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

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jbpatter44
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Year and Model: 1991 Volvo 240
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jbpatter44

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

Post by jbpatter44 » Sat Feb 08, 2020 8:07 am

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 » Sat Feb 08, 2020 12:27 pm

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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Platform: P80 1998 C70, B5234T3, 16T, AW50-42, Bosch Motronic 4.4, Special Edition package, Plant: Uddevalla Sweden.
Platform: X40 (Nedcar) 2003 S40, B4204T3, 14T twin scroll AW55-50/51SN, Siemens EMS 2000. Plant: Born Netherlands.
Platform P2 2005 XC90 T6 Executive, B6294T, 4T65 AWD, Bosch Motronic 7.0, Plant Torslanda Sweden.
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93Regina
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Re: 1991 240 runs very rich. Starts OK but idles very slow

Post by 93Regina » Sun Feb 09, 2020 11:07 am

jbpatter44 wrote:
Sat Feb 08, 2020 8:07 am
1991 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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