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Author Topic:   1999 Mercury OptiMax 200 Runs Poorly Above 2,300-RPM
tamtam posted 03-25-2012 03:52 AM ET (US)   Profile for tamtam   Send Email to tamtam  
Hi. I´m David from Spain. I have a problem with my 1999 Mercury Optimax 200-HP outboard engine. The engine [starts] right, but when arrive at 2,300-RPM the engine falls off. The engine doesn't stop but runs jerkedly. If put into REVERSE gear, the engine will run up to 5,000-RPM, and If I accelerate with the throttle with the gear case in NEUTRAL, the engine will run up to 5,000-RPM, too. But, when I test in the water and put the engine into FORWARD gear, all goes well until 2,300-RPM.

The engine has 275 hours, I changed the spark plugs and cleaned the filters and pumps. In the past I had problems with it, and the mechanics did not find the cause. Finally, thanks to a internet forum, we found the troubl; it was the crankshaft position sensor. I replaced it and [the 1999 Mercury OptiMax 200 has been] OK up to now. Please--I need help. Any idea what is the matter this time? Thanks you very much.

jimh posted 03-25-2012 08:10 AM ET (US)     Profile for jimh  Send Email to jimh     
From your narrative, it appears that the engine will run above 2,300-RPM only when the load on the engine is limited. When you accelerate the engine to 5,000-RPM in NEUTRAL, there is very little load. And when you accelerate the engine to 5,000-RPM in REVERSE, there is also less load because the propeller is probably ventilated. Therefore it seems that the limitation of 2,300-RPM when in FORWARD and trying to propel the boat is from the load on the engine.

One reason an engine would bog down under load is from loss of power from one or more cylinders. Have you checked the spark ignition for each cylinder individually? Insert an in-line spark tester in the high-tension spark wire to each spark plug, one at a time, and observe for the presence of a spark during the time the malfunction occurs. You can make this test on the water with the engine pushing the boat. If you make the test late in the day as the sun is setting you will be able to see more easily the spark jump across the spark gap in the tester.

If your test shows that there is good spark to all cylinders when the problem is occurring, then the cause of the problem is probably related to fuel delivery.

Teak Oil posted 03-25-2012 09:44 AM ET (US)     Profile for Teak Oil  Send Email to Teak Oil     
When you pulled the spark plugs did they all look the same or was one or two blacker or wetter than the others? May indicate an issue with the coil on that particular cylinder.

Also it is not recommended to run the engine to 5000rpm too often or too long without a load on the motor. When sitting still or on a hose outside of the water you could starve the water pump and damage it

lakeman posted 03-26-2012 06:07 AM ET (US)     Profile for lakeman  Send Email to lakeman     
It is a possibility that your throttle position sensor is the problem. I had this problem for years, the TPS, was not bad, but some how after long time periods without use, the shift cables would become stiff, after use,they would lessen up and it would run properly. On the dark side the TPS, could be bad.
tamtam posted 03-28-2012 05:40 AM ET (US)     Profile for tamtam  Send Email to tamtam     
Thanks very much for your answers, I´ll try all you say and I´ll tell you the results.
Many thanks for your kindness.

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