... yet, as that requires taking it to the Mercury shop and $$$. It's definitely on the list if I can't eliminate the other possibilities first.

Fuel pressure at the rail is between 43 and 46 psi running on hose water - no load, key on but engine off. Air temp is ~70 if that makes a difference. Interesting about checking at all RPMs. I will be taking my gauge on the next trip to test just that.

Really appreciate the help. You provided great information. I love working on the boat when I have to but would rather have it completely reliable.

Follow up: while vacuum testing the pressure regulator, this afternoon, I discovered that the two hold down screws were a little loose and allowed the regulator to be turned by hand. It didn't have a lot of play in it, but it did turn kind of freely by hand. The two o-rings were in very good shape and the regulator consistently held 10 psi.

Could the regulator being loose be enough to allow a vacuum leak or would it have to be a ruptured diaphragm to be a contributing factor?

Looks like the next step will be to set it up for a scan test.

BUP

iTrader: (9)

Possible vapor lock

bottom pad filter in the Gen III cool fuel. The most important fuel filter in the fuel system. Becomes restricted and can cause vapor lock to.

Any paint peeling inside the fuel cavities of the gen III cool fuel cell ? Common issue with these.

Did your gen III cool fuel get winterized properly ? They need to be drained completely 100 % - hate to tell everyone. That's why the new gen III cool fuel system comes with a blue drain in the front of it to prevent damage for freeze damage and so you not have to struggle .pulling off the back hoses. Even pulling back hoses that did not drain them completely unless you jack nose of boat sky high, Just saying and one hell of tip here. I replaced 3 of these alone from freeze damage at 1100 bucks a pop just for the cool fuel system this year..

when you crank engine over is your tach working for that engine ?

even if yes tach signal working - possible bad crank and or cam sensor or its connection or its circuit might have problem ie: wiring / pin and so on.

could even be possible IAC or any of its circuit to have a problem.

Try this and be prepared to pull back the throttle ASAP if the engine starts.

Move throttle to half position then crank engine does it start then

if not move throttle to full throttle position - did it start then ?

donzi matt

iTrader: (1)

BUP does the air drain system drain the cool fuel system? Reason I ask is because I did NOT drain mine this year, but I did use the air drain system, followed up by running 6 gallons of -50 antifreeze through the engine. Everything is fine this year, but I want to make sure I do it the correct way next fall.

BUP

iTrader: (9)

DM merc is on their 4 th improved with the Gen III cool fuel.

1 st was one bracket that held 2 water hoses in place with stud and nut on the back side of the cool fuel to be taken off and bow of boat sky high as it can go if all possible to drain the cool fuel completely.

The next improved version cool fuel changed to with to plastic barbs that screwed into back side of cool fuel and the water hoses attached with clamps to plastic barbs for easier take off to drain the cool fuel.

Then the next improved cool fuel changed again as Merc added a blue drain plug on the back side of the cool fuel to make it even easier to drain. Nope that still did not drain them 100 % unless you could put the bow of the boat sky high to help it drain..

Then its final change was to get rid of the blue drain plug on the back side of the cool fuel and put it on the front side of the cool fuel to make it easier to drain and to drain completely.

Merc had to do this as they had to warranty some new boats because the cool fuel could never drain 100 %. plus techs complained about. It does not matter the app nor the air system or not - The Gen III cool fuel cell has to be drained.

What saved you is running the anti freeze thru the system and if you not draining then you will have to do this completely and check the freeze protection of your anti freeze that you ran thru the cooling system and or the non closed cool portion. .

BUP

iTrader: (9)

latest Gen III cool fuel, its been out for a couple years now.

you can see the drain plug location on the cool fuel in the small image part # 3 showing the front of it.

http://www.marinepowerservice.com/Bo...3&block_nbr=45

PDQH2O

Again great tips. Fortunately, Southern CA really has no "winter season" where freezing is a concern. Off season is usually between 2 and 4 months however, the filter obstruction and peeling paint inside the box could be a problem that I haven't yet checked. Given fuel and additive formulations these days, I could easily see that to be a problem. I'm not sure that the fuel block has ever been 100% drained unless the shop did that as part of the fuel pump replacement.

The boat gets 87 to 89 pump gas. The only additives I run is STA-BIL at the end of the season and Lucas fuel system cleaner in the first trip and periodically during the season. Off season is usually between 2 and 4 months at the most.

I've checked the IAC and that looks to be OK. Everything is in place nothing missing or damaged.

The tach works well but I haven't yet tried the half or full throttle test. That will happen in a couple of weeks. If the tach were involved wouldn't it also affect cold starts? Just curious what part the tach might play.

Also hoping that there will be a code or two that leads to the problem and solution.

With respect to DM, my air drain system has two plastic lines that go to the water pump and have the barbed quick connects. Gotta be real careful removing them so as not to score the lines, then make sure they are properly seated on reinstall.