Cause of sudden failure of multiple coil packs - '04 V70 na Topic is solved

[jrschwit]

What might be the cause of multiple coil packs failing within minutes of each other? The only explanation that I can come up with is that I had just done a compression check but did not disconnect the coils from the electrical harness. So, could the few "firings" of the coils without the plugs installed have caused the failures?

Background: I needed to replace the PVC box and a couple vacuum hoses. While waiting for parts, I checked compression and cleaned the top of the cam cover thoroughly. I did not disconnect coil packs from the harness, simply set them aside out of the way. After complete assembly, the car started and ran perfectly for about five minutes. Then started to miss on one cyl. Tried a quick test drive with expected lack of power, followed quickly by flashing CE light, digital warning to "reduce speed or shift down" and transition to what appeared to be limp mode. I changed out bad coil pack from a known working P2 and all was good. Another test drive with a second coil failure within minutes and same results. Changed that coil and all was good but a third coil failed during next test drive. So I changed that coil and the two remaining and the car since drove 40 trouble-free miles. Coils were branded Volvo and are likely factory original on this 200K mile car.

Any ideas as to the cause? I'm reluctant to chalk it up to coincidence. Note that I'm relatively new to vehicles with coil packs.
Jim

[scot850]

Pull the covers off the coil packs and check the plastic bodies. You will find probable cracks on the opposite side to the wiring connector and the 2 sides closest to that. Disturbing them may have been the final straw and they started shorting.

Dis new coils fix the issue? Did you clean the surface where the coil bolts fit as these are the grounds for the coils. If oil or dirt is there or they were not torqued correctly can also be an issue. Wiring harnesses also can get brittle so check those did not crack removing them.

Neil.

[vtl]

The 8 mm bolt that keeps the coil at the valve cover is actually its high-voltage ground. Without that ground the coil burns. If you keep the ground contact in good shape those coils almost never die.

[abscate]

High voltage discharges without grounds, bad. I’m guessing that was probably the cause.

Good to know. Probably still covered under the FreeCP program so I should be ok. I couldn’t swear I’ve not made the same mistake

[jrschwit]

Thanks for the replies. Abscate said best what I suspected; high voltage discharge without ground. I'll consider it a lesson learned.

And, yes, I did check grounds, and attaching cap screw.

Jim

[dikidera]

The 8 mm bolt that keeps the coil at the valve cover is actually its high-voltage ground. Without that ground the coil burns. If you keep the ground contact in good shape those coils almost never die.

Really? I mean the engine has one massive ground connection at the valve cover to the chassis, and two other on the valve cover through the coil wiring. But the spark plug itself is grounded via its connection to the engine. When the coil fires, the high voltage jumps the gap on the spark plug and its discharged through the spark plug body and threads to the engine itself is what I am thinking. I have not looked at the coil but I thought the coil itself, the bolt holes are isolated by a good chunk of plastic.

However if this is the case, this is new information for me to try and isolate my misfires. The bolt holes are indeed dirty and because of an oil leak I am sure threads and whatnot are a bit dirty.

Btw, I once tested the coils by removing the coil from its spot and discharging it into the cam cover. I had no ill issues at the time.

EDIT:A random google search about this led me to this repair guide of the wiring harness if anyone is interested https://www.davebarton.com/pdf/5Cylinde ... sGuide.pdf

[vtl]

The 8 mm bolt that keeps the coil at the valve cover is actually its high-voltage ground. Without that ground the coil burns. If you keep the ground contact in good shape those coils almost never die.

Really? I mean the engine has one massive ground connection at the valve cover to the chassis, and two other on the valve cover through the coil wiring. But the spark plug itself is grounded via its connection to the engine. When the coil fires, the high voltage jumps the gap on the spark plug and its discharged through the spark plug body and threads to the engine itself is what I am thinking. I have not looked at the coil but I thought the coil itself, the bolt holes are isolated by a good chunk of plastic.

Yes, really. Ground connection to valve cover through "ear" is meaningful for these Bosch coils. Bad or no ground partially discharges a high voltage capacity back through the low voltage part of the coil, this is how they burn. I can't find the schematic for this coil right now.

Keep contacts clear and torqued to spec, and the coils will outlive the rest of the engine. Yours are probably Denso, those ones I don't know how critical is it to keep them grounded.

[dikidera]

My coils should be the same as his, my engine is NA and so is his. I also think the coils are the same for T5 and NA.

[packetfire]

While everyone replying is absolutely correct, I have had individual coils go bad on that engine in 2 different v70s (an 01 and and 04) at random times, prompting me to carry a spare wrapped in bubble wrap next to the spare tire, as that 5-cylinder runs very rough on only 4 cylinders. Now "you messed with it", and this is the most likely proximate cause of the failures, but those coils do wear out over time, and depending on your miles, your coils may have been well past their expected lifetime.
From what one sees online, the prudent Volvo owner replaces all of them every 200K miles, as this is when they start dying for no apparent reason on even scrupulously maintained engines.

I strongly disagree with the contention that they "almost never die", and searching these forums provides the proof that they are more commonly failing than one might suspect. The good news is that they are easy to replace, not expensive, and VIDA tells you which coil to replace, and is never wrong about it.

[scot850]

They can and do fail. The casings crack and as the crack extends they short out. Oil leaks into the spark plug area from the oil filler cap seal or a leaking pcv hose or cvvt solenoid or gasket can also cause issues.

I had a set of the IPD HD coils and one failed after a year. They were all fitted and torqued after I cleaned the ground/hold down bolt hole and lightly sanded it.

Neil.