MK4 GTi misfire issue

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tendyfish
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Registered for: 6 years
Car Make: VW
Car Model: MK4 GTi
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MK4 GTi misfire issue

Post by tendyfish »

Hello everyone. I'm in need of assistance as i'm trying to diagnose an issue with my GTi.  Brief history: I was driving around town in a bit of a hurry so was a bit heavy on the pedal shifting at around 4k rpm. Suddenly i felt the car jerk and started shaking and felt like i lost all power with no throttle response and a funny smell in the cabin was like smoke from fireworks, i however managed to drive slowly to get home, was 1.5kms away anyways.  Next morning i ran a VCDS scan  to reveal the following Misfire codes:
16684 - Random/Multiple Cylinder Misfire Detected 

            P0300 - 35-00 - 
16685 - Cylinder 1 
            P0301 - 35-00 - Misfire Detected

I started off with swapping all four spark plugs with relatively new one i had , no change. Cleared the error codes from VCDS and swapped out cylinder  #1 coilpack with #2, ran the scan, but no errors showed up but engine still jerking. Changed the entire set of coilpacks with new ones and still there was no change. Finally tried cranking the engine with at least one coilpack unplugged. noticed that coilpack #1 whether plugged or unplugged behavior was the same. Leading to believe that there was completely no combustion in cylinder #1, took a closer look and noticed the spark plug was coming out soiled with black oily substance and a peek inside the cylinder showed there's some black liquidy substance, probably oil and petrol. Immediately thought it was a head gasket failure but its missing key symptoms i.e  Overheating, Oil in coolant bottle, white smoke from exhaust, Mayonnaise in oil fill cap, oil or steam from the edges. So i really dont really get whats going on, i've attached a video of the engine jerking and sound from the exhaust. Help!

https://youtu.be/90_xSxZptbU


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THANAS
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Re: MK4 GTi misfire issue

Post by THANAS »

Have you done a compression test to confirm your suspicion regarding the compression on cylinder 1? The symptoms do line up with a compression issue to an extent.
tendyfish
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Registered for: 6 years
Car Make: VW
Car Model: MK4 GTi
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Re: MK4 GTi misfire issue

Post by tendyfish »

THANAS wrote:Have you done a compression test to confirm your suspicion regarding the compression on cylinder 1? The symptoms do line up with a compression issue to an extent.
it turned out to be a faulty spark plug, when removed it looked fouled and had cracks in the ceramic insulator

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