Sudden misfiring.

My 2008 XC90 3.2L FWD with 137k has been awesome. Aside from a headliner adhesive failure a while back, I’ve really only needed to do brakes and filter changes. I’ve been a driveway mechanic all my life and avoid dealerships like the plague (unless I can’t get OEM parts anywhere else).
I noticed some light pinging at lower RPMs under a load and figured I’d get some new plugs to see if that helped since the ones in there were probably the originals. I went with some quality Denso U-Groove plugs, checked the gaps and when I fired her back up, she was misfiring on two cylinders (the two furthest from the belts, don’t know the #s). I’ve double-checked everything. Bought 3 new coils, swapped them around and even threw the old plugs back in, same issue. Multimeter shows no anomalies across all the coil packs. I don’t have a code reader and don’t see why thrown codes would cause this. Already spoke to several mechanics and the local Volvo dealership to no avail. Any thoughts?

 

possible causes 1) wrong plugs for your engine. 2) mechanical damage to the wire harness going to the coils 3) plugs were not correctly torqued. My suggestion - 1) buy some Genuine Volvo plugs to ensure you have the exact correct model (no sense in trying to save $20 here) 2) inspect the connectors going to the coils. Consider doing a dark garage/mist test to see if you can see any arcing. 3) consider something other than the plugs. Did you do anything else during the tune up that may have knocked off a vaccuum line or damaged an intake air tube? 4) borrow a code reader from Autozone et al. Usually they lend them out for free or score one for under $30 at Harbor Freight. Mine has come in handy a few times.

 

the correct plugs for these care are expensive and not widely available. i've changed plugs on mine twice (the service interval is around 75k) and each time had to get them from a source that sells oem parts (they come 6 to a pack in a blue volvo package).

 

$64 at Tasca Parts for a set of 6 Genuine Volvo plugs that will carry you for the next 60K miles or so.

 

FCP Euro.com for all my parts.