1991 240 runs very rich. Starts OK but idles very slow

jbpatter44 · Post by **jbpatter44** » 08 Feb 2020, 08:07

1991 240 runs very rich at low speeds. It starts OK but idles very slow and will load up and die soon if left idling. Fuel mileage is VERY poor. Oxygen sensor is new. Problem is the same with three different air mass meters.

Post by **RickHaleParker** » 08 Feb 2020, 12:27

How is the exhaust system condition?

Leaks in the exhaust system will suck in air and cause the O2 sensor into detecting a leaner than actual Air/Fuel mixture is lean. The fuel management will try to correct by enriching the Air/Fuel mixture resulting in a overrich mixture.

A good inspection or better yet smoke test the exhaust system.

93Regina · Post by **93Regina** » 09 Feb 2020, 11:07

jbpatter44 wrote: ↑08 Feb 2020, 08:071991 240 runs very rich at low speeds.

Cold start injector leaking, or ECU's temp sensor AWOL.

With the control unit connected, connect a voltmeter across LH ECU terminals 13 and 5 (ground) for Bosch LH 2.4 systems or terminals 2 and 5 (ground) for LH 2.2 systems. This unit is in the passenger side footwell, under the plastic cover. Remove the cover of the large electrical connector to access the backs of the pins for the test. Turn the ignition switch ON.

At 68F (20C) the voltage should be 2.0 +/-.5v volts.
At 104F(40C) the voltage should be 1.2 +/- .3volts
At 176F (80C) the voltage should be .5 +/- .2volts