MerCruiser Power Problems

[tsal]

Hi all,<br /><br />I have a 1989 4.3 Alpha 1 Mercruiser. It starts OK, and idles OK, but after about 30 minutes, the high speed RPM drops to about 2,500. I can idle down, but when I try to throttle up it coughs and pops out of the exhaust. If I remain at idle for 20 minutes or so, or shut it down for the same amount of time, then my top end is back. Any ideas would be appreciated - I think it's fuel related, my brother feels it is electrical...

 

[wavskipper]

Re: MerCruiser Power Problems

Does it heat up significantly ? Could be a lot of carbon on the heads inhibiting your "burn" of the fuel . Don't think electrical would cause this.

 

[tsal]

Re: MerCruiser Power Problems

Nope, it's not heating up too much; Probably about 120-140F

 

[trevorcday]

Re: MerCruiser Power Problems

I just fixed a 5.0L mercruiser with similar symptoms. It turned out to be the ignition sensor inside the distributor cap. This motor had the Mercury Thunderbolt IV electronic ignition.

 

[tsal]

Re: MerCruiser Power Problems

Thanks, I'll check that out; is there a way of testing this?

 

[johot321]

Re: MerCruiser Power Problems

http://www.marinemechanic.com/site/tbolt-IV-trouble.gif <br /><br />Try this site. Trent sent it to me and I was able to troubleshoot my problem back to the ignition sensor.<br /><br />But I'm leaning towards a fuel problem as well. My igntion sensor would'nt allow the engine to fire at all.I would make sure the fuel tank was vented properly, by pass the water seperator (temporarily with an in-line filter just to test it),and change your fuel filter.

 

[port jeff boater]

Re: MerCruiser Power Problems

im also having similiar problems. i have a 1986 140 3.0 mercruiser and when i give her full throttle after about 4 or so minutes i get a rattling(friend says its a ping) and then the rpms drop and the boat slows, after bringing the throttle back for about 15 seconds i give it full throttle and after about 4 or so minutes i get the rattling back and the rpms drop and the boat slows, i replaced the water separator, no evidence of water in it,, replaced the fule pump filter,that looked pretty clean, replaced the inline carb filter, that was grey and had a little dirt in it,, havent taken her out yet, if the same problems what could it be????? also changed the fuel supply line from the water separator to the fuel pump,, thanks alot,, im losing sleep over this..