Misfire 2nd cylinder P0302

[SMarshall]

I have a seat Ibiza 1.2 MK3 at high rpm like 4000rmp my engine light starts flashing and the car goes into limp mode. I have to switch the engine off and turn it back on then its all good again I have changed the plugs and coils but hasn't fixed the problem. while the car is in limp mode I have unplugged the coil and fuel injectors separately and does not make a difference in the engine shaking or noise it is just the 2nd cylinder what is misfiring. Took it to my local garage he told me to change spark and coil what I have already done then said about getting a compression test? it only misfires under load at high rpm like driving at 70 on motorway any suggestions on what to look at next? I know a bit about cars but not an expert or anything.

[GreenV8S]

SMarshall said:

my engine light starts flashing and the car goes into limp mode

The ECU has detected a fault. To start the diagnosis you need to read the fault codes to see what the ECU thinks is wrong.

[SMarshall]

I have its 2nd cylinder missfire code P0302

[Coilspring]

Compression test is a good logical next move.

[Munter]

Also look at the state of the wiring to the coil on no2.

[Coilspring]

Munter said:

Also look at the state of the wiring to the coil on no2.

Swap the plug and coil, to 2 different cylinders, see if the misfire goes to another cylinder or stays on no 2.

[Coilspring]

Re reading the original post.

Valve springs could be the issue. Very very unusal fault if so.

[GreenV8S]

SMarshall said:

while the car is in limp mode I have unplugged the coil and fuel injectors separately and does not make a difference in the engine shaking or noise it is just the 2nd cylinder what is misfiring.

Are you saying that once it goes into 'limp mode' the 2nd cylinder doesn't fire at all?

[Sardonicus]

Dont dismiss a faulty fuel inj/driver either far more common nowadays than years ago

[SMarshall]

Update I did a compression test here are the results

Compression test

Cylinder 2 - 153, 150
Cylinder 1 - 153
Cylinder 3 - 150

Wet test
Cylinder 1 - 200,
Cylinder 2 - 210
Cylinder 3 - 205

I also swapped the fuel injector and the misfire has remained on cylinder 2.
I think the compression test should be higher but cylinder 1&3 aren't misfiring so this cant be the problem right? they are all no more than 10 difference.
I have not done a leak down test. I have been reading the web and come across a few people with this problem. https://forums.seatcupra.net/index.php?threads/mys... so I am going to try his fix and will update on my progress. any other thoughts or advice?

[Sardonicus]

If the inj driver within the DME/ECU is failing no amount of external parts swapping will rectify, you may need to get this output scoped to confirm that this is indeed failing and causing the misfire just food for thought and worth getting tested

Edited by Sardonicus on Sunday 3rd March 19:55

[SMarshall]

So get the ECU tested? fuel rail did not work been playing with it all day and it's still misfiring
So it's not
sparkplugs
coils
fuel injectors
low compression
fuel rail
fuel injector wires

What to do next?

[Richard-D]

Can you replicate the symptoms with the car in neutral or is it only under load?

[SMarshall]

So when i drive it will stutter and if i carry on with the foot down it will go into limp mode i don't mean foot all the way just a bit of gas and when in neutral it doesn't stutter but if i keep it at 3500 rpm it will start flashing

[SMarshall]

Also changing yhe fuel rail and injectors have slightly gotten rid of the stutters not completely gone but not as much as before

[SMarshall]

So I have been reading a little and have been looking at my co2 or lambda sensor. I have an oxygen sensor 2 staying at the same volt while the first one is going up and down as it should could this be a cause of a misfiring cylinder 3 has a misfire code also and sometimes a random misfire code. I am not getting a bad o2 code though. Would I be wrong in thinking that o2 sensor 2 is bad causing the ECU to send wrong or not change the fuel causing it to misfire?

[GreenV8S]

If you have upstream and downstream sensors then the upstream (pre cat) sensor reading will normally fluctuate a lot more than the downstream (post cat) one. The cat acts as a buffer and smooths out the rich/lean fluctuations.

[SMarshall]

Oh okay, but shouldn't the 2nd one still move it is stuck at 0.44. is that normal then?

[GreenV8S]

SMarshall said:

Oh okay, but shouldn't the 2nd one still move it is stuck at 0.44. is that normal then?

0.44 what?

It's not normal for it to be completely static. It should be roughly half way between the min and max values you're seeing short term from the upstream sensor while the engine is running steadily at moderate load and revs. Both sensor readings would normally fluctuate a lot if you stab the throttle.