4 CYL GM dies after running 30-45 Min

[asbennett]

Hi - I have a problem I have been chasing for sometime now. I have a 1982 OMC 4 CYL 2.5L I/O. Fresh water open cooling with 2 barrel carb. After running the first 30-45 minutes the thing dies at WOT. If I throttle back to idle it will run fine. No problems starting, no problems idleing. Just when running full throttle after the first 30 minutes. Once it starts it will die everytime I throttle up. Sounded like fuel problem so I replaced the fuel pump (mechanical pump) - rebuilt the carb with new float. Temp guage reads fine - oil pressure reads fine. Replaced plugs - noticed the 1st 2 cyl plugs were very black - last 2 were normal. (not sure if this is related). I don't know what else to try - please put on your thinking caps and help if you can.

 

[B_Eager]

Re: 4 CYL GM dies after running 30-45 Min

Just as a thought, not related but possible. Bypass the shifter engine cut out switch located on the side of the motor. Heat or heat exspansion could be tripping it.

 

[snapperbait]

Re: 4 CYL GM dies after running 30-45 Min

Vapor lock perhaps?...

 

[dpminc]

Re: 4 CYL GM dies after running 30-45 Min

possibly a restricted fuel tank vent. These things can get plugged with corrosion, wax etc, and the hose can get blocked, kinked, etc. Also, a marginal coil could be suspect as this would still allow idle, and would not reach problems until the coil heat soaked.

 

[Boatist]

Re: 4 CYL GM dies after running 30-45 Min

OMC Stringer<br />I would have done exactly what you did as sounds like a fuel pump. I guess I would also check the fuel filter or better yet replace the fuel filter at the carburetor fuel line input. Make sure your crank case vent open and Flame aresstor not plugged up.<br /><br />Lots of stuff you could check but probably better to isolate problem first. To run need Fuel air mix, proper timed spark, and compression. I would start testing out on the water.<br /><br />First when it fails take off the fuel fill cap to make sure it is not a fuel vent. <br />Next I think I would put a timing light on and go on a test run to see if light still flashing when it fails. You can actually check the timing mark and note position when working ok then check again while failing. At WOT will probably be off the degree wheel. This should tell you if got a bad Coil, Dist Cap, Points, condensor, Rotor, or water in dist cap.<br /><br />Are you sure you put in the new fuel pump? Hook up a fuel pressure gage between the fuel pump and the carburetor and make sure pressure at least 4 PSI. Could also hook up a vaccum guage on the fuel pump input should have no real suction. Could be plugged fuel pickup screen in tank. Be careful of fuel leaks when checking fuel pump input or output. Any chance you have added a fuel pick line for a Kicker motor where fuel pump could be sucking air or a loose fuel hose between tank and fuel pump? A small leak in fuel line where it comes up to fuel pump?<br /><br />If you check your fuel pressure and spark while it is failing should have a idea which way to go.<br /><br />Make sure come back and tell us what fixes it.

 

[asbennett]

Re: 4 CYL GM dies after running 30-45 Min

Good ideas, Thus far - I have checked the compression 137 PSI - (Book suggest 130). +/- 2 PSI between each CYL. New mechanical fuel pump - after the engine died since replacing the pump - On the water I took the fuel line off the carb and cranked - pleanty of fuel - will check the pressure next. I have NOT checked the tak (vent, pickup, lines) That i next. Also, I have a distributor cap, rotor, points, and condensor to replace. I will let you know how it goes. Is there anything else to replace will I have it apart? Keep the ideas coming - I chased this all last year with no luck - I am determined to not give up until I find the problem. Thanks-

 

[DaveM]

Re: 4 CYL GM dies after running 30-45 Min

OMC, I had a seemingly similar, yet vastly different problem that was apparently temperature related. Confused? I sure was. With the advice from this board I connected a portable tank to my engine. It was readily apparent I was not getting any gas from the tank, but only on warm, sunny days. It ended up being the anti-siphon valve. But you've checked the fuel line. Hmmm.<br /><br />Do you have to let things cool down before restarting? <br />I'm siding with Boatist. If your tank is properly vented, then I would be looking at the coil. I've heard it said they go out with a wimper.

 

[DJ]

Re: 4 CYL GM dies after running 30-45 Min

OMC,<br /><br />Also check the ignition coil. It should have only about 9.5 volts going to it. If it has 12 volts or more, it will overheat.<br /><br />If it has 12v, you will need a ballast resistor in the ignition wire going to the coil. These are available at auto stores and are OK for marine use.

 

[MarkC]

Re: 4 CYL GM dies after running 30-45 Min

Me too about the coil. I had similar symptoms fixed by a new coil---though in my case the engine wouldn't run at all for about twenty minutes after it cut out.

 

[asbennett]

Re: 4 CYL GM dies after running 30-45 Min

Just to clearify: Would the coil fail at high RPM's and not low RPM's? This thing will idle all day after it starts to cut out - but once it starts to cut out, it dies everytime I throttle up. Would this be the same with vapor lock? Keep the ideas coming - don't let this thing beat us!

 

[Blue Thunder]

Re: 4 CYL GM dies after running 30-45 Min

Sounds like burnt points to me.<br /><br />BT

 

[DJ]

Re: 4 CYL GM dies after running 30-45 Min

Too much voltage will also cook the points.

 

[Boatist]

Re: 4 CYL GM dies after running 30-45 Min

OMC Stringer<br />Did you replace the Carburetor input fuel filter where the gas line comes into the CARB or at least check it??<br /><br />You could change half of your engine and not fix the problem. For this reason I would suggest you isolate the problem first. To do this you neeed to get it in a failing mode. At that point I would check spark with a timing light because it is eaiser, make sure all four cylinders have spark. <br /><br />If spark ok then need to check fuel pressure at input to the Carburetor. Should be 3.5-6 PSI at idle speed. Should also pump one pint is less than 45 seconds at Idle. The way I would check is rig a T at Carb input and hook up fuel pressure guage. Also have timing light hooked up and take for a test run. You will either loose Fuel pressure or spark. Once you know where problem is then easy and cheap to fix.<br /><br />If problem is loss of spark. Then hook up dwell meter to minus side of coil. Should be 31-34 degrees. Check for 10 volts on plus side of coil. Then check the spark wire from the Coil to distributor cap. I like to use actual wire for this short peice. Pull the distributor cap and look for moisture in top. Clean or replace points. Points need to be clean shinny with no burrs. Points spring needs to have some tension, 19-23 inch oz. Gap set to .019. Check or replace condensor. Should be.18-.23 Microfarads. Check both ends of wire from pionts to minus side of coil. Not likely will loose all 4 spark plug wires. You can remove the capacitor on the plus side of coil to make sure it is not shorting out. Only there to stop radio interference. Last check centricifical advance in distributor.<br /><br />Loss of fuel pressure. Make sure rod that pushes fuel pump are not binding up. Check for fuel line air leaks. Remove fuel cap and listen for air suction. Leave cap off for a run. Check screen at fuel pick up.

 

[raulmanny]

Re: 4 CYL GM dies after running 30-45 Min

Have you check the condition of the fuel tank? Is the boat is 20 years old and has an aluminum tank, is very possible that the tank is corroded inside creating a mud-like material that clogs the fuel line. Try installing a in-line squezze pump and if the pump collapses is because the motor is suctioning gas but the line is clogged.

 

[ICEMAN]

Re: 4 CYL GM dies after running 30-45 Min

HI, All this information is on track to finding the problem, but I'm going to go in a different direction. AFTER checking everything in your fuel system and ignition system, It's possible your problem is in the intermediate housing or lower unit. There is a shaft and bearing assembly passing thru the intermediate housing. I had one where the oil in the intermediate housing was contaminated with water and bearing was binding up after running for a while. The motor acted like it was loosing power, leading to fuel or ignition problem, but this bearing was the culprit. Just a bit of Info that might help.

 

[medic]

Re: 4 CYL GM dies after running 30-45 Min

Iceman, <br /><br />Did changing the oil fix your problem?