Here is my story....bare with me its long winded but starting to run out of patience. My boat is a 2001 Baja 272 with a 496/425HO with 100 hours

2 weeks ago - Went to poker run and put boat in water and fired and stalled. Tried to re-fire and only turned over and didnt start. Come to find out electric fuel pump not kicking on and priming. Took boat out of water and brought to a mehanic at poker run. Disconnected the relays on top of the motor and blew on them and reconnected. Fuel pump went on and boat fired. Put boat back in water and fired up at dock. Went to join run and got and plane then started pulling throttle back around 3000 rpm when motor started to detonate and pop/bang. Boat went off plane to idle. Tried few more times and same result. Went back to dock and changed fuel/water separator. Took boat back out and everything worked great rest of the day on a 70+ mile poker run. Ran boat next day burned through all fuel and ran great.

1 weeks ago - filled boat with 70 gallons mobil 89 octane and used stabil marine stabilizer in fuel. Pulled boat 200 miles to Alex Bay and fuel pump did not kick on when we got to launch. Took apart relays again and this time filed them with nail file and used compressed air to blow out debris. Fuel pump came on and boat fired. Used boat all weekend and went to Canada with no issues.

Last Night - Installed 3 new relays and used di-electric grease on all relays along with all other harness connectors on top end of motor. Ran boat with muffs and fuel pump came on and no issues.

Tonight - Put boat in water and fired up and idled out. Went to get on plane and motor started to spit/sputter and detonate and went to idle. Did same thing 3 more times when trying to plane but would idle OK. Changed fuel water separator again and primed motor few times. Motor started but would not run higher than idle and motor sounded like it was running on 6 cylinders and would diesel at idle and die. Got towed back to dock and back on trailer

Did my guardian mode kick in?

Assume one of these 3 issues are possible?
- Low pressure or high pressure fuel pump has now gone bad?
- IAC Valve bad
- Crank trigger bad

I assume my best bet is to bring to someone with a scanner and hopefully now will get a code to figure out what is wrong?

Any and all advice is appreciated!! Trying to get fixed for next weekend to go back up to Alex Bay.

Getting frustrated here and need some advice!

Wes

I had a similar issue years ago with a Crownline 225 w/VP 496. I was plagued with fuel pump/starter relay issues for the first year. I would have to pull and replug the relays a couple times a year. I finally ordered a whole new fuse block minus the relays and fuses, pulled the old one and replaced all the fuses and relays and wahlah, no more problems. Turns out the contacts inside the block had fallen slightly and would not make contact all the time with the relays. IIRC, Merc and VP use the same brand of fuse block, this may be part of your issue with the relays.

Might want to add MAP sensor to your list. I had one engine (525EFI) do something very similar to what you described ... local shop couldn't get it in to scan/repair for several weeks, but said it was "probably" IAC, so bought a new one and had it overnight-ed. Installed new IAC and had same problem (minus $250 for part and expedited shipping). Boat went into their shop a couple of weeks later and problem was MAP sensor. So now I have a good, used IAC sitting on a shelf in my garage.

i would check the main system plug on the back of the motor and clean it real good

look... please... do yourself the biggest favor you can possibly do and buy yourself the FACTORY worshop manual ( not some aftermarket manual... the FACTORY manual) . then follow the simple step by step diagnostics for trouble shooting each component in the injection IF you believe thats where the problem is. shotgunning these issues by just " get an iac" no... get a map sensor... " no get an ecu " are just absolutely flat out wrong.

the trouble shooting flow chart is easy. you need a volt meter and the abilty to read and follow directions.

two things will be true when you are done...

1) the boat will be fixed

2) you will have a solid and fundemental understanding of how the system works and what each component actually does.

the second one will save you lots and lots of time and money in the future.

for the record, i took ALL the relays out of my boat and just let the ecu control the prime time. i had seperate switch for fuel pumps on and ignition on then start as a 3 position mil spec switch all driven by the key. that got rid of all sorts of junk and potential issues like yours.

i'm not suggesting that's your fix. your fix is to intellegently id the specific component failure and fix that and the boat that ran perfectly before will do so again... but just blindly throwing parts at it is simply a dumb ( and expensive) way to proceed.

That was kinda my point ... "probably" IAC, etc - $250 for a part that I didn't need. Once it was scanned, they knew what it needed ... and they needed another $300 out of my pocket.

On an 01 496, change the crankshaft sensor as a matter of whether you think it needs it or not if it has not been previously changed. Go to regular parts house and get one for a 2004-2009 2500HD GM truck with an 8.1L engine.
Next, check the fine inlet screen on behind the inlet fitting on the primary lift pump mounted on a bracket under the fuel water seperator. These are very small and fine and clog very easily with furel and fuel tank debris. Listen and make sure both the primary lift pump and the secondary Coolfuel hgh pressure pump are operating. Next, put a fuel pressure guage on the engine and measure the fuel pressure at idle and at higherr rpms if you can get the engine there.
Did the engine alarm at any time during these stalls, backfires and power reductiuons? You need a scan tool to se if there are any active fault codes, keeping the engine in "guardian" state where depending on the powerr level reduction it can be idle limited and will run on 4 cylinders very roughly.

Regards,
Ray @ Raylar

Heres an update on todays findings and answers to some of your questions. Thanks to everyone for your input and Ray especially...i understand you are the 496 guru.

-I changed the fuel water separator out on the water when the boat died (had a spare on board) but didnt have any fuel to put in it and was afraid to put in the fuel from the old one i took off. I primed it with the ignition 5 times prior to starting in the water yesterday. When unscrewed it today and it did not have hardly any fuel in it. I filled it with fuel and reinstalled

- Pulled the plugs and 3-4 of them did not look good. Very black, even the electrode and internal porcelin and smelled like gas and wet. These plugs were installed about 20 hours ago. I reinstalled a new set of plugs today

- Cleaned the main terminal with wire brush and all connectors. Reassembled and tightened appropriately

Put muffs on and boat fired right and sounded great and healthy. Water coming out of the pipes good and responsive.

Taking to my friends marina tomorrow who has a scanner to look at fuel pressure, fuel pumps, crank sensor, and check to make sure fuel lines aren't clogged at screens.

Hope this resolves and successful test run later this week on water under load to see if things are resolved.

Wes

Ray -

In regards to alarms. This is my first boat so this is all new to me. About 3 weeks ago before this started a loud 2 beep sound started as soon as the boat was backing away from the dock. The mufflers were off and open exhaust. I could not figure where it was coming from until i opened the access door under the helm where the fuses and wiring was at. The beeps were coming from here. Oil pressure, water temp, drive oil and depth of water all were OK. Disconnected all fuses on panel and reassembled and alarm went away. Boat ran great all night and strong.

Last weekend i ran the boat with the mufflers on and faintly could here beeps coming from under the helm again when heading back to boat launch. If the exhaust was open i would of never heard this alarm as it was very faint.

Other than that....no alarms or beeps

Had the same problem with high pressure fuel pump not always turning on or staying on with '02 496. Tried everything you tried in addition to replacing the high pressure fuel pump under warranty. Still had the intermittent problem. By dumb luck, discovered the pins in the electrical connector on the wiring harness that connected to the fuel pump motor were bent and not making good contact. Replaced the connector and the problem was solved.