Hey all,
I hope stones aren't chucked my way. Yet more data to digest. I'm learning as I go, so pardon in advance for the newbie style.
The main differences from before are the not as radically different wet/dry compression numbers, some air from the crankcase in the leak test, and vacuum numbers.
Pre: engine warm, having been driven roughly 10 city miles.
Tests, in order done.
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Vacuum (attached to the PCV manifold inlet, PCV itself venting):
-at idle: 12.75" steady.
-at 1500: 15.75-16" slight fluctuation (1/4" gauge increments).
-at 3000: 16" steady.
Based on a Chilton's vacuum troubleshooting chart for a Chevy van, no obvious symptoms other than low overall compression were seen. The others being various forms of fluctuation and shakiness depending on acceleration, etc.
Compression:
In redoing my compression test of last winter, I was much more careful and deliberate. I documented more carefully, used less oil, and tested in a better manner overall.
Testing was done one cylinder at time. That is, dry of cyl 1, wet of cyl 1, dry of cyl 2, wet of cyl 2, etc. Injectors unplugged, throttle wide open, uniform 5 cranks per test, plugs out of all cylinders, and exactly 1.25 teaspoons of 30w oil precisely poured into each cylinder. Cylinder 1 is front, per the spark plug wires.
Cyl- dry/wet, difference
1- 150/154, +4 2- 130/140, +10 3- 104/113, +9 4- 146/161, +15I then tested wet again without adding more oil. The theory being that the extra cranks while testing subsequent cylinders allowed the oil to possibly seal better.
Cyl- dry/wet2, difference
1- 150/159, +9 2- 130/143, +13 3- 104/119, +15 4- 146/164, +18Vacuum again:
On a hunch, I tested vacuum again immediately after the dry/wet2 compression test. The theory being that if the rings were now sealing better, vacuum should be improved if the rings were at fault.
-at idle: 12.25" (climbed to 12.75" after roughly 1 minute)
-at 1500: 15.5"
So no change in vacuum.
Leak testing:
100 psi, 6 cfm, 20 gallon air setup, piston at TDC and verified to have remained there after being pressurized. Test done only on the worst cylinder, 3. This was done after the second vacuum test of course, so residual oil from the compression test should have been burned off.-Good amount of air coming from the tailpipe. Good meaning enough pressure that when the pipe was plugged by hand just momentarily and released, a hefty blast of pressurized air resulted.
-No air from the intake heard or felt. Although this may be a case where the amount leaking from the exhaust covered it.
-Indeed, some air from the crankcase. With the crankcase intake and dipstick plugged, a little air could be felt from the PCV hole. If that hole too was plugged, the pressure built to the point where a good, strong puff occurred. It took, say, 10-15 seconds for that pressure to build. On a hunch I stuck the compression gauge on the PCV hole to see if it would register. After 30 or so seconds it appeared to ever so slightly tick a bit. With pegged being 10 psi, probably it just nudged past 10 psi, assuming the gauge is accurate that low. 20 psi is the first line. The gauge did not tick again after two minutes or so.
Summary:
The dry/wet compression numbers don't look as catastrophically bad as before. So I'm encouraged that the rings may not be totally lost. Yet, I'm burning oil, have some hot air coming from the oil filler hole while running, notice a slight worsening of idle when the oil filler cap is removed, and have some air coming from the PCV hole during the leak test. So something must be up with the rings, the question being how bad?
The exhaust valves seem terribly out of whack. Even with a cracked header, the air coming from the tail pipe is major. Could this be the result of the timing belt being one tooth off? It was done by a shop shortly before I got the car.
Vacuum is quite low, but steady. How it can be so steady with one cylinder having wildly low compression? Perhaps the gauge is not that accurate? It's a U.S. made, approx. 25 year old unit with hyper accurate markings. Brand I did not note.
I've poured MMO in each cylinder, cranked over by hand several times, and will now let it sit 36 hours. Compression test to follow.
Comments on any facet of the tests would be appreciated.
Thanks, Doug