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buoyskier
09-27-2004, 12:35 AM
94 Prostar 205 Indmar 350/275, starts fine runs fine for first 30 min. Begins to run rough. Engine will rev to 4400 rpm after a short time RPMs begin to drop. Engine starts to sound deeper and will not rev above 4000 RPMs. If I turn off ignition problem stops, but cycle repeats after short time. Does anyone have any ideas? I have replaced module and coil. Checked fuel pressure, pressure remains constant.

JimN
09-27-2004, 01:01 AM
What module- ignition? If the exhaust sound gets deeper when it starts to run bad, I would suspect decreased raw water intake. Check the impeller and oil cooler. Clean the flame arrestor, too. See if the exhaust hoses are soft and look into the exhaust flanges to see if they're blistered or melted.

captkidd
09-27-2004, 11:51 AM
I have the same boat and engine, and I agree with JimN. Mine did the same thing a few weeks ago when the impeller went out. Apparently the ECM prevents the boat from revving when it is overheated in order to protect the engine. Mine would idle fine, but when I tried to accelerate from a stop it would start cutting out, and the engine made the deep sound you described. I then checked the temp gauge and it was way up. I replaced the impeller on the water and it ran fine afterwards.

JimN
09-27-2004, 11:55 AM
If you do need to replace the impeller on the water and it has overheated, wait till it cools down to start it again. If cold water hits really hot cast iron, it tends to crack.

buoyskier
09-27-2004, 10:02 PM
I don’t think the problem is water related. Installed new impeller and cleaned spark arrester, this spring. I’ll check the exhaust. I am guessing that the change in tone is from the motor retarding timing or actually losing power in a cylinder. Are there ignition components that fail due to heat?

JimN
09-27-2004, 10:28 PM
Just about everything can fail from heat. Have you checked the plugs, cap, rotor, wires, PCV valve, injector spray pattern, compression, etc? Verify the timing, too. You can't just put the clamp on the #1 wire and start it up, though. You need to put it into diagnostic mode. If you have or can get a code reader, plug it into the diagnostic port and get it into diag. mode. Get the RPM up to 1000 and it should be stable idle. If it jumps around, either the rotor shaft bushing is worn or it's not in diagnostic mode. This mode cancels spark stabilization and if you put the clamp on the wire without doing this, the timing mark jumps all over the place.

Just because you replaced the impeller in spring, doesn't mean it can't be bad now. It doesn't take very much time to check, so I would start there.

André
09-27-2004, 11:03 PM
If it can still rev 4000 rpm,then i THINK it's not in revs reduction mode...???

JimN
09-27-2004, 11:15 PM
RPM reduction gets you to about 2000 RPM and even then, it's not pretty. It alternates injectors on TBI and injector banks on MFI.

jimmer2880
09-28-2004, 07:51 AM
I thought only LT1's had the reduction mode. I didn't think the TBI motors had reduction????

Am I wrong here? (again! :uglyhamme )

JimN
09-28-2004, 10:04 AM
They both have RPM reduction and the rev limiter. With RPM reduction, you get normal fuel delivery to 2000 RPM. Above 2000 it removes half of the fuel delivery by alternating between the two injectors or banks of injectors.

jimmer2880
09-28-2004, 12:22 PM
They both have RPM reduction and the rev limiter. With RPM reduction, you get normal fuel delivery to 2000 RPM. Above 2000 it removes half of the fuel delivery by alternating between the two injectors or banks of injectors.
Do you know what year did they start doing that on TBI systems?

captkidd
09-28-2004, 02:40 PM
Mine is a '94 and I believe it has it; I know for a fact that when the engine is overheated that it won't rev normally, but I'm not sure if this is the reduction mode that was mentioned. It was described in the brochure as a "limp home" mode that allows the engine to run enough to get you back to the dock, but not much more.

JimN
09-28-2004, 02:47 PM
As soon as they started using injection, they had RPM reduction. Mainly because they could, I assume. They probably could have with a carb'd motor, but it wouldn't work by cutting the fuel to half of the cylinders like an ECM can. They would need to make the spark intermittent.

jimmer2880
09-29-2004, 07:31 AM
Hmmm... interesting. I've had mine up over 180 when a water-pump belt broke in NOVEMBER! Not many people on the river then. Anyway - it never went into reduced RPM mode.

But - after reading JimN's responce on another thread - sounds like limp mode doesn't start until 204° Whereas on an indmar Supra LT1, it comes in at 180°

Anyway... I learn something new everday. Guess I can go back to bed now.:D