Wednesday, July 11, 2012

1999 Merc Optimax 200hp RPM goes High?

RPM stays there for few minutes then goes up.

At our boat repair Store we have seen several issues that could cause this type of scenario.

  • Sticking air regulator, 
  • Or the fuel pump not keeping up with demand, 
  • Or fuel pump is slow to react to throttle changes.

Its recommended to get the following test done:---

  • Get "Leak Down Test" done on the cylinders, 
  • Compression and spark test also needs to be done. 
  • Ignition test also should be done.
  • Do the self test on engine.
  • Inspect air compressor and fuel rails, test air system with shop air per tech service.
  • Inspect the injectors,if dirty clean them.If worn out replace injectors.
  • Inspect throttle position sensors.
If all this basic tests goes well then, attach the pressure gauges to the engine and test the air and fuel pressures under load. The fuel pressure should not "flinch" when the throttle is gagged, the air might do "One" wiggle.

ON many such cases its seen that Cylinders gets damaged,

These engines are very susceptible to cylinder damage.
The cylinder gets damaged due to water in the air lines, remove the lower air cross over hose and look for signs of water and corrosion, if present, more investigation is required.
To confirm the problem with engine,get the dyno test done.

Can i use Diagnostic tool to confirm the issue?

Yes you can use,but it will not detect the exact accurate fault in such cases.

There are lots of testing you can do before the "Diagnostic Computer" comes into play. In this case most of all issues are apparent in the mechanics and not in the electronics.


The leak down test and load test each cylinder. The load testing of cylinders require disconnecting each coil Pack one at a time and testing for the load change in the engine to determine that all cylinders are pulling their own load. It also shows if you have any issues at all with a particular cylinder.If you notice any problem with a cylinder,then it has to be replaced.

Getting this possibilities checked will help.

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