Originally Posted by JimN
The ECT (Engine Temperature Sender) with two wires ONLY sends signal to the ECM, not the gauge and your comment contradicts itself.
I think you are saying that that there is a temp switch, a temp sender, and a MEFI temp sensor as well? The switch has a single wire and is up by the thermostat at the front of the engine and screws into a horizontal opening. it causes the CEL/ alarm when above 181 degrees and the bimetallic switch closes the single wire link to ground (through the MEFI). This may affect other aspects of the engine operation- I'm not sure. This doesn't feed the temp guage ( through the mefi or directly) as is only open or closed signal. The second single wire sensor in the manifold that sits nearby and screws in vertically and feeds the temp guage. My temp temp switch was bad but ran boat for a week with the CEL and couldn't tell the difference in performance so believe it acts solely as a warning w/o affecting anything else (realize later models have limp mode to better protect engine but if a 2001 tbi does, mine isn't working).
The temp sender (2wire plug you refer to) provides variable resistance signal to the MEFI to tell iit how hot it is so as to adjust one aspect of the fuel curve map. If bad, it will cause engine to run rich. As said, There is also another single wire sensor in the manifold so that one must feed the gauge correct? So gauge could read fine showing the engine is up to operating temp but MEFI thinks engine is cold and dumps in more fuel than needed? Changing any of the single wire sensors won't fix the rich condition. He needs to check the sensor that has 2 wires and determine the resistance hot and cold then replace if out of spec
Jimn- is this logic correct?