Cyclinder Leakage

[ABTgolfer]

Hi guys,

What can you tell from a Cyclinder leak test indicating that you have a leak in your cyclinder? Tuner is telling me a possible cracked piston!!! I have doubts as he failed to replicate the test in front of me. He was using a analog cyclinder test kit from "Snap-On". Any help would be much appreciated.

Cheers,

[S2 Ant]

I'd have considered a cracked piston to be highly unlikely but i guess nothing is impossible.
How did he come to that conclusion just from doing a compression test tho?

Was the compression on one cylinder a lot different to the others?

[ABTgolfer]

Thats exactly what I asked him. And as he failed to replicate the compression test to show a leak, I have serious doubt on his claims. Only on Cyclinder 1. My initial problem is an intermittent misfiring on Cyclinder 2. So he did a leak test on all cyclinders.

Also noticed heavy deposits on intake valves and I am suspecting that the misfiring is due to that. Any idea? Changed my plugs and coil packs already.

Cheers,

[john_o]

I guess this is a progression from the other thread.

are the misfires during warmup enough to light the CEL ? Is it ok when warm then? (dont get hung up on some misfires)

The key thing about a compression test is to make sure the procedure is repeated exactly the same across all 4 cylinders.
It should be consistent across all 4
Leak test easier but valves must be shut. A leak issue may indicate piston sealing issues or a valve sealing issue.

silly question but I assume it hasnt been overevved and you might have a bent valve/s?

(leak test (pressurise cylinder and see how much 'leaks' past rings etc) is different from a compression test(plugs out turn over engine on starter and see how much 'compression' that cylinder can generate in x seconds...))

Id get hin to repeat the test/s and show you the values.......

buildup on intake valves is normal for the TFSI (as its direct injection so intake is never 'washed' by fuel)
can cause misfires if really bad but I suspect not your issue.
(some people have tried 'seafoam' to clean it, or best way is to have it all apart and clean it properly then fit a catch can kit that bypasses the PCV and to some extent prevents further buildup)

Another thing to check is that the wiring harness around cyl 2 for the coilpack is in good condition....

[gillm]

what compression are you getting on all 4 cylinders ?

[PDT]

A cylinder leakage test works by pressurising the engine cylinder with compressed air (approx 100PSi) and closing both the exhaust and intake valves by turning the crankshaft and measuring the valve position to ensure they are closed. If the cylinder does not hold compression then you have 3 posibilities:

1. hiss noise in inlet manifold: inlet valve not seating correctly
2. hiss noise in exhaust manifold: exhaust valve not seating correctly
3. hiss noise from dipstick hole/crank breather: air passing the piston - damaged cylinder wall, broken piston, insufficient seal from piston rings.

There is also a possibility of the compressed air escaping past the head gasket into a neighbouring cylinder. I use the Snap-on leakdonw tester, it is very good. What are your symptoms?



(pwrote this before the replies were posted)

[v2brett]

hi mate i had a random missfire (cylinder 3)on mine a bit ago and it would only happen after the car had been driven for an hour or so, anyways after swapping plugs and coil packs it turned out to be a faulty injector on mine.
hth but might not be the case on yours