2010 VW Golf 1.4L TSI Compression Leak

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victor2k
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Re: 2010 VW Golf 1.4L TSI Compression Leak

Post by victor2k » Wed Jul 19, 2017 9:55 pm

STC wrote:A bent con rod could affect intake vacuum on a petrol engine with an operational throttle flap - yes !

This is a GDi - they are different
Also TSI will use a throttle unitJ338 according to SSP405.And the recorded data show a closed throttle..

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RYM6746
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Re: 2010 VW Golf 1.4L TSI Compression Leak

Post by RYM6746 » Thu Jul 20, 2017 10:16 pm

These engines suffer with carbon build up around the intake valves (due to no fuel washing it away) .If the inlet manifold is fitted with intake runner flaps try manually opening them at idle and see if this improves 1.The compression reading. 2.The misfire improves.
It probably won't totally cure the misfire but should make a difference. IF this is your problem.

It may at the very least eliminate carbon build up on the valve

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Re: 2010 VW Golf 1.4L TSI Compression Leak

Post by STC » Fri Jul 21, 2017 10:57 pm

These engines suffer with carbon build up around the intake valves (due to no fuel washing it away)
This is the downside of many GDI offerings on the market, the other common failing is water trapped at the far end of the fuel rail. Seen it on Fiat and Alfa Romeo cars.

If it was to affect Cyl 3 then why would Cyl 2 walk away unscathed ?


I would like to see a Dynamic Compression Test at max Rpm - 5000 + rpm

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RYM6746
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Re: 2010 VW Golf 1.4L TSI Compression Leak

Post by RYM6746 » Mon Jul 24, 2017 2:12 pm

I have seen the build up on all 4 cylinders but it was slightly worse on one cylinder just enough for the ECU to start picking up a misfire.

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Re: 2010 VW Golf 1.4L TSI Compression Leak

Post by STC » Mon Jul 24, 2017 9:19 pm

RYM6746 wrote:I have seen the build up on all 4 cylinders but it was slightly worse on one cylinder just enough for the ECU to start picking up a misfire.
Is that some thing you have seen in the past or is it what you have found on this car.


This coking up issue, is it really the fact that manifold injected petrol is not keeping the valves and intake ports clean ?
Without EGR would there be any significant carbon build up ?

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Re: 2010 VW Golf 1.4L TSI Compression Leak

Post by RYM6746 » Tue Jul 25, 2017 12:42 pm

I have seen it on a VAG high pressure petrol engine. Sorry I can't be more specific with an engine code but it was approximately a year ago and I can't remember the customers name to even look up the history. But it had NO fault codes and no real running issues other than a slight misfire at idle only. Another garage had already moved the coils and plugs around with no success. I could see the misfire on the scan tool counting up. Not all the time, more so when hot.I was aware of the issue due to articles I have read. It just so happened the easiest thing to do was manually pull a vacuum on the intake runner flap diaphragm as it was right on top of the engine. It instantly improved the idle and the misfire counter did carry on counting up but much slower than before. After inlet manifold removal you could see that buy opening up the intake manifold flap that it would allow the air to pass through the second intake valve thus improving combustion. As for what causes it fully, I am unsure. But I would guess crank case gasses from the breather system accompanied by EGR gasses and cold dry intake valves play a part. The fix was merely cleaning the backs of the valves with the intake manifold removed. I have also seen the same problem on a BMW common rail diesel that was just choked up from the EGR valve all the way to the inlet valves but it was the same symptom, diagnosis and fix.

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Re: 2010 VW Golf 1.4L TSI Compression Leak

Post by STC » Thu Jul 27, 2017 11:14 pm

Rym

Quite plausible, that is why after a positive Cylinder Leak Test Result I kept reinforcing the point that Low compression can be many things other than Valves, Gasket or Rings. And it Can.

However in this case, from the evidence presented thus far i'm thinking possibly a broken valve spring and have seen and diagnosed this on a similar engine.

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Re: 2010 VW Golf 1.4L TSI Compression Leak

Post by AdvTechTS » Thu Dec 21, 2017 5:29 am

Hello all, my sincere apologies. I keep forgetting to tick the notify me box :oops:
I am humbled by the amount of discussion this has produced.

As many of these diagnostic cases go the customer never gave me the opportunity to do further diagnosis. I haven't seen the car since. I would really like to know for myself...

At the time I felt that the cylinder pressure waveforms ruled out a bent conrod and valve clearance issues but I'm by no means a guru on these. My suspicion was that the shop air (115PSI) was not enough to create a noticable leak. I have used cylinder leakage tests on Carb and PFI engines with great success for nearly 30 years. But the higher pressure of GDI played a part in my theory but also if you consider the components in the combustion chamber the teflon seal would have to be the weakest link???

Thanks again for all of the input and if the car ever returns (possibly on a tow truck) I'll be sure to try to close this case!

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