Misfire code after heavy acceleration but only twice this year

LOB · Post by **LOB** » 04 Dec 2017, 02:28

I've got code P0305 (fifth cylinder misfire) once and P0300 (multiple misfires) once on two separate occasions this year. The check engine came on, on both occasions, when I was cruising at 55 mph for hours and then made a kickdown acceleration. The engine hesitates and doesn't gear down as anticipated. This has only happened during these circumstances and everything in the ignition is newish except the single coil (850 GLT -97 , LPT). I've never heard a single misfire on this 90000 mile well maintained engin and it drives like new except on these two occasions. Does anyone now why I get the misfire code? Real problems on the horizon?

Post by **wizechatmgr** » 04 Dec 2017, 04:38

By chance, do these happen right after or during precipitation?

LOB · Post by **LOB** » 04 Dec 2017, 08:21

wizechatmgr wrote: ↑04 Dec 2017, 04:38 By chance, do these happen right after or during precipitation?

No, it happened yesterday in dry cold weather. It took five months since I cleared the code to reoccur.

Post by **scot850** » 04 Dec 2017, 10:23

Could be a bad plug wire or spark plug has a hairline crack. When were the sparkplug wires last replaced? I have seen the #5 wire get trapped under the plastic cover and it can then short out. However, I would expect that to be more frequent than that.

When was the fuel pump and relay last replaced as well as the fuel filter? Have you checked the fuel pressure?

Neil.

Post by **shaker_chi** » 04 Dec 2017, 10:26

I had the same issue with my 98 T5. Turned out I had a bad spark plug wire. Take a look at yours, I believe there is a date code on each. Mine were original to the car, so I replaced them with the 8mm IPD version and replaced the plugs with O/E
Volvo plugs. I haven't had the problem since.

Post by **rspi** » 04 Dec 2017, 10:47

You could also have a minor intake manifold gasket leak. Spray around there with starter fluid and see if the idle changes.

LOB · Post by **LOB** » 04 Dec 2017, 12:14

Thanks! The wires are 18 months or so (OEM, "Bougicord") the spark plugs are about the same age, Volvo original (albeit from a Chinese vendor at AliExpress, I don't(didn't) think the market is big enough for counterfeit Volvo sparkplugs to be worthwhile/profitable. The packaging looked 100% original and I know by experience that the Chinese hardly ever can counterfeit logos and packaging 100% authentically.(?)). I'll check the manifold gasket with starter fluid and if the wires are bent somehow.

LOB · Post by **LOB** » 04 Dec 2017, 12:17

Double post...

jalwlb · Post by **jalwlb** » 13 Dec 2017, 06:56

With the engine idling after dark and blocking as much light as possible, check the coil for mild arcing. If you see blue electricity, a new coil should solve your problem.