Time for new coils on V70? Cracks, corrosion.

Post by **FireFox31** » 21 Jul 2022, 16:01

My 2000 V70 with 226k miles started idling rough accompanied by P0301 Cylinder 1 Misfire Detected. First thing I checked is the 22 year old original coils. Consensus on MVS is that they last a long time and we can swap in a used one when one fails. In a P2 forum post, precopster says "When the exterior casing cracks they misfire." Do you think 20+ years is too long to run these coils, even as spares? Is it finally time to replace them with new ones when they fail?

My misfiring cylinder 1 coil has a crack beneath the rubber boot. The other four coils have the same crack. The cylinder 1 coil also has corrosion on the metal visible on the underside of the coil. No other coils have that corrosion. All coils have corrosion on the metal on the top side of the coil.

Are there any benefits to running new Bosch coils aside from worry free maintenance? For example, might they improve gas mileage or throttle response? I suspect you'll say "New coils are overkill because they'll severely outlast out cars", but maybe that's better than stopping to replace a used coil each year or suffering bad gas mileage from a misfire and not realizing it.

Buying used coils from an untrusted source (eBay, junkyard) seems like a potential waste of time and money if they don't work or fail quickly. Is there a way to test a coil before installing it? $50 for a Bosch coil from FCP seems like a time and hassle savings.

Thanks for helping me, and perhaps all of us, make this preventative maintenance decision.

Side note, what's the torque spec for this top engine bolt? I removed it by mistake thinking it was a coil bolt. And what's the torque spec for coil bolts? All the Haynes has is "Engine top section to lower section - 17 Nm", and it suggests those are the outer edge where the grounding straps connect.

: Engine bolt torque spec?; PXL_20220721_202915690.jpg (430.36 KiB) Viewed 593 times

Post by **abscate** » 21 Jul 2022, 19:03

On the head cover bolt , just put it back in at 10 Ftlb. That’s a firm wrist twist on a 6 inch ratchet. The sealant keeps the cover on , not the bolts.

If you are in run to fail mode, replace with a used coil. I have loads.

You can’t ohm test Them to confirm good, you can only confirm bad.

I usually test them on one of the cars before putting them in the car kit with a spark plug as spares.

Two 99s are run in PM, two in run to fail presently.

Post by **scot850** » 21 Jul 2022, 19:24

Did you try the old swap-aroo test to see if the issue transferred to another cylinder?

Once they crack they can run for a good long time but it is not a guarantee. I replaced my old 00 V70 base with new 'Volvo' OE (supposedly) from one of the online Volvo parts sellers. One was DOA. They did swap that and another that was damaged in the shipping. I sold that car to a buddy and about 2 years later #3 failed. He replaced that with a NAPA new coil and it failed again about 40,000km later. On removing it, it had rust on the coiled contact at the bottom and some sticky stuff on the underside from a crack. Swapped it again with a used Volvo stamped part with no cracked and all good again.

I did look to see if I could find a high temp., non-conductive epoxy that I could glue the cracks with to prevent them potentially worsening or shorting. No luck so far!

I would do what our friend abscate suggests and have a couple of tested used spares and keep them in the car. A set of new ones are pricey and if buying Bosch make sure it is from a reliable source and not a copy part!

Neil.

Post by **FireFox31** » 21 Jul 2022, 21:47

scot850 wrote: ↑21 Jul 2022, 19:24 Once they crack they can run for a good long time but it is not a guarantee.

Thanks for the input. I see you received similar input in your 2017 thread about coil cracks (thanks "Similar Topics" feature!).

I swapped coils 1 and 2. The car still has a slightly rough idle. I drove 15 miles without a CEL, then drove hard and got the CEL. Interestingly, the error code was for cylinder 1 misfire. Swapping the coil didn't move the error. I'll tackle this issue in another thread to keep this one about coil age and wear.

Perhaps cracked coils are still as acceptable in 2022 as they were in 2017. Does anyone else have input for or against this? Thanks.

Post by **volvolugnut** » 22 Jul 2022, 07:54

Years ago I read about a guy who rebuilt coils for Ford Flathead engines. These coils were of a unique shape and mounted on the front of the engine on top of the distributor. Purists needed good coils but want original looks. The guy would take old original coils and heat them for days to dry out any water accumulation. I believe he resealed them somehow after drying.
After this treatment they were often good for years.
How does this relate to modern Volvo coils? I think any cracks will allow moisture to enter the coil over time and start to degrade and short the insulation. In time the coils will fail. Efforts to seal the cracks should help.
volvolugnut

Post by **erikv11** » 22 Jul 2022, 08:26

In June earlier this summer I replaced all five coils on the 07 XC70. They were factory units at 186k and 15 years. The car was running fine, no misfires, and from the top the coils looked fine (I didn't inspect them more thoroughly). I did the replacement basically on a whim, as preventive maintenance for a big drive coming up in a few weeks. The only thing I changed was five new Bosch coils and the OCI was up; I put in the same Rotella T6 as always.

Average mpg for my wife's commute instantly jumped from 19 to 23, I was really surprised. It has held there about 6 weeks now. That's a 20% improvement.

Post by **FireFox31** » 22 Jul 2022, 12:22

erikv11 wrote: ↑22 Jul 2022, 08:26 Average mpg for my wife's commute instantly jumped from 19 to 23, I was really surprised. It has held there about 6 weeks now. That's a 20% improvement.

Thanks, this is the feedback I'm really interested in. Can we determine if we all suffering bad fuel economy with no other symptoms due to cracked, corroding, weakened coils?

Some FCP reviews for P2 and P3 coils have mentioned immediate improved fuel economy, throttle response, smoothness of idle, etc. I wonder if those people had slight misfires which they didn't notice, wasting fuel which wasn't burnt. I wonder if P2 and and P3 are more susceptible to bad coils. I drove my sister's P3 with a failing coil and the car would severely lose power for an instant under load. Are P80 coils and engines so much different from P2 and P3?

Maybe I'll buy the coils during the current FCP summer sale, get the car to a stable condition and check its mpg, then swap in the new coils to see how things change. Expensive test, but would be interesting.

Post by **rguzz** » 22 Jul 2022, 13:21

I agree, the way I understand it coils can fail with subtle symptoms over time and new ones will provide stronger spark and all the advantages therein. Of course I would replace only with oem units as you almost certainly will. It will run better almost for sure.