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William B
William B, Auto Service Technician
Category: Car
Satisfied Customers: 393
Experience:  Associate Degree Automotive Technology, Master ASE, Master BMW, Master Mazda, 30+ years experience
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1985 325e: rich..sitting..intake..different mass air flow meter tried

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I have a 1985 325e. It runs rich after sitting about 45 minutes,at start up.After clearing it self it runs excellent.New intake boot new t.p.s. new 02sensor,new thermal time swith,temp switch,different mass air flow meter tried. different motronic substitued,??????Help    Thanks, Rick
Submitted: 10 years ago.
Category: Car
Expert:  William B replied 10 years ago.
HeyCustomerthanks for the question,

It maybe that one or more of the fuel injectors are leaking down, causing a flooded condition when hot and sitting for a short time, (45 minutes) but the fuel has evaporated if it sits for a much longer time period, like overnight.

I would hook up a fuel pressure gauge, run car til hot, shut off and check fuel pressure for the 45 minutes or so. When you shut it off to check pressure, put a pair of fuel pinch pliers, (available at most auto parts stores), clamped on the fuel return line to keep pressure on the injectors. To see if there is a complete loss of fuel pressure, it should stay about the same pressure as when shut off for at least five to ten minutes. If it drops to zero in that 5 to 10 minute time period, then more than likely one or more of the injectors maybe leaking internally into the engine, causing a rich condition.

Running pressure should be about 35 psi. with vacuum line connected to the fuel pressure regulator.

There is a BMW TSB, technical service bulletin, about hard hot starts at a higher altitude, where basically BMW recomends holding the throttle at about half open position when hot starting, due to the thin air at high altitude. Not sure what altittude you are at, might be something to try, all the same, just to see if it makes any difference.

Naturally, BMW also mentions the grade of fuel, as a possible cause of a hard hot start, or for that matter any hard start condition.

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Customer: replied 10 years ago.
Reply to William B's Post: William, The 1985 Bmw 325e that runs rich? Here is what i found so far,Fuel pressure is fine,No leak down in residuel pressure,We live about 25 miles south east of Duluth Mn. Its 85 degrees at home 46 degrees in duluth any how If the coolant stays above 140 degrees starting is fine. When starting it cold and letting it idle the coolant gets to about 125 degrees and the mixture goes rich and if you give it gas its really bad will die if you try to rev it up,must rev it very high to clear, impossiable to go any where but at 140 degrees and above it runs like new, 29.5mpg Thanks,[email protected] AKA.Customer
Expert:  William B replied 10 years ago.
Well from what you are telling me the water temperature is the key. It looks like you have changed the temp. sensors. I assume no teflon tape or any sealers are on the threads, since the ground connection maybe be through the housing threads into the block. also assume the cooling system was bled to remove any air.

I see that you have tried "different air flow meter" and "different motronic" and you are sure these two parts worked ok on another vehicle? Or were they just used ones that may or may not have worked right? I know it is expensive to replace those type parts, but if used ones are installed, and you have no idea if they worked right, then it is hard to say if they made any difference.

That being said, I would not be afraid to take the water temp sensors out again, put in water on a hot plate with a thermometer and an ohm meter hooked up so that you can measure the resistance of the sensors and check the temperature of the water, so that if there is a "break" in the resistance during the warm up of the water, I suppose then you might have false information sent to the control unit, resulting in a rich condition. Most of those type components work on a high resistance when cold, and as they warm up resistance drops, so any "break" in resistance, meaning an open circuit, then resistance is "infinity" or off the charts, which might richen the mixture above what it was even when cold. (Water temp sensor for the control unit has 50 f = 7 - 11 k ohms, 68 f = 2.1 to 2.9 k ohms, 176 f = .27 to .4 k ohms)

You do not mention the mileage on the vehicle, naturally high miles could mean carbon buildup on the back of the intake valves. Bulletin on this condition and the driveability and running problems are most always when engine is cold or warming up, problem is gone when at operating temp.

Is the check engine light on? I assume not, but any codes or diagnostic help would be handy for this type problem.

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