Audi A3 2002 1.6 petrol misfire ?

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Wed 24 Feb 2016 08:04
Audi A3 2002 1.6 petrol misfire ? - HarlequinVW

Hello Everyone.

I have a weird problem with my Audi A3, maybe someone has come across this before, or can provide helpful suggestions of where to look….

The car is an Audi A3 1.6 petrol 2002 with a AVU engine. It’s covered 280,00 miles but has been well serviced, there is for instance absolutely no cam wear and the head is yellow inside, not black. The car runs on LPG as well as petrol.

The problem is that is has a misfire on cylinder 2.

It’s not the ignition. As the coil, leads and plugs have been changed. Also the coil (which is used for 2 cylinders) has been inverted, the fault stayed on cylinder 2.
It’s not the fueling as all petrol injectors all spray the same. Also the problem does not change when switching between petrol and LPG fuel.
It doesn’t appear to be the engine either. A compression test gives the same pressure on all cylinders.

Any ideas?
The only idea I have is a sticking valve. It can keep up at tickover, for the compression test, but not when the engine’s running…. A long shot, however, since the problem one of the tappets did tick for a few seconds when I started the engine one time. That hasn’t happened since I’ve owned the car, which is since 2012 and 100,000 miles ago.

Help!
Mark

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Wed 24 Feb 2016 11:42
Audi A3 2002 1.6 petrol misfire ? - Railroad.
A sticking valve or a tight tappett could well be the cause. I've mentioned it many times on this forum, but the tool you need is a vacuum gauge to measure inlet manifold vacuum. A fluctuating needle indicates a sticking valve.

Does the misfire occur just the same when running on LPG as well as petrol? Sometimes on LPG the valve clearances can be too tight resulting in a misfire. Even though the valve clearances are hydraulically regulated a worn or gummed up valve lifter could be your problem, but again this will show up on a vacuum gauge.

Google how to use one and how to interpret what it tells you. Alternatively use a scantool and analyse live MAP sensor information, which tells the ECM manifold pressure, or negative pressure as the case may be here.
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Wed 24 Feb 2016 11:55
Audi A3 2002 1.6 petrol misfire ? - HarlequinVW

Thanks for the reply Railroad. I will try and swap the tappets on cylinder 2 with another cylinder, without removing the head, to check that.

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