vtraudt

I had the head rebuilt (they changed 28 out of the 30 valves).
New gaskets, bolts, etc.
New timing belt etc done, correct timing (engine turned over 10 times, checked and verified).

Before installing the engine, thought I run a leak down (just to be sure):
TERRIBLE, values between 40-75% leak.

Took cams out again, and did a leak down. All cylinders improved significantly, some to 5% leak.

Is it possible that the hydraulic lifters 'lock up' (in fully extended position), causing the valve NOT to close fully?

If that is NOT a possible explanation, only seems to leave they did not grind the valves to the correct height?

vtraudt

Well, I took the lifters out, some where 'springy', others not.
Took the lifters apart, soaked and cleaned, assembled.

Still, terrible leak down values on the these brand new heads.
Even with cams removed (and consequently valve fully closed), still 30% leak AT BEST (up to 70% worst).

Finally decided it is either the valves, or head gasket.

Removed all the stuff (including intake and exhast manifold).
Before taking the heads off, poured some mystery oil in and did the leak test again:

https://www.dropbox.com/s/i94jd922ydnwhye/MVI_6763.AVI

What you see is a 30% leak, and Yellowstone like bubbling out of the intake valves!!!

Conclusion: **** poor valve job.
Heads are back to shop that did the job.

vtraudt

I have misfires on cyl 3. Idle, part throttle.
coils, plugs, injectors swapped/changed.
compression 170 psi on all 6
leak down below 6% on all 6

Is it possible that a hydraulic lifter is not pressurizing (getting 'stiff'), cause a valve to NOT open at the right time (or sufficient lift) to cause misfire on that cylinder?

I have bank 1 right now in position with cam marks lining up. cyl 2 and cyl 3 exhaust valves are closed. Pushing down on both cyl 2 goes 'hard'. One of cyl 3 goes down noticeably easier. Without oil pressure, what I am 'feeling' is only the internal spring of the hydraulic lifter I assume. But a weak (or leaking) lifter would potentially cause this valve to not open at the right time (or not far enough).

Possible that a leaky lifter would cause the observed misfire on cylinder 3?

Prospeeder

Im assuming the belt broke and you bent valves. Are you trying to reuse the lifters? BIG nono on these 5v engines. They get damaged and can extend the valves and even rebend them. Had this happen on a 1.8T with the same lifters, rebent all the same valves after a few minutes of running. I have read rebuilder bulletins warning of always replacing the lifters on VW/Audi engines with bent valves.

vtraudt

Not on this engine. No belt broken. Compression 170 psi uniform across all 6. Leak down under 6% on all 6.

I did have another (actually 2) 2.7T with broken/jumped belt and bent valves. On those, I took the lifters out, soaked/cleaned them and made sure that they are not 'stock open'. Replaced a couple that I did not like.

Then obviously:
- light test with valves installed
- leak down with cams out (to ensure new valves etc. seal good)
- compression test and leak down with cams in
- turning engine over by hand
- cranking engine and compression test

Both engines running fine.

vtraudt

THIS car:

Misfires as described above. Anything that I can think of changed/swapped/measured/tested/traced.

Today:
- got 6 Noid lights, will hook up to spark signal and run engine.
- ditto injectors
- maybe cyl 1-3 Noids on spark and injector
- bought Oscilloscope. Plan to look at spark and injector signal on cyl 1-3
- plan to look at crank (engine speed) sensor signal. not sure if one or a few bad or dirty or contaminated flywheel teeth would created consistenly misfire on only ONE (here: number 3) cylinder
- try even smaller gap (what is practical minumum gap? current is 0.0029 on copper NGK BKR7E)
- try much larger gap (say 0.040?)

Also observe 'rich' exhaust, but likely just from unburnt fuel of cyl 3 (indicating that fuel is injected but not burnt).

What mechanical, cylinder specific (cyl 3) defect is even perceivable that could lead to misfire (unburnt fuel) with perfect compression test and perfect leak down test results?

Observation from several drives:
- bad running when cold
- white smoke when cold
- when oil temp starts to come up (after coolant temp at normal operating temp), no smoke; engine runs decent, fairly smooth with VERY little throttle (-3 to zero vacuum on boost gauge). Not so smooth at idle and higher boost.
- when idling for longer periods, engine 'chokes up', 'coughs' and runs 'normally bad'. Repeat after a while
- after 'coasting' (rolling in gear with closed throttle), engine 'chokes' and needs to 'free up' first before running smooth if above part throttle is found
- after boosting, engine 'chokes' and needs to 'free up' first, see above

Assumption for 'choking': at higher vacuum more unburnt fuel builds up, ditto after boosting, and needs to be 'cleared out' again first.

Unconfirmed observation: car drinks gas like crazy (twice the normal fuel consumption).