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10/9/17 10:15am - Original Message: '89 C4 white smoke from exhaust'
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Joined: 10/6/2017
Posts: 2

I am going to be finished paying off a C4 in a week and will be picking it up at the same time. It has been in a heated garage for 5 months during winter and when we started it up a bit of white smoke was coming out of the magnaflow exhaust. i even have a video so you can see. Its probably from sitting around for a long time but im not a mechanic. Thoughts?

I didn't find the right solution from the internet.
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10/19/17 12:08pm - Reply: 'Re: 89 C4 white smoke from exhaust'
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Valley Center, CA - USA

Original owner 89 C4 Coupe,Silver with Red Int, late model C6 wheels

Joined: 7/11/2016
Posts: 3
Check the vacuum modulator unit on the transmission and line from the transmission to the intake. Once the rubber diaphragm inside the modulator ruptures, the engine will suck ATF into the intake causing white smoke. It could be just a pinhole in the diaphragm at this point You may find trans fluid in the line or dripping from the modulator once the line is inspected. Replacing the modulator is easy and it is usually preset from the manufacturer. A small set screw inside the unit, accessible from the vacuum port, is a fine adjustment to shift points. Hope this helps.

Macho007 is correct about the smoke color. ATF has a tendency to appear white. If the issue is only at start up it is likely not the modulator valve. One diagnostic tip: If it is the modulator, during deceleration (as in coasting down a long hill or from a freeway off ramp) added vacuum will pull fluid to the intake which will be visible upon acceleration. Watch your mirror for telltale vapors or have someone follow you to verify what is taking place.

The smell of the emissions will also be a tip to the origin. We all know the smell of oil, coolant and fuel. Pure water or condensation will smell slightly musty or damp. There may not be enough to have any odor at all.

Assuming there is no oil/water cross contamination there could be a small intake gasket leak but usually the white smoke would be constant not just at start up. It could be a small enough leak where coolant/water  accumulates when the vehicle sits over night or for days.

|UPDATED|10/19/2017 9:08:35 AM (AZT)|/UPDATED|
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10/19/17 10:43am - Reply: 'Re: 89 C4 white smoke from exhaust'
Macho 007
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Plant City, FL - USA

1988 Corvette Hatchback. Interior and exterior Black. Automatic.

Joined: 5/16/2015
Posts: 14
The white smoke may also have been caused by condensation of moisture collected from sitting for an extended time. White is usually water, blue is oil, and black is a rich fuel mixture. Hope this helps.

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