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

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jbpatter44
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Joined: Sat Feb 08, 2020 7:56 am
Year and Model: 1991 Volvo 240
Location: Arizona

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

Post by jbpatter44 »

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.
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RickHaleParker
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Re: 1991 240 runs very rich. Starts OK but idles very slow

Post by RickHaleParker »

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.
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93Regina
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Re: 1991 240 runs very rich. Starts OK but idles very slow

Post by 93Regina »

jbpatter44 wrote: Sat Feb 08, 2020 8:07 am1991 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
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