2001 4.3L Mercruiser - Engine Stops Randomly

[Big6ft6]

Hey guys I have a 2001 4.3L LH Mercruiser that I just picked up. The boat and engine look very clean and either meticulously maintained or very low hours (no hour meter). I'm having problems with the engine just stopping, I've replaced the fuel filter, and it is still happening. What should I check next?

Back story:

I was only able to do a short test drive, but the seller started from cold just fine, and I was able to drive it out on the lake for 5 minutes or so before it started raining and we had to head back to the pier, but other than stalling when shifting in to reverse during initial launch from the pier everything seemed great so I bought the boat.

So the next nice day I ran her on the muffs in the drive way wanting to make sure nothing happened during a longer run time. She fired right up, and once she was running for 10 minutes or so and I was confident that oil pressure and engine temp were stable I went in to the house to just let her run for a while, I wanted to let her run for a while before I took the family out on the real water, but after a few minutes in the house I heard the rpms drop, then the engine just stopped. (the boat came with 3/4 of a 41 gallon tank of gas)

I went out and it took a few cranks and coughs but it started back up and ran fine. But the problem persists the engine will run fine, but it always eventually stops. The amount of time it runs before stopping varies from 5 to 30 minutes. Being confident that it will always restart I took it out to the lake today and she ran beautifully at all speeds. So I opened her to full throttle for some cruising and after about 10-15 minutes of perfect operation she just stopped running and came to a stop. All gauges look great and stable while running. Good oil pressure, good temp etc.

After stopping out on the lake she restarted after some cranking and coughs, and the first climb through the rpms she kind of stumbled, but after that and we were back in business. I cruised around at various speeds for another 20 minutes and it didn't happen again.

Knowing my boat will eventually stall out on me takes a good bit of the joy out of having a boat. My next idea is to jump the oil switch next time out to see if that stops the problem. Is this common symptom of a bad oil pressure switch? I see lots of posts but none really explaining the common symptoms other than when it is totally dead. What about a bad fuel pump?

My biggest fear is of course a cracked block or leaking exhaust manifolds...but this doesn't seem like that right?

Thanks for listening, and thanks for any ideas in advance.
Nate

 

[Bondo]

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

Got the serial number,..??

 

[tpenfield]

Kill switch . . . See if the connections or the switch itself is becoming corroded.

 

[Big6ft6]

Sorry Bondo, I know you get tired of asking that! it is a Carbed 2bbl.

It is leaking oil (slow drip) from the oil pressure switch not sure if this makes the oil pressure switch more or less likely to be the culprit, but thought I'd add that. I will jump the switch next time out but since it can run so long between problems it will take a while before I'm convinced the problem is solved. Any other things I should look at/test in the mean time?

 

[Big6ft6]

Thanks Supreme...does the fact that it starts right back up make the kill switch more or less likely to be the culprit?

 

[Luv2fish36]

There is an updated improved oil switch kit for your motor assuming yours has an electric fuel pump. Just make sure you ask for the KIT when ordering the part that way you get the switch, plug, wires etc.... When the oil switch has pressure (meaning the engine is running) the switch tells the fuel pump to run. If the switch is bad or the connections are corroded then it will cause the fuel pump to run intermittently but most of the time just not at all.

While your in there take off the distributor cap and look down below under the rotor. Do you have the old style ignition pickup sensor? It will look like a computer brain chip. If it has corrosion on it I'd replace it with the new sealed style. they are known to cause headaches. Also look at your distributor cap. See anything growing in there? Replace.

when it stalls going into reverse that's most likely just a worn/stiff shift cable issue.

when it dies on the hose at idle that's probably a carburetor issue. Tuned wrong, dirty or a bad carb. Or if it's cold outside with moisture in the air while your running it may just be icing up on you. If it were me I'd take a look in the carb. The 2 barrel is very easy to take apart to inspect.

 

[Big6ft6]

Thanks Luv2fish! I'll check those. Yes electric fuel pump.

To be clear the engine quits at all speeds. Yesterday I was cruising at full speed for 10-15 minutes before it just suddenly died in the middle of cruising.

When it would quit on the muffs in the driveway I'd be running at 1500 rpms. So it isn't just dying at idle, the engine randomly quits at all speeds. It just stops running.

 

[bman440440]

if it where me I would check the oil pressure switch like stated above... but here is how I would do it.... and keep in mind this is just for testing and not a fix (the fact that it has a leak is the red flag in my mind) to the problematic oil pressure switch... get yourself a heavy duty paper clip and jumper the wires on the connector to the switch together and run it... if it doesn't happen any more you know the problem and get the pressure switch KIT and you are good to go! that's my 2c you can take it for what its worth!

 

[Big6ft6]

Thanks Bman! I was wondering if anyone had ever used a paper clip since both wires are terminated with female connectors. I'd probably wrap with electric tape since I need to drive for a while to be sure problem is gone.

 

[bman440440]

Thanks Bman! I was wondering if anyone had ever used a paper clip since both wires are terminated with female connectors. I'd probably wrap with electric tape since I need to drive for a while to be sure problem is gone.

Yes many have done this to check it... and yes the tape is a good idea too

 

[Scott06]

When it stalls check and see if you have fuel in the carb by removing The flame arrester and pump the throttle and see if good streams if you’ll come out of the two Accelerator pump nozzles

also at same time check if you have spark by take coil lead off the distributor ground it an crank the engjne-looking for a good hot blue spark. If there check at the plugs to ensure something simple like a cap and rotor isn’t loosing spark

if if you have an electric fuel pump it will be powered through the oil pressure switch. If there’s no fuel and it seems to run great otherwise may be losing yhe fuel pump power intermittently, jumper out the switch to test.

 

[QBhoy]

Another option is that it has water in the fuel perhaps. Also possible that the tank pick up is getting blocked with crap occasionally.
Does is sometimes run on and splutter a bit with pre ignition after key is turned off ?

 

[Big6ft6]

Thanks for the tips everyone, I jumped the oil pressure switch and drove around for 1.5 hrs with no stall. I'm cautiously optimistic this was the problem as this is the longest it has run without stalling. I will post back if this ends up not being the solution. Any recommendations for reputable source for new switch, can I buy here from iBoats?

 

[kulle]

Thanks for the tips everyone, I jumped the oil pressure switch and drove around for 1.5 hrs with no stall. I'm cautiously optimistic this was the problem as this is the longest it has run without stalling. I will post back if this ends up not being the solution. Any recommendations for reputable source for new switch, can I buy here from iBoats?

You are lucky it turned out to be that switch, basically a $30 part, easily replaceable. I was having same issues where the boat would run in idle for 15-45 secs, I suspected that switch after I found a small drop of oil underneath. Long story short, I had overall random/intermittent shuts offs and had a boat place repair for ~$375. Got the boat back and took it out only for it to run longer but still shutoff. I think that switch was bad but still have intermittent shutoffs. I had to replace ujoint and exhaust bellows and when i took off exhaust bellows I found a water shutter valve lodged in the exhaust bellow. I am sooooo hoping that some how was lodged in the exhaust pipes causing the shutoffs and it eventually made its way to the exhaust. If i replace this all and it still fails, i think i'll just leave it at the dock with keys in it. 1993 sea ray 4.3L