Can anyone tell me how to identify coil problems? My car seems to be running a little rich and is not too happy at idle (a light burble from the engine, like a small misfire). Does anyone know what resistance they should measure?
You can run a very simple test, four times over.
Get a normal/old ingnition HT lead
If you have access to a hall effect time light then life becomes very easy, if not you will also need a short fine piece of bare copper wire and another price of insulated wire with a crocodile clip at each end.
The object of the exercise is to sequentially put the HT lead in as an extension lead between the coil pack the the top of the spark plug.
If using the hall effect probe the the timing light should flash. This will indicate that HT pulses are being sent down the wire to the spark plug. This does NOT mean that the spark plug is ok.
Alternatively, when you put the HT lead extension in, then at the coil end leave a shore pigtail of the fine copper wire emerging so it is visible and accessible.
Now connect the wire with the crocodile clip to a good earthing point. Run the engine at idle and then use the other bare end of the wire to get very near just about contacting the pigtail, thus allowing the spark to jump to ground. If you can see and hear the spark then the coil is firing well. If the engine revs drop a little then this indicated that the spark plug is working.
Pull the grounding wire away and the revs should pick up.
NOTE!!! DO NOT leave the HT short/jump in place for more than a couple of spark cycles and DO NOT repeat test for a good 20 seconds. When you short/bypass the spark to ground thne the injected fuel to that cylinger will not be burnt and will be blown down the exhause to the CAT. This will cause excessive burn/heat to be generated and potentially damage the CAT if left in place too long. For this reason I would also only recommend doing this when the engine and CAT are cold, completing the quick cylinder buy cyling test with minimum engine running time.
If on the cylinder/coil/plug you are testing the revs do not drop (assuming it sparks at the 'jump' end, then you have either a faulty plug or no/poor compression.
