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ECT/ECU 200 1989

posted by  someone claiming to be tjts1 on  Thu Apr 21 13:13 CST 2005 [RELATED]

80MPH is not going to cause 16mpg even if the car is loaded. There is definitely something wrong with your car.
First suspect is engine coolant sensor (ECT)


The second suspect the engine control unit (ECU). The model year is notorious for ECU problems. One is an outright failure. In my case, after I replaecd the failed 556 ECU in our automatic 89 240 with an 933 ECU from a 91 740 fuel economy went up from 21mpg to 27mpg highway. I do most of my driving between 70-80mph. 89 was the first year for LH 2.4. All later NA 8 valve LH 2.4 ECUs from any 740/940 are improved versions of the same ECU and fully compatible. Make sure the 3 digit ECU number is 9XX not 5XX. A used ECU at the JY costs about $30-$40. LH 2.4 ECUs has 35 pins.
Known ECU problems

ECU application list
Good luck
Justin





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