No spark after 2 min. - 4.3 Merc., tachometer involved?

robbmcc

Cadet
Joined
Aug 10, 2007
Messages
7
Hi All,
Been thru the FAQs and searched a bit so now I'm posting - first time so I hope I get this right.

First, this is a 2004 Mariah with 4.3 carb Mercruiser. It was winterized last fall and now I can't get it going. I turn the hose on (still on trailer luckily) and start it and it runs perfectly for about 2 min. then dies and won't restart for a couple of hours when the same scenario will repeat.

New fuel separator filter installed, cleaned screen on carb where fuel line comes in and fuel pump has 12V while cranking but it is not fuel I believe. I hooked up a spark detector to one of the spark plug wires at the spark plug (and also did this at a couple of other plugs just to verify) and had visual confirmation that what is happening is this: after 2 minutes spark goes away. Then it got dark outside and I had to pack it in. I realizednext I need to confirm spark between coil and distributer goes away, right? Then I don't know what as I am new to this. But reading the Mercruiser manual last night it mentioned disconnnecting the tachometer grey lead while testing, hmm, I did notice that when it reaches the no spark stage the tachometer was going berserk. Could a short in that tach wire cause a no spark? Maybe the shaking of the running motor chafes and after 2 min. it shorts? Just looking for some next logical steps from some experts. Can't wait to get over this afternoon and thanks in advance for any advice.


Robb McC
 

Don S

Honorary Moderator Emeritus
Joined
Aug 31, 2004
Messages
62,321
Re: No spark after 2 min. - 4.3 Merc., tachometer involved?

Yes, you will need to verify that you have lost spark. Disconnect the gray lead from the tach and see if it keeps running.

One question, are you giving the engine some throttle or just leaving it at idle when you start? Are you getting any black smoke just before it dies?
 

robbmcc

Cadet
Joined
Aug 10, 2007
Messages
7
Re: No spark after 2 min. - 4.3 Merc., tachometer involved?

Thanks Don,
No black smoke just dies and yes just a little throttle, not much. It actually doesn't matter I've tried revving a little higher and it still dies at around the 2 min. mark.

Robb McC
 

robbmcc

Cadet
Joined
Aug 10, 2007
Messages
7
Re: No spark after 2 min. - 4.3 Merc., tachometer involved?

Don,
So the tachometer it was. I went over last night, checked spark between coil and distributer (disappeared after 2 min. just like at the plugs) then tested the coil per a post I saw here (coil good) then disconnected the gray wire at the tach that goes back to the coil/dist. Bingo! boat now runs perfect and doesn't die after 2 minutes. Will shop at my convenience for a tach or perhaps with nothing to lose disassemble it and see what I can see. Thanks to you and this forum which is an invaluable source of troubleshooting info for me.
Robb McC
 

Maclin

Admiral
Joined
May 27, 2007
Messages
6,761
Re: No spark after 2 min. - 4.3 Merc., tachometer involved?

:) Good deal, I was watching this one, glad that was it...it has happened to me before on more than one automotive OEM in-dash unit.
 
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