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200 ford,customer concern of oil burning out of exhaust after idling upon acceleration(engine had 800 miles on it after rebuild)leaking down test revealed 40-50% on cylinders #3,4.removed engine,removed pistons,#1 and #2 rings were switched,cylinders were hourglass shaped honed approx. .0005 tighter in the middle with a minimum of .0025(OK).ring end gap was .018 approx.1" down in bore,cast iron rings were on the pistons.the cylinder walls were rougher than normal for a honing maching,rehoned block on ck-10,installed plasma upper ring,iron second rings,reassembled,road test approx.100 miles,if vehicle idles for more than 15 seconds then throttle is applied rapidly large puff of blue smoke,no smoke going down the road.pcv valve was removed,vehicle has manual trans.
 

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my parents use to have a 1994 crown vic with a 4.6 liter that did this same thing, I never did figure out what was causing it. My last rebuild which was a vortec 350 is doing the same thing, I traced it to a intake leak, now I have the intake sealed, it`s still doing it so I hope there is a answer to this one myself. I knew the valve guides in the crown vic were shot, but I didn`t think they were shot to the point they would cause it to smoke like that, it only did it after the car idled, when vacuum was the highest which usually points to a intake leak, but I don`t think it was related to the intake on the ford since there isn`t a oil source near the intake like there is on a chevy. I tried the pcv also, as well as anything else I could, but didn`t find out why it did it.
 

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I'm gonna bet the umbrella seals for the valves cracked or slid up. that's what happened to my 200, the umbrella seals got cracked and allowed oil in, and huge puff at idle. check them, I bet there cracked. some of mine were cracked, some of them were in peices in the bottom of the oil pan ( became hard and disintergrated ). the motor was otherwise in great shape.
 
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