1984 3.0 Mercruiser quits suddenly.

[180American]

My 1984 Mercruiser 3.0 140 (1984 Wellcraft American)ran great for last 2 seasons until this year. First day out we went for about a half mile at 3/4 throttle and it quit right now. Almost felt like the engine locked up or vapor locked. It barely turned over at first and after 5 or 10 minutes it started ok. On the way back to the dock at around 2000 RPM it did it again. I've drained the fuel tank, it was clean, blew out the pick up tube, checked the anti siphon valve, replaced the fuel line, checked fuel pump for pressure and flow, rebuilt the carburator, installed new elctronic ignition, replaced the coil, spark plugs, set the timing, replaced all fuel filters. After all this it does the same thing. In fact, it will idle and run forever in neutral and up to 1500 RPM in forward gear, at 1800 rpm it quits abruptly every time. I can also run it in the driveway in or out of gear at any RPM with no problem. Anyone want to buy a boat?

 

[SpinnerBait_Nut]

Re: 1984 3.0 Mercruiser quits suddenly.

Welcome to iboats 180American.<br />Don't be to rough on the boat yet.<br />Let's get this over to the Merc/Volvo/OMC I/O forum for some help.

 

[lilmandavis]

Re: 1984 3.0 Mercruiser quits suddenly.

ill give you 200!

 

[Don S]

Re: 1984 3.0 Mercruiser quits suddenly.

You seem to have thrown a lot of parts and money at it for no reason.<br />Did you you loose spark?<br />Did you loose fuel to the engine?<br />Did you loose all power to the engine and gauges?<br />Did you check for any water in the cylinders or on the old plugs.<br />Without an answers to those questions, you shouldn't have replaced anything.

 

[Mile-High Mariner]

Re: 1984 3.0 Mercruiser quits suddenly.

Whew, boy, you did get a little happy with the shower of parts, didn't you! Don's right (duh) but, since you've already replaced all that stuff, I would recommend you check your compressions. Also, I'm a little suprised that, with all of the other work you've done (did you really blow out the fuel tank?), you haven't changed the oil. Note the oil level before you drain it, strain the oil when you do, and check your strainer material as well as the filter for metal. You may even want to pull the oilpan and examine the bottom of the sump. I'm reaching here, but you may have some valvetrain issues related to debris in your oil, and that debris may be coming from the lower end. Check it out, and share what you find.<br /><br />Also, check your EST module (it sits at the base of the distributor) - even with NEW electronic ignition systems, the module could be faulty, or you may even have the wrong one. DO NOT use an aftermarket module; experience has proved that only the GM original works, and the Quicksilver part will be your only best bet.

 

[180American]

Re: 1984 3.0 Mercruiser quits suddenly.

Ended up being a bad fuel pump. With a gauge tee'd in and on the first run the pressure held at 5 psi at 1800rpm then the engine quit. Second time it fluctuated and dropped to 4 psi then quit. Third, fourth, and fifth time at around the same rpm the pressure fluctuated wildly from 2 to 5 psi and stayed that way even at idle. Near as we can tell the diaphram is tight enough to keep the pressure steady when cold but after 15 minutes or so of operation and heating it looses it's tension and causes the pressure to fluctuate. <br /><br />The parts replaced were'nt for not. The fuel line was in the boat since 1984 and cracking, I've put points and condensor in it for the past 2 years and with the est it runs smoother than ever, there was an eighth inch of crud in the carb. bowl and the accel. pump was rotted. The coil was the only thing I questioned and was high dollar so I took to my parts store and had it tested, found out resistance was very low as well as output voltage.

 

[rplky]

Re: 1984 3.0 Mercruiser quits suddenly.

SBN... thought I was the only wildcat on iboats

 

[harveje]

Re: 1984 3.0 Mercruiser quits suddenly.

180American <br /> <br />Did you have to cut your metal line from the pump to the carb or is it rubber? They make a carb nut with a small barbed fitting to checking pressure but I can't find one..

 

[180American]

Re: 1984 3.0 Mercruiser quits suddenly.

Didn't have to cut anything. I put a pipe tee in the pump and finnessed one side together to hook up the carb line and fitting and the other side went to the gauge. Pretty slick set up and it worked. Nothing bent or damaged.