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d3 4.2 v8 coil packs

Old 06-02-2013, 08:34 AM
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Default Actually, they can and do cause misfires...and on our W12's

As I posted recently, if the connector or the sensor isn't firm up at the wiring block by the air boxes, the relevant 02 sensor reported a resistance too high, and indeed the car started stumbling at and off idle. Really obvious on a W12 when its normal state is you can hardly tell its running given the 12 cylinders. First time it really came home to me that rather than a sensor just going bad at the tip..and sometimes being almost inaccessible to replace..it could just be a wiring issue inadvertently caused by prior underhood maintenance.

Not sure this has anything to do w/ OP's issue on a V8, but I have satisfied myself an O2 sensor loose connector (even barely visible and still nominally plugged together) can lead directly to running issues.

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Old 06-02-2013, 08:38 AM
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Default +1

This approach is both logical and easy.
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Old 06-02-2013, 08:42 AM
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Originally Posted by carterleeds View Post
may i ask, can the injectors be removed and cleaned or be replaced full stop? just a question not a task to be carried out.
Yes to both of your questions, but injector cleaner should do the trick.
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Old 06-02-2013, 08:56 AM
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I was wondering - electronically - how does the system know when a cylinder is misfiring? How does a cylinder is considered misfiring?

Everything is controlled by the ECU - ECU senses the crankshaft - camshaft - ECU sprays the gas to the cylinder - ECU send the pulse to the coil pack to ignite the detonation - How can ECU record misfiring? How does ECU define a misfire?

Does anyone has the description of this operation? please share because I can't imagine how the block diagrams work with this misfiring stuff.

If the misfiring is defined by something else - then some sensors must be bad - If the engine runs - detonation exist - then gas and fires are there.

To me, misfire means gas sprays in cylinder #1 but fires is in cylinder #2. But ECU controls all these - it can't be.

The question is again - misfiring is based on VCDS in conjunction with the performance of the engine - stuttering? shaking ? lost power? vibration while accelerate? or just VCDS alone?

All my life driving fuel injection cars, never once I had a problem with gas filter, injectors and always used regular 87 octane gas - from Arco to Costco to whatever the cheapest gas I could find and all my cars lasted 175k miles.



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Old 06-02-2013, 09:08 AM
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Default Knock sensors

Skipping voluminous details, it's based on knock sensors. Since there are multiple of them screwed into the motor, the ECU does the calculations and can triangulate where physically (i.e. the cylinder) is acting up based on out of spec vibration (sound if it were in audible spectrum) it is reading. Given there is a trig type calculation going on by interpolating location, sometimes it's a bit inexact on cylinder from scan data when I have seen/reviewed it--reading may "bled over" to an adjoining one--but it's pretty close. Obviously in "normal" operation, those same sensors are running closed loop with the ECU (from the baseline ignition/fuel/RPM/torque type maps) and then plug coil timing outputs to advance the timing until detonation is detected and then backing it off from there, plus throwing in the O2 and MAF loops for the mixture feedback and smog overlay. FWIW, those sensors seem pretty bullet proof. Been around on Audis in volume since the 5000 turbo in mid 80's; may have been in the Ur-Quattro for starters.

If you look at something like the Bosch or Motronic guides or SSP's its documented a lot more.
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