Mercruiser 4.3 LX

[TraceyHill]

This is my first time on a forum, so forgive any etiquette bumbles or whatev.

My father bought a boat for us to use. My husband uses it for fishing even though it isn't designed for fishing (speedboat) and no way to mount a trawling motor....ANYWAY, yesterday we're out on the river b/c salmon are running. I'm driving and have to put the engine (Mercruiser 4.6 LX) in gear (it's about trawling speed) and now and then put it back into neutral. Should have known something was up when I was having to put on the blower because of the heavy gas fumes. Close to the boat's dock, the engine just QUIT.

The dipstick registered oil, but barely, there was plenty of fuel in it.....we dumped 5 gal of gas in it anyway and about half a quart of 10W 30 oil in it. It acts like it wants to start, but doesn't. Fiddled with the carb a bit and although it didn't start, at least that seemed to make it ALMOST start a few times.

At a loss. Can't figure out how an engine with 42 hours on it and not too much use, went from working just fine, to not working at all.

Heeeeeelp!

 

[farmer9009]

Re: Mercruiser 4.6 LX

Re: Mercruiser 4.6 LX

Welcome.
We will need some aditional info to get started:
Engine year, and serial number if possible.

 

[Technorunner]

Re: Mercruiser 4.6 LX

Re: Mercruiser 4.6 LX

You dident se any fuel leaks on the fuelline to the fuelpump and from the fuelpump to the carb??
Is it only the engine that is 42H old or the boat as well?. If only the boat you can have bad fuel lines from tank to the fuel pump. That would cause the fumes at first when the fuel in the fuelline was dribbling out and then sucking air in instead of fuel. I would start with checking the fuel line from tank and also check fueltank wenting not to be clogged up with a bug or corrosion. IF the boat and fuel lines are older then the engine. Second i would check the fuelfilter and if with glasbowl look for cracks in bowl and near the O-ring seat.
A new Engine can take some oil before completly broken in. So might not be a problem. I would focus on the fuel issue first and then watch the oil consumption carfully after getting it running good again.

 

[TraceyHill]

Re: Mercruiser 4.6 LX

Re: Mercruiser 4.6 LX

Okay fellas, here's what we've got (finally). The engine is a 4.3 LX V6 Mercruiser (1993-1995). Here's what got accomplished yesterday:
- pulled gas out of the tank, hoping to see water mixed with the gas.....no water mixing with gas. Added stabilizer anyway.
- cleaned carburetor thoroughly with carb cleaner.
- checked to see that points were getting spark - they were.
- pulled the spark plugs (which were unbelievably filthy and just thrashed). Replaced the plugs with exactly what came out of the engine (which were two different sizes). Didn't pay enough attention to which size plug came out of which hole so made a best guess effort.
- Turned the key, aaaaand...... fired! Quickly switched it off again, put everything back together and went to start it up again - aaaaaand turning over, turning over, no spark. Wouldn't fire. Took it back apart again, added fuel directly to the carb, adjusted idle every which way, but still wouldn't fire (not for lack of trying!).
- Removed plugs one at a time - 2 were fouled. Switched the two that were fouled with a different sized one (longer replaced the fouled shorter plugs), tried starting it again and nothing.

It just won't FIRE. And I can't understand why. The Secor book isn't terribly helpful for diagnosing.

Could I have a blown head gasket? How do I tell? I'm told a compression check isn't the way to go......

Does it SOUND like anything familiar to any of you? I can't help thinking I'm missing something obvious, but who knows.

 

[achris]

Re: Mercruiser 4.6 LX

Re: Mercruiser 4.6 LX

OK.. The plugs you should have in are NGK BR6FS or AC Delco MR43T. Please, throw that seloc manual in the garbage, they are worst than useless. Download a proper manual here -> https://docs.google.com/open?id=0B1TAvwZ3TjhfYWRiMDZmNDctMzgzZi00MmIzLTkxNGItMGY1NGExYjJmOGJh, and here's one for the drive -> https://docs.google.com/viewer?a=v&...YWRiNy00ODUyLWFmNzgtMTBmMzhlNGY4Mzk3&hl=en_US

Now you need to determine why it isn't starting... I know that sounds obvious, but there are 3 possibilities (basically).
Spark (at the right time), fuel (in the right ratio with air) and compression.

Don't know who told you a compression test was no good... They got that seriously wrong... Go ahead and do a compression test. Then get an old spark plug and connect it to one of the plug leads, lay it on the metal of the block and crank the engine. You should see a nice fat blue spark....

HTH,

Chris.........

 

[TraceyHill]

Re: Mercruiser 4.6 LX

Re: Mercruiser 4.6 LX

Thanks for the info, Chris. I'm still concerned about a blown head gasket (you're right - that Secor manual was a huge waste of $37). It's the blown head gasket that can't normally be detected with a compression check. Oddly, the right rear piston is the only one that keeps getting oil on it - can't figure that one out. Will make sure all plugs are to spec and see if we can't get the compression checked - I think that's all that's left to do. Grrrrrrrrrr..... will check back with results.

 

[RogersJetboat454]

Re: Mercruiser 4.6 LX

Re: Mercruiser 4.6 LX

It's the blown head gasket that can't normally be detected with a compression check.

That's not right.
A blown head gasket in most cases can certainly be detected by a compression test. If I were to guess, it sounds as though your carb needs to be taken apart, completely cleaned out, and rebuilt. BUT.... Do the basics first like achris mentioned (compression, spark, and fuel)

 

[Volphin]

Re: Mercruiser 4.6 LX

Re: Mercruiser 4.6 LX

Okay fellas, here's what we've got (finally). The engine is a 4.3 LX V6 Mercruiser (1993-1995). Here's what got accomplished yesterday:
- pulled gas out of the tank, hoping to see water mixed with the gas.....no water mixing with gas. Added stabilizer anyway.
- cleaned carburetor thoroughly with carb cleaner.
- checked to see that points were getting spark - they were.
- pulled the spark plugs (which were unbelievably filthy and just thrashed). Replaced the plugs with exactly what came out of the engine (which were two different sizes). Didn't pay enough attention to which size plug came out of which hole so made a best guess effort.
- Turned the key, aaaaand...... fired! Quickly switched it off again, put everything back together and went to start it up again - aaaaaand turning over, turning over, no spark. Wouldn't fire. Took it back apart again, added fuel directly to the carb, adjusted idle every which way, but still wouldn't fire (not for lack of trying!).
- Removed plugs one at a time - 2 were fouled. Switched the two that were fouled with a different sized one (longer replaced the fouled shorter plugs), tried starting it again and nothing.

It just won't FIRE. And I can't understand why. The Secor book isn't terribly helpful for diagnosing.

Could I have a blown head gasket? How do I tell? I'm told a compression check isn't the way to go......

Does it SOUND like anything familiar to any of you? I can't help thinking I'm missing something obvious, but who knows.

Those are Chevy Vortec heads on that engine. Best plug is the AC Delco MR43TS for proper reach into the center of the combustion bowl, but you can use MR43T as well, they are just a tad shorter. What are the plugs fouling with? Oil? Gas?

V

 

[Utahboatnut]

Re: Mercruiser 4.6 LX

Re: Mercruiser 4.6 LX

I would also look at the condition of the dist. cap, rotor, wires and connections into the cap and onto the plugs. Also as asked above what are the plugs fouled with oil or gas? when you are trying to start you have it hooked up to a hose right? even a few seconds with a dry impeller and you will have additional problems to fix. A compression test is NEVER a bad thing so do that too if you have access to a tester and know the procedure. Report back with findings on questions asked above.

 

[achris]

Re: Mercruiser 4.6 LX

Re: Mercruiser 4.6 LX

Those are Chevy Vortec heads on that engine. Best plug is the AC Delco MR43TS for proper reach into the center of the combustion bowl, but you can use MR43T as well, they are just a tad shorter. What are the plugs fouling with? Oil? Gas?

V

Incorrect... That is a Gen II engine, not a Gen +...

 

[Volphin]

Re: Mercruiser 4.6 LX

Re: Mercruiser 4.6 LX

Incorrect... That is a Gen II engine, not a Gen +...

Ooops! Chris is right! Mis read the year. Sorry... carry on.

V

 

[Pete104]

Re: Mercruiser 4.6 LX

Re: Mercruiser 4.6 LX

Gen II with points?

Check your lanyard before you go tearing the world apart!

 

[achris]

Re: Mercruiser 4.6 LX

Re: Mercruiser 4.6 LX

Gen II with points?

Check your lanyard before you go tearing the world apart!

I think she means the pointy ends of the spark plugs... As they are getting spark... Lanyard's fine...

 

[TraceyHill]

Re: Mercruiser 4.6 LX

Re: Mercruiser 4.6 LX

Utah - Plugs fouled with oil. The boat is in the water (died there, no where to take out unless I get it towed). My husband is going to find someone who has a compression tester. (But, blonde question here: if when the [new] plugs are removed, there's a hissing of air escaping as each are taken out, wouldn't that indicate adequate compression, at least to get it to start?) Distributor, et seq, clean and operable (at last report). The engine was purchased with the boat and had checked out initially just fine. We've maybe put an additional 15-20 hours on the engine since the boat was purchased. Granted, that's a bit of use, but not really when you consider we live on the Willamette River (Portland, Oregon). Funny no one asked if I was running it in salt water......... (haha!), which I am not. I'm at least 40 miles upriver from the mouth of the Columbia.

 

[TraceyHill]

Re: Mercruiser 4.6 LX

Re: Mercruiser 4.6 LX

5/13 update to above: just read the thread following this one and now have a question: could it be that because the oil level dropped so low before my husband caught it that the oil filter needs changing? And would that be a contributing factor?

I have to admit to a pretty high level of frustration right now......my husband is capable to a point and then I think he reaches a point where it goes beyond his capability (but he can't admit that). He says he doesn't want to rebuild the carb, that the carb cleaner should have done a good enough job (looking down into it, it certain LOOKS a lot cleaner - silver metal instead of crusty black). He also claims it would have to be retimed after removing/replacing the carb. Unfortunately, we're not in a position to pay Cook Engine $100/hr to diagnose, even if we could float the damned thing downriver 20 miles to their shop.....

So here's my question: Could it be the way the engine has been used in the past few weeks? After being wintered over in dry dock, the only person to use the boat has been my husband who has ONLY used it for salmon fishing on the river. In other words, he used the motor as a trawling motor, switching between idle (approximate trawling speed) and neutral. I realize it's hard to guess when the real problem hasn't been conclusively diagnosed, but anyone willing to hazard a best guess?

This is soooooo frustrating.........

 

[Bondo]

Re: Mercruiser 4.6 LX

Re: Mercruiser 4.6 LX

Utah - Plugs fouled with oil. The boat is in the water (died there, no where to take out unless I get it towed). My husband is going to find someone who has a compression tester. (But, blonde question here: if when the [new] plugs are removed, there's a hissing of air escaping as each are taken out, wouldn't that indicate adequate compression, at least to get it to start?) Distributor, et seq, clean and operable (at last report). The engine was purchased with the boat and had checked out initially just fine. We've maybe put an additional 15-20 hours on the engine since the boat was purchased. Granted, that's a bit of use, but not really when you consider we live on the Willamette River (Portland, Oregon). Funny no one asked if I was running it in salt water......... (haha!), which I am not. I'm at least 40 miles upriver from the mouth of the Columbia.

Nope,.... It's irrelevant...

 

[Bondo]

Re: Mercruiser 4.6 LX

Re: Mercruiser 4.6 LX

5/13 update to above: just read the thread following this one and now have a question: could it be that because the oil level dropped so low before my husband caught it that the oil filter needs changing? And would that be a contributing factor?

I have to admit to a pretty high level of frustration right now......my husband is capable to a point and then I think he reaches a point where it goes beyond his capability (but he can't admit that). He says he doesn't want to rebuild the carb, that the carb cleaner should have done a good enough job (looking down into it, it certain LOOKS a lot cleaner - silver metal instead of crusty black). He also claims it would have to be retimed after removing/replacing the carb. Unfortunately, we're not in a position to pay Cook Engine $100/hr to diagnose, even if we could float the damned thing downriver 20 miles to their shop.....

So here's my question: Could it be the way the engine has been used in the past few weeks? After being wintered over in dry dock, the only person to use the boat has been my husband who has ONLY used it for salmon fishing on the river. In other words, he used the motor as a trawling motor, switching between idle (approximate trawling speed) and neutral. I realize it's hard to guess when the real problem hasn't been conclusively diagnosed, but anyone willing to hazard a best guess?

This is soooooo frustrating.........

Nope,...

Cleanin' the visible parts of the carb is also irrelevant,... It's the Internal passages that plug up...
'n timing is a distributer thing, not a carb thing,...
Though a full service, 'n complete Tune Up, probably ain't a bad idea...

Yer ole man can continue to screw the pooch, or you can drag it to somebody that Knows what their doin',....
It sounds like Yer better half is in Way Over 'is head, already at this point....

 

[achris]

Re: Mercruiser 4.6 LX

Re: Mercruiser 4.6 LX

Here's something that might help.... Go buy a can of 'Power Tune' from your local friendly Merc dealer. While cranking the engine spray the stuff down the carb, for about 20-30 seconds. Pull the spark plugs out and give each cylinder a shot. Put the plugs back in and crank for about 3 seconds. Now, wait 20 minutes for the power tune to work its magic. Crank the engine with the plugs in. If it doesn't start, give the throttle a pump to shoot some juice in... You might just get lucky.

I completely agree with Bondo, cleaning the outside of the carb is purely cosmetic and does absolutely nothing for the inner works, but hey, if it make him feel good... D:

Don't know what he means by having to re-time the engine after a carbie clean.... Sounds more like a salesman's story to me....

Good luck, and I think it might be time to work out how to get it down the river to a mechanic... (or just pay me and I'll fly over and fix it.... For free if you put me up for a week or so... )

Chris.......

 

[Deese566]

Re: Mercruiser 4.3 LX

Ok , here goes my opinion. You mentioned about haveing to turn the blower on because of fumes. I think what is happening is you possibly have trash in the carb an the float needle is not shutting off the flow of fuel when the boat is at idle or low rpm's when the carb is full. Its basically flooding the eng. Ya say it wants to start but just wont quite do it. Its flooded. Yall removed the plugs an im thinking the plugs were soot black or wet oily black. The gas fumes you were smelling was most likely the rich exhaust comeing out around the transom an rolling back into the boat. Did ya happen to notice if there was black or blackish gray smoke around the stern area. The boat sat for a day or two new plugs were installed an it fired right up. You shut it down to do something an it never started again. What happened the cyl's dried out from sitting a day or so ,new clean plugs helped , it started an ran a few min ,but when you shut it down it continued dripping fuel down the intake causeing it not to refire when ya tried it the second time. When you cleaned the carb by spraying carb an choke cleaner down the throat an into the intake ,that realy doesnt do anything. Someone in the other post hit it right on the head. The problem is in the internal part of the carb. If you can get started again remove the nut on top of the flame arrestor an only when you shut the eng off or it stalls on its own ,quickly remove the flame arrestor an look down the throat of the carb an see if fuel continues to dribble down into the intake. Speaking from exp ,please dont ever remove the arrestor an look down the carb when that eng is running. Espeacialy when your diagnoseing a fuel prob. From what you were describeing this is just something to look at. A dirty carburator. Good luck to ya

 

[larr630]

Re: Mercruiser 4.3 LX

Hi Guys. Had the same issue with my 4.3l. The motor has a safety feature. You need to replace the oil pressure safety sending unit. Its located on the passenger side of the motor right below the last spark plug. Runs about $65.00 These sending units go bad even if you have good oil pressure. It stops you from blowing the motor if you loose oil pressure. But mine went bad and it would run for a few seconds and die. I replaced this sending unit, and it runs fine. Let me know if that works. It is the oil pressure switch and the safety switch that both need replacing.