Testing Coil Packs

[thefoolmccool]

Hi,

Sorry I tried search but couldn't find the answer.
Coil pack is gone in my mums car - I just cant find out which one.
The car is a 2001 polo 1.2E (6 valve).
I have all the coil packs out and a multimeter - does anyone know how to test?


Cheers
Kev

[Crasher]

You should test them by a fault code read and only remove the one shown as being at fault. The most common reason for coil pack failure is removing them and now you stand a good chance of having another one fail quite soon. There is no successful test for coil packs (apart from a fault code read) and cranking the engine over without the plugs properly earthed can destroy a coil pack instantly.

[thefoolmccool]

OK I have now fixed the misfire problem. It turned out to be a bad coil pack on cylinder no. 3.

I bought a new coil pack from my local dealer - (about 26 quid). I then replaced each coil pack with the new one until the misfire was gone. At the same time I replaced the spark plugs. The plug from cylinder no. 3 was a slightly different colour than the others (a little more brown around the cathode (white bit)). There was also a vacuum pipe that runs across the back of the engine with a small hole worn in it. I repaired this with gaffer tape and rubber pipe.

Then I plugged the car into my mates vagcom and cleared the codes - however I was able to get the engine man light out by taking the battery off for a half hour.

Hope this helps anyone in the future.

[thefoolmccool]

But now I have a new problem, the car idles very rough. It idles at 770 - 800 RPM (as read on the computer) but it feels really rough. It feels like a four cylinder car firing on only three.

At any other times the car is perfect - I couldn't get it to miss when under load in any gear or any rev range. It only seems to be when the car is idling. I can make it worse by turning on the lights or the fan. The engine shakes quite vigorously.

Has anyone any ideas what may be wrong. My next approach will be to replace the other two coils. I might also try a compression test.

[Crasher]

If a VAG-COM read shows the same cylinder as before, then you may have a valve burning problem. I suspect you have another faulty coil pack though as the usual cause of failure is removing them so your swapping them about has probably finished them off. A very common problem on the 3 cylinder engine is the valve timing jumping due to a design fault in the chain tensioner but this isn't as common on the 6 valve as it is on the 12 valve. You will need VW locking tools to check the cam timing. This often happens after an oil change.

[DFMM]

But now I have a new problem, the car idles very rough. It idles at 770 - 800 RPM (as read on the computer) but it feels really rough. It feels like a four cylinder car firing on only three.

At any other times the car is perfect - I couldn't get it to miss when under load in any gear or any rev range. It only seems to be when the car is idling. I can make it worse by turning on the lights or the fan. The engine shakes quite vigorously.

Has anyone any ideas what may be wrong. My next approach will be to replace the other two coils. I might also try a compression test.

Looks like voltage-drop is a clue. Check your earth-strap from the body-to-engine/gearbox. I have had to wire-brush the ends of this braided strap, then refit it with vaseline to stop future atmospheric salt corrosion ( white furry stuff ).
This can also cure reluctant starter motors/solenoids.