Coil test

[andy15]

From time to time I'm receiving the error P0354 or P0351 (coil malfunction). It always goes off after some time.
Last week i decided to remive the coils and check the resistance. I know that wires 1 and 3 are for primary circuit and 2 and coil end is the secondary.
I checked coils in left bank and I had between 1.8-2.5 ohm on primary, what looks ok, but on secondary there was no connection at all on all 4 coils.
The car is running fine (I guess) so I don't think all 4 coils are damaged. I may be doing something wrong. Could anyone share some experience on that?

 

[davy83]

i am not sure about the electrical testing of the windings, but in my experience the coils start to loose high voltage insulation and the spark weakens because the power is being lost into the insulation. This is really hard to test for. The test i have heard of (and tried my self) is to disconnect each of the coils one at a time, with the engine running, and the ones that are not working well make the least difference to the engine running note. The error code does identify which coil it thinks is faulty, i forget how you work out which one is which, but you can, and i think there is a thread here some where that gives you this info!
On secondary winding measurement this is a small step up transformer and its probably stepping from 5-6v to 10-15kV so you would expect the secondary winding to be 3000 times different than the primary. However its the inductance that counts so its hard to say what the winding resistance should be, but its likely to be a lot higher just because there will be thinner wire and more of it.