Okay, first time using this tool for me & after some web research I tried several diff. methods of use. I made readings at TDC, about 1/2 way down & at BDC. IMHO none of it told me anything reliable, going to pull my block after only 2K to see what went wrong.

Here are current symptoms:

After sitting a few days no smoke on start, drive to town, park at work, on start up big cloud of smoke & continues to smoke at idle & a nice cloud when under throttle. Let it sit a few days & its clear again?? Leaking guides I would think would smoke on every start up due to oil sitting on the valves.

As a background after a minor rebuild at 78K (rings, valve job), break in was clean, car ran like new again. At 1600 miles did a driving school at local track (www.thunderHill.com). Car continued to run awsome, lots of 4-4800 RPM pulls down the short straights & into/out of turns. Not one problem.

Drive home was fine, 31 MPG on the way home.

Following weekend is Memorial parade, club I belong to (www.corvettesoflakecounty.com) participated. Hot sunny day, stuck in a slow parade the car was running warm but not overheating, cooling fans would kick on, temp would drop in a normal repeating cycle. Crowd kept asking for a burnout... I finally complied. After the tire smoke began to clear I noticed smoke still pouring out the back of my car... uh oh!! Run a compression test the next week, all checks out fine at approx. 150 across the board. Figure I might have sucked an intake gasket. Pull the intake & replace the gasket... nope not that. Same symptoms...

Borrow the leak down tester... run the tests. Lots of weird things like high readings but if I pull the air & immediately hit it again the leak drops to only 2 or 3%?? Went through each cyl. 4 diff times and some of them are just never consistant. Some however were fairly consistant every time. Local shop thinks the diff. readings is due to oil in the cyl. giving a hydraulic ring seal & false low readings. My head says pull the damn thing, my heart says... and the horse is me.

Here are the readings:

If you see two # w/ a dash, that is where I got a high reading & then pulled the air & immed. hit it again, 2nd number was usually much lower but a couple of times it went the other way?? Blanks or n/a I didn't get a test in that area. Test 3 (t3) was only a BDC test cycle. That whole test gave me sucky numbes (IMHO) but other BDC test were not that bad which makes me think the whole day was a waste of time.


Cyl # test1 t2 t3 t4

1 tdc 4% 5% n/a 18-3%
1/2 5% n/a 12-3%
bdc 4-16 3 4-16 6%

2 tdc 3% 3% n/a 2%
1/2 8-2% n/a 2%
bdc 11-1 12 2%

3 tdc 8% 5% n/a 17-2%
1/2 13-3%
bdc 11% 15-3 13

4 tdc 2% 3% n/a 2-11%?
1/2 13% 15-1% 17-2%
bdc 2 5 12 3

5 tdc 24-9 17 25-5
1/2 20-4
bdc 15-4 15-4 13

6 tdc 2 15-2 n/a 13-2
1/2 5 25-5
bdc 5 12 20-13

7 tdc 17 1 2
1/2 3 2
bdc 2 17-1 16 2

8 tdc 3 3 2
1/2 2 15-1 2
bdc 14 11 11 4

Sorry the columns got off a little. Any and all feedback is always welcome... thanks in advance.

 

When you put air in the cylinders did you check to see where they were leaking? That is,if air is coming out the dipstick tube or PCV hole its leaking past the rings. Air coming out the TB would br an intake valve problem, etc. You may narrow the problem down a little this way.
I havent done a leakdown in years but my memory says over 10% is a problem, but I only did it at TDC, at the time nobody suggested to me any other way.

 

All leaking appeared to be rings. I actually had the valve covers off & all the rockers backed off. I tightened them down enough to cause a leak on each one & you can definately hear when air goes either to intake or exhaust. From what I could tell, not the case on any of the cyls. Lots of air noise from the pushrod cavities, aka lower end...

 

Sounds like time to take it apart. That sucks.

 

What color is the smoke-I mean is it oil burning or fuel? The Compression test seems fine. What did the plugs look like when you pulled them? With 1600 on the rebuild and the run you made it seems to me like rings have seated well-which leads me to believe yours is a fuel related problem-did you have your injectors replaced or rebuilt?

 

SMOKE:
Blue = Oil
Black = Gasoline (rich mixture)
White = Water (steam)

This applies to smoke coming out of the exhaust pipes. I have seen overflowing trans fluid hit the pipes and burn almost white, like water, but that smoke isn't coming out of the pipes.

RACE ON!!!

 

I was taught to do leak down tests on a hot motor with:
1- the throttle held at WOT
2- each cylinder at TDC COMPRESSION.
3- some Mechanical means/divice to prevent the motor from turning over because leaving it in gear is dangerous as car can lurch forward.
4- 100lbs test pressure minimum, sufficiant to test and make
computing % easier.
Any eading other than TDC Compression is totally bogus because you
have valves partially open etc.
Temp also influences test results, typically I do one bank starting
with a hot motor, restart motor and let it get back to temp,
then do the other bank.
I suspect a bent valve, sticking valve, broken valve springs, or combo
of all.
From experience always leak down motors after a valve job.
I have sent back more than a couple of cylinder heards back to
the machine shop becuase they were not sealing. Wise saying about
"trust but verify" applies here.
IF the rings are worn you can usually hear air escaping out the dip
stick.

 

most of the plugs have some light oil on them...

The way it happend all at once leads me away from the valves.

Would not enough ring end gap cause problems at high temps... as in causing them to break?

I just have no time this week or perhaps even next to work on it. Thinking about burning a week of vacation to devote effective time to the job.