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Mike ProStar 99
09-21-2009, 11:35 PM
I have a 1999 ProStar 190 with the LTR motor that has always ran great until this summer when I took it to a lake at 5500 ft and then to Lake Powell at about 3600 - 3700 ft. It was tough to get it started and keep it idling. After I got it running, it ran rough and very rich. I replaced the MAP sensor, and checked to make sure I had no air leaks in the intake after the 1st lake. I should mention that I live just above sea level and the boat always runs great here so when I made the first changes I thought that would cure the problem. Unfortunately, when we got to Powell it had the same problem so I replace the fuel pump with my new back up and that did not fix the problem either. I have talked to a few Mastercraft techs at different dealers and they have not been much help. I live 3-4 hours from the nearest Mastercraft dealer so I was wondering if anyone had any advice on what to check next before I spend the time and money of taking it to the dealer so they can tell me it runs great. Which it does if you are not at a high altitude lake.

Any suggestions would be greatly appreciated.

DooSPX
10-20-2009, 01:09 PM
I know this is an old post, and was forgot about. but I hope I can help.
even though the LTR is EFI, the computer may not be able to compensate for huge differences in O2 in the air.

JimN
10-20-2009, 04:04 PM
I know this is an old post, and was forgot about. but I hope I can help.
even though the LTR is EFI, the computer may not be able to compensate for huge differences in O2 in the air.

5500' isn't a huge difference to the ECM. They test boats and calibrations at up to about 7000', last time I heard.

JimN
10-20-2009, 04:26 PM
I have a 1999 ProStar 190 with the LTR motor that has always ran great until this summer when I took it to a lake at 5500 ft and then to Lake Powell at about 3600 - 3700 ft. It was tough to get it started and keep it idling. After I got it running, it ran rough and very rich. I replaced the MAP sensor, and checked to make sure I had no air leaks in the intake after the 1st lake. I should mention that I live just above sea level and the boat always runs great here so when I made the first changes I thought that would cure the problem. Unfortunately, when we got to Powell it had the same problem so I replace the fuel pump with my new back up and that did not fix the problem either. I have talked to a few Mastercraft techs at different dealers and they have not been much help. I live 3-4 hours from the nearest Mastercraft dealer so I was wondering if anyone had any advice on what to check next before I spend the time and money of taking it to the dealer so they can tell me it runs great. Which it does if you are not at a high altitude lake.

Any suggestions would be greatly appreciated.

Think about what there's less of at that altitude- air. A fuel pump may have been needed if it needed more air but at high altitude, less fuel is needed. If a tech was no help, I hate to say it but I'm not sure they understand the system. These motors don't have an Intake Air Temperature (IAT) or Mass Air Flow (MAF) sensor so they use a Manifold Absolute Pressure (MAP) sensor. This finds the barometric pressure as soon as the key is turned ON and along with the ECT (Engine Coolant Temperature) sensor, it delivers fuel according to the fuel mapping tables that were arrived at through testing, which measures the exhaust components to find the correct fuel/air mixture. If either of these sensors is bad, the fuel mixture won't be correct.

When you tried to start it, was it easier if you opened the throttle? Once you got it to start, did the exhaust smell strongly of gasoline? Did it run smoothly or not? If not, did it run more smoothly after about a minute? Was the air temperature high when this happened?

If it started after the throttle opened, it's possible that the ECT is showing a low temperature and the ECM is causing more fuel to be delivered. It's also possible that the IAC is sticking after the motor shuts down. If the IAC is at fault, the exhaust should smell normal at anything above idle and if the ECT is bad (reading cold), the mixture will be rich at all RPM. If it ran rough at first and smoothed out, it's possible that high temperature caused the motor to 'heat soak' while it was off and when this happens, the ECM tries to protect the motor by restricting fuel delivery- a motor that can't run at high RPM can't get as hot and the ECM will shut off the injector banks, alternating between them. Once it reaches normal temperature, fuel delivery goes back to normal and it runs like it did before.

If the IAC never opens enough, it will always be hard to start with the throttle closed. Look at the throttle plate to look for a small hole that would be about 3/16". If it doesn't have one, contact MC and ask if your motor is one of the ones that needed to have the IAC home position changed. Rochester deleted the hole without notifying MC or Indmar and this resulted in some hot start issues under the right conditions. They'll need the boat and/or motor serial number.

If the ECT is showing extremely high resistance (indicates extremely low temperature), it may start OK when it's cold but never when it's hot, especially with high air temperature.