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  Mercury 150-HP OptiMax Runs Well At Idle But Stalls on Throttle Up

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Author Topic:   Mercury 150-HP OptiMax Runs Well At Idle But Stalls on Throttle Up
btet posted 07-29-2010 03:12 PM ET (US)   Profile for btet   Send Email to btet  
My 1999 Mercury 150-HP OptiMax engine starts and idles great, but when [I] give it some throttle, [the OptiMax] cuts out and dies. I have changed [the spark] plugs and fuel filter. [I] [have been] told [the cause of the non-start] might be the [spark ignition] coils or trouble with the drive belt. [Has] anybody [encountered a Mercury 150-HP OptiMax which would not start and the cause was the spark ignition coil or trouble with the drive belt] before?
grosseile88 posted 07-30-2010 09:41 AM ET (US)     Profile for grosseile88  Send Email to grosseile88     
I owned a 1998 Optimax for 10 years and loved it. The problem you are describing could be the fuel injectors. Any clogging or blockage will stop them from doing their job or spraying a fine mist of fuel and oil into the cylinder. The problem with those engines be so high tech they are really hard to trouble shoot unless you take it to dealer and hook it to computer. Could also be a faulty rpm limiter gone awry and thinks your engine is overheating or something. Unfortunately the only way to save a lot of frustration is to hook it up and find the error codes. Gook luck!
jimh posted 07-30-2010 10:01 AM ET (US)     Profile for jimh  Send Email to jimh     
Re the possible cause of the stalling being due to an ignition spark coil or the drive belt:

The engine stalls when the fuel-air mixture is no longer combustible. There are three elements to the combustion:

--spark
--air
--fuel

If you can verify that you have good spark, you can eliminate the spark as a source of the problem. To test for spark ignition at each spark plug, insert an in-line spark tester into the spark plug wire lead. If there is a loss of spark when the engine throttle is increased, it should be noticeable while observing the in-line spark tester. The presence of good spark would tend to eliminate an ignition spark coil as being the cause of the problem.

The "drive belt" operates from the engine crankcase and drives two important auxiliary devices, the automotive-style alternator and an air compressor. The air compressor is critical to operation of the OptiMax engine, which relies on the Orbital Combustion Process, a technology developed by ORBITAL, an Australian company, and used under license by Mercury in their OptiMax engines. The air compressor supplies air at an elevated pressure to a distribution system which feeds electrically operated injectors that push the air into the combustion chamber. If the air compressor is not able to produce air at an elevated pressure, the Orbital Combustion Process will not work properly. This could lead to stalling, as it affects the fuel-air mixture.

If the "drive belt" is not operating the air compressor properly, the drive belt could be the cause of the stalling.

To proceed further in testing and diagnosis of the problem, it would be helpful if you had a factory service manual, and any specialized test equipment required. Mercury engines tend to use a proprietary digital diagnostic test tool, which is expensive and often difficult to obtain.

btetr posted 08-12-2010 02:10 PM ET (US)     Profile for btetr  Send Email to btetr     
Thanks for ideas,but i think it might be Merc mechanic time as i am not set up for anything more than i have already done
contender posted 08-12-2010 04:18 PM ET (US)     Profile for contender  Send Email to contender     
btet: crank the boat up on your trailer, pull the plug wires one at a time, to see if you have a dead cylinder. If you have a spark (should be able to see it) then you know that that cylinder is not getting fuel. Use a plug puller with a towel so you do not get shocked, or let one of your friends do it....good luck
RM posted 09-13-2010 05:01 PM ET (US)     Profile for RM  Send Email to RM     
Hope this helps:

I have just gone through a similar issue with my 150HP 2000 opti. It would be hard starting, stall on its own or when put in gear, run rough and get my alarm horn going off.

IT ended being a few things:

1. cracked tracker valve (its only a rubber diaphram) - easy to change, only 4 allen screws but cost $125

2. Both throttle position sensors were flakey(was causing the alarm horn to go off)

3. The VST float needed adjustment (was allowing to much fuel in)

After this the engine starts easy and idles smoothly, throttles up without stalling and actually runs quieter.

Check out this site ThePelicanServices.com

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