Mercruiser 4.3LX Hesitation and loud click?

[fester]

Hi Everyone,

I’m now the proud owner of a 2001 Maxum 1800SC (Engine is a 1996 4.3 LX/LXH ALPHA AND BRAVO (GEN +). Took it out for the first-time last Sunday and ran like a dream.................. until things got a little weird.

After a few runs with water skiing, I noticed some hesitation on full acceleration.. Eventually it mustered up the courage to get to plain and continued as normal for another 1 or two runs between skiing. Then hesitation occurred again and heard a click (backfire?) noise from the engine compartment it continued but stopped on idle.. took 1 or two attempts to get it going again however eventually got it back to the slip on low speed.

Previous mechanic (who was also the broker) asked me to check the fuel pump. Started engine with cups in my back yard with no issues in idle or in throttle/gear. With the engine off I could hear pump going like a flushing cistern . Next he asked me to bypass the oil pressure sender (pic attached) and it also worked without issue. He said it could be a coil issue and might need replacing.

History of the boat.. Previous owner hit the outleg and prop.. Had a complete engine rebuild and new outboard leg 2017. Got a mechanic to give it the once over before I purchased it.. Unfortunately, he didn’t do a compression test but said everything else looked in order. The boat ran perfectly on the water during the two tests we did before purchasing and we did put it through its paces.

Previous work done before I bought the boat:

• Fully reconditioned engine with New exhaust manifoulds all work completed 2017
• Alpha one gen 2 drive. new gearbox, propeller, impeller kit, gimble bearing, drive & exhaust boots & control cable kit, new gauges fitted all work completed 2018.
• fully serviced 2018.
• New starter motor/battery/battery switch fitted 2019.
• fully serviced 2019.

I’m tempted to try bringing it out on the water again to see if it reoccurs but a little apprehensive in case something goes wrong. I’m a complete newbie when it comes to boating and I’m learning fast as I go. Any advice would be appreciated.

Thanks everyone!!

[jrsick]

Do you have a mechanical fuel pump and a carb? If so, there may be a semi-clear tube running from the fuel pump to the carb. Not the fuel line. Trace this semi-clear tube to where it enters the carb, is there milky brown stuff coming out?
You'll need to remove the flame arrestor and look into the carb.
I'm thinking the cistern sound you hear could be a failed fuel pump.

[mmwjr]

The need for an oil pressure switch it has an electric fuel pump. Backfiring is the sign of either timing or backpressure. Is this a salt water boat and how old is the exhaust?

Do you have the Thunderbolt V ignition? Timing should be verified.

[fester]

Thank you both..

It's an electric fuel pump.. It's freshwater only.. Exhaust manifolds were replaced about 2-3 years ago by the mechanic I believe.. Other than that I don't really know.. If there is anything I can do/check please let me know and I can send on some pictures..

I'm now not 100% certain it was a backfire... My brother just pointed out it could have been a life jacket ring hitting off the side of the engine cover. However, the hesitation and stalling was definitely there.. He also mentioned oil pressure and temperature gauges were normal. Thunderbolt V is written on the Flame arrestor. See pics of the engine attached.

What else can I try?

[mmwjr]

How old is the fuel? Possibly water in it.
If you are just cruising around does this happen?
Sounds like the fuel may be vapor locking as the engine is hot from water sports then shut down to let rides on/off. When the engine is shut down the temps rise as no cooling water is flowing, this can result in vapor lock. Fixes have included a spacer under the carb to wrapping the fuel line. I think there may be a mercruiser service bulletin on this.

[fester]

Thanks again Mike.... That's two things you have helped me out with.. If you ever make it to Ireland IOU a pint! (beer!)

Don't know too much about the state of the fuel.. We did fill up the tank before we went out on the water and took toughly 74 Litres (I think its 100L tank?).... so thats 26L of fuel I don't know how long has been in the tank..

If you are just cruising around does this happen?

It was fine for the first hour or so.. and it was started/topped 2-3 times before the hesitation started.. It started out of the blue when I was about to tow my brother and got progressively worse.

I've googled around to find out more on the vapor lock.. Some mention this shouldn't be an issue if its fuel injected or has a fuel pump on the line? Is this true? If you have a link to that mercruiser bulletin that would be great.

Thanks!

[mmwjr]

Beer! I might have to swim across the pond for that!

I’ll see if I can find the bulletin. Ignition coils can act up when they get hot but need to cool down before they can produce a good spark again.

[Phillbo]

Don't shut it off between pulls... let it idle for a while.

[jparsons121]

Coming at this from another angle. Check/replace the fuel/water separator. If fuel was iffy, filter may be "full" and passing a bit of water which can cause these symptoms.
Also, check the purple/white wire next to the carb an be sure it's not grounding out. It should not be connected to anything. It's used when setting the base timing only and if it grounds, timing will be retarded and can cause hesitation, etc.

[fester]

Thanks again everyone for all the advice.

Attached is the service bulletin from Mercruiser I found regarding the vapor lock. Is there anything a newbie can do to verify its definitely a vapor lock issue? I would like to take it back out on the water to verify (at the risk of using paddles to get it back to the slip!). I could leave the blower running on full time and see if it helps. I normally run the blower only when starting the engine.

I'm also tempted to buy a clear marine grade tube and install it between the pump and the carb.. That should show me if its an airlock issue if it contains bubbles or air? Also thinking about investing in a fuel PSI gauge that I could install permanently. That would help diagnose a fuel pump issue and also teach me some plumbing :-)

Don't shut it off between pulls... let it idle for a while.

Great suggestion but I would be discouraged as I'm 110% committed to safety.. I would hate to think an engine could become a 200HP meat grinder for a skiier

@jparsons121 Thanks for those suggestions.. I'll give the fuel filter a shot. Is it considered OK to reuse the same one?.. I'll probably dump whats in it into a clear container, observe, fill with fresh fuel and rescrew the same one back on?. Or should I just buy a new one? It was "fully serviced in 2019" by the previous owner so I'm guessing it was also changed during that time. Will also look for that wire and isolate it with insulation tape if necessary.

I'm learning! :-)

[fester]

Hey everyone,

I brought the boat out on Sunday and same thing happened unfortunately. To eliminate the vapor lock I decided to run the boat on the water without turning it off. It ran fine for about an hour or slightly more and heard two bangs from the engine compartment and started to stall. Turned key before ignition to try and hear fuel pump but it sounded completely dead - no noise at all. Anyway.. started no problem again, but eventually stalled. It would cut out at getting to any speed and now it was beginning to cut out at idle. After waiting for ~5-10 mins started it again, low speed and got a good bit back towards the slipway before it cut out again.
Thoughts:

1. Should the pump have sounded like the flushing cistern after an hours use? I previously posted a youtube video below of what it sounds like on land.
2. I filled up the tank with ~27Litres of fuel which was what we used the last time it was out. Could this be a tank level issue or something?

Any further advice would be very much appreciated. Paddling back to the slip wasn’t fun.. LOL!

[mmwjr]

Reviewing the video I could not tell if the engine was still turning over while the noise was occurring. If it truly is the fuel pump making that noise that is not normal however it sounded like a belt driven noise to me which is why I asked if the engine was still turning over. I have heard Volvo electric fuel pumps make noise when their bad but they make it all the time.

[fester]

Thanks mmwjr, In that video I stop the engine and put the key to standby (not off) at around 8 seconds.. You can see the belts on the motor stopping. You can also hear the pump without the engine running after 8 seconds.

I brought the boat out again today to try narrow it down. This issue starts occurring around 40-45 minutes out on the water. This duration seems to be consistent. It doesn't matter if I start stop it each time or keep it running. So when it started happening again, I was hearing popping sounds from the engine and it would struggle/eventually stall.

I tried bypassing the oil pressure sender for the fuel pump using a piece of shielded wire and unfortunately didn't rectify the problem.

My cousin noticed that the oil pressure gauge was going down when the problem starts to happen. After idle for a few minutes it starts fine again and will last for a few minutes under low speed. On the gauge it would show roughly 40PSI, dropped to 20 when problems occurs and eventually to 0 when it cuts out.

If you have any suggestions please shout :-)

Many Thanks!

[mmwjr]

20 psi is plenty of oil pressure at low rpm.

Other things that may be the problem, clogged fuel tank vent, bad ignition sensor in the distributor, bad ignition coil.

[jrsick]

Next time you get the problem try checking inside the distributor cap for moisture. That's about the right amount of run time for moisture to build inside the cap if you have a crack or bad seal.

[fester]

So who doesn’t love a happy ending to a sad story? I replaced the distribution cap & coil. The engine now runs without a hiccup! Thank you so much to everyone on here for all their help.

The finer details.. The coil looked pretty old and could have been the original with the boat? I tested it with a multimeter and it appeared to be within limits however doesn't indicate how well it performs under load or heat.. Second, the distribution cap and to my surprise (!?!?) had moisture around the edge of the rotor cap bottom. The replacement had a gauze layer to be installed to prevent recurrence and was missing from the original installation.

For anyone considering undertaking the same.. its pretty easy to change the two components. I took my time to learn ignition systems on youtube and how they work.. fascinating stuff!

I’m delighted.. Thank you all again!

[mmwjr]

Glad you resolved the issue, thanks for posting your findings