4.3 lx runs strong for 5 minutes then crap

[ohioriverrat]

4.3 lx mercruiser with 4 barrel weber. 50 hours. ran perfect last summer.

de winterized my boat this year, which pretty much consisted putting the plugs back in and hooking up the hoses.
it started up just fine. let it idle for about 10 minutes in the yard to let the fogging oil burn off. was purring like a kitten. shut it down then next day took it to the river. the boat fired up, idled out from the docks, opened it up and it ran like a champ ... for about 3 minutes.. then it sputtered and died. started back up, turned it back towards dock and limped it back to the dock, starting and stopping several times - would not plane out and would not run over 2000 rpm. i could let it sit for a few minutes and it would start easily but barely run over an idle.

so i took it back to the shop that winterized it, told them, a week later and 650 dollars later they told me it was a bad fuel pump.

well i was a little chapped at the price but happy to have the boat back none the less.

piled in the family for a fun filled memorial day weekend - epic conditions on the ohio - flat clean water, water temp near 80, air temp around 90

left the docks..ideld out to the river opened it up - ran for about 5 minutes..started to stutter exactly the same turned towards the dock it died. wouldnt even idle back to boat ramp. had to get a tow.

acts like it is running out of gas..

so ofcourse the boat shop denies all responsibility. assured me the fuel pump was bad, but it must have other problems too..

i ofcourse first suspect bad fuel.
not the case - i went and bought an above deck fuel can filled it with fresh premium, new fuel hoses, and everything all the way to the carb except for another pump.
next i jump into the plugs and distributor - distributor is nice and dry, not too bad inside so i just scuff up the points a little to clean them up. pulled a couple plugs too.. nothing telling there either , looking normal as they should. but that doesnt stop me from putting in new ones.
plug wires you say... negative, swapped out a set i knew to be good with no change.

keep in mind, i can run this boat in the yard and you can barely tell anything is wrong except for the occasional miss but once you put it under load its nothing but trouble. spits and sputters, quits when you try to open it up, idles pretty well, but the more gas you give it the worse it sputters.

so ive done some research and here are some possibilities
but i need some more information on how to test these things
oil pressure switch -
ignition amplifier -

before anyone asks, i ran all the previous gas out of the system before i started changing plugs. but seriously... its not bad gas here folks. i doubt it is the carb because it runs perfect for a few minutes until it gets up to temp. the choke is working correctly i am sure. if i let it cool down for about a half hour 45 minutes it fires up and runs perfect for another 5 minutes or so. just far long enough from the docks to be a real pain in the ***

anyone have any other ideas or experience? im not talking about similar experience, but something more exact since it is the same exact thing every time.

 

[StitchSC]

Re: 4.3 lx runs strong for 5 minutes then crap

I am definitely not a pro, but clogged fuel vent? Try running it with the fuel cap open....or fuel filter / separator?

 

[Nashport_native]

Re: 4.3 lx runs strong for 5 minutes then crap

sounds to me like the float in the carb is sticking.....under no load it would let enough fuel in to keep it running, but as you get it out on the water and open it up, the float isn't dropping down, letting enough fuel in to keep the bowl filled up.

 

[ohioriverrat]

Re: 4.3 lx runs strong for 5 minutes then crap

stuck float would be my next guess if it were something that were more intermittent. but i had the boat out no less than 7 times working on it this weekend. that wouldnt explain why it would run well for 3 to five minutes then suddenly loose power and idle barely back to the dock. let it sit for 30 to 45 minutes and same thing. also i had someone squirting a little fuel down in the carb when it starting acting up, it made it spit and sputter but not take off and go. thats when we deduced it had to be electrical. so out came the plugs and wires, the coil felt slightly warm to the touch but not hot at all. i dont know if it is electrical at all, but i am grasping at straws, i ran accross a post by someone describing these same symptoms and he eluded to the oil pressure switch. - if it is faulty then it shuts the fuel pump off after a few minutes. it then is able to run for a couple minutes on built up pressure.. sounds good right?, but i would guess that if the fuel pump quit working then it would not run what so ever. or would it????

its def not clogged fuel vent, filiter or otherwise, i reran all new fuel lines from a totally new tank by passing the water fuel seperator since i knew for a fact there was no water in the new tank. i plan on re installing the seperator, that was only for trouble shooting purposes.

the thing is i cant hear the fuel pump kick on or run at all. i know that it is not supposed to kick on until it senses some kind of oil pressure, at least i think so...

 

[daymienrules]

Re: 4.3 lx runs strong for 5 minutes then crap

whenever trying to diagnose something electrical like that, I like to wire a small l.e.d. into the circuit. If the fuel pump is getting power, light will be on. If something is cutting the power to fuel pump, such as the oil sensor, the light will go out.

 

[ohioriverrat]

Re: 4.3 lx runs strong for 5 minutes then crap

whenever trying to diagnose something electrical like that, I like to wire a small l.e.d. into the circuit. If the fuel pump is getting power, light will be on. If something is cutting the power to fuel pump, such as the oil sensor, the light will go out.

there is alot of good advice on this site, but this has to be by far the best tip i have ever ran accross. i do not know if i will be able to locate a 12v led in a timely fashion but i will definitely keep my eye out for one for this little trick!!!!

 

[oceanbarrel]

Re: 4.3 lx runs strong for 5 minutes then crap

not to be funny but i had a truck that used to do the exact same thing. It turned out it was a stuck float. I tapped the side of the carb with a hammer and it worked fine from then on. The only other thing I can think of is some kind of safety cutout device.

 

[6meter]

Re: 4.3 lx runs strong for 5 minutes then crap

If I remember right, with a car, at start up the ignition system bypasses the oil switch because you won't have oil pressure when first turning the key.

 

[SeanMcl]

Re: 4.3 lx runs strong for 5 minutes then crap

Check the fuel pickup in the tank. My boat had a very, very similar issue and that's what it turned out to be.

It idled fine, would restart fine, then die after 2 minutes like it was running out of gas. Which it was. Next time yours dies, turn the key off and check the fuel level in your carb float bowl. If it is dry in there you are starving for fuel.

Here is my old thread where I posted my symptoms and fix.

http://forums.iboats.com/showthread.php?t=339249

 

[fossill]

Re: 4.3 lx runs strong for 5 minutes then crap

I'd be tempted to check the ignition module. They usually act up when they get hot if they are going south.

 

[ohioriverrat]

Re: 4.3 lx runs strong for 5 minutes then crap

Check the fuel pickup in the tank. My boat had a very, very similar issue and that's what it turned out to be.

It idled fine, would restart fine, then die after 2 minutes like it was running out of gas. Which it was. Next time yours dies, turn the key off and check the fuel level in your carb float bowl. If it is dry in there you are starving for fuel.

Here is my old thread where I posted my symptoms and fix.

http://forums.iboats.com/showthread.php?t=339249

i replaced the tank with a temporary above deck and bypassed water fuel seperator just to be sure. just a tank, pump, and hose to the carb

 

[ohioriverrat]

Re: 4.3 lx runs strong for 5 minutes then crap

if it was the float then how would letting it sit for 30 to 40 minutes allow the engine to run perfect again for about 3 to 5 minutes? if i let it sit for 15 minutes it will still not run right.it has to be a 30 minute plus rest time for it to "reset"

i called the boat shop that put on the fuel pump and they told me that its probably still the fuel pump, they must have put on a bad one, they said they have put on 3 this month that were bad. if thats the case then it must stop working when it gets hot, but still works well enough for the boat to idle and barely run... just doesnt add up.

 

[silverfalcon28]

Re: 4.3 lx runs strong for 5 minutes then crap

Just boght a boat a few days ago and put it on the water for the first time friday evening.I to have the same problem and was wondering if you have located and or fixed the problem?

 

[silverfalcon28]

Re: 4.3 lx runs strong for 5 minutes then crap

sorry to hi jack you again but it sounds like you have the same prob i had.So i was at my job (24hr shifts) and researched religously for 8+hr's. I came across a quite few answeres on your thread.i went for the simpler/cheaper solutions.

down to brass tax.
changed the fuel/water seperater filter.
added sea foam to the tank.
followed the instructions exact on the prestone carb and choke cleaner (as wel as the sea foam and did so.
also tooki my wrench and tapped ligh ly on the fuel pump.
checked the breather line and it was good.

now she purr,s like a kitten.hope it helps

 

[ohioriverrat]

Re: 4.3 lx runs strong for 5 minutes then crap

sorry it took so long to get back, but i did inded fix the problem. after dropping another 500 at the boat shop - they rebuilt the carb, cleaned my ground wires and unhooked my stereo... it still did the same thing only now it took about 7 to 12 minutes to do it.
i recommended to the mechanic that he put on a new coil.. he basically refused, and proceeded to call me an idiot in a round about way. saying - "all these idiots and shadetree mechanics always wanna put put on new coils, and its never the coil, id like to have all the good coils that people replace when they don't have to.."

i replaced the coil and the boats runs perfect. once i got back in there i could plainly see that the coil had leaked oil - tar type goop out of the top.

36 dollars later - i reluctantly/ hopefully took the boat out - it ran perfect all day, and has ever since.

i tested the old fuel pump, nothing was wrong with it. it was all the coil the whole time

 

[fsjcowboy]

Re: 4.3 lx runs strong for 5 minutes then crap

Good call.

 

[saltlydawg]

Re: 4.3 lx runs strong for 5 minutes then crap

I had the same problem with my 4.3 and it was the float sticking as well. She would idle fine but throttle advancement would cuase her to die.

To fix the problem I filled a new fuel filter half way up with Sea Foam and installed it. The quick shot of cleaner made her fog for about 30 seconds and then ran great, with excellent throttle response. Many times the fuel sitting in the Carb bowl makes a sticky varnish as it sits for extended periods of time like witnerization. A stabilizer can help, but the fuel still breaks down and coats parts.

Good luck and I would love to hear what the final diagnoses turns out to be.

 

[whitney]

Re: 4.3 lx runs strong for 5 minutes then crap

sorry it took so long to get back, but i did inded fix the problem. after dropping another 500 at the boat shop - they rebuilt the carb, cleaned my ground wires and unhooked my stereo... it still did the same thing only now it took about 7 to 12 minutes to do it.
i recommended to the mechanic that he put on a new coil.. he basically refused, and proceeded to call me an idiot in a round about way. saying - "all these idiots and shadetree mechanics always wanna put put on new coils, and its never the coil, id like to have all the good coils that people replace when they don't have to.."

i replaced the coil and the boats runs perfect. once i got back in there i could plainly see that the coil had leaked oil - tar type goop out of the top.

36 dollars later - i reluctantly/ hopefully took the boat out - it ran perfect all day, and has ever since.

i tested the old fuel pump, nothing was wrong with it. it was all the coil the whole time

You and I have been on similar paths. Glad to hear you got it worked out too! I chased fuel for a long time before pulling the coil.

Here's my thread if anyone wants to compare/contrast heat soak related performance problems due to bad coils: http://forums.iboats.com/showthread.php?t=430118

Was yours as bad as mine?

 

[glas-tron]

Re: 4.3 lx runs strong for 5 minutes then crap

I had the same problem with my 4.3 and it was the float sticking as well. She would idle fine but throttle advancement would cuase her to die.

To fix the problem I filled a new fuel filter half way up with Sea Foam and installed it. The quick shot of cleaner made her fog for about 30 seconds and then ran great, with excellent throttle response. Many times the fuel sitting in the Carb bowl makes a sticky varnish as it sits for extended periods of time like witnerization. A stabilizer can help, but the fuel still breaks down and coats parts.

Good luck and I would love to hear what the final diagnoses turns out to be.

just fixed my boat after years of trouble shooting. it was nothing more than a bad coil. I have a 91 merc with a 4.3 and thunderbolt ignition. it would randomly lose power at high rpm. I also noticed that you could feel a slight loss of power at high speed when i use the trim. That should have been a clue that it was not fuel related. just wanted to contribute to the thread due to the fact that it helped me fix my boat.

 

[achris]

Re: 4.3 lx runs strong for 5 minutes then crap

This is a 2 year old thread.... Please do not write in the archives... Start your own thread....