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Old 06-07-2008, 11:18 PM
repeeples's Avatar
repeeples repeeples is offline
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rpm reduction? please help...

hey gents: first time, long time. i am a new owner but have been reading on the site for awhile. i want to get all the details in, so sorry for the lengthy post. I NEED HELP!

i have a 2000 ps190 that i got in Oct of '07. It had 115 hours on the LTR engine. I had it in the water once just after buying it before we had it winterized. During that initial outing after about 10 minutes of running great the boat had a sudden drop in engine RPM and my temp gauge stopped working. I called our mechanic (mastercraft certified) and he said it was likely a problem with insufficient grounding which he would beef up when he de-winterized the boat - not to worry. the boat still has the same problem now after the grounding re-do, minus the gauge glitches. the mechanic and i went out on the boat together and it did the same thing plus the engine had a 'lean pop' so his next thought was insufficient fuel delivery. we replaced the fuel pump and the problem persisted - so now i have a spare fuel pump. the boat has new spark plugs.
the engine runs like a charm so i believe it is an electrical issue as opposed to mechanical. like i said it runs for about 10-15 minutes from cold then the rpm's drop off. the only way to get it to run normal again is to turn it off and back on...each time it runs for a shorter period before rpm reduction.
my mechanic's next idea is to ohm test each electrical connection in the wiring harness and/or borrow another MC owner's ECM to see if there is a problem with ours.

does this sound familiar to anyone? any help or ideas would be greatly appreciated.
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Old 06-08-2008, 04:36 AM
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edwinfuqua edwinfuqua is offline
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The sudden drop in engine RPM, can you give more detail? In RPMs what is it doing and in performance what is it doing?
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Old 06-08-2008, 07:17 AM
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JimN JimN is offline
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You need a new mechanic. If he remembers anything from MC training, the first step, which he did, is verify the complaint. The second is 'do a visual inspection, including a wiggle test of the wiring'. Third, do the proper diagnostics, including connection to a diagnostic computer. Fourth, verify that the problem has been corrected.

Since "80% of all driveability issues are fuel related", he needs to check the fuel pressure, not just replace parts. His inability to correctly diagnose this problem shouldn't cost you money. Next, he needs to look at the data, especially where the ECM indicates whether the motor has overheated. An overheat is one of the only reasons the ECM goes into RPM reduction and if it has registered an overheat, the impeller and raw water cooling system need to be inspected. If they didn't replace the impeller in the time you have owned this boat, you need to talk to the service manager about this.
If the impeller is missing vanes, there's no way they replaced it, either last fall or this spring, so they should make whatever repairs are necessary, on their dime.

The mechanic should learn to diagnose these systems on some other boat, not yours. If he doesn't know how to look for the cause of the problems, it will be very apparent, very soon. He'll use the "shotgun method" of diagnosis, replacing part after part, until he finally "finds it", only by coincidence.

He needs to start by collecting the data and checking the raw water cooling system. If that reveals nothing, the ECT (Engine Coolant Temperature) sensor needs to be checked, along with the wires to the ECM (if the sensor proved bad, the wires are a moot point). If that doesn't show anything, and either the visual inspection or data should have let him know if the block grounds are clean, tight and working, THEN he needs to check the harness.

The diagnostic computer is only a tool but it can save a lot of time if the tech knows how to interpret the data. If he doesn't and just scratches his head, he needs more training before being let loose on these boats.

Yes, I'm being harsh but I have absolutely no tolerance for people replacing parts as a method of diagnosis. They should only be changed after proving faulty and you said nothing about a fuel pressure test, him taking a fuel sample or doing the normal diagnostics. How much gas is in the tank? If it's less than 1/2 full, top it off and see if the problem suddenly "vanishes". If it does, it's dirty gas and a clogged filter. Since the pump has already been replaced, I suspect dirty gas if topping it off fixes it, or bad raw water intake causing an actual overheat. If it's an indicated overheat and the raw water intake if good, the thermostat may be sticking closed or the ECT may be bad and these are easily checked.

Is, or has, this boat run in salt/brackish water with a fresh water cooling system? If so, has it been thoroughly inspected for the effects of the salt/brackish water?

Last edited by JimN; 06-08-2008 at 07:19 AM.
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Old 06-08-2008, 02:14 PM
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repeeples repeeples is offline
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Quote:
Originally Posted by edwinfuqua View Post
The sudden drop in engine RPM, can you give more detail? In RPMs what is it doing and in performance what is it doing?
i dont know alot about engines, but it almost sounds like a 2 stroke engine going into 4 stroke - like it is missing every other time. if you increase throttle while it is missing, it seems to bog down more. every few seconds, the rpms will return to 'normal' for the throttle setting, then immediately fall again.
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  #5  
Old 06-08-2008, 02:24 PM
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repeeples repeeples is offline
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Quote:
Originally Posted by JimN View Post
You need a new mechanic. If he remembers anything from MC training, the first step, which he did, is verify the complaint. The second is 'do a visual inspection, including a wiggle test of the wiring'. Third, do the proper diagnostics, including connection to a diagnostic computer. Fourth, verify that the problem has been corrected.

Since "80% of all driveability issues are fuel related", he needs to check the fuel pressure, not just replace parts. His inability to correctly diagnose this problem shouldn't cost you money. Next, he needs to look at the data, especially where the ECM indicates whether the motor has overheated. An overheat is one of the only reasons the ECM goes into RPM reduction and if it has registered an overheat, the impeller and raw water cooling system need to be inspected. If they didn't replace the impeller in the time you have owned this boat, you need to talk to the service manager about this.
If the impeller is missing vanes, there's no way they replaced it, either last fall or this spring, so they should make whatever repairs are necessary, on their dime.

The mechanic should learn to diagnose these systems on some other boat, not yours. If he doesn't know how to look for the cause of the problems, it will be very apparent, very soon. He'll use the "shotgun method" of diagnosis, replacing part after part, until he finally "finds it", only by coincidence.

He needs to start by collecting the data and checking the raw water cooling system. If that reveals nothing, the ECT (Engine Coolant Temperature) sensor needs to be checked, along with the wires to the ECM (if the sensor proved bad, the wires are a moot point). If that doesn't show anything, and either the visual inspection or data should have let him know if the block grounds are clean, tight and working, THEN he needs to check the harness.

The diagnostic computer is only a tool but it can save a lot of time if the tech knows how to interpret the data. If he doesn't and just scratches his head, he needs more training before being let loose on these boats.

Yes, I'm being harsh but I have absolutely no tolerance for people replacing parts as a method of diagnosis. They should only be changed after proving faulty and you said nothing about a fuel pressure test, him taking a fuel sample or doing the normal diagnostics. How much gas is in the tank? If it's less than 1/2 full, top it off and see if the problem suddenly "vanishes". If it does, it's dirty gas and a clogged filter. Since the pump has already been replaced, I suspect dirty gas if topping it off fixes it, or bad raw water intake causing an actual overheat. If it's an indicated overheat and the raw water intake if good, the thermostat may be sticking closed or the ECT may be bad and these are easily checked.

Is, or has, this boat run in salt/brackish water with a fresh water cooling system? If so, has it been thoroughly inspected for the effects of the salt/brackish water?
thanks jimn - the impeller and raw water cooling system are working fine: the impeller was replaced during de-winterization and it remains cool to the touch during operation, engine temperature also stays around 160-170 per the gauge. the boat has only been in clean fresh water lakes.

i take partial responsibility for the fuel pump replacement without fuel pressure tests. he offered to test fuel pressures and i should have been patient and let him. the fuel tank has been well over 1/2 full when this occurs.

thanks so much for the reply, i'll pass this info along....
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  #6  
Old 06-08-2008, 03:07 PM
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JimN JimN is offline
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I would definitely recommend a fuel pressure test and a fuel sample. Let the sample sit for a while to let any water settle out. You can do this, if you want. Get a clean, clear bottle and get a hose that has a fitting for inflating a tire on one end. The other end can be open, stuck in the opening of the bottle. Turn the key to ON, let it squirt and turn the key OFF for more than 5 seconds. Repeat this 5-6 times, or until you collect about 1/2 of the bottle (8 oz is a good amount).

Next, have the coolant temperature sensor tested for resistance range when cold and hot. I suspect that this is the cause if the engine is actually running at normal temperature. Also, make sure the exhaust manifolds and risers are clear, followed by inspection of the thermostat.
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