Engines dies on rough sea.

[asbennett]

OMC 2.5L 4 Cyl 1982 120HP I/O with a 400 series outdrive. My boat was running fine over the 4th of July holiday weekend. I took it out the following week and after running wide open on and off for about 1 hour the engine started to die. Symptoms are as follows: Engine starts fine and idles fine. Will run full WOT then drop about 500 - 1000 RPMs. After about 30 seconds of dropping RPMS the engine drops to idle. It will sit at idle with no problem. *** I noticed on smooth water that the problem did not occur. If I turned hard or hit a wake it started to act up again. The 19 gal fuel tank was at least half full. Two years ago the points / plugs and coil were replaced for a similar problem. Any ideas? Coil bad again? Fuel problem - maybe the pick up tube in the tank?

 

[Boomyal]

Re: Engines dies on rough sea.

How old is your fuel pump? If it is original I would highly suspect it. A dying pump acts erratic, usually starting by starving the motor at high rpm/load. I think the rough water is a coincidence.<br /><br />If by chance it is not a coincidence you could have a carb float starting to leak.

 

[Haut Medoc]

Re: Engines dies on rough sea.

I agree with boomyal, if the fuel pump is 22 years old it probably should be replaced anyway. Most are real easy to do.J

 

[asbennett]

Re: Engines dies on rough sea.

Fuel pump is 3 years old. Should I replace it anyway? What are some other "clues" to look for?

 

[elpaso]

Re: Engines dies on rough sea.

Rough water only ? Should have no effect on fuel pump.<br />But debris, rust etc. in tank could block fuel flow tube.<br />Also could jam float in carburetor.<br /><br />Does engine - pop-backfire-surge-anything.<br />What makes problem stop or go away ?

 

[Wingnutt]

Re: Engines dies on rough sea.

Also while youre checking things out, take a look at your float level in the carb. Over time these things develop leaks (from the haet cycles and viberation) and can cause the feul level in the bowl to rise. It sloshes into the venturi in rough water and can cause your engine to run rough or stall. Hope this helps.

 

[asbennett]

Re: Engines dies on rough sea.

Bringing the boat back to idle makes the problem go away. The carb was re-built 2 years ago - I am still going to check the float and also look for debris and other clues. More to come...

 

[asbennett]

Re: Engines dies on rough sea.

There is no pops or backfires just starts to die (looses RPMS) just like you you expect if you ran out of gas - except there is gas in the tank and when I pull back to idle it will run (at idle) all day.

 

[crazy charlie]

Re: Engines dies on rough sea.

Check and change your carb filter,it may have an automotive filter in it instead of a marine.An auto has a check valve that would close at a certain angle and the rough seas may mimic the angle hence opening and closing the valve.Just a thought ,worth taking a look at.Charlie

 

[Rainmaker]

Re: Engines dies on rough sea.

You may also want to check the fuel tank vent. A clogged vent will cause these symptoms.

 

[asbennett]

Re: Engines dies on rough sea.

I have checked the points and rotor cap - no problems there. I checked the out drive fluid - all looks clear and full (checked because I am having a hard cluck after shifting into gear). Checked fuel filter (it is about 2 years old - replaced). I still have to check the tank vent. I had put a new fuel sending unit in the tank (19 Gal tank) about 1 month ago. No problems with the install - do you think I could have knocked the fuel pick-up tube loose or something inside the tank? Maybe it is sucking air when the waves get rough? More to come...

 

[Boomyal]

Re: Engines dies on rough sea.

Did you check the anti-syphon check ball and seat in your tank pickpup assy.?

 

[asbennett]

Re: Engines dies on rough sea.

No - can this be checked without removing the tank? it's a real pain to get that thing out.

 

[DaveM]

Re: Engines dies on rough sea.

My first thought was the anti-siphon valve. The best way of checking is to use an aux. gas tank. But if it is a real pain to get to, then just replace it.

 

[balbarracin]

Re: Engines dies on rough sea.

I am having a similar problem. I have a 1990 4.3l v-6 with carb. I can run it at about 4500 RPM in the drive way but when I get to the river and it is rough it will act like it is not getting any gas. Sometimes it will die but 9 times out of 10 it just decelerates. If you back off of it to about 3000 rpms it will run ok for a while. I noticed the fuel pump had been replaced with one from NAPA could this be the problem?

 

[bradrulz]

Re: Engines dies on rough sea.

oh man! this is absolutely the same symptom i'm diagnosing right now with my recently purchased 1979 OMC 120HP I/O. I mean I was speed-reading through all the posts in hopes of finding a definitive answer. Let's please keep the channel open. I'm personally leaning towards my COIL, as it's pretty old and gunked up. My number 4 cylinder most likely has a broken or worn out ring, as it only tested 60 psi (versus the 110-120 for the others), then jumped up to ~200psi after the wet test.<br /><br />And I have a new alternator, relatively new fuel pump, plenty of good gas. So strange, i mean almost EXACT symptoms... was out cruising fine for about an hour, water temp warmed up to around 160F, really banging heavy waves, then periodic rpm failures, dragging us down. Sometimes she'd stall right out, sometimes i could save her by pulling her into neutral, usually she'd stall. Then, 10 seconds later, after you look yer buddy in the eye, half panicked, half wanting to laugh, she'd crank right back up again, and head on out. Shortly thereafter, same thing, until she dragged down in rpm's. We limped back to shore, and in the 5mph no-wake zone she purred like a kitten (yeah, even on only 3.5 cylinders). <br /><br />-brad

 

[Haut Medoc]

Re: Engines dies on rough sea.

Dumb question, have you changed your water separaters? This sounds like a fuel problem. It's starving for gas, and even a little water is no good. A fuel pump on it's way out will act erratically high R.P.M. J

 

[Boomyal]

Re: Engines dies on rough sea.

OMC, unscrew the fitting, in the top of your tank, that has the hose running to your fuel pump. Pull the whole assembly out. It will also contain the pickup tube, going to the bottom of your tank. Some where in that assembly should be the check ball and spring. My '75 did not have one, but I think all had them by the 80's.<br />My pick up tube was made of plastic. It looked so brittle that it could have snapped off at any time. I soldered a copper tube in its place.

 

[asbennett]

Re: Engines dies on rough sea.

I am going to focus on the fuel tank and lines going to the pump - then from the pump to the carb to make sure fuel is getting through. Tough problem to test out of the water since it only happens when hot.

 

[John Harting]

Re: Engines dies on rough sea.

I know this issue hasn't been active for 18 months but I have the same issue on my 2.5L 4 banger on my houseboat. I will be crusing at 3K RPM, and the motor drops to idle, does not stall or run rough. Put the shifter into neutral, engage forward and it goes back to 3K RPM with no problem. It does the same thing when holding the houseboat to shore when we are staking it down, which is when it can get exciting (drops into idle and the wind starts pushing it to shore). No rough seas here, new fuel pump, rebuilt carb, copper fuel pickup in a custom 120Gal tank with 90+ gallons of fuel. I consider myself a pretty good mechanic but I cannot figure out how it goes from 3K RPM to 600 RPM with no starving or ignition symptoms and recovers every time. I didn't see the results of some of the suggestions here and wanted to reopn the topic if possible.