2003 Crusader V8 Fuel Injected engine sputtering when hitting waves and turning

So I am having a problem with my 2003 crusader inboard fuel injected V8 engine. When I hit waves or when I turn abruptly the engine sputters and drops about 1500 RPMs. This happens only when there are waves or if I turn sharply. It the water is flat the boat runs just fine with no problems. I have checked all electrical connections for grounds and ignition wire set up and have run the engine on a external tag to eliminate fuel issues. My mechanic who takes care of my other small boat engine is mercury trained and is checking into this for me as a favor. He noticed some issues with the distributor cap so I've ordered one of those to replace, but this has us both stumped. It sounds like the key switch is being shut off and then turned right back on, but it only happens with sharp turns and when I hit waves under load.

Any help or insights would be so appreciated!

Maybe check this:

MEFI-4? If so, there may be an issue with your fuel pump relay. Edit: I wrote this for fuel pump relay, but it could be your ignition relay too. Fuel pump, ignition, and start relays are the 3 on engine. If you saw your gages quit too, its ignition, otherwise likely fuel pump.

There are 3 relays on top of engine, port-side. One of them is the fuel pump relay. This may be your issue. The 4 wires leading from the relay sometimes break inside insulation over time from flexing. You may need to buy, or make-up a pigtail with the relay socket and 4 wires.

To test; Turn key on, do not start, you should hear fuel pump kick on then stop when pressure is up. Now at that point, wiggle the wires leading from the fuel pump relay. Go all the way to where they join up with the rest of the engine harness (about 12 inches or so). If pump kicks off and then you hear it turn on again, that is very likely your problem. To absolutely verify after that, take relay out. Then with your meter test on socket connectors that connection is lost intermittently by wiggling wires again. Obviously, pump will now be out of the circuit, so you will not hear it.

If that's it and you want to make up a pigtail harness, post back up and I could send link to vendor to obtain relay socket and crimp connectors. You'll need an electronic-style crimper that rolls the connector as it crimps. Also, if this all has proven true, for the repair it is best to solder the new wires into the existing harness. Knowing how far back to cut the old wires is a challenge. Farther away from relay increases your odds of cutting out the broken wire.

Good luck, Noel.

your boat has accumulated over 20 years of 'aging'...so it could very likely be a marginal electrical connections.

I'd be inclined to start with the relays...and then the ignition switch...many times, you can use a dead blow hammer to simulate wave interactions...

If you have twins, you can usually use the 'good side' for parts interchange is you suspect one.

I would also check the main engine harness connector...

A bit of an update. So I have made sure this isn't a fuel problem and have used an external tank which changed nothing. Then changed distributed cap and rotor and that didn't do anything. Checked fuel pressure and that stays within specs when the issue happens. Finally checked timing and during the time the engine sputters you can literally see using a timing light the engine have power, then lose it, and then immediately get the power back so we are trying a change with the plugs and wires and the ignition coil. The boat has constant power feeding the coil during the time it's spitters so that's where we are at.

based on your update, I'd be inclined to get a scan tool hooked up and see which signal is dropping out.... Pretty certain your engine has the 'crab cap' (HVS) distributor which means the ignition system is driven by the ECU with no timing adjustment..

Plugs and wires seem an unlikely cause to issue you described above. I suggest that you tie her up at the dock, start her, and start wiggling wires on the harness. Something is kicking out on a wave or bump.

ALSO: You may also see if an auxiliary pigtail from the engine harness had made its way into your bilge. Maybe a transmission temp sensor wire, or some other not-used auxiliary wire from harness is laying in bilge.

Bilge water will rush over wire when sea conditions change and "make" the connection (like the switch being closed). That will put your engine into "safe mode" where RPMs drop. Your immediate recovery is to go to idle, and engine will disregard "fault", then you'll be on your way again-until it happens again. So take a peek to see if a stray pigtail is laying in bilge. Zip-tie it up high and dry and retest under same sea conditions.

Good luck, Noel.

Well the new coil and wires didn't do the trick either. Yes, I know some suggested it wouldn't, but I had to rule it out. Thus far i know this is happening under load. It occurs only after 2500 rpm and when you turn the wheel hard or hit a wave. The engine has been scanned and it's not throwing any codes when the fault happens and the fuel pressure stays steady and doesn't drop. Also the timing does not skip as that was checked. Going back out again later this weekend to check that there are no wires in the bilge and also to ensure that behind the steering column where all the wiring is connected that there is nothing happening there when this occurs. My mechanic who is a mercruiser tech and not a Crusader mechanic has offered to take a look, but he is stumped at this point as well.