Help deciphering leakdown test results
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From: Birmingham, AL
Help deciphering leakdown test results OK, so let me start from the beginning. My car currently has 49K miles on it. I had the tune damn near perfect, running OLSD. I got a set of heads a little over a year ago. Best I remember, the guy told me they had to be milled ever so slightly. I got dual springs and Ti retainers. These were just hand ported heads from a local guy. Everything was fine after the heads, then my tune started degrading. It began leaning itself out and I kept adding to my VE table. Now, some cells are up to 120 and the air/fuel still isn't right. I thought it might be the w/b so replaced the sensors. Nope. Thought it was an injector. Replaced those, same thing. So, at my wits end with this thing, I did another leakdown test. This was my second time to do this. First time was before the heads and all 8 cylinders were fine. I had the pinched fingers to prove it. 
Well, this time when I did it, the results were as follows: Drivers side front to back measure in percent leakdown: 15 45 15 43. Paass. side front to back: 41 45 42 33. All were measured at 100 psi. I can't really tell where the rushing air is going, but I know it's going somewhere. How likely is it that I killed 6 cylinders all at once? Or, could this be a head problem? I removed the rockers from the pass. front and got the same results. I know all were tested at TDC of the compression stroke. The two 15s above were showing normal. Engine was cold when test was conducted. Did a compression test on first 2 cyls on pass. side and got 160 psi after several revolutions. Any ideas? Tomorrow I will try to listen through the dipstick hole for this missing air and report back. TIA
Well, this time when I did it, the results were as follows: Drivers side front to back measure in percent leakdown: 15 45 15 43. Paass. side front to back: 41 45 42 33. All were measured at 100 psi. I can't really tell where the rushing air is going, but I know it's going somewhere. How likely is it that I killed 6 cylinders all at once? Or, could this be a head problem? I removed the rockers from the pass. front and got the same results. I know all were tested at TDC of the compression stroke. The two 15s above were showing normal. Engine was cold when test was conducted. Did a compression test on first 2 cyls on pass. side and got 160 psi after several revolutions. Any ideas? Tomorrow I will try to listen through the dipstick hole for this missing air and report back. TIA 
Even if everything is fine your gonna hear air escaping into the crankcase past the rings, what you should not hear is air escaping through the intake or through the exhaust system. Those are the two place I would listen for escaping air.
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Re'
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From: Was New Orleans, but swam to Baton Rouge
That is a lot of leakdown. I would be looking for air in either the cooling system or crankcase. There is a change the valves may be bent and not seating properly causing the leak. How did you verify you were at TDC?
Thread Starter
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From: Birmingham, AL
I verified I was at TDC by turning the crank until air stopped coming out of the spark plug hole. I know there will be some air escape, but I'd think that's a bit excessive. Just trying to figure out if I could've messed up that many cylinders at one time.
First off I would put the rockers back on. Get a straw or something to stick in the cylinder rotate till on TDC with both rockers up. This verifiys that both valves are closed and the cylinder is on TDC. What you are listing for is air through the exhaust or intake/TB. Air through one of this would indicate that you might have bad intake/exhaust seat, a bent valve or to long of pushrods but you said the car ran fine before so you pretty much rule out pushrods. Also sometimes when I have done leak down test when I hooked the shop air up it push the piston down opening a valve. Another note when doing the comp test warm the engine up to operating temp and only crank three times. Then check your gauge. The more you crank the higher the reading.
