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7.4 mpi question

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Old 06-01-2007, 09:22 AM
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7.4 mpi question

I have a 2000 model 7.4 mpi engine has a continual problem of occasional reduced power from 4000 to 3000 rpm. Problem occurs sporatically and will last for 14 to 30 minutes then operate normally again. Boat is located in rural area without access to scan tool. Have changed fuel pump pressure is now about 50. Same problem. several local mechanics have looked no answers. I am thinking could be a knock sensor issue but am not sure where to proceed from here.Any Ideas?
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Old 06-01-2007, 03:11 PM
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More than likely is getting hot and shutting itself down. The computer will go into a "protection" mode if it thinks it's too hot to prevent you from melting a motor down. Have you checked your sea pump impeller?
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Old 06-01-2007, 10:12 PM
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Actually, that engine does not have any Protection or Guardian mode. You may have a spark plug wire too close or touching one of the knock sensor wires.

If you don't have access to a scan tool, you can check codes with only a paperclip and 12 volt LED. If you do a search for "Code Tool" you should find several posts about how to do it.

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Old 06-02-2007, 11:02 AM
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I concur with Dave. Could be the knock sensor. Could also be a loose or corroded wire. Check your power wire. It starts at the starter, then goes to the circuit breaker on top of the motor, then to your dash, then back to your motor as the purple wire and possibly through a kill switch. If it's loose or has a bad connection it can intermittently kill your motor.
Last thing that you could check is your fuel pump. They don't last forever. You will need to check the pressure on your fuel rail. The pump is inside the fuel cooler box on the port side of your motor. It's sold as a complete assembly for about 300 bucks.
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Old 06-07-2007, 01:39 PM
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Default problem continues

Went to alaska and personly checked motor. Starts and idles fine. Ran a ddt scan no error codes found. Fuel pump has less than 50 hours and checks ok at 45 psi. I will be changing all the consumable ignition components. saturday. Cap rotor wires and plugs. I have heard these motors were often having problems with the map sensor without a code showing on the ddt? I have located a laptop and will run it saturday as well to see if i can find any sensor anomolies. Anyone have any other ideas? One other thing i was wondinging if the injectors on this motor have the fuel inlet screans like the outboard do I have had those clog up before. Usually that results in overall performance issue however.
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Last edited by fliar; 06-07-2007 at 05:37 PM.
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Old 06-07-2007, 09:55 PM
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They do have screens and are subject to clogging. Also look at connections and battery issues, etc.
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Old 06-10-2007, 01:35 PM
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I have similar problem whith mine 7,4 mpi-98
It runs great the first ten minutes but when the temp is rising to normal 65 celsius the rpm wont go above 3700.
I have change both knock sensors and the ect sensor and igot no error codes.. got good compression and fuel pressure.
Anybody got a ide what to check next??
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Old 06-10-2007, 02:17 PM
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I checked with a local and he said that no error code does not mean that a sensor doesnt have a problem. He recommended a laptop so all sensor values could be evaluated. good luck I am still working on mine as well.
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Old 06-10-2007, 02:38 PM
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If you get it fixed post the problem.. and i will as well.
Good luck

Thomas
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