Big misfire when accelerating

artistjohn · Post by **artistjohn** » 31 Aug 2017, 14:10

My 2007 XC70 runs fine most of the time. Has 145k on it - always maintained. When cold, will accelerate to highway speed, no misses, but after cruising smoothly for awhile at 70 mph, any increase of speed, no matter how gentle, causes engine to miss and car to buck hard. Gas mileage is stable, and driving around town does not miss, but I don't step on it as a rule. Have had some rodent issues around engine. Is this a bad coil issue or some chewed wires? No trouble lights in info center. Where to look? Appreciate any tips.
Artistjohn

Post by **chrism** » 31 Aug 2017, 16:06

My wife's 2005 S80 2.5T is starting to do the exact same thing - slowly getting worse. I think I'm going to pop a new set of plugs in it as the ones in there now have about 90,000 miles on them. Keep us posted as to what steps you take in solving the issue.

Georgeandkira · Post by **Georgeandkira** » 31 Aug 2017, 16:46

Do the easy stuff first: (Inspect intake air hoses for splits, plugs, MAF cleaner spray, ETM cleaning (if necessary), fuel filter). Add a 20 oz. bottle of Techron concentrate before a stint of local driving.
After that, jump on it and try to get it to throw a code.

artistjohn · Post by **artistjohn** » 31 Aug 2017, 18:48

chrism wrote: ↑31 Aug 2017, 16:06 My wife's 2005 S80 2.5T is starting to do the exact same thing - slowly getting worse. I think I'm going to pop a new set of plugs in it as the ones in there now have about 90,000 miles on them. Keep us posted as to what steps you take in solving the issue.

Will do, thx!

artistjohn · Post by **artistjohn** » 31 Aug 2017, 18:52

Georgeandkira wrote: ↑31 Aug 2017, 16:46 Do the easy stuff first: (Inspect intake air hoses for splits, plugs, MAF cleaner spray, ETM cleaning (if necessary), fuel filter). Add a 20 oz. bottle of Techron concentrate before a stint of local driving.
After that, jump on it and try to get it to throw a code.

Thanks! Hoping it is a simple maf issue or air sensor. Could be a coil insulator crack and the misfire throws off the firing order and the injectors... so many possibles.

adriggs1 · Post by **adriggs1** » 01 Sep 2017, 08:18

Had a similar problem in my 2001 s60. The fuel filter I'm assuming ends up becoming clogged and the engine misfires under acceleration due to a lack of flow from the gas pump. It happens almost every time I need a new fuel filter. I would only get a misfire under hard acceleration or as in your case cruising and pushing on the gas. Still could be a myriad of things but this was the case for mine, hope it helps!

artistjohn · Post by **artistjohn** » 03 Sep 2017, 18:40

Many thanks for the tip. I will add that to the long checklist!

Post by **abscate** » 04 Sep 2017, 02:14

90000 on plugs? Despite the marketing , there are probably 60000 miles overdue.

Start there

These cars like OEM , three conductor Copper plugs for non turbos, and one conductor copper plugs for turbos , gapped st 0.7mm or 0.028 inches

You will have to gap new single conductor plugs

Post by **oragex** » 04 Sep 2017, 07:53

Original poster, are you saying the car misses only at 70mph/highway speed, while it never does so at lower/town speeds?

Post by **chrism** » 04 Sep 2017, 09:15

abscate wrote: ↑04 Sep 2017, 02:14 90000 on plugs? Despite the marketing , there are probably 60000 miles overdue.

And to think they were only about $1.50 each back when I bought them. (They're about $2.00 now - dang inflation!) NGK copper core single electrode. It will be interesting to see what they look like when I extract them.

Actually I'm running the same single electrode NGKs in my 2.4 NA car and it runs fine. Not sure if they'll pan out well in the long run in that car yet as I've only got about 55-60,000 miles on that set so far.