68 Z/28 Engine Smoking - Any Ideas?

**Hotrodpaul** · #1 10-22-2009, 09:46 PM

If the smoke is black, I would look at the carb, while a bluish smoke would be oil related. As suggested earlier, pull all the plugs and check the color. A dry black sooty residue indicates a rich condition, possibly a carb problem. An oily black residue indicates oil passing through the Intake Valve guides or Rings. Oil passing through the Exhaust Valve Guides will cause blue smoke but may not affect the plugs. If a particular plug shows these symptoms, look to that cylinder for the problem, such as rings, valve seals, or leaking Intake Manifold Gasket. Reading the plugs is the first thing I would do.

Paul

king_midas · #2 10-22-2009, 10:18 PM

Brake fluid?

**njsteve** · #3 10-23-2009, 06:36 AM

[ QUOTE ]
Brake fluid?

[/ QUOTE ]

Forgot about that rare problem: Once in a great while you'll find a master cylinder with a bad rear seal, combined with a vacuum brake booster with an equally bad front seal. The result is the large vacuum hose running from the booster to the intake sucks the brake fluid residue into the intake and burns it. Saw that happen once in 30 years but it was a wild one to diagnose!

**SuperNovaSS** · #4 10-23-2009, 06:50 AM

Come on..........Are you being serious Steve?

JoeG · #5 10-23-2009, 07:12 AM

Global Warming.......

**njsteve** · #6 10-23-2009, 04:58 PM

[ QUOTE ]
Come on..........Are you being serious Steve?

[/ QUOTE ]

Absolutely. One of those totally freaky, million-to-one things that will (hopefully) never happen to anyone else in the universe ever again. Discovered it by accident when they pulled the vacuum hose off the engine and noticed the paint curling around the fitting on the intake - you know how brake fluid attacks paint - that was the first clue.

68 RS Z/28 · #7 10-26-2009, 03:45 AM

Thanks to all who have chimed in with an idea either here or via e-mail. I really do appreciate all the suggestions and have been trying to work my way through some of the possibilities. Today I found some time to do a compression test. Cylinders 1-7 pumped up nicely and read between 155 and 160 pounds. When I went to 8 however.....problems. The reading varied between 30 and 90 pounds. I don't have a leak down tester, but I did order one and it will be in on Tues or Wed so I'll see what that tells me, but there is something definately wrong with #8. I'm not sure its related, but for fun I pulled the valve covers and found that the rocker stud on the intake valve had snapped. The rocker was still on what was left of the stud, but the upper portion was just laying there. I was pretty surprised to see this since the studs were replaced when the engine was done. Also, there were NO funny noises - the car sounded good. Just prior to doing the compression test I had noticed that while all the other plugs looked more or less normal, the plug on 8 looked like it had never been fired - which I suppose makes sense if it wasn't getting the fuel/air mix. I did confirm that it has spark. So all in all, I think I've found a major problem, but I don't think its the reason for the low compression - with the valve stud snapped the valve should be closed and compression wouldn't be affected. I also don't see how this would affect the smoking issue. Anyway, it will be Wed at the earliest before I get the leak down results and then obviously the heads come off. Any comments/suggestions would continue to be appreciated.

**SuperNovaSS** · #8 10-26-2009, 03:51 AM

The snapped stud definitely accounts for the low compression.

Jason

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