496 HO issue... Please help!
 

Hello... I wanted to say first off that this forum is awesome. I've read quite a few threads and I'm very impressed with the activity and the amount of members.

Here's my problem... I have a 2002 Formula with a Merc 496 HO with 112 hours on it. After I run the boat on plane for approx 5 to 10 mins around 3k or so, not WOT or anything, she starts to cut out, backfire, then stall out. Gauges all read normal. I get just a single beep at startup and nothing when it quits running. I can let it sit for 20 mins and she'll fire right up and run like a champ then... Same issue. I've replaced the plugs and low pressure fuel pump with no change in performance.

The boat was trailered to MI from north Tx... It ran fine down there on a small lake before I brought it back. Dont know if the long haul caused the issue or not. I've also pumped the fuel out of the tank and started fresh.

I think it's a fuel delivery issue but i dont know if its electrical or mechanical? Any feedback would be great!

probably need to take the fuel rails off and clean them out..i'm having fuel delivery issues to, and my rails were full of crud and water... sounds like your high pressure pump could be getting hot and not flowing enough fuel as well

Paddles:

I've seen a few such fuel situations in quite a few early model Merc 496's. In those cases it was caused by the inside of the injector fuel rail rusting inside from moisture in the fuel system especially from sitting in winter to summer temperature variations. You have a 2002 engine with only about 100 hours use and that means it has sat way to much unused!
First put a fuel pressure guage on the Schraeder valve on the fuel rail and check the fuel pressure at , key on engine not running, engine on idling, vacuum line disconnected from fuel pressure regulator on Cool fuel regulator under the black plastic cover and then at speed when the engine sputters, and stalls.
The key on fuel pressure should be about 43-45 psi and about the same when engine on a idling with vacuum to the regulator pinched off or disconnected and should stay up between 40-43 psi when running at 3000 rpms. If there are issues with the fuel pressure from these readings then the problem could be in the fuel filter, fuel pump side of the system.
If however these readings all seem to be good then it could be the dreaded rust in the fuel rail problem! The check for this involves removing the fuel rail and injectors and carefully removing the injectors, giving a good look up inside the fuel rail for signs of rusting and debris. When take the injectors out of the rail, turn them upside down over a nice white paper towel and spray some good carb cleaner up into the inlet side of the injector where the fine screen is and then tapping the injector down onto the towel and see what comes out. If you get any real debris out of the injector this way you should have the injectors cleaned and re-flowed by an injector service shop or replace all the injectors. You will also have to replace the fuel rail itself with the newer ones which were finally plated by GM in later models to stop this problem.
I am not saying this is definitly what is wrong here, but with early 2000 Merc 496's that sat alot it has been a big problem.

A sitting unused for long periods marine engine is a problem waiting to happen.

Hope this helps and let us know what you find or figure out on the engine and its problem.

Best Regards,
Ray @ Raylar

Thanks for the replys... I put the fuel pressure gauge on and with the key on it reads 43 psi and with it running the needle viberates around 42psi. I took it for a run and made it about 1/2 way to the middle channel from metro and it quit. I was alone so i couldnt read the gauge while driving. I'll take a friend along tomorrow. My question is, if it were something in the fuel rail... rust, debris, ect.... Wouldn't it run crappy all the time? I'm leaning more towards a hp fuel pump heating up and causing the issues.

I'm still going to pull the fuel rail and injectors just to verify it's not the issue and to eliminate the possibility.

Is it going into guardian mode? Do you have access to a scan tool?

If it's a fuel pump the fuel pressure will drop and be low when it starts to quit. Sometimes debris in the injectors slowly drops back into the injector screens when fuel is flowing thru the injector and then when it's enough blockage at a certain higher rpm its just like cutting fuel off to the injector.
It could also be a problem with the crankshaft sensor as early Merc 496's had many failures and sometimes the sensor stops working at certain rpms. You can also try cleaning and replugging all sensor plugs and connectors and cleaning and tightening ground wires as loose or bad coonections there can show up at certain rpms and vibration levels with intermittant disconnection and ECM shut offs.

Best Regards,
Ray @ Raylar

From what i'm being told guardian mode is more of a reduction in total power rather than a total loss or shut down/ stall. I have had a service shop hook up to it with a pc, low pressure fuel gauge and high pressure fuel gauge while out on the water which is how i arrived at changing plugs and the low pressure fuel pump. But they never experienced the shutdowns i am.

Ray, the problem isnt occuring at certain rpms, i can rip all through the revs and different speeds across the lake for a certain amount of time without a flaw, it seems to be more temp driven, but i will know more in the am when i take the fuel rail and injectors off.

Where abouts is the high pressure fuel pump located? I've googled images and the only results that seem to populate reference the low pressure pump that is located behind the water/fuel seperator.

The high pressure fuel pump is under the black plastic cover of the cool fuel unit which is located on the opposite side from the low pressure lift pump by the side engine mount.
I don't think what you are describing is a guardian shutdown, but either a fuel cutoff or electronic/electrical shutoff or interrupt.
Hope you find it quickly and its fairly minor. That low engine hour usage over so many years is the ultimate culprit.

Best Regards,
Ray @ Raylar

Thanks Ray

I bought the boat last month from a place in northern Tx. I had a survey done where they spent over an hr on the water with no issues. I then drove down to pickup the boat and at that time i also took the boat for a ride with no issues. I starting to believe the long haul back on a the trailer with an 1/8 tank of gas sloshing around caused the issue. The gas probably broke up all the sediment in the tank. The seperator was full of crud so i imagine everything after the seperator downstream still will have some debris in and around it. I'll know soon, heading to the boat now.

If it is electrical, where should i start? I've gone through the connection points already.

Thanks again

Well... The injectors and fuel rail had debris as expected... I cleaned both really well with carb cleaner and re-installed. Then i turned the key to the on position and purged the fuel rail multiple times with my pressure gauge to help eliminate any air. She fired right up as expected.... Took it for a ride and still the same issue... Dies after a short run. I was able to grab a few readings of the fuel pressure gauge at 3000 rpm running fine and it read between 38-40 psi when it dies it def dropped somewhere between 25 and 30. I guess i will have to order a hp fuel pump and try that.

Im just glad its the beginning of the season.

Fuel pump / s also maybe fuel pressure regulator

Check and make sure your ECM harness plug is good and tight making good connections. Check ground on back of block.

In other words before randomly throwing money at it check the simple things first.

Question... The 4"-5" round cylinder that is approx 14" long that spands in front of the engine just under the intake, what is that? I noticed that the one side of it that feeds into the top of the block was getting very hot. Much hotter than the other side. The hoses felt fine on both sides.

I will check the grounds and re-check the electrical connection points tomorrow.

Thanks again for all the feedback.

I had crappy gas destroy the fuel filter, fuel/water separator, AND the fuel pumps on BOTH of my 496HOs, 2003 vintage, a few years ago.

After replacing all 6 components, all ran great. Then I had a drive go bad. Still missed the poker run.

The cap it off, later than night I flipped a car into the woods and put myself in ICU.
That was a pretty ****ty weekend!

I'd recommend replacing the fuel pump, and also the inline filter.

Heat exchanger.

You know this is sort of old school here but it sure sounds like a clogged fuel tank vent to me. After running about 15 minutes a partial vacumn is formed in the tank causing a lack of flow. After sitting the pressure equalizes and all is well again. See if a dirt dobber has built a nest in the vent line. You should be able to take the fuel cap off and easily blow through the vent. Alternatively you can take the cap off and run it and see if the problem persists. Don't do this if the cap is in such a position that water can enter during operation.

Good luck,

Dan

Thanks Dan,

I did try running without the gas cap on a few days ago and it still acted the same.

I've followed the fuel lines from the water seperator to the low pressure pump, then under the block amd around to the high pressure pump, then up to the fuel rail.... I don't have a fuel filter?

I'll have to remove the panel going towards the tank and see if its hiding back there somewhere.

My inline fuel filter is about 12" in front of my fuel/water separator, but that's how my boat was rigged. I'm not sure if yours is the same. But, when I did take mine off after all my stuff went south, it had so much crap in it that it rattled.

Thanks,

Is there anything inside the heat exchanger that could stop water flow or would need serviced?

Replace the crank sensor. I'm not guaranteeing it by any means, but I've seen it over and over again in the automotive world. Not that expensive and it eliminates that possibility. Just be careful not to break it off in the block.

Why don`t you listen to RAY??

Maybe, but it really doesn't sound like you're having cooling systems problems. Or are you?

Sounds like moisture and crud buildup has damaged the fuel delivery system.
Just a few things to check and do, recheck the inlet screen on the low pressure pump inlet for more debris or clogging.
If the fuel rail is rusted inside, replace it, the ehtanol fuel and moisture will keep it rusting and it will damage the injectors again.
Your fuel pressure is dropping when the motor starts to pull back so that means something in the fuel delivery is doing one of two things, one flowing lower volume whcih can drop pressure or something is dropping pressure which delivers less volume.
Either one will do what you are seeing with the engine.

You can also check that crankshaft sensor as I mentioned , but be careful when turning and removing it if it rusted in place as you can snap it off and thats a big problem.

Best Regards,
Ray @ Raylar

I am and have been....what makes you think I'm not?

I've contacted AIS Accurate in Az and will be sending the injectors to be flow tested, cleaned and rebuilt. However, my concern is not the injectors at this point. I'm thinking that if they were restricted enough to cause an issue then the boat would not run at all at higher rpms where more flow is needed. Yes it's obvious that the filters inside the injectors will have debris in them, no doubt about it... but I would be hard pressed to think that the injectors alone are the culprit due to the performance I'm experiencing.

I've also called into a few places to get pricing on a new/upgraded fuel rail.

Thanks

Well...I'm not dead set against having some sort of cooling/temp issue. After all, once I run for a while the motor and everything attached to it does "warm up" to some degree and that's when the backfiring/ shutdown occurs. But the temp gauge never goes above 163 deg.

I did read where someone had a t stat replaced and the carrier was left out which allowed water to flow past it to the sending unit for the gauge, but never opened up to allow water to flow thru the block, causing the issue... I haven't pulled the t stat yet.

My question is still, what all is involved with the heat exchanger? If there is something internal that acts like a t stat... opening and closing based on temp, then maybe that component is failing which is causing the one side of the exchanger to be much hotter than the other.

I believe you're reaching here. 163 is a good number and one side of the exchanger is naturally warmer duriing normal operation. There's nothing in the exchanger itself but two sets of isolated tubes. The T-stat is located at the coolent inlet port of the exchanger on the underside. If the engine warms up from cold to 163 then stabilizes the T-stat is working as it should.

Check that crankshaft sensor issue also.

Best Regards,
Ray @ Raylar

My issue with the crank sensor was not the same as yours, but I would also suggest looking into that. Here was my experience.

http://www.offshoreonly.com/forums/g...t-no-code.html

The local shop has a crank sensor in stock so i'll try that. I'm just gun shy to throw a hp fuel kit on it right away... Afterall I'm being quoted $420, and i dont know that is for sure my issue. But... B.O.A.T... Is was it's turning out to be.

Also called Formula today and they are researching any issues/warranty info I may have based on the HID and serial number of the engine.

Update:
Today I replaced the hp fuel pump and took it for a ride.... Same problem,
I did spend a lot more time watching the fuel pressure gauge and I was able to keep the boat running by throttling back as soon as the pressure began to drop. The pumps would catch the pressure back up to 38 psi at idle then I could throttle up again for a short period of time. I noticed a huge difference in the noise coming from the booster pump when I lost pressure... Almost like its being starved of fuel.

My question is, what all makes up the pickup portion of the fuel system? I see on the top of the tank where the fuel line from the booster pump attaches there is a 90 deg fitting... Is the pickup tube attached to the bottom of this fitting or does it sit just below this 90 inside of the tank?
Also, does the pickup tube have a screen/ filter on the end?
I'm thinking that something is blocking the pickup inside the tank. My plan is to run with a separate fuel cell to rule out anything inside the pickup/fuel tank. Then if it runs without a problem I'll know it's nothing after the tank.

Any thoughts?

anti-syphon valve? is that spelled right?

If the fuel pump is starving it's pretty easy to back track and fix it. 38 is still low. pull the fuel line off coming from the tank and put some air pressure to it and see if there is something in the line or pickup. Depending on the location of sender and pickup, you might be able to use a video scope and peek at the end of the pickup itself..

Post 32 is assuming you already tested BOTH fuel pumps, filter etc.

They've both been replaced...

The stand pipes in the fuel tanks clog up all the time. Could be that simple.

How do I get to them?

Not sure what model Formula you have, mine is an SS. I think most of the SS's that have the in floor storage compartment will have a access panel in the bottom of the ski storage, Open that and it is right over top of the fuel sender. Very easy to access

Got to the pickups but I'll have to drill an access hole in the ski locker to remove them completely. I see i have 2 pickups, one for each engine? Anyone know if I can tee the two together and put a raycor inline before the booster pump? Or will that supply too much volume?

Just thinking i could reduce my clogging chances by using both...

Have your issues been resolved????

I have been going through this problem for the last 2 weeks . I replaced and checked everything . I took apart booth of my filter housings .(spin on type ) I found a bee lodged in the last barbed fitting that I checked. Wtf. seems to have cured it.