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Misfire detected

04-13-2017, 05:51 PM
Hi everyone, I am new to the forum and I badly need some help!

I bought an Audi A2 1.4 2003 Petrol for my wife.

When I bought the car the engine warning light was already present. The previous owner meant that the engine issues were no big deal and that car handled well even if the engine light comes on. When I drove the car home the engine warning light came on, and the car drove terrible, lack of power. I had to pull over and restart the engine many times to get the warning light to clear so that I was able to drive home. When warning light clears, the car ran normally.

The previous owner had the car into repair several times because of the engine warning light, but the repair shop was never able to solve the problem. They had done a lot of diagnostic and even changed the ECU and 1 coil/coilovers.

I have very little experience when it comes to repairing cars and I am on a budget. That said I got a friend which used to be a car mechanic that helps me out. He also has access to VCDS, but as he explained his skills using VCDS is not that good.

VCDS reports that there is a misfire cylinder 2 (P0302 - 35-00 - Misfire Detected). I can drive the car fine, but very often when car come to a stop still, the engine warning light comes on and the car then runs terrible. This also happens when I start the engine and let it idle for 1 3 minutes without hitting the accelerator. If I start driving right away, there is no problem as long as it does not idle for above a minute or so. What we have done so far:

- Changed ECU (Second hand ECU)
- Replaced injector on cylinder 2
- Swapped coil/coilovers between cylinder 4th and nr 2, also from 3th and nr 2.
- Replaced knock sensor
- Replaced spark plugs
- Replaced fuel filter
- Regular service, oil, oil filter, air filter.
- Compression tests on all cylinders:
o Cylinder 1 = 16.2 Bar
o Cylinder 2 = 17.1 Bar
o Cylinder 3 = 16.8 Bar
o Cylinder 4 = 17.8 Bar
- Fuel pressure and fuel pump delivery rate:
o Fuel pressure while engine idle: 47 psi
o Fuel delivery 1600 cm3 in 30 sec (battery 12.80 V, ignition off, remotely/manually run)
- Inspected the engine loom wiring harness. Measured resistance between the different connectors such as to coils and injectors. This was just a quick and dirty check to see if we can verify if there was some resistance difference it the readout between the different connectors/pinouts for the units, no difference was noticed.
- Tried to spray starter gas around the intake manifold looking for leaks, but no rise in idling.
- Throttle housing calibration done using VCDS, OK
- Checked and verified timing belt alignment, OK
- Cleaned MAF sensor, OK
- Coolant sensor, OK
- EGR valve calibration done using VCDS, OK

We noticed that there was a color difference while changing the sparkplugs. Sparkplug on cylinder nr 2 was much darker than the others. We used a flashlight inspecting each piston through the sparkplug hole, and we noticed that the piston on cylinder 2 was a little wet compared to the others.

When we disconnect the fuel injector on injector 2 while the car is running, there is just a slight difference in how the car is idling. When we disconnect any other injectors there is a very clear difference in idling. When my friend used VCDS and advance measuring blocks selecting Lamda readout, misfire cylinder 1-4, he thought that the lambda sonde/O2 readout was variating too little, close to 0 all the time. He decided to disconnect the O2 sensor. When disconnected O2 there was no misfire registering in VCDS and the engine was idling much better, no engine warning light. My friend had a new aftermarket O2 sensor lying around which is for an Audi A3 1.6. The wiring color code is the same as the original car O2 sensor/connector, so we decided to replace the O2 sensor with the one for the Audi A3. The readout in VCDS for the O2 sensor now showed a much more variable readout than before, but the misfire count on cylinder nr 2 started again, and as soon as it reached around 85-100 misfires the engine warning lamp came on again and then also the O2/Lamda readout stopped and went to 0. When we clear the TDC (misfire cylinder 2) for the engine while engine is running, the O2/Lamda readout start displaying values again, but so does the misfire counts for cylinder 2, and then engine warning comes on and O2 readouts stops again.

So we concluded that if O2/Lamda is disconnected there is no misfire readout in VCDS, the engine runs smoother and no engine warning light.

My friend is suspecting that cylinder nr 2 may have leakage problem in the intake manifold, or there is some kind of vacuum leakage (have not been able to trigger the problem using starting gas), maybe EGR issue (do not know is there is EGR tube for all 4 cylinders, or just one common tube/vent)

I sincerely hope that someone here is able to point us in the right direction, maybe there is something that we are missing or overlooked.
LOG from VCDS:
Address 01: Engine Labels: 036-906-034-APE.lbl
Control Module Part Number: 036 906 034 CA
Component and/or Version: MARELLI 4MV 5949
Additional Info: WAUZZZ8Z73N006323 AUZ7Z0B2128047
1 Fault Found:

16686 - Cylinder 2
P0302 - 35-00 - Misfire Detected

Readiness: 1010 0101

Today we removed the intake manifold, we discovered that the intake on cylinder number two was oily and brownish.

The other intakes were nice and clean and so were the valves.
Further inspection reviled that one of the valve on cylinder number two was covered in oil/carb.

We have not dismantled the valve cover but it seems like the valve guide or at least the valve seal is broken.

Since its oil on the valve rod we suspect the cylinder number two is at least burning oil, will this result in misfire and is it possible that it draw air through the valve seal?

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