How does the ignition system work?

[LittleRedRocket03]

My car won't start and I'm trying to diagnose what is wrong with it. I am having problems troubleshooting it because I honestly don't know how the ignition system is controlled. I understand that it is a waste spark system but I am not sure about the controlling of the electrical flow. I assume that the red wire going into the coil is the power wire. Are both sides of the coil pack saturated at once since there is only one power wire? If both are saturated at once then how does it only fire one side of the coil at a time? I reset the DTCs on my car and the same two codes come up. P2301 and P2304 for high resistance on both sides of the coil.

[stead34]

Permanent supply, controlled ground to the primary windings, two sets of windings cylinders 1 and 4 is one winding, cylinders 2 and 3 the other windings, primary and secondary windings for each pair. What resistances do you have through the windings of the coilpack.

[LittleRedRocket03]

I have 1.3 ohms through the primaries and 13 kohms through the secondaries. It's an MSD coil

[LittleRedRocket03]

How is the grounding controlled? Are the black wires running to the coil from the MME a ground for each primary side?

[stead34]

1.3 ohm does seem abit high on the primarys, new from lohen.co.uk they say it should be 0.052 ohm(they must mean 0.52) for the msd they sell. The ground is controlled by the MME, you need a oscillosope to see this signal as its so quick, it only energises the coil for a split second before it collapses the electro magnetic field it generated in the primary windings.

[LittleRedRocket03]

So it grounds out the whole coil through the one black and yellow signal wire?

[stead34]

Dont know the colours but it does them in pairs, so three pins minimum, feed then 2 trigger signals(ground).

[LittleRedRocket03]

Okay well one reads 0V running through it while the engine is cranking and the other one reads -2.7V like it's picking up no continuity, but this was done with a NAPA multimeter and not an oscilloscope. I put the leads in between the coil and the MME for each test

[stead34]

You put the red lead on the positive terminal of the battery and the black lead clamped on the signal cable to the coil pack using a bed of nails or something similar. Multimeters are way to slow, if you google ignition oscilloscope patterns you will see what information this device would give you. A high resistance in the primary windings will give you a weak spark or no spark, the pattern on the oscilloscope would show a low kv. Immobilise the engine(fuel pump fuse) remove the spark plug, ground it to engine block, turn the engine over and see if the plug sparks, if weak then you know you have a problem with the coil pack, renew plugs and coilpack...Make sure battery is charged and you have good engine earth

[LittleRedRocket03]

I did that and I have no spark on all cylinders. It's a brand new coil the last, one was definitely fried because one secondary side of the coil was open and to plug wires had very high resistance. Is it possible that the MME is fried and isn't interrupting ground causing no secondary voltage?

[stead34]

Yes its good possibility, you may aswell pay to have that diagnosed as it will need to be programmed if one is required, you dont want to change something so expensive without it being diagnosed properly, I would be abit careful as, is the new coilpack not compatible with the MME, the ecu may not be grounding the coilpack as a fail safe not to cause damage because of a higher resistance in the primary windings(because its got a fault code it may not function). in this case just a new coilpack required. Was it the old coilpack that fried the MME, If this is the case then just a new MME needed, or did the new coilpack fry the MME, in this case both would need to be changed, as it has a fault on both primary circuits something has caused the damage which is most likely the coilpack, being non genuine there will always be a doubt, look in the manufacterers technical data to see what the primary windings should be for your coilpack you have, if its higher than standard then this may be it, as obviously the MME is checking this resistance or it wouldn't bring up a fault code. also as a caution you have got to be carefull how you test circuits controlled by ecu's as this can fry them also, you cant send voltage into these units or they can just die on you, so a resistance test is out of the question unless its disconnected, and probing with a test light is a no no also as this has a potential of 12v untill grounded if you have connected it to positive looking for an earth...