Mercuirser 4.3LX 1993 has spark but wont start

[mr-steve-jones]

Hello All,

Its my first visit to the forum and I've checked a lot before posting my first thread.. Any advice really appreciated!

I used the boat last weekend, stood up while driving and pulled the kill switch. Since then it has not started. First I got a "click" without turning over a few times (as if flat battery) and then a very slow turn of the crank after a few mins (as if batteries self recovered slightly). I suspected battery problems so I got a tow back and trailered home. I purchased a battery tester with load and without recharging both batteries check out at 12.8V and 12.6V and drop only 1V under load test, so both check out good. The engine is now cranking well, so thats a mystery!.

I first checked the kill switch. I get 12V from the ignition switch purple wire to the kill switch when key is on, the switch works fine and I can measure 12V at the +ve of the coil when the key is turned to "ON". Kill switch OK.

Fuel.
The fuel is only 1-2 weeks old and ran fine for 3 days, even on the day the engine died. I push the throttle and the barrels of the carb are wet and I can smell fuel.

Spark.
I took off the central spark lead and it sparks rapidly to ground when the key is turned. I took off a couple of plug leads and get a spark to ground from them. (And a belt to my hand.. Thats a powerful kick!)

I renewed the connection on the oil pressure switch but think this is not the issue from what I read this would only stop a started engine, and isn't used on startup?

So please help...
I have fuel,
I have spark,
I guess I must have compression as the engine was running until I killed the switch.
I'm starting in neutral, not in gear.

One thing I notice is that the fuel pump continues to run for a few seconds after I stop cranking sometimes>? Is this normal to re full the carb fuel chambers?

Any advice on where to look is really appreciated..
Many thanks.. I'm in England.

 

[Bondo]

Re: Mercuirser 4.3LX 1993 has spark but wont start

Ayuh,... Welcome Aboard,....
Pull the Sparkplugs for a look...

Killin' it so quickly like that, ya mighta backwashed the exhaust, 'n sent water into the cylinders...
How's the oil level,..??

Ya need Fire at the sparkplugs,...even though ya see it at the coil wire...

 

[mr-steve-jones]

Re: Mercuirser 4.3LX 1993 has spark but wont start

Hello Bond-o,

The oil level is fine and the right colour.

"Backwashed the exhaust" sounds nasty..

If I take the plugs out what am I looking for?

Cheers,

Steve.

 

[Bondo]

Re: Mercuirser 4.3LX 1993 has spark but wont start

If I take the plugs out what am I looking for?

Ayuh,... Spark plug color, condition, spark, and/ or water...

 

[mr-steve-jones]

Re: Mercuirser 4.3LX 1993 has spark but wont start

Bond-o,

You are a genious !.. I am really sad right now. It's 23:00 UK time so I'm having a whisky now to drown my sorrows.

I went straight for taking the risers and manifolds off before the plugs. They were soaking inside :-(

That would explain why when I turned the key to re start it, the engine wouldn't turn over and appeared to give the impression the batteries were flat. it was hydraulically locked. When they eventually turned, that would be the mother load of water being squirted somewhere, allowing a sluggish turn over I guess?

I took all 6 brand new spark plugs out and they were soaked and black probably from exhaust carbon. I cranked the engine to release any water and the engine spun freely once again. Thats a good sign as the crank still seems OK.

I sprayed penetrant release oil into all 6 pots and cranked the engine to give some protection. The weekend I had planned has changed somewhat :-(

I'll drop the sump off in the morning, clean and flush it all out with new oil and change all filters and put it back together.. Fingers crossed in hope that I've bent nothing

Thank you very much for your advice, I'm just so annoyed your diagnosis is right!.. Why couldn't it have just been a loose wire??? ARGGGHHH!

I'll post again tomorrow to advise if all is well.. It's great to have such a pool of experience at everyone's finger tips. I think my next post will be... "How to stop your exhaust flushing?"

Thanks again.. spot on diagnosis!

 

[Bondo]

Re: Mercuirser 4.3LX 1993 has spark but wont start

I think my next post will be... "How to stop your exhaust flushing?"

Ayuh,... If yer boatin' in the Brine, ya wanta get that thing runnin', ASAP, Pronto...

Sorry I was right,...

The exhaust shutters usually stop that from happening,...
They're supposed to be at the top of the y-pipe...

 

[Don S]

Re: Mercuirser 4.3LX 1993 has spark but wont start

I used the boat last weekend, stood up while driving and pulled the kill switch. Since then it has not started.

If you were in salt water, and it's had the cylinders full of salt water for a week, I usually call them junk. They will not turn over again the salt water rusts the cylinders and rings together so fast is scary. 1 day MAYBE 2 if you are lucky, but not a week.

 

[mr-steve-jones]

Re: Mercuirser 4.3LX 1993 has spark but wont start

Don,

I was on a river.. Tidal but right near the fresh water source rather than the sea.. Water didn't tast salty when I drained the manifolds so fingers crossed

I'll plug the compression tester in first and hope I don't need to use my sears honing tool ;-)

 

[mr-steve-jones]

Re: Mercuirser 4.3LX 1993 has spark but wont start

Successful Update....

Dad came round to help out and calm me down today

Compression tester gave results all between 125 and 160 PSI so we were confident it would run, so we drained all oil and filter and replaced with new. These seemed OK since I don't have any history on the engine and its 18 years old.

Built it back up and it fires up and runs perfect again

Its not lumpy or rough. Need to take it down the river now to run it at the slipway for half an hour or so to get it hot and get some confidence back.

I'll run it for a trip on this oil then change oil and filter again.

Bond o, thank you for the brilliant advice.. Within 24 hours I'm up and running again. Turns out both of the exhaust flappers are snapped in half, so they are on order tonight so I won't suffer the same fate again..

Its been a steep learning curve, but I'm a lot more confident now.

I hope this can be a lesson to all to check the exhaust shutters are working.... It could have been an expensive job!!!
Steve.

 

[Bondo]

Re: Mercuirser 4.3LX 1993 has spark but wont start

I hope this can be a lesson to all to check the exhaust shutters are working.... It could have been an expensive job!!!

Ayuh,... It Coulda been New motor time....

Glad it worked out for ya Steve...