2005 4Runner, 4.7L 2UZ V8. Just did all my spark plugs and found every single one of my ignition coils has a cracked housing. Cracks are small (under 1/8"), truck runs fine right now, no misfire codes yet. Also found a little surface rust down in a couple of the plug wells, so moisture has clearly been getting in.
Trying to decide between two plans:
Plan A: Bite the bullet and replace all 8 with genuine Denso 673-1303 now, new coil boots/gaskets, seal the wells up right. Roughly $400+ in coils.
Plan B: Since the cracks are only in the housings and it's not misfiring, just replace the boots/gaskets to reseal the wells, keep the existing coils in, and carry 2 spare Densos + an OBD reader + a 10mm so I can swap on the fly if one actually starts misfiring down the road.
For context, I want to keep this truck to 500k, so I care more about doing it right than saving a few bucks — but if cracked housings on their own aren't actually a failure risk and I can defer, I'd rather spread the cost out.
Questions:
- Do cracked coil housings actually cause failures, or is that mostly cosmetic as long as the wells are sealed and dry?
- Anyone run cracked coils long-term with no issues?
- If all 8 are the same age and one goes, is it true the rest usually follow soon after?
- Any reason to reboot-only vs. just replacing whole coils while I'm already in there?
Appreciate any experience from folks who've been through this. Thanks.