# 99' Optimax 200 throttle issues!!!



## captbone (Nov 12, 2007)

Having a throttle issue above 4000rpms. Runs great up to around 4200rpms and then drops down and surges back up without touching the throttle. Tried different rpms above 4000 and the same thing occurs. Check light came on but not beeping. Changed plugs/water sep/water pump/impeller last summer and only been out a few times since. Been putting star tron in at every fill up and have had no fuel issues. Has been running great up to this point. Other treads suggest a stator problem? Going to check rectifier and stator current this weekend. Anyone have any issues similar with a optimax.


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## SlingShaft (Apr 25, 2010)

*Optimax surging*

Hey there,
I have twin 99 200 Optimax's on my boat and my best bud has twin 99 225's on his boat. Between us we are getting better at diagnosing problems....albeit not because we are curious....or want to learn, lol. We both bought used engines and the problems associated. 
I had some surging problems also on one of my motors and it was the alternator. About $100 on Ebay but make sure you get the right one as Mercury changed them a couple times, use your serial number! I had to replace my port fuel rail also but I think that was due to me "lookin" for the problem...without knowing what to look for. Mine were running at last test drive (looking for wood to bloody my knuckles on!).
Have you checked your fuel rails? Crank the motor, turn it off after a few seconds, and press each Schrader valve (tire stem looking thing on top of each rail) and verify that one has ONLY air and the other has ONLY fuel.....keep in mind that fuel should shoot out of the stbd side rail as it is supposed to build to: 
"Fuel Pressure at Starboard Rail Schrader 88-92 PSI.
Air Pressure at Port Rail Schrader is 78-82 PSI." (FYI, 80 PSI isn't enough to blow a dirt dobber nest out of the line, story for another time).
There should be a 10 PSI difference, if not then you probably have a bad tracker valve (not a bad thing as they are fairly cheap to replace).

It is probably the alternator but if it isn't, check the rails as they are easy checks.

Good luck,
William


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## The Maintenance Shoppe (Nov 5, 2007)

The optimax's use three stages of fuel pumps and an air pump. The air and fuel pressure have to be 10 psi different between each other. The air pumps are also prone to breaking reed valves and piston rings, causing contamination of the air injection system. 
I would assume troubles could also be caused by a weak link in the fuel system. Eg. one of your pumps not keeping up with demand under load. We are very proficient at diagnosing these computer controlled HPDI engines. We also have the computer diagnostic software for them, so we can retrieve and reset the trouble code that is tripping your check engine light.
FYI, if you decide to bring it in to us we will be able to diagnose it within a day or 2.


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## Sequoiha (Sep 28, 2007)

One other thing you could look at is the TPS, Throttle Position Sensor, this is a potentiometer that can wear out, we have lots of these in the past. you can check it with a DVOM on the resistence scale, take it out of auto range and look for a clean sweep.


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