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TBI engine sensors on 1994 Prostar205

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  • TBI engine sensors on 1994 Prostar205

    Does anyone know how many sensors are on the standard TBI 275HP engine in 1994???? I'm tracking down a rich run condition.

    TPS - on throttle body
    MAP - hose to back of engine location of sensor
    Knock sensor - driver side of block
    Coolant sensor - driver side of thermostat
    IAC - on throtte body (not really sensor)

    Is there a intake temperature sensor to check intake air temp?? others???

    thanks

    Rob
    Last edited by rspiecha; 08-05-2005, 01:55 PM.

    2005 MariStar 210VRS - MCX - ACME #845
    1994 Prostar 205 TBI 350 (SOLD)

    War Eagle

  • #2
    Originally posted by rspiecha
    Does anyone know how many sensors are on the standard TBI 275HP engine in 1994???? I'm tracking down a rich run condition.

    TPS - on throttle body
    MAP - hose to back of engine location of sensor
    Knock sensor - driver side of block
    Coolant sensor - driver side of thermostat
    IAC - on throtte body (not really sensor)

    Is there a intake temperature sensor to check intake air temp?? others???

    thanks

    Rob
    There is no inlet air temp sensor on your engine.
    You have all of the sensors identified. Is the engine coming up to temperature? That engine has a 143 degree thermostat so it should be running close to that temp. You have to be a little careful because the temp sender that sends the signal to the gauge is not the same as the coolant temperature sensor that sends a signal to the ECM. If the engine is running cold or if the ECM thinks it is riunnung cold because of a faulty coolant sensor, it will enrichen the fuel by keeping the injectors open longer. You can check the accuracy of the CTS by removing it from the engine and placing it in a container of water. If the water temp is 77 degrees F the resistance between the two terminals of the CTS should be close to 2796 ohms, at 95 degrees 1802 ohms, at 113 degrees 1188 ohms, at 140 degrees 667 ohms at 176 degrees 332 ohms and at 212 degrees 177 ohms. WE see engines with thermostats stuck open or faulty CTS to be the biggest reasons for rich running.

    Rngine Nut
    Engine Nut
    Indmar Marine Engines
    Power to the Sport

    Comment


    • #3
      Thanks for responding. A couple of years ago, www.skidim.com talked me into installing 160 degree thermostat. I have a MAP and CTS on the way to see if this will fix it. The temperature guage gets its reading from a small pencil size sensor on top of the thermostat housing, the CTS is to the driver side of it. With a screw holding the wire. The gauge sensor is a push on connector correct????

      Do you think I should go back down to the 143 degree thermostat????

      Thanks

      Rob

      2005 MariStar 210VRS - MCX - ACME #845
      1994 Prostar 205 TBI 350 (SOLD)

      War Eagle

      Comment


      • #4
        The temperature sensor that sends info to the ECM has a 2 wire plug with yellow and black wires. The gauge sensor has a tan wire, possibly with a black stripe. The MAP sensor is a vacuum sensor. Before replacing all of the sensors(possibly unnecessarily), why not start with the basics and check the flame arrestor, plugs/wires/cap/rotor, verify the timing, check compression, fuel pressure/quality/filter/regulator and see if the injectors are leaking? The IAC won't cause a rich condition. If it's open too far, the idle speed is too high and if it's not open far enough it will either stumble or won't idle at all unless you crack the throttle.

        Exactly what is it doing (black smoke, gassy smell, bogging, fouling plugs, leaving fuel deposits in the water behind the boat) and what have you done to diagnose this problem?

        If you lost the fins on your impeller and the problem started immediately after, you may have parts of the impeller stuck in the thermostat.

        Also, since you have one of the early TBI motors, the ECM is mounted at the side of the motor with the MAP sensor tube going downhill from the throttle body plate to the sensor. This sometimes causes gas to collect in the tube and cause erroneous map sensor data. Try removing the tube from the MAP sensor and see if any gas comes out, and if the tube is cracked, broken or brittle, replace it.

        Comment


        • #5
          This two wire coolant temp sensor is located where?? I have found a single wire sensor on top of the thermostat housing that when I disconnect (a round push on type plug) will cause the temp gauge on dash to drop. To the driver side of this temp sensor is another sensor with a single wire going to it with a nut holding it down on the sensor. I do remember another sensor on the drive side of the engine going into the head, with two wires. Is this the sensor you are talking about???

          Thanks for the help so far.

          thanks

          Rob
          Last edited by rspiecha; 08-07-2005, 02:57 AM.

          2005 MariStar 210VRS - MCX - ACME #845
          1994 Prostar 205 TBI 350 (SOLD)

          War Eagle

          Comment


          • #6
            the temp sensor for the ecm is on the side of the block above the ecm.it has two wires
            ,a black&yel.the one beside the t-stat housing is the overheat light on the dash.

            Comment


            • #7
              if you had accsess to a scan tool life would be much easier.you can get a dtc tool from skidim for around $100.

              Comment


              • #8
                Originally posted by rspiecha
                This two wire coolant temp sensor is located where?? I have found a single wire sensor on top of the thermostat housing that when I disconnect (a round push on type plug) will cause the temp gauge on dash to drop. To the driver side of this temp sensor is another sensor with a single wire going to it with a nut holding it down on the sensor. I do remember another sensor on the drive side of the engine going into the head, with two wires. Is this the sensor you are talking about???

                Thanks for the help so far.

                thanks

                Rob
                The CTS on older units may have been insyalled in the side of one of the cylinder heads. Later models had extra ports in the intake manifold for tyhe CTS, temp sender, heater etc.

                Engine Nut
                Engine Nut
                Indmar Marine Engines
                Power to the Sport

                Comment


                • #9
                  thanks guys, several things to look at. The sensors are cheap and easy to replace. I don't see any harm replacing them given they are 11 years old.

                  One last question, does the 1996 Prostar 205 have any additional sensors over the 1994?? The reason I ask, I'm running the MEFI-2 computer on the 1994 that originally came with the MEFI-1 computer. The dealer did this, no more MEFI-1 are available. $1000 bucks, it really sucked, but the boat is flawless.

                  Thanks

                  rob

                  2005 MariStar 210VRS - MCX - ACME #845
                  1994 Prostar 205 TBI 350 (SOLD)

                  War Eagle

                  Comment


                  • #10
                    There aren't any additional sensors, but they were about at the end of the line for the MEFI 1 controller, anyway. The MEFI 3 won't work on yours without modifying the harness because they went to (-) output on the relay drives and internalized the knock sensor module electronics.

                    Comment


                    • #11
                      As JIMN indicated, there are no additional sensors. It is extremely unlikely that your ECM is bad. Your rich running issue is most likely due to a mechanical issue (stuck thermostat) or a sensor issue. Have you had your dealer hook up a scan tool and check for codes or sensors out of range?

                      Engine Nut
                      Engine Nut
                      Indmar Marine Engines
                      Power to the Sport

                      Comment


                      • #12
                        Engine Nut. any mods to do in switching to a mefi2 ecm in a 94 tbi?

                        Comment


                        • #13
                          No mods, just make sure to get the right calibration ID and checksum for your motor. By now, there have probably been quite a few updates if you haven't had any and these will generally help in economy and smoother transition of power through the throttle range.

                          Comment


                          • #14
                            The computer was replaced last fall. I assume they have the correct and most recent flash on it. The TPS was also replaced with the ECM, it was showing 1 degree of rotation at closed position. The knock sensor, CTS, MAP are all cheap components. I thought I would replace them before having to haul the boat back to the dealer 3 hours away. The thermostat was replace about 2 years ago. The temp gauge is right on with the temperature of the thermostat.

                            Thanks guys for all the info.

                            Rob

                            2005 MariStar 210VRS - MCX - ACME #845
                            1994 Prostar 205 TBI 350 (SOLD)

                            War Eagle

                            Comment


                            • #15
                              The temperature gauge has nothing to do with what the ECM sees. If you want to buy the sensors, go ahead but I wouldn't change them until you find out they're actually bad. If the rich condition is at idle and all other speeds, it's most likely the two wire temp sensor. A TPS with a constant fault causes the ECM to default at 12% throttle position with no variation read. If this causes richness, it won't be a lot.

                              Have you done the basic testing I listed in an earlier post? I don't remember seeing any compression specs. Remember, low compression will keep the gas from burning completely. This test needs to be done dry, after the motor has been warmed to normal operating temperature. To do the dry test, you can either remove the injector harness from the injectors or remove the fuel pump relay(or fuse). Having gas getting into the cylinders during the test skews the results higher than they should be.

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