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Smoke on startup, occasional miss, yet smog test was perfect

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Smoke on startup, occasional miss, yet smog test was perfect

Old 12-07-18, 09:56 AM
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myf16
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Default Smoke on startup, occasional miss, yet smog test was perfect

My 1990 has only 145k miles. Last month's 15 mph smog test numbers vs (max allowed) were: HC 6 (71), CO .01 (.48), NO 2 (524). Close to zero emissions.

Yet when I start the car after parking overnight there's a big cloud of smoke in my rear view mirror. This was true before the smog test. Also the car has an occasional miss (noticeably momentary loss of power) while driving at 30 to 50 mph. I had a persistent coolant loss with no drips which I interpreted as a head gasket leak. I cured that with Bars Leaks rather spending an absurd amount of time and effort than taking things apart. The oil has always looked clean, and I haven't noticed any decrease in level, but I drive only 250 miles per month. So a very slow oil loss is possible.

One other clue. In order to pass the smog test I had to replace the upstream oxygen sensors. The sensor on the right bank was black and oily looking and had resistance too high to measure (rather than the normal 6 ohms). With new sensors it smogged perfectly as it has for many years.

What's your diagnosis and course of treatment? Just drive it this way?
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Old 12-07-18, 11:07 AM
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jaaa
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Originally Posted by myf16 View Post
My 1990 has only 145k miles. Last month's 15 mph smog test numbers vs (max allowed) were: HC 6 (71), CO .01 (.48), NO 2 (524). Close to zero emissions.

Yet when I start the car after parking overnight there's a big cloud of smoke in my rear view mirror. This was true before the smog test. Also the car has an occasional miss (noticeably momentary loss of power) while driving at 30 to 50 mph. I had a persistent coolant loss with no drips which I interpreted as a head gasket leak. I cured that with Bars Leaks rather spending an absurd amount of time and effort than taking things apart. The oil has always looked clean, and I haven't noticed any decrease in level, but I drive only 250 miles per month. So a very slow oil loss is possible.

One other clue. In order to pass the smog test I had to replace the upstream oxygen sensors. The sensor on the right bank was black and oily looking and had resistance too high to measure (rather than the normal 6 ohms). With new sensors it smogged perfectly as it has for many years.

What's your diagnosis and course of treatment? Just drive it this way?
Your big cloud of smoke on start up sounds like the ACV valve on the power steering pump. It tends to go bad with age and leak. There are two vacuum tubes that lead back to the intake and when that sensor leaks- you are pouring oil back into your intakes- hence the smoke. If you pull the tube ends off the sensor and find oil, your sensor is bad. Either buy a new sensor or pull the sensor off and plug it with a bolt. You don't really need that sensor.
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Old 12-07-18, 01:20 PM
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myf16
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Thanks so much. This would explain a lot. The car DOES lose power steering fluid and it's not ending up on the garage floor.

I will report my results.
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Old 12-07-18, 06:21 PM
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Originally Posted by myf16 View Post
Thanks so much. This would explain a lot. The car DOES lose power steering fluid and it's not ending up on the garage floor.
Then it's ending up inside your alternator. Check it soon and if so you better do something about it quick before your alternator dies.
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Old 12-10-18, 10:09 AM
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well the engine burns the majority of the PS fluid through the valve hence the puff of smoke on startup, but yes some of it can also drip onto the alternator which will cause it to prematurely fail.
replace the $3 o-ring at the bottom of the PS reservoir to stop this leak (if any).
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