Technical Car Experts Answers everything you need: high rpm in neutral

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.

HOW TO DO LEAK TEST?

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.

Thanks.

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Thursday, February 9, 2012

high rpm in neutral? Inconsistant high RPM in neutral?

You could have a problem with the throttle cable.Inspect the cable that connects the foot pedal with the throttle body to make it go "zoom, zoom". Its also possible that the inside of the throttle body is gummed up with dirt, dust, varnish and soot. Clean the throttle body with throttle body cleaner liquid available at local auto parts store.Take off the air intake hose, and spray everything inside there until it is clean and shiny. Be aware you may have trouble starting it the first time after cleaning.But once it starts and runs properly,then for second time it will run smooth like before.

But if that is not helping,then problem is faulty TPS.Throttle position sensor located in throttle body.

To see how throttle body looks,see the image shown below :----

Also there is IAC idle air control valve motor on throttle body.If it gets dirty,the same problem will be noticed.Try cleaning the idle valve first and see,if that is not helping,then it has to be replaced.

Other possibility is vacuum leak.
To access the vacuum leak method by professional mechanics is use starting fluid. Simply spray around the engine with it running ( not on the exhaust ) and listen for a change in engine noise. Once You have found the area, turn the engine off and check for cracked vacuum hoses or leaky gaskets.

This will help.

Thanks.

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