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Bad coil/s - misfire V70-XC70

posted by 16Victor on Wed Oct 15 13:38 CST 2008
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last visit: Sat Mar 5 14:18 CST 2011

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OK, did a compression check because of some symptoms (slightly rough idle, v. slow coolant use). Found #5 to be low. Buttoned it up and drove it, 1/2 later I'm getting a big miss and it's throwing codes for #5 misfire and cam position sensor issue.

I figure the #5 low compression is due to the rings getting carboned up from a failing coil. More on that later.

I'd pinched the cam position sensor wires under the cam cover (due to the harness sleeve being disintegrated). Soldered in patches for both wires and tie-wrapped them out of the way. That solves the cam position code issue.

During this time I determined #5 coil to be dead (verified via watching and swapping) and replaced it with a new one.

Drove it 40 min. tonight - running great. Accelerating from a light, it starts to misfire bad. Throws a #3 misfire...wth? Clear that code (yes I carry the frigging code scanner with me) and limp it home, missing badly.

At home, I see it's got a code for random cylinder misfire.

Also it gives me that burning plastic smell which I figure is from the now-fully-exposed wires over the cam cover.

Going out now to meter and test all the coils but was wondering...

- do coils fail all-of-a-sudden or gradually?
- did I reassemble something wrong, causing additional coils to fail?
- is there a driver circuit in the ECM that could be failing?
- any other thoughts?

Will post more after I diagnose more...tia,

Ron

PS '99 V70XC, 137K miles, Volvo brand plugs (prob new at 96K when I got the car)

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Bad coil/s - misfire V70-XC70

posted by KlausC on Mon Oct 20 07:38 CST 2008
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last visit: Fri Oct 24 10:15 CST 2014

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When you did your compression test, were the coils "firing" when you turned the engine over? Or were the coils attached to the plugs and the plugs grounded somewhere?
You might have fried the coils by pinching the wires or not having good contact with the plugs.
Use a vacuum hose to insulate the coil wires.

Klaus
--
Just driving a 1998 V70R :)

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Bad coil/s - misfire V70-XC70

posted by 16Victor on Mon Oct 20 10:41 CST 2008
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last visit: Sat Mar 5 14:18 CST 2011

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I had popped the coils off the plugs and set them aside. I did not disconnect them from the harness. Sounds like I might have indeed killed them, and now I have plausible reason as to why.

Thanks very much,

Ron

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Bad coil/s - misfire V70-XC70

posted by 16Victor on Wed Oct 15 14:46 CST 2008
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last visit: Sat Mar 5 14:18 CST 2011

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Some measurements:
Ohmmeter, across pins 3 & 4 on the coil (which get neutral and 12V, respectively):

Metering one way, I get wide open on all but #3 and the old failed #5 which are 12-15Mohm.

With leads reversed I get ~.5Mohm on 1, 2, 4, & 5, 1Mohm on #3, and 5Mohm on old #5.

#3 and #5 are similar in meaurements and both don't spark across a grounded test plug, all others do.

All 5 original coils have same date code 99w123.

Checking upstream wiring, metering back into the harness I get voltage where I expect it at #s' 3 and 4 (coil power), and consistent ohm readings both directions on the signal wire, open one way and ~26kohms the other. So I don't have a failed power transistor that I can tell.

I think *I* am breaking these coils! I don't have any confidence I had a coil issue before I took them off!! But how??

In another forums some guy said it could be an alternator but I can't make sense of that.

Thx for your help,

Ron

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Bad coil/s - misfire V70-XC70

posted by 16Victor on Sat Oct 18 07:09 CST 2008
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last visit: Sat Mar 5 14:18 CST 2011

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Oops posted the below to another thread...

99 V70, turbo AWD, Dealer says all 5 ignition coils bad. Can I fix myself?

...but since nobody's replying to this I'll post my experiences in the hope the solution (if I ever get there) may help another in the future.

Current status:
Replaced #3, now #4 throwing a misfire code. Sigh.

Thought: When I pulled the plugs for a compression check, I not only disturbed the coils but also cleaned/wirebrushed the plugs. Somehow I disturbed this engine's fragile balance.

Checked the Owners Manual, it says change plugs at 30,000 max, 15K with city driving (which we do). Existing gen-u-ine Volvo plugs had a least 40,000...combined with my cleaning them, they might have pushed the coils over the edge.

Other things:
- pull the rubber boots off and look for cracks in the coil body. Doesn't necessarily mean they're bad but it ain't a positive sign either.
- the burning smell is not the wires, it's the coil frying itself. That's one reason why I'm back-seating the wire issue. Besides, where they are, the wires will heat soak so fast that the sheathing can't really affect the wire temp.

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