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Charles, Marine Mechanic
Category: Boat
Satisfied Customers: 3862
Experience:  US Navy (Ret) Certified Mercury Marine Tech with over a decade of repair experience.
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My 2008 150 optimax is not getting full power. In neutral,

Customer Question

Hi my 2008 150 optimax is not getting full power. In neutral, it will rev to 2500 then a continuous alarm. In gear, it will run out to 4200 , has low power and no alarms are going. BOat has just been serviced. Have checked fuel and plug leads - any thoughts
Submitted: 1 year ago.
Category: Boat
Expert:  Charles replied 1 year ago.

Hello, my name is***** will assist you today.

Would you please post the serial number of the engine?

What all was done in the service of the boat?

Customer: replied 1 year ago.
Serial Number is ***** Re the service. It was a full service , plugs, water pump etc. The alternator was also replaced
Expert:  Charles replied 1 year ago.


When you are underway and the power is lost, is there also an alarm?

Do you have a multimeter?

Customer: replied 1 year ago.
Re the power, it is slow out of the hole and there is no alarm. The engine sounds OK, just down on power. There is no alarm whilst underway.
Customer: replied 1 year ago.
I do have a multimeter
Expert:  Charles replied 1 year ago.


First inspect the plug wires fro the top 2 cylinders. The temp senders are really close to the plugs. Sometimes the sender will rub a hole in the boot. If they are good. Preform the test on page 3 of this bulletin. Do this to all 6 coils. Somewhere you do have a bad one, just need to locate which one it is.

Customer: replied 1 year ago.
ok - will go and look and get back to you
Expert:  Charles replied 1 year ago.

Sounds good. i willl be here for a few more hours tonight and most all day tomorrow.

Customer: replied 1 year ago.
the pcm is reading 0.5 ohms, which is what they say is OK . Should I Still test the coils?
Customer: replied 1 year ago.
charles., have checked teh pcm and all coils.. they are all good.
Expert:  Charles replied 1 year ago.

Hello, when you had replied, I had already logged off.

Did you look at the boots for the top two spark plugs? If they are grounding out, there wil be black marks on the outside of them?

Which spark plugs did the shop install?

Customer: replied 1 year ago.
The boots seem ok. The plugs they put in are the expensive ones? Cant remember the type.
Expert:  Charles replied 1 year ago.

Do you have a gauge that can read fuel pressure of at least 40 PSI?

Customer: replied 1 year ago.
Charles, I dont. I have checked the fuel flow to the engine and this is OK.
I am surprised I am getting the warning alarm in neutral - It is a continuous alarm that seems to kick in at 2500rpm.
There is no alarm when the engine is in gear - just limited power
Expert:  Charles replied 1 year ago.

The alarm in Neutral, is just that, a neutral overspeed warning, it does activate at 2500 RPM and is normal. I am thinking that you have a failed grommet in the VST, a gauge would tell us that.

Customer: replied 1 year ago.
Ok - any other way of checking it...can it be removed and inspected?
Expert:  Charles replied 1 year ago.

Yes there is. You can open and inspect the grommet on the top of the high pressure pump. Part 30 in the diagram.

Customer: replied 1 year ago.
charles, have had a look at doing this and decided itis too difficult to do on the edge of the lake. Will be returing home tomorrow and will try to do next weekend. thx
Expert:  Charles replied 1 year ago.

No worries. On the weekends I am on here most all of the day.

Customer: replied 1 year ago.
Charles, Is there any risk to running the motor at low power?
Expert:  Charles replied 1 year ago.

If the grommet is the issue, you will be down on power and could run the motor lean. That would be the main issue.

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