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Author Topic:   OptiMax Won't Run Over 4,000-RPM

SMSovis posted 09-26-2012 06:23 AM ET (US)
Hello, I am having [a problem] with my 1998 OptiMax 200-HP outboard engine. Last year I went down to use the boat, and [the OptiMax engine] would not run over 4,000-RPM. All the filters and the all plugs were changed and all was well again. This year--same deal: put the boat away with no sign of [problems] and came back on Friday after work and yet again same [problem]: won't run over 4,000-RPM.
This time I changed the plugs again--all looked fine--and no dice. Checked the fuel, hooked up an auxiliary tank, and [the cause of the problem seems to be] not a gas [problem]. Next, figured it could be the throttle sensors, as this has been a problem in the past with this motor, so I replaced those (at a cost of $400), and again no dice. Judging by what fixed it the previous year I figured it could be the plug wires. Bought a new set and all looked fine except for the port side bottom one which looked almost burnt. Upon closer inspection a fairly large hole was in plug boot. Wires didn't help, so my next guess was the coil associated with that cylinder. I replaced that, and again no change except it now turned 300-RPMless.
Could this motor possibly be in guardian mode?
What are the signs of bad injectors?
Can the computer be reset without the the actual computer?
Is the air pump driven by a pump? I ask because whatever is wrong seems to be continually failing due to recent RPM drop again.
Any thoughts or advice would be a huge help. My last try is going to [instill Se Foam in] the motor, check the voltage at the altenator--should it be 14.7-Volts--check the pressure at the VST tank--35-45 PSI--and check the pressure on the rail and the fuel rail. I am at a loss so any idea would be great. Thanks in advance. Also the motor sounds terrible right around 2,500 RPM.
RevengeFamily posted 09-26-2012 07:42 AM ET (US)
You need to be logical with your approach to diagnosing your problem. Start with a simple compression test on all cylinders.
SMSovis posted 09-26-2012 07:49 AM ET (US)
Compression is fine-- forgot to mention that. Also [there are] brand new 1000-MCA cranking batteries.
jimh posted 09-26-2012 08:40 AM ET (US)
If "guardian mode" is intended to limit the engine speed, it would seem that 4,000-RPM is not much of a limit. I would think that a speed limiter would cuase the engine speed to be limited to much less than 4,000-RPM. There ought to be an explanation of "guardian mode" in your owner's manual.
To see if the cause of the problem is isolated to one cylinder, try disconnecting the spark plug wire from one cylinder at a time and running the motor. If you find that loss of spark on one cylinder does not affect the engine speed, you can suspect that cylinder was not operating properly.
jimh posted 09-26-2012 08:43 AM ET (US)
Also, you should see some sort of evidence of a bad cylinder on the spark plug electrode. The color of the insulation or the amount of oil or soot on the electrode can be used as a diagnostic indicator. If all the spark plugs look identical, then you can assume all the cylinders are operating in the same manner. This would tend to rule out a malfunction in one cylinder as being the cause of the problem.
If no individual cylinder is the cause, then you must look for a cause in components that are common to all cylinders.
SMSovis posted 09-26-2012 08:54 AM ET (US)
Thanks Jim.
I have run it with each plug wire off an have found no difference at all.
Going to check the PSI levels for both air and fuel and try sea foam then I think I am done with boat ting for a while.
This season this boat has made me broke and provided me with little joy and caused an unreal amount of stress....
ukuslayer posted 09-26-2012 10:42 PM ET (US)
Are you getting any alarms? If not I would be leaning to an air or fuel problem in the rails. Check your psi on both rails. Could be a bad air or fuel regulator diaphragm or a bad diaphragm on the tracker valve. Do you have a service manual? Has the air filter on the air compressor ever been changed on this engine? Without a manual some do not even know this filter is there. Filter is located in plastic shroud above the flywheel. Shroud is easily removed and filter is located on the shroud itself when you flip it over you will see it. Be sure to install the shroud properly when re installing. I am leaning towards a diaphragm on one of the regulators or tracker valve though. I have 1999 225 optimax my self and have been through a few problems with it. The service manual was the best purchase I ever made for my engine!!!! Any questions let me know and I will look in my manual to help if I can.
Aloha,
Sean
RevengeFamily posted 09-27-2012 06:56 AM ET (US)
My shop manual says that for model year 1998, if one TPS fails you will have a check engine light illuminated on the dash and your engine is limited to 3,000 rpm... if both TPS's fail then engine runs at idle speed only.
I have to agree with Sean, your next step is checking and comparing air pressure (80psi) and fuel pressure (90psi)in your fuel rails.
I am experiencing a similar problem which I plan on investigating further this weekend. I will keep you posted as to what I find in my 1999 225 Optimax.
Norm
SMSovis posted 09-27-2012 07:59 AM ET (US)
So we fixed the motor last night.... PSI was correct on the rails. narrowed it down to cylinder #4, switched the injectors around with cylinders we knew were good and it still didn't run. When we pulled the air injector a piece of metal came out with it which didn't look good. Compression tested the motor and it was perfect. When we pulled the plug out of cylinder 4 the electrode was touching the platinum tip.... Long story short we came to the conclusion that the original problem was a bad coil. Some how in process the # 4 cylinder hydro locked with gas and the explosion twisted the plug. It finally runs right again!
Looking forward to getting a big bass on the fly rod this weekend......
jimh posted 09-27-2012 01:29 PM ET (US)
If there was no combustion in cylinder #4 you should have discovered that with the test in which its spark plug wire was pulled.
jimh posted 09-28-2012 10:32 AM ET (US)
The diagnostic test in which each cylinder's spark plug wire is pulled off is a test to see if the cylinder under test affects engine speed when its spark is disabled. This test can be useful for diagnosis even if the problem is not related to spark ignition failure in the cylinder. Let me explain.
If a particular cylinder has lost combustion, when the engine is tested with the technique of removing the spark plug wires from each cylinder, one at a time, the expected result is that the engine speed will decrease when the cylinder is disabled by loss of spark. If a cylinder is not producing combustion, even if the reason has nothing to do with its spark ignition circuit, removing the spark plug wire should produce no change in engine speed. This is the indicator that the cylinder under test did not have combustion.
The test presumes, of course, that loss of spark ignition in a cylinder will cause loss of combustion. This is more or less a certainty for spark-ignition engines.
Even if a cylinder has no combustion because of a problem completely unrelated to spark ignition, the lack of combustion should be detected by the spark plug wire drop test.
For example, a cylinder that is not producing combustion due to lack of fuel will show no change in engine speed when the spark plug wire is removed. The test indicates that there is a problem in the cylinder related to lack of combustion, and not that the problem is always related to lack of spark ignition.
ukuslayer posted 09-28-2012 10:49 PM ET (US)
Interesting, so was it part of the spark plug or the tip of the air injector that came out?
I ask because I heard with the original air injectors on these motor, the black ones sometimes the tip would break off and cause major engine failure. I replaced all the black air injectors on my engine with the new Blue ones. It took a while for me to do this because I bought them all off E-bay when the deals were there. Otherwise they are $350.00 a pop for each one of them.
Anyway glad to hear the engine is running good again. Good luck on your fishing this weekend.
Aloha,
Sean
jimh posted 09-29-2012 11:24 AM ET (US)
Sean--thanks for the interesting account of the air injectors. That there was a strong secondary market on e-Bay for air injectors for the Mercury OptiMax tells me that those injectors must be replaced in rather substantial volume. You don't see repair parts listed on secondary markets unless there is a high demand for them.

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Author	Topic: OptiMax Won't Run Over 4,000-RPM
SMSovis	posted 09-26-2012 06:23 AM ET (US) Hello, I am having [a problem] with my 1998 OptiMax 200-HP outboard engine. Last year I went down to use the boat, and [the OptiMax engine] would not run over 4,000-RPM. All the filters and the all plugs were changed and all was well again. This year--same deal: put the boat away with no sign of [problems] and came back on Friday after work and yet again same [problem]: won't run over 4,000-RPM. This time I changed the plugs again--all looked fine--and no dice. Checked the fuel, hooked up an auxiliary tank, and [the cause of the problem seems to be] not a gas [problem]. Next, figured it could be the throttle sensors, as this has been a problem in the past with this motor, so I replaced those (at a cost of $400), and again no dice. Judging by what fixed it the previous year I figured it could be the plug wires. Bought a new set and all looked fine except for the port side bottom one which looked almost burnt. Upon closer inspection a fairly large hole was in plug boot. Wires didn't help, so my next guess was the coil associated with that cylinder. I replaced that, and again no change except it now turned 300-RPMless. Could this motor possibly be in guardian mode? What are the signs of bad injectors? Can the computer be reset without the the actual computer? Is the air pump driven by a pump? I ask because whatever is wrong seems to be continually failing due to recent RPM drop again. Any thoughts or advice would be a huge help. My last try is going to [instill Se Foam in] the motor, check the voltage at the altenator--should it be 14.7-Volts--check the pressure at the VST tank--35-45 PSI--and check the pressure on the rail and the fuel rail. I am at a loss so any idea would be great. Thanks in advance. Also the motor sounds terrible right around 2,500 RPM.
RevengeFamily	posted 09-26-2012 07:42 AM ET (US) You need to be logical with your approach to diagnosing your problem. Start with a simple compression test on all cylinders.
SMSovis	posted 09-26-2012 07:49 AM ET (US) Compression is fine-- forgot to mention that. Also [there are] brand new 1000-MCA cranking batteries.
jimh	posted 09-26-2012 08:40 AM ET (US) If "guardian mode" is intended to limit the engine speed, it would seem that 4,000-RPM is not much of a limit. I would think that a speed limiter would cuase the engine speed to be limited to much less than 4,000-RPM. There ought to be an explanation of "guardian mode" in your owner's manual. To see if the cause of the problem is isolated to one cylinder, try disconnecting the spark plug wire from one cylinder at a time and running the motor. If you find that loss of spark on one cylinder does not affect the engine speed, you can suspect that cylinder was not operating properly.
jimh	posted 09-26-2012 08:43 AM ET (US) Also, you should see some sort of evidence of a bad cylinder on the spark plug electrode. The color of the insulation or the amount of oil or soot on the electrode can be used as a diagnostic indicator. If all the spark plugs look identical, then you can assume all the cylinders are operating in the same manner. This would tend to rule out a malfunction in one cylinder as being the cause of the problem. If no individual cylinder is the cause, then you must look for a cause in components that are common to all cylinders.
SMSovis	posted 09-26-2012 08:54 AM ET (US) Thanks Jim. I have run it with each plug wire off an have found no difference at all. Going to check the PSI levels for both air and fuel and try sea foam then I think I am done with boat ting for a while. This season this boat has made me broke and provided me with little joy and caused an unreal amount of stress....
ukuslayer	posted 09-26-2012 10:42 PM ET (US) Are you getting any alarms? If not I would be leaning to an air or fuel problem in the rails. Check your psi on both rails. Could be a bad air or fuel regulator diaphragm or a bad diaphragm on the tracker valve. Do you have a service manual? Has the air filter on the air compressor ever been changed on this engine? Without a manual some do not even know this filter is there. Filter is located in plastic shroud above the flywheel. Shroud is easily removed and filter is located on the shroud itself when you flip it over you will see it. Be sure to install the shroud properly when re installing. I am leaning towards a diaphragm on one of the regulators or tracker valve though. I have 1999 225 optimax my self and have been through a few problems with it. The service manual was the best purchase I ever made for my engine!!!! Any questions let me know and I will look in my manual to help if I can. Aloha, Sean
RevengeFamily	posted 09-27-2012 06:56 AM ET (US) My shop manual says that for model year 1998, if one TPS fails you will have a check engine light illuminated on the dash and your engine is limited to 3,000 rpm... if both TPS's fail then engine runs at idle speed only. I have to agree with Sean, your next step is checking and comparing air pressure (80psi) and fuel pressure (90psi)in your fuel rails. I am experiencing a similar problem which I plan on investigating further this weekend. I will keep you posted as to what I find in my 1999 225 Optimax. Norm
SMSovis	posted 09-27-2012 07:59 AM ET (US) So we fixed the motor last night.... PSI was correct on the rails. narrowed it down to cylinder #4, switched the injectors around with cylinders we knew were good and it still didn't run. When we pulled the air injector a piece of metal came out with it which didn't look good. Compression tested the motor and it was perfect. When we pulled the plug out of cylinder 4 the electrode was touching the platinum tip.... Long story short we came to the conclusion that the original problem was a bad coil. Some how in process the # 4 cylinder hydro locked with gas and the explosion twisted the plug. It finally runs right again! Looking forward to getting a big bass on the fly rod this weekend......
jimh	posted 09-27-2012 01:29 PM ET (US) If there was no combustion in cylinder #4 you should have discovered that with the test in which its spark plug wire was pulled.
jimh	posted 09-28-2012 10:32 AM ET (US) The diagnostic test in which each cylinder's spark plug wire is pulled off is a test to see if the cylinder under test affects engine speed when its spark is disabled. This test can be useful for diagnosis even if the problem is not related to spark ignition failure in the cylinder. Let me explain. If a particular cylinder has lost combustion, when the engine is tested with the technique of removing the spark plug wires from each cylinder, one at a time, the expected result is that the engine speed will decrease when the cylinder is disabled by loss of spark. If a cylinder is not producing combustion, even if the reason has nothing to do with its spark ignition circuit, removing the spark plug wire should produce no change in engine speed. This is the indicator that the cylinder under test did not have combustion. The test presumes, of course, that loss of spark ignition in a cylinder will cause loss of combustion. This is more or less a certainty for spark-ignition engines. Even if a cylinder has no combustion because of a problem completely unrelated to spark ignition, the lack of combustion should be detected by the spark plug wire drop test. For example, a cylinder that is not producing combustion due to lack of fuel will show no change in engine speed when the spark plug wire is removed. The test indicates that there is a problem in the cylinder related to lack of combustion, and not that the problem is always related to lack of spark ignition.
ukuslayer	posted 09-28-2012 10:49 PM ET (US) Interesting, so was it part of the spark plug or the tip of the air injector that came out? I ask because I heard with the original air injectors on these motor, the black ones sometimes the tip would break off and cause major engine failure. I replaced all the black air injectors on my engine with the new Blue ones. It took a while for me to do this because I bought them all off E-bay when the deals were there. Otherwise they are $350.00 a pop for each one of them. Anyway glad to hear the engine is running good again. Good luck on your fishing this weekend. Aloha, Sean
jimh	posted 09-29-2012 11:24 AM ET (US) Sean--thanks for the interesting account of the air injectors. That there was a strong secondary market on e-Bay for air injectors for the Mercury OptiMax tells me that those injectors must be replaced in rather substantial volume. You don't see repair parts listed on secondary markets unless there is a high demand for them.