Momentary engine cutoff ... stumped

[DaltonGang]

I have 2 8.1 496 engines. Low hours and 5 years old.
I've asked this on a FB group but got a huge variety of possible causes but nothing concrete so I'm asking here just to cover it all.

My boat runs perfect for 20 minutes at no wake zone. I get to the ocean and open it up to 2500-3500 rpms. After 10 minutes or so the starboard engine dies and starts within literally 1 second. I feel a quick power surge and see the tach drop from 2500 to 0 and back to 2500 almost instantly.

then it does it about every 5 minutes and even when I slow down. The ignition buzzer beeps every single time also. It's not the warning, its the start up buzzer. One day I took it out and it never did it at all after 2 hours of cruising around. This last Sunday, did it again. It has to be something electronic. It's not fuel related and the engine runs perfect.

I don't want to assume but it seems like at its peak running temp is when it occurs. I did finally stop it for about 30 minutes and floated around and then got it up to speed again and it did fine for about 10 minutes again. I went down to engine bay and wiggled every wire I could get my hands on. Cannon wires, ignition switch, sensors, batteries, grounds, computer harness. Nothing made it occur.

Things I will try next
*Switch engine computers and see if port starts doing it
*taking cannon plug apart and look for corrosion
*possibly replace neutral safety switch??
*see if alternator wires are shorting on something
*replace engine temp sensor
*replace oil pressure sensor?
*replace ignition switch if I can figure it out (has like 10 wires coming off of it)

Anyone else experience this? Any other suggestions?

 

[hughespat57]

nuetral safety unlikely it only prevents cranking the starter in gear

however another member recently had a similar issue on a 4.3
Main Battery cable at starter corroded, burnt and loose

 

[CaptRonn]

Check the circuit breaker for the ignition, it could be going bad.

CB's going bad are usually intermittent in nature.

 

[DaltonGang]

Check the circuit breaker for the ignition, it could be going bad.

CB's going bad are usually intermittent in nature.

Interesting, haven't heard that yet and its easy to test. I'll switch circuit breakers from engines and see if it happens on port instead.

 

[tdschafer]

I had a similar issue with my '97 330 a couple of years ago. Had my mechanic stumped as it would be fine cruising around for about 10- 20 mins and then pffffttt.....starboard engine would die. It would start back up after 5-10 mins & I was able to run back at about 2500-3000 rpms but if I opened it up, it would die again. They originally thought it was the ignition coil heating up & failing. When that wasn't it, they swapped ignition modules. They were also convinced it was electrical as you could smell gas fumes. Anyway, it turned out to be the fuel line to the motor. Although they were CG rated for the ethanol gas, they failed. The inner lining was separating when it got warm and the fuel pump suction collapsed it choking off the motor. They tested it with a small external fuel tank they ran to the fuel pump & it ran well. Replaced all the fuel lines & never had a problem since.

 

[DaltonGang]

I had a similar issue with my '97 330 a couple of years ago. Had my mechanic stumped as it would be fine cruising around for about 10- 20 mins and then pffffttt.....starboard engine would die. It would start back up after 5-10 mins & I was able to run back at about 2500-3000 rpms but if I opened it up, it would die again. They originally thought it was the ignition cool heating up & failing. When that wasn't it, they swapped ignition modules. They were also convinced it was electrical as you could smell gas fumes. Anyway, it turned out to be the fuel line to the motor. Although they were CG rated for the ethanol gas, they failed. The inner lining was separating when it got warm and the fuel pump suction collapsed it choking off the motor. They tested it with a small external fuel tank they ran to the fuel pump & it ran well. Replaced all the fuel lines & never had a problem since.

thanks for the reply. That issue to me does sound like fuel. Mine is definitely electric. I had all my fuel lines replaced last year, fuel filters, etc. All with the latest fuel line that ethanol won't affect. I think my only course of action is buying the cheap stuff and replacing it. Like sensors, ignition switches, etc and maybe I'll get lucky. I'm going to switch engine computers also and test it. I'll clean all battery connections, any wires that may have corrosion, and on and on. I got my work cutout for me but hoping I get lucky and find it with some easier tests.

 

[CaptRonn]

My problem was the strbd engine would shut off and not restart without engaging the emergency start and keeping the emergency start switch held down. Release the emergency start switch and the strbd engine would quit.

I traced out all the wires and continuity checked. Replace the start switch on the helm. Cleaned all contacts. Yet it still happened.

So then I looked at what was in line of the strbd ignition wiring. Basically it goes through a Carling 10A circuit breaker then a keyed on/off switch then to the helm.

Oddly enough, if you turn off the CB in line, then go to the bridge it duplicates the problem I was having. I could start the port engine, then by engaging the emergency switch and hold it down start the strbd engine, and once again if I released the emergency switch, the strbd engine quit.

I have since replaced the 10A Carling CB in the ignition line. Back when I was doing aircraft electronics I have seen CB's that on occasion would start to have intermittent problems (dropping connection without tripping). I have assumed that was my problem.

 

[DaltonGang]

My problem was the strbd engine would shut off and not restart without engaging the emergency start and keeping the emergency start switch held down. Release the emergency start switch and the strbd engine would quit.

I traced out all the wires and continuity checked. Replace the start switch on the helm. Cleaned all contacts. Yet it still happened.

So then I looked at what was in line of the strbd ignition wiring. Basically it goes through a Carling 10A circuit breaker then a keyed on/off switch then to the helm.

Oddly enough, if you turn off the CB in line, then go to the bridge it duplicates the problem I was having. I could start the port engine, then by engaging the emergency switch and hold it down start the strbd engine, and once again if I released the emergency switch, the strbd engine quit.

I have since replaced the 10A Carling CB in the ignition line. Back when I was doing aircraft electronics I have seen CB's that on occasion would start to have intermittent problems (dropping connection without tripping). I have assumed that was my problem.

this is one of the first things I'm replacing. I need to find the exact CB that I need. I may just swap port and starboard for testing instead of buying one but I don't know. I have ignition switches on order because they are cheap and easy. The CB was my next thing. The odd thing (I could be wrong) is it seems to only do it once fully hot. It's strange that its fine for 30 minutes until I crank it up to 2500-3500 rpm. (although it should be at full running temp after 30 minutes but its never at a load just putting around) A few weeks ago I went 2 hours without it having an issue then last trip it started again. Same route, same weather, etc. Although this last trip had rougher water. Anyway, I'll eventually get it figured out...hoping sooner than later so I can enjoy the summer.

 

[CaptRonn]

Switching them would be what I would do. They are $40+, so no need to buy if you don't need to.

 

[DaltonGang]

Figured I'd follow up on what caused this issue. Months ago I swapped out the 4 engine manifolds and they are pretty heavy. In hindsight, I should've removed spark plugs. While installing the new manifolds I must've rested one on a spark plug and it cracked. Over time it actually caused the plug wire to come off. I found this and replaced all plugs and it resolved the issue but then I had another one. At over 3000 rpm I would get a misfire on this same engine. I ended up buying an engine scanner and tested every ignition coil and they all were fine. I replaced all spark plug wires, still a misfire! I took a chance and just replaced the iginition coil on the suspect spark plug (cracked one) and it solved the misfire issue. Engines are running perfect now.

 

[PlayDate]

That is good news but it is a bit troubling since a single plug misfiring does not shut an engine down. What you originally described sounded like a 12v loss to the entire ignition system. Trust me finding that is not easy. The power wire to the ignition system routes through a maze of connections for each engine. I counted them up once and found 50+ points where the wire could be compromised.

I had one customer that the engine would die if he jumped a wake or was hit by one. It turned out the guy had done a bunch of helm gauge work and loosened the the main ignition power wire for his starboard engine. The only way we found it was to run a separate 12v wire to the engine's ignition to eliminate the engine itself and start following the harness back. Once we knew the engine was okay......it is just a (long) process to find a broken wire or connector.

 

[DaltonGang]

That is good news but it is a bit troubling since a single plug misfiring does not shut an engine down. What you originally described sounded like a 12v loss to the entire ignition system. Trust me finding that is not easy. The power wire to the ignition system routes through a maze of connections for each engine. I counted them up once and found 50+ points where the wire could be compromised.

I had one customer that the engine would die if he jumped a wake or was hit by one. It turned out the guy had done a bunch of helm gauge work and loosened the the main ignition power wire for his starboard engine. The only way we found it was to run a separate 12v wire to the engine's ignition to eliminate the engine itself and start following the harness back. Once we knew the engine was okay......it is just a (long) process to find a broken wire or connector.

Yeah I thought it was odd too but keep in mind, the spark plug wire was totally off the plug and just flopping around. It was creating an arch at higher RPMs and hitting something. Ever since I fixed all of it I haven't had one issue. I've put on probably 8 hours on the boat since then. This 4th of July I was in really rough water (stuff falling off shelves) and still no issue. So the coil was causing the misfire, but the engine dropping power for that 1 second was the spark plug wire arching on something I'm convinced. Either that or the computer was freaking out (maybe grounding) and thankfully I didn't fry the computer.