dipstick vomiting oil @ WOT
05-10-2009, 12:27 AM
#16
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Join Date: Mar 1999
Location: Kernersville, NC
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Something has to be going on to lose that much vacuum.
Some of the research that I have done suggests that a valve may not be sealing properly. That may backup as to why your vacuum has dropped. Since you did switch heads......something to think about. I would think that a compression/leakdown test would find the problem.
Some of the research that I have done suggests that a valve may not be sealing properly. That may backup as to why your vacuum has dropped. Since you did switch heads......something to think about. I would think that a compression/leakdown test would find the problem.
Last edited by ACE1252; 05-10-2009 at 12:40 AM.
05-10-2009, 06:56 AM
#17
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Location: Cherry point NC
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Something has to be going on to lose that much vacuum.
Some of the research that I have done suggests that a valve may not be sealing properly. That may backup as to why your vacuum has dropped. Since you did switch heads......something to think about. I would think that a compression/leakdown test would find the problem.
Some of the research that I have done suggests that a valve may not be sealing properly. That may backup as to why your vacuum has dropped. Since you did switch heads......something to think about. I would think that a compression/leakdown test would find the problem.
I'm definatley gonna do a leakdown, but I can't do it until next weekend. In the meantime, I'm gonna check my vac gauge. It's entirely possible that the gauge may have fouled up too. It's been sitting outside unplugged, so it might be fouled with condensation or something.
05-10-2009, 08:02 AM
#18
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Location: Kissimmee, Fl, USA
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Leaky valve sealing yields a fluttering vacuum signal, not a steady, but low, signal. In addition, poor valve sealing doesn't lead to crankcase pressurization as the valves 'leak' iinto the manifolds when they don't seal, not the crankcase.
It could be that the low compression and the crankcase pressure build up are unrelated but it is tempting to group them together. Low compression readings and lower than expected power could indicate a cam install one tooth off if the cause is independent of the crankcase issue. If the low compression and the crankcase pressurization are not related then it appears that the exhaust valve seals are allowing exhaust gases to escape into the crankcase, especially on closing throttle conditions....a sudden closing of the throttle after running the engine wide open. This isn't a valve sealing problem so compression readings shold remain high.
Sounds like a lot of speculation and it is. It's difficult to diagnose things from a distance......
Good luck!
It could be that the low compression and the crankcase pressure build up are unrelated but it is tempting to group them together. Low compression readings and lower than expected power could indicate a cam install one tooth off if the cause is independent of the crankcase issue. If the low compression and the crankcase pressurization are not related then it appears that the exhaust valve seals are allowing exhaust gases to escape into the crankcase, especially on closing throttle conditions....a sudden closing of the throttle after running the engine wide open. This isn't a valve sealing problem so compression readings shold remain high.
Sounds like a lot of speculation and it is. It's difficult to diagnose things from a distance......
Good luck!
05-10-2009, 08:48 PM
#19
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Join Date: Feb 1998
Location: Ft. Wayne, IN
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Sounds like the rings to me. My '95 Z28 was puking oil out the dipstick, checked the PCV system - no problems there. Pulled the engine out this winter and tore it done - found seven broken top piston rings! My car is NA, but driven hard. The cylinder walls still had a perfect cross hatch in them with no scars or marring marks. I am just going to ball hone the cylinders and install new bearings, rings and put her back together. Good luck!
Jeff
Jeff
05-10-2009, 09:38 PM
#20
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Location: Cherry point NC
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Sounds like the rings to me. My '95 Z28 was puking oil out the dipstick, checked the PCV system - no problems there. Pulled the engine out this winter and tore it done - found seven broken top piston rings! My car is NA, but driven hard. The cylinder walls still had a perfect cross hatch in them with no scars or marring marks. I am just going to ball hone the cylinders and install new bearings, rings and put her back together. Good luck!
Jeff
Jeff
05-12-2009, 05:31 AM
#22
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Join Date: Sep 2004
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2)At WOT, the oil dipstick literally spewed oil all over the place. The dipstick dislodged, and shot oil all over the shock tower and header. It made lots of white smoke.
These two discrepancies point directly to bad piston rings, but I just did a compression test recently, and it had 170-175psi in all 8 cylinders.
These two discrepancies point directly to bad piston rings, but I just did a compression test recently, and it had 170-175psi in all 8 cylinders.
Let's start with the compression test that was done with other heads on but not since the new heads were put on. What's up with that?
Forget the low vacuum level and focus on the crankcase apparently pressurizing. All engines function with a vacuum in the crankcase. Yours has what appears to be pressure and yet you never tried to measure the amount of vacuum. What's up with that??????
Then there is this jewel. "Before I started tinkering with the valvetrain last winter, the car ran like a top. It had no excessive blowby, no vomiting dispstick, and no other discrepancies."
You changed something, something happened but what could be wrong????? Yet your going off in some direction that had nothing to do with what you did.
Last, let's all think about the possibility of blow by causing your problem. If that were the case, you would be burning oil so bad you would foul the plug in the bad cylinder(s).
At this point a vacuum manometer and a leak down tester are you best friends.
05-12-2009, 01:20 PM
#23
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Location: Cherry point NC
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I have so many problems with your information or the direction of your investigation I don't know where to start.
Let's start with the compression test that was done with other heads on but not since the new heads were put on. What's up with that?
Forget the low vacuum level and focus on the crankcase apparently pressurizing. All engines function with a vacuum in the crankcase. Yours has what appears to be pressure and yet you never tried to measure the amount of vacuum. What's up with that??????
Then there is this jewel. "Before I started tinkering with the valvetrain last winter, the car ran like a top. It had no excessive blowby, no vomiting dispstick, and no other discrepancies."
You changed something, something happened but what could be wrong????? Yet your going off in some direction that had nothing to do with what you did.
Last, let's all think about the possibility of blow by causing your problem. If that were the case, you would be burning oil so bad you would foul the plug in the bad cylinder(s).
At this point a vacuum manometer and a leak down tester are you best friends.
Let's start with the compression test that was done with other heads on but not since the new heads were put on. What's up with that?
Forget the low vacuum level and focus on the crankcase apparently pressurizing. All engines function with a vacuum in the crankcase. Yours has what appears to be pressure and yet you never tried to measure the amount of vacuum. What's up with that??????
Then there is this jewel. "Before I started tinkering with the valvetrain last winter, the car ran like a top. It had no excessive blowby, no vomiting dispstick, and no other discrepancies."
You changed something, something happened but what could be wrong????? Yet your going off in some direction that had nothing to do with what you did.
Last, let's all think about the possibility of blow by causing your problem. If that were the case, you would be burning oil so bad you would foul the plug in the bad cylinder(s).
At this point a vacuum manometer and a leak down tester are you best friends.
I'm gonna do the leakdown test on thursday. I didn't even know there was a way to measure crankcase vacuum.
As for your bolded comment, it's really not burning oil badly at all. I haven't driven it far enough to get an accurate representation, but I haven't noticed a decrease in oil level or any quantity of smoke from the tailpipe.
05-12-2009, 06:50 PM
#24
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Location: Cherry point NC
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TIME OF DEATH: 1941 EDT, 12 MAY 2009. REST IN PEACE
To investigate further, I took it on a 25mile drive to get it nice and hot, and see what kind of oil burning is really going on. As I drove, the oil pressure steadily sank lower and lower, until it was at ~5psi at any RPM off idle. As I increased RPM, oil psi stayed at 5psi.
Once I got it home, I parked it and let it idle. The RPM idled at a nice clean 900rpm. at 7:41pm, the oil pressure gauge gracefully sank to zero, and the red CHECK GAUGES light illuminated.
There was a steady puff of white smoke coming from the oil filler cap. The tailpipe had no visible smoke. I said goodbye one final time and shut her down.
Afterward, I checked the oil, it was clean, and full. Next I tested the vacuum gauge. It worked fine.
To investigate further, I took it on a 25mile drive to get it nice and hot, and see what kind of oil burning is really going on. As I drove, the oil pressure steadily sank lower and lower, until it was at ~5psi at any RPM off idle. As I increased RPM, oil psi stayed at 5psi.
Once I got it home, I parked it and let it idle. The RPM idled at a nice clean 900rpm. at 7:41pm, the oil pressure gauge gracefully sank to zero, and the red CHECK GAUGES light illuminated.
There was a steady puff of white smoke coming from the oil filler cap. The tailpipe had no visible smoke. I said goodbye one final time and shut her down.
Afterward, I checked the oil, it was clean, and full. Next I tested the vacuum gauge. It worked fine.
05-12-2009, 09:18 PM
#25
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Join Date: Feb 2004
Posts: 4,800
Sounds like the rings to me. My '95 Z28 was puking oil out the dipstick, checked the PCV system - no problems there. Pulled the engine out this winter and tore it done - found seven broken top piston rings! My car is NA, but driven hard. The cylinder walls still had a perfect cross hatch in them with no scars or marring marks. I am just going to ball hone the cylinders and install new bearings, rings and put her back together. Good luck!
Jeff
Jeff
Hard driving doesn't break rings. Detonation does. You just have to bring yourself to understand why it detonated.
I have sold individual pistons to a couple individuals who had the same problem and their mod lists shared one important detail with your's.
05-12-2009, 10:02 PM
#28
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Join Date: Feb 2004
Posts: 4,800
I was refering to the guy I quoted. Your mod list is short and hopefully incomplete so I don't know what your problem was. Please let us know what you find though.
If it is just a piston or two or something like that where a few stock pieces would get you back on the road lets us know, someone will have some leftovers.
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