01 sea ray 180 3.0 merc rough running stalling elec feedback?

chris180searay

Recruit
Joined
Oct 18, 2010
Messages
2
my 3.0 mercruiser will not run right unless I disconnect my alternator. I start it without the 2 pin connector in the alternator and it runs perfect. plug in the 2 pin connector and instantly, the spark gets erratic and it eventually dies.charging at 14.0 volts. I am auto tech, but I am stumped on this one. all my cables and connections ohm out perfect, no crazy voltage drop anywhere. new battery and distributor last year. was running perfect till last weekend. I threw in a known good coil for the hell of it. seems as if the alternator is back feeding. as a sidenote, while its idling like crap if I operate the trim motor or unplug/plug in the elec choke it clears up for a second or 2. please, any insight would be helpful!!
 

achris

More fish than mountain goat
Joined
May 19, 2004
Messages
27,468
Re: 01 sea ray 180 3.0 merc rough running stalling elec feedback?

Hi Chris and welcome to iBoats.

Can we start with an engine serial number please. This makes it easier for people trying to help you to be able to look up your engine and see exactly what we're working with. Also, what ignition system? The 3 litre has had 3 different systems over the years. Being 01 it's most likely EST, but we do need to confirm that...

Have you had the alternator tested? You can take it to any auto shop and they should be able to test it. Or try swapping in a known good one. If you have a shorted diode in the alternator it's possible the AC on the output could affect the ignition system. The use of the trim pump may be enough to reduce the amplitude of the AC spike enough to stop messing with the ignition system..


Chris........
 

chris180searay

Recruit
Joined
Oct 18, 2010
Messages
2
Re: 01 sea ray 180 3.0 merc rough running stalling elec feedback?

thanks for the reply, it is a 3.0 lx 140 hp. it is a delco est ignition. I had the alternator tested and everything looked good!! he told me the diodes were good. I still wonder if it is an issue though. its the only thing that makes sense to me still. is this something I could possibly measure?
 

achris

More fish than mountain goat
Joined
May 19, 2004
Messages
27,468
Re: 01 sea ray 180 3.0 merc rough running stalling elec feedback?

If you have an oscilloscope you could check the main power for spikes and fluctuations...

A simple check for AC ripple is to use a multimeter set to the AC volts range and put that on the alternator output. The meter will show 12 volts for a brief time, then drop to 0. If it stays above 0, you have AC ripple....

Chris......
 
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