Mercruiser 5.0 Misfiring

[dremison]

Serial #: 0W663009
Sea Ray 240 Sundeck with a Bravo 3.
Over the course of this last summer, I had a few incidents where at either full power or at a slow no-wake taxi the boat will either cut power for a split second and then reengage immediately or a couple times it has just shut off entirely. It restarts immediately except in once case, and even then it just took a little bit extra gas to get it going again.
I just replaced all the plugs, wires, distributor and cap and had a repeat incident this weekend at 3800 RPMs, where it just cut out but immediately restarted.
I am disappointed that spending $300+ in OEM parts didn't fix the problem, but I would like to get this figured out before she goes away for the season. I don't think it is gas, since it has done it multiple times across multiple different tanks of gas over the summer, and it got a new fuel filter at the beginning of the season.
Any ideas as to what else could be causing an issue like this?

 

[Bondo]

and even then it just took a little bit extra gas to get it going again.

Ayuh,...... Carbed, Efi, or Mpi,..??..??

 

[Scott Danforth]

how old is the fuel?

did it backfire before quitting?

do you have a crab cap?

 

[Scott06]

Serial #: 0W663009
Sea Ray 240 Sundeck with a Bravo 3.
Over the course of this last summer, I had a few incidents where at either full power or at a slow no-wake taxi the boat will either cut power for a split second and then reengage immediately or a couple times it has just shut off entirely. It restarts immediately except in once case, and even then it just took a little bit extra gas to get it going again.
I just replaced all the plugs, wires, distributor and cap and had a repeat incident this weekend at 3800 RPMs, where it just cut out but immediately restarted.
I am disappointed that spending $300+ in OEM parts didn't fix the problem, but I would like to get this figured out before she goes away for the season. I don't think it is gas, since it has done it multiple times across multiple different tanks of gas over the summer, and it got a new fuel filter at the beginning of the season.
Any ideas as to what else could be causing an issue like this?

Sounds more electrical wonder if you are losing 12 v run, either loose battery connections or grounds, or cannon plug between helm harness and engine harness

 

[alldodge]

Serial shows MPI and HVS distributor

Just went thru this a short time ago with another member here and it might be a failing shift interrupter switch. That is if you have an Alpha drive and not a Bravo

 

[dremison]

Ayuh,...... Carbed, Efi, or Mpi,..??..??

MPI

 

[dremison]

Serial shows MPI and HVS distributor

Just went thru this a short time ago with another member here and it might be a failing shift interrupter switch. That is if you have an Alpha drive and not a Bravo

It is a Bravo 3 - it'd be nice if it was that easy.

 

[dremison]

how old is the fuel?

did it backfire before quitting?

do you have a crab cap? View attachment 411176

New fuel, no backfires ever and I do have a crab cap. Swapped it out this past weekend, in fact.

 

[dremison]

Sounds more electrical wonder if you are losing 12 v run, either loose battery connections or grounds, or cannon plug between helm harness and engine harness

I will check connections when I get back out there this weekend. I didn't even think to look electrical - I just assumed it would be something with the fuel system.

 

[alldodge]

Put a pressure gauge on the rail and see if it stays close to 43 psi

 

[kd4pbs]

If it has one, exercise the dead man switch. Perhaps it's getting a bit of some high resistance due to not being used much?

 

[dremison]

Put a pressure gauge on the rail and see if it stays close to 43 psi

Forgive my ignorance, but I’m not sure what you mean.

 

[alldodge]

Forgive my ignorance, but I’m not sure what you mean.

Go to local auto store that loans tools and get a fuel pressure gauge

Connect gauge to fuel rail by removing cap item 19 and attach to item 18
Turn key ON don't start and see what the gauge reads. Might turn off/on a couple times to see if there are any variations

Now start motor and see what it does
Take it for a run and see what the gauge does

https://www.mercruiserparts.com/bam/subassemblydetail/51444458/28194112

 

[ESGWheel]

Please allow this note of caution. While monitoring the fuel pressure throughout these variety of situations, given you do not seem familiar with doing it, I would like to add some safety tips. If you are well familiar, ignore this post, but just in case

• First off the type of pressure gauge to borrow or buy is same as in this link. Notice that there is the main hose to the gauge (that is hooked into the fuel rail) and this smallish and long clear plastic tube. When done using the gauge you press the little side button to relieve the pressure and will get a little squirt of gas in that clear hose.
• Second, prior to installing the gauge, zip tie that clear hose in a coil just like in the picture. And then, since need to monitor fuel pressure underway, secure the gauge in such a way as it will not flop around nor get caught up in the rotating belt. Zip ties work great. You also need to have the face of the gauge such that its easy to read simply by looking. Said differently you do not want to be underway and holding the gauge to read it or keep it from getting caught in the belt. Think about it, if you are holding it and boat hits a wake, and it drops out of your hand, that black hose will have about 45 psi of gas pressure behind it and if it tears…
• Third, this requires 2 people to do underway. Someone to drive the boat and someone to read the gauge.

Here is a great video of using this gauge at several points to get an understanding of how to use, link.

Not trying to be an alarmist, this is a perfectly safe thing to do, but appropriate measures need to be taken as highlighted above. Be safe and thanks for listening.

 

[dremison]

Please allow this note of caution. While monitoring the fuel pressure throughout these variety of situations, given you do not seem familiar with doing it, I would like to add some safety tips. If you are well familiar, ignore this post, but just in case

• First off the type of pressure gauge to borrow or buy is same as in this link. Notice that there is the main hose to the gauge (that is hooked into the fuel rail) and this smallish and long clear plastic tube. When done using the gauge you press the little side button to relieve the pressure and will get a little squirt of gas in that clear hose.
• Second, prior to installing the gauge, zip tie that clear hose in a coil just like in the picture. And then, since need to monitor fuel pressure underway, secure the gauge in such a way as it will not flop around nor get caught up in the rotating belt. Zip ties work great. You also need to have the face of the gauge such that its easy to read simply by looking. Said differently you do not want to be underway and holding the gauge to read it or keep it from getting caught in the belt. Think about it, if you are holding it and boat hits a wake, and it drops out of your hand, that black hose will have about 45 psi of gas pressure behind it and if it tears…
• Third, this requires 2 people to do underway. Someone to drive the boat and someone to read the gauge.

Here is a great video of using this gauge at several points to get an understanding of how to use, link.

Not trying to be an alarmist, this is a perfectly safe thing to do, but appropriate measures need to be taken as highlighted above. Be safe and thanks for listening.

That is very helpful and thank you for taking the time to spell that out. I will report back after this weekends trip out.