sweet928

Hi All, I have a 79' OB. I've noticed in the cold weather and after sitting for a a week or so, the car has a fuel mixed with oil smokey smelling white exhaust when warming up. The car has a high idle when warming up like an old carborated set up. Then when it warms up in a few minutes and the idle drops down, the smelly, white, smokey exhaust from the tail pipe is gone. No smoke or smell at all when warmed up and non while driving hard on and off the compression. Car runs fantastic and strong so just wondering is this normal for the OB's with the old type intake set up?

76FJ55

K-jet cars will have an increased idle speed similar to carbed cars. The J-ket system usa an aux air valve to let air bypass the throttle plate to increase the RPMs during warm up. it is controlled by a bimetalic spring whick open the air passage to increase RPM on a cold engine and closes it on a warm engine. this valve typically (not sure of precise location on the 928) is mounted on the back side of the therlostat housing. It also has an electrical heating element in it so it is controlled both by engine temp and is limited in open time by the electrical element that is heated when the ignition is in the run position. The white smoke is most likely condensation generated during the combustion process. At least this is the most common cause of white smoke on cold engine start up. A warm engine produces water during combustion as well bu when the engine and exhaust are hot the vapor usually doesn't condense since it isn't cool enough till it is well outside the cars exhaust system.

As for the smell I couldn't say for certain. but your cold start mixture may be out of limits. Does your car have cats? cars with out cats tend to produce stinkier exhaust especially during cold start when there is incomplete combustion and a richer mixture.

Edit: I see you do have cats now that I read your sig line. what cats are you running? even with cats if they arn't up to temp they will be ineffecient and may not be able to fully process the combustion gasses on initial cold start.

sweet928

Thanks for the info. PO put in headers and ss system w/ Borla and either custom or off the shelf cats of unknown origin. He did a state inspection on car right before I picked it up and emissions passed. However that might not mean much if the cold start is a different situation. So what's the best way to check if anything needs tweaking? Is it even something I need to bother with? Sounds like it might just be the exhaust set up and cats. Don't mind as long as it's not harming anything. Car runs like a beast otherwise. This is my first winter with it since purchase and can't stop taking it out of winter storage to drive it. Cold weather and dense air makes it feel a tad bit more responsive then normal -- which is already stellar. Woo Hoo.

GlenL

I'd keep an eye on the coolant level. Could be a head gasket leak.

The CIS system is really complex with subtle interactions.

You might try removing the connector form the cold start injector. That's on the front of the plenum. Could be running too rich for the needs of the engine.

And how cold is cold? That'll make a fast-turning V8 look like it's putting off a lot of smoke when it's normal.