2001 V70 P0442, P0420 before, now misfiring?

[acsmith818]

Hello all.

I drive a V70, FWD, non-turbo with approximately 169,000 miles. The vehicle seems to perform well generally. About three weeks ago it passed the TN-Davidson County emissions test with only EVAP status as Not Ready. Catalytic converter status was Ready in OBD-II.

Shortly thereafter the Check Engine light came on. I had codes read at a parts store; the codes given were P0442 (small emission leak) and P0420 (cat. converter efficiency below threshold). I have not noticed any of the indicative symptoms of a bad cat. converter (foul-smelling exhaust, poor fuel economy, poor performance especially at high speed), so I figured it is probably a cracked J-hose or something, and resolved to get around to it when I had time.

I took the car to Import Specialty Services in Nashville, about one week ago, where they performed a courtesy inspection. They discovered no obvious mechanical faults, reported that the transmission and timing belt appeared in good order, and advised that the codes may indicate a bad cat. converter, recommending further testing when possible.

Yesterday I had some free time, and I wanted to "road-test" the car, as it were, to see if I noticed anything while driving. I went for a highway drive of about 200 miles. The car performed well during this time. Fuel economy was in the mid 20s MPG. I noticed no problems with accelerating or difficulty under load, with A/C on, or anything. All seemed well.

Last night I went to a friend's house, and afterwards went to drive home; I made it about 1.5 miles away from there when the Check Engine light (previously illuminated) started to flash. A message appeared: "Drive Slowly, Urgent Service Needed." The car lost most power, though was still operable; the engine noise switched from smooth to a rhythmic "thunking" sort of sound. I pulled over and had the car towed home. I would have had it taken to a shop but this was about 11:00 PM. (Thank goodness for Roadside Assistance...) Later attempts to start the car result in successful starting, but a continuance of the unpleasant sound.

I have read various posts on Volvo forums that indicate that the flashing CEL means cylinders are misfiring. Is this likely to be accurate? Is there likely to be a relationship between this and the codes read earlier?

Resolutions for misfire appear to include replacing spark plugs and/or coil packs. Is this the appropriate action? How can I tell if these parts are faulty? Are other actions in order here?

Finally, is it currently safe/non-damaging to drive the car (limping) to a shop for further action?

Thank you all for any assistance you can provide.

[xHeart]

How old is the battery?

[mrscullini]

do you know if the misfire is isolated to an specific cylinder? have the coil packs ever been replaced? i would start by replacing the coil packs and plugs. while you are at it, check the compression on all cylinders.

if you don't have a scanner, it is worth picking up one. the autel seems to be a pretty decent unit.