Polo 1.2 12v misfire at 4500rpm

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griffdm
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Drives: 2006 Polo 1.2 12v (BME)
Location: Wales

Polo 1.2 12v misfire at 4500rpm

Post by griffdm »

Hi,

I have a polo 1.2 12v with a misfire on Cylinder 3 code P0303. We have removed the head to replace 2 valves on Cylinder 2 that were damaged when the timing chain slipped. compression is fine across all 3 cylinders.

Misfire comes in between 4000 - 5000 rpm triggering the engine light and P0303 code. once cleared it runs fine below 4000 rpm

I have changed the plugs, coil pack, swapped injectors still i get the fault.

The engine is a bme

Anyone got any ideas?

Thanks
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alexperkins
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Re: Polo 1.2 12v misfire at 4500rpm

Post by alexperkins »

Check the coil pack and injector wiring on the culprit cylinder
OwiLlewelynEllis
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Re: Polo 1.2 12v misfire at 4500rpm

Post by OwiLlewelynEllis »

Check the CO2 censor on the exhaust, I had a similar problem and that's what caused it :)
griffdm
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Drives: 2006 Polo 1.2 12v (BME)
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Re: Polo 1.2 12v misfire at 4500rpm

Post by griffdm »

Morning, Been busy so not had chance to post update,

It turned out to be worn exhaust valve guides, I had all 6 replaced. Common fault on these engines.

Replaced the timing chain and bits as they stretch over time.

All running lovely now.
Polo from Hell
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Re: Polo 1.2 12v misfire at 4500rpm

Post by Polo from Hell »

I've a theory (based on the £1K I've thrown at trying to find the problem with a similar misfire - see my "THE common problem" post) but perhaps the fact that griffdmn's Polo was misfiring at 4500 rpm is typical of misfire caused by the "common valve guide" issue. That is to say, perhaps misfire that is due to the worn valve guides only occur at higher revs?

The misfire on my Polo, happens from start-up and continues throughout the rev range, even when at idle. I wonder if the misfire in OwilLlewelynEllis's Polo was similar to mine, or similar to griffdm's?

Since his misfire was solved by replacing the O2 sensor, my theory is OwilLlewelynEllis's misfire was like mine, throughout the rev range. Using a VAG-COM scanner, I've discovered that the O2 sensor isn't working on my car. Although the issue might be a faulty sensor, the problem could equally be with the wiring or in the ECU (although the ECU is less likely). I'm about to replace the O2 sensor, to eliminate it.

If the new O2 sensor still reads as failed, then either the ECU is not receiving the signal (faulty wiring) or the ECU isn't able to process the signal (ECU fault).

I'll let you know how I get on.
Polo 9n3 crazy
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Re: Polo 1.2 12v misfire at 4500rpm

Post by Polo 9n3 crazy »

Had same issue with my Polo.
I tried everyting, spark plug, wiring loom, all valves, coil, compression test, etc.
Spent around £250 in parts and labour. Car still had the same issues.. I tried swapping the injectors from cylinder 1 to 2.
The misfiring moved from 1 to 2. Injector that I moved to 2 was blocked.
Bought a set of injector rail for £20 on ebay and wiped them and installed.
Car back to normal.
Sorted..
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