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1991 Mazda MPV Question: Cold Start Misfiring , then Runs Great.

 

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rossco, 3.0L V6, Marysville, WA, November 08, 2011, 11:30
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When Starting Cold Engine it Misfires ( Rough Fast Idle )for about a Minute then is fime and Runs Great. Restart is great up to about 2 hours . I installed New Distributer with Igniter,Set Timing,new Spark Plugs,New Wires, New Fuel Filter. Fuel Pump is original,20 years old..
This is driving me crazy !! Any Suggestions would be a big help.

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  • Answer #1

    November 09, 2011, 05:40
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    Any check engine lights on?

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    rossco, November 09, 2011, 13:17
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    Actually No Check Eng. Lights , Getting closer tho , i think the Fuel Pressire reg. assy. may be leaking down overnite ,as it starts and runs perfect when warm ,even after gust 5 minutes o running from a cold start. Also if i jump the Yellow Test connector (fuel pump override) on the driver side fender and turn the key on for 10 sec. it will cold start perfect at say 50 deg. TX. Ross

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  • Answer #2

    patrick mannion from Greg Solow's Engine Room, November 09, 2011, 07:46
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    I would look for vacuum leaks that may seal up as the engine warms up causing a lean fuel mixture misfire. Many automotive repair shops have a machine that generates an inert non flammable low pressure smoke that looks similar to cigar smoke. The intake manifold is sealed off, and smoke is put into the engines intake manifold. The smoke then fills the engines crankcase and if there are any vacuum leaks from gaskets, hoses, or housing smoke emits from the source of the leak. Some mechanics will use propane or aerosol carburetor cleaner, with the engine running they will spray the cleaner or propane around the intake manifold and vacuum hoses. A leak will cause a "lean mixture" condition, when the flammable fuel (carburetor cleaner or propane) comes in contact with the source of the vacuum leak the engine idle speed will raise as the engine has received "fuel". this method of finding a vacuum leak works but is not recommended as it can easily cause a fire.
    There is a company that independent auto repair shops get their information from, this same information is available inexpensively for people that work on their own cars.. The information is year make and model specific, covering repair procedures, torque specifications, fluid capacities and specifications, service bulletins, component locations, wiring diagrams ect.... Alldata is very easy to navigate http://bit.ly/AllData_Repair_Manuals_Online

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    rossco, November 09, 2011, 13:18
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    Hey tx. Great Idea... Its only 20 years old !! Vac hoses don't last forever.. Getting closer tho , i think the Fuel Pressire reg. assy. may be leaking down overnite ,as it starts and runs perfect when warm ,or even after gust 5 minutes of running from a cold start. Also if i jump the Yellow Test connector (fuel pump override) on the driver side fender and turn the key on for 10 sec. it will cold start perfect at say 50 deg. TX. Ross

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