vibration/misfire saga, part 2405!
01-10-2007, 12:11 AM
#26
For what it's worth, here's a picture of an ignition capacitor on a 5V 4.2
<center><img src="http://pictureposter.audiworld.com/11861/imgp0332.jpg"></center><p>It's the black thing with the brown wire and metal tab.
You don't officially have these on the 4V engine -- they're not in the service manual -- but if you do, they could be where you describe them (the 4V coil wiring harness appears to be below the coils). If they exist on your car and are wired to the +12V that feeds every coil, a bad one could mess with the ignition or even blow the fuse for the coils (which would be noticeable).
It would seem reasonable that if you find a part which looks like the one in the photo, and its single wire disappears into the ignition coils' wiring harness, and it looks gross and melted, and your have misfires, you might want to change the part.
I don't agree with rompbogger123 that they are there to protect the electronics. The spike that comes when the field collapses would result in a big voltage across that coil's power transistor, so each has to be protected individually. That must happen inside the power output stage. Most references to such capacitors on other cars say they help with radio interference. Can you hear the ignition between AM stations?
So anyway, if I were sure that's what your mystery black part was, I wouldn't feel too uncomfortable going for a test run with it unbolted from the head and wrapped in electrical tape to keep it out of the circuit (and tied away from the exhaust manifold if necessary).
Also, your wiring diagram shows one wire on each side coming out of the ignition coil wiring harness and grounding on the cylinder head. It's for the coils' secondary windings that feed the spark plugs. Make sure each side has a clean tight connection.
Tom
You don't officially have these on the 4V engine -- they're not in the service manual -- but if you do, they could be where you describe them (the 4V coil wiring harness appears to be below the coils). If they exist on your car and are wired to the +12V that feeds every coil, a bad one could mess with the ignition or even blow the fuse for the coils (which would be noticeable).
It would seem reasonable that if you find a part which looks like the one in the photo, and its single wire disappears into the ignition coils' wiring harness, and it looks gross and melted, and your have misfires, you might want to change the part.
I don't agree with rompbogger123 that they are there to protect the electronics. The spike that comes when the field collapses would result in a big voltage across that coil's power transistor, so each has to be protected individually. That must happen inside the power output stage. Most references to such capacitors on other cars say they help with radio interference. Can you hear the ignition between AM stations?
So anyway, if I were sure that's what your mystery black part was, I wouldn't feel too uncomfortable going for a test run with it unbolted from the head and wrapped in electrical tape to keep it out of the circuit (and tied away from the exhaust manifold if necessary).
Also, your wiring diagram shows one wire on each side coming out of the ignition coil wiring harness and grounding on the cylinder head. It's for the coils' secondary windings that feed the spark plugs. Make sure each side has a clean tight connection.
Tom
01-10-2007, 10:41 AM
#29
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When this appears: on hot engine or immediately after start ?
1. Try to change igntion coils between 8 and other cylinder.
2. Check ignition coil isolators (rubber parts) for damage
3. And check grounding of ignition coils wiring (4 brown wires in front of heads)
2. Check ignition coil isolators (rubber parts) for damage
3. And check grounding of ignition coils wiring (4 brown wires in front of heads)