Mercruiser V-8 Missing After Engine Gets Hot

[joyceenglish]

1997 Mercruiser 5.7L V-8 I/O 210hp Thunderbolt V-Ignition System<br />Desperate!! Small area with limited boat mechanics who know what they are doing.<br /><br />Our boat runs great for about 45 minutes to an hour and then it starts hesitating and missing. You can let it cool off for a while and it will run great for another 45 minutes or so. This is not constant running. I am talking about with stopping to put kids on and off tubes. We have changed the plugs and put in a new tank of fuel. After doing this, with just myself in the boat and not pulling anyone, I ran the boat nearly non-stop for over 30 minutes at various speeds. I would stop for a minute or two and recrank it. It ran perfectly. Today we took it back out, and after about an hour, it started missing again.<br /><br />When it starts this missing, it only misses when the engine is underway and pulling a load. If you stop and shift into neutral, it won't miss a lick. Any help would be appreciated. Our next thought would be new plug wires. Also but maybe totally un-related is that it is difficult to start if it sits for any amount of time. We had new distributor cap and coil wire put on at the end of last season. <br />If we take it to the only reliable service center around here, they will put it in the water for a few minutes and say that it runs great. <br />Is there any place on line that I can see a diagram of marked parts on the engine so I can no where to check. I have small amount of knowledge about engines, but can probably figure it out with a little help. Also, is it damaging to the boat to continue to run the boat in this condition? <br />E-mail if necessary to jenglish8577@yahoo.com

 

[hondon]

Re: Mercruiser V-8 Missing After Engine Gets Hot

First of all ,when is the last time you changed the water pump impeller in this unit?If you do'nt know ,or never have ,you are way over due to do so .An overheat may well be causing your trouble.

 

[conimicut1]

Re: Mercruiser V-8 Missing After Engine Gets Hot

when you say it gets hot, what do you mean, the temperature gauge is showing the engine going over 140-160 degrees or the engine gets to normal operating temperature and shows a problem after driving for awhile? If you have a temperature problem, it could be a impeller or manifolds/riser. If it is not a overly hot engine, it can be the carb, particularly the float.

 

[DaveM]

Re: Mercruiser V-8 Missing After Engine Gets Hot

This sounds a lot like what I was experiencing, except I would out right stall after cruising for a while. After getting a tow in and back home it would fire right up and purr like a kitten. People told me the cause was everything from fouled plugs to needing a carb rebuild. Replaced plugs, cap, rotor, and fuel filter all to no avail. <br /><br />It turned out to be corroded terminals on the fuel pump. The pump would begin to fail only after things warmed up. It ended up starving for fuel while under load. I replaced the pump and she runs better than ever. <br /><br />Here's what to look for, provided you have a similar pump (I'm told Merc. and VP were the same). Locate the wire pump leads, they will plug into a plastic connector that forms a Y on top of the pump. Unplug the wires and see if this Y connector moves at all (newer pumps have this connector integrated into the pump). If yes, you can pop it off and look for corrosion. Or maybe better to just replace it before it gets worse.<br /><br />Good luck.

 

[joyceenglish]

Re: Mercruiser V-8 Missing After Engine Gets Hot

I replaced the coil and the last two times we have went out, it has not cut out. However, a couple of times I thought that it sounded like it wanted to. I don't know if I was being paranoid or not. It would not stall out all together, it would just start missing. I finally figured out what was wrong with it being hard to crank. It was my own stupid fault. I did not have the throttle moved over far enough. I did not realize that it had to go over past the forward gear mark, to be receiving gas. I read the whole manual, and finally realized what I was doing wrong. That problem is solved.<br />I think your idea about the fuel pump could definitely be on the nose. If it messes up again, that will be my first move. Do you think I could just clean the leads, or do you think I might out to just go ahead and replace the fuel pump? This is our 6th summer to use the boat. We do not use it in winter at all. It stays covered under and open shed with a roof in the winter, so is it possible that they could be getting corroded just from moisture?<br />Thanks for the help.<br />Joyce English