No I am not this will be my first leak down test.
Most mechanics have performed a compression test, and following that start replacing big chunks
of real estate. And when asked if they have ever performed a leakdown test, some will act like
you are discussing going from simple addition straight to calculus?
That's not true at all. Those who want to know exactly where to pinpoint the problem (so that
they can retest after the repair and have true confidence in the fix) will routinely run a leakdown
test, partially to cross-check the results of the compression test, and again for the increased
diagnostic resolution.
It's easy to do. For our V8 engines:
1) Pull all 8 spark plugs. (I'll assume they are already out due to the compression test.)
2) Mark the harmonic balancer every 90°.
3) Rotate the engine to #1 TDC on the compression stroke, and apply compressed air via the spark plug
opening. Listen carefully at the throttle body, exhaust tip, and oil fill opening.
Write down the results for
this cylinder.
4) Repeat step #3 (7) more times, until you have the results for all 8 cylinders.
5) Post the results of both the compression test & the leakdown test so that
we can roll around in the data and figure out what the engine (via your testing) is telling us.
HINT: You really want to get each piston as close to TDC as possible, for only when the connecting
rod is straight up and down will the piston stay in place. If you are off a few degrees, the 100 psi
x the surface area of the piston can move the crank a full 180° in a flash. And DON'T leave the
ratchet/socket combo on the crank bolt while you are testing, for it can fling that bad boy across the shop
if the crank moves...ask me how I know this. :0)
NOTE: Race teams can & will justify having a leakdown tester gauge (some even insisting on a
specific diameter orifice) in order to quantify exactly how much the ring seal has changed from race to
race. (And of course verify the valve/seat sealing too.) The lower the leakage rate the more the
tendency of these folks to post them. (Usually in % -- for example, you apply 100 psi and see that
on the 1st gauge, and the 2nd gauge shows '92', so they would refer to this as 8% leakage. See attached.)
****
But we aren't a race team trying to track the piston ring seal over time. Instead, we just want to
know if the intake valve, exhaust valve, or rings are where we need to focus in order to make this
bad cylinder good again. So all we need is compressed air fittings specifically designed to apply air
to a cylinder via the spark plug holes. (See 2nd attachment.)
Back in the day compression testing was a common skillset, even amongst the shade tree
mechanic community. But leakdown testing was pretty exotic for most automotive mechanics, but
was more common in the piston-engine aircraft community.
But now you know as much as I do about all this. It may take a try or two in order to get the hang
of it, but once you add this skill to your repertoire this will become an unfair advantage during any
future troubleshooting session that starts to delve into the mechanical health of the powerplant.
So there you have it. Compression test results for all 8 cylinders. Then take the NAPA compressed
air adapter, apply that to each cylinder in the firing order, further refine your diagnosis, and then
share the wealth with the forum.
I don't mind a problem, but I hate a mystery. Our goal is to have incontrovertible proof of what exactly
needs to happen in order to get all 8 cylinders to act exactly the same on your new build.
I am looking forward to your next status update.
Best of luck --