Low compression all cylinders 2001 1.9 TDI AWX

[m.ramsdale]

Hi,

My 2001 passat 1.9 TDI AWX has recently been treated to a new turbo (well reconditioned) and a head rebuild. At the same time I cleaned all the mess from the intercooler pipework and sludge from EGR, inlet mainfold and inlet ports on head. The head rebuild consisted of:-

0.0012" skimmed and also removed from top of valve stems
new valve guides and oil seals
valves refaced
full set of injector rings replaced
new hydraulic tappets
new camshaft bearing shells

Once all back together the performance was very different, worse in parts of the rev range and better in others. Beyond 1700 rpm the performance is much better and I attribute this to the new turbo - the compressor on the old one had very worn blades. Below 1700 rpm the car seems less powerful than before the rebuild - this could be subjective given the better performance above 1700 rpm. The car is also ever so slightly reluctant to start - nothing bad, but it might fire up instantly and then die and start straight away on the next attempt. There is also a slight roughness (misfire??) at idle.

Anyway, enough background. I took it for a compression test today and it was between 210-220 PSI on all cylinders! Oh Dear My understanding that it should be a minimun of 300PSI and ideally 450 PSI+.

What gives me heart is that all cylinders have identically low compression readings so things like cam lobes, piston rings etc are unlikely (I would expect 1 cylinder to be worse than others in this case). I can think of 2 possibilities - too thick head gasket or static timing of by a notch. Original gasket had 3 holes and 3 notches - I replaced it with one with 3 holes from ebay.

My questions are:-
What would do you think - can timing or head gasket cause this?
What else could cause such an issue on all cylinders?

BTW car has done 149K miles and has been well looked after by me since 78K, but I don't know before that.

Thanks,

Marc.

[kenney]

Compression pressures:New: 25...31 bar, wear limit: 19 bar
worn piston rings is in fact a possibility,and since you skimmed the head and used the same thickness of a head gasket,then that is not the probem,check the basic valve timing,to make sure it is ok, there is a wear limit of 19 bar and the measured compression 21-22 bar is over the wear limit,

[m.ramsdale]

Thanks for your answer Kenny. I am getting 210-220psi which I figure as being between 14-15 Bar - i.e. Way below the minimum 19 Bar. Have I got my conversion from psi to bar mixed up? 14.5 psi = 1 Bar

[PCDoctor]

Your conversion is bang on.....

Good luck....

[martin1810]

Diagnosing faults on an engine that has been repaired is a nightmare. I would start by repegging the timing to ensure it is spot on. Diesels are not easy to compression test. Are you sure the results are correct. After the timing is checked, get someone to run a cylinder leak down test. That is much better than a compression test.

[kenney]

sorry didn't register the psi for some reason, however with a compression of 14 bar i can't see the engine running without a lot of smoke,are you sure the test was carried out with the correct equipment,

[m.ramsdale]

I agree. The first opportunity I get I'm going to check the timing belt timing. However, after having already done a few before I not sure how it could be done wrong. Could anyone explain that if the crank and cam are pegged correctly how it is possible to mis-time the engine?

As for a lot of smoke, I'd say no, but there is some smoke. I am also using 1 litre of oil every 1000 miles - not great, but not a disaster?

[m.ramsdale]

Martin, one thing you said concerned me - diesels are not easy to compression test. What are the common mistakes and pitfalls? My understanding would be that the purest compression test would involve the bare engine and no inlet or exhaust manifold connected - that way you are testing the engine alone - i.e. no obstructed inlet reducing compression etc. Is this correct?

[kenney]

It is not necassary to remove the manifolds to acheive a correct ready,what is necassary is a correct compression tester.Was this just a service job or had the belt broken?If you have locked the engine with the correct tools the timing should be ok.Personally i'am not sure but i can't see the engine starting with a compression of 14bar

[martin1810]

Martin, one thing you said concerned me - diesels are not easy to compression test. What are the common mistakes and pitfalls? My understanding would be that the purest compression test would involve the bare engine and no inlet or exhaust manifold connected - that way you are testing the engine alone - i.e. no obstructed inlet reducing compression etc. Is this correct?

You just disable the injector loom. Take out the glowplugs, screw in adapter, add tester and spin engine over until reading won't go any higher. For diesels you need good quality connections and tester because of the high pressure. As Kenney says, I can't see the engine running with 14 bar. Not without alot of white smoke at the start.
Timing shouldn't be wrong but always start at the beginning. Repeg timing. Then look at cam/valves to make sure they are all in the positions you expect at that point.
Then get some one to do a cylinder leak down test. That is far better than a compression test because it gives you a clue as to where the gas is going. I wonder if your valves are closing properly.