My son has a 1999 S70 with 94,000 miles on it. It has started to run really rough, like one of the spark plugs isn't firing. I replaced plugs and connectors about 38,000 miles ago. Was wondering how often they need to be replaced on this car. Also was wondering if the coils on top of the spark plugs go bad and would that give me the symptom noted above. I read a similar post on hear about where someone had a leaky head gasket. This does not appear to be the case here though. Thanks for any help!

 

Note also the check engine light is on and the code reader thru a couple of codes one is a cylinder misfire code P0303

 

I have a 99 S70GLT, plug change interval is 30K miles. I use genuine Volvo
plugs, the extra cost is very little over that many miles.

Not sure what you mean by changing the connectors?

You have a misfire code for cylinder 3. You could swap the coil from cyl 3 to
another cylinder when you change the plugs and see if the code goes away,
stays on 3 or moves to the other cylinder.

Code goes away indicates bad plug.
Code moves indicates bad coil.
Code stays on cyl 3 indicates some other problem with cyl 3 (injector, compression).

 

Your coil packs are to the age where they start to fail. Easiest way is to do what was suggested, move the coil pack, testing to see if the misfire moves. In my experience, it is a waste of time.

There are ususally two issues. Either the coil pack is dead or the wiring to the coil packs is compromised (broken). I've seen both at my dealership. A broken wire will lead to a bad coil pack.

I buy Bosch coils packs for about $40 each and ususally have a dozen or so in stock. Sometimes I replace them all.

As far as spark plugs, I use the standard Denso plug which works quite well.

 

I will test this out this weekend. I should have just ordered some coil packs but will have to get them locally.

 

The coil in cylinder #3 did indeed need to be replaced. In checking the plugs (while replacing them), the plug in cylinder #3 was the only one that wasn't coked up suggesting that it wasn't firing. New plugs and a new coil for cylinder #3 and the car now idles smoothly again.

 

I have a 2003 S60 and yesterday my car started shaking as if it was going to either blow up or shut down. After review it appears it may be the spark plugs, so they were replaced (but not the problem) so turns out there are 2 coil packs that were bad. Is it unusual to have 2 out at the same time and/or that 1 was out but didn't notice it? Went to Pep Boys picked up 2 new ones, installed them and while installing them a 3rd one went out. Has anyone had this same problem wherein it was simultaneously?

 

The coils sometimes do fail in rapid succession. They're all the same design, same age, and running in a similar environment. It sucks when you have to change 5 or 6 at the same time, but it DOES happen. If you'd been able to predict it, I'd have gone with the IPD replacements. They cost about the same, but are made to be a bit more durable. However, most "aftermarket" coils are actually genuine Volvo coils in a different box, so there's usually no problem with those, either.

 

I replace them all the time and generally keep 4 or 5 in stock.