XC70 Random Misfires Suddenly even after Replacing Coils/Plugs
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    1. #1
      Junior Member josephku's Avatar
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      XC70 Random Misfires Suddenly even after Replacing Coils/Plugs

      Hey everyone! It hasn't been that long since I was on here sharing my issues with my Cooling System Refresh/PCV Service. It has been a month now since I did the work, and everything has been running great up until Saturday. To give some back story, I was driving back from NY towing a trailer (approx. 2200-2300 lbs), while driving on the Interstate going about 60 MPH I suddenly lost power and the CEL started flashing.

      I pulled into the breakdown lane, the car was still running but idling very bad (rough and jumping between 600-900rpm). I checked the engine to see if there was anything obvious, but everything looked fine (no fluid loss, etc.). I started the car again and it was still running rough, but I noticed the CEL was never triggered (only flashing before). I wasn't too far from the next exit so I was able to make it off the Interstate and to a conveniently placed Autozone. During the trip off the highway, the CEL came on steady. My Ultraguage (OBDII reader) did not show any active or pending codes though, which I thought was odd. I had an OBDII scanner in the car too and I checked with that, and got nothing too.

      I tried unplugging all of the coils one by one to see if I can narrow it down, and it seemed like cylinder #1 did not change when unplugging the coil. Although after plugging all the coils back in and sitting for a bit it was definitely running better.

      I had Autozone check the codes on my car, and they came back with 5 trouble codes:
      • P0300 - Random/Multiple Cylinder Misfire Detected
      • P0301 - Cylinder 1 Misfire Detected
      • P0302 - Cylinder 2 Misfire Detected
      • P0303 - Cylinder 3 Misfire Detected
      • P0304 - Cylinder 4 Misfire Detected


      I cleared the CEL before driving again, and the only code that came back (at least on the Ultragauge) was P0301. I already had new ignition coils, spark plugs, and a fuel filter set aside that I've been meaning to put in, so I replaced all of those after getting home. But this made no difference, it is still misfiring/running rough. You can hear it at the exhaust, and sometimes it sounds worse than other times (just idling).

      Sorry for the novel, I just wanted to give as much info as I could. This one is really confusing me, but I am going to get VIDA on it tonight to see what that gives me..
      2006 XC70 (236K) - Silver/Black --- Hella 500FF Driving Lamps | IPD Skid Plate | Yokohama Geolandar A/T G015 | Too Many Antennas | Utility/Micro-RV Build
      2004 S80 T6 (126K-148K) - Black/Black - RIP

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    3. #2
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      Which spark plugs did you use? Iíve had misfires from both improper plug gap and using cheap aftermarket coils in the past.


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      2001 V70XC w/ 168k: Mystic Silver

    4. #3
      Junior Member josephku's Avatar
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      Quote Originally Posted by dalecarlian View Post
      Which spark plugs did you use? Iíve had misfires from both improper plug gap and using cheap aftermarket coils in the past.
      Yeah I heard the same thing so I used Volvo plugs, which are pre-gapped but I checked all of them, they were all at .028

      Ignition coils I put in are Bosch
      2006 XC70 (236K) - Silver/Black --- Hella 500FF Driving Lamps | IPD Skid Plate | Yokohama Geolandar A/T G015 | Too Many Antennas | Utility/Micro-RV Build
      2004 S80 T6 (126K-148K) - Black/Black - RIP

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    6. #4
      Junior Member josephku's Avatar
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      Ok so I checked with VIDA and it looks like Cylinder #1 is the only one in VIDA that registers a misfire. Strange that the Autozone OBDII reading was different, and my scanner had nothing.. anyway I tried unplugging the injector while running on cylinder #1 and after a second or two the revs dropped and it ran rougher, so it seems like that injector is doing something at least.



      Is there a way to test the injectors while still in the car?
      2006 XC70 (236K) - Silver/Black --- Hella 500FF Driving Lamps | IPD Skid Plate | Yokohama Geolandar A/T G015 | Too Many Antennas | Utility/Micro-RV Build
      2004 S80 T6 (126K-148K) - Black/Black - RIP

    7. #5
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      I don't know these engines well at all (new to Volvo), but codes like that make me think VVT hardware at the top of the ddx in other engines. How do vvt issues present in these, and have you ever serviced that?

      Besides that, move an injector between cylinders to see if the code tracks. Have you done any fuel injector service (like running PEA additive through the fuel system w/the gas) any time recently?

    8. #6
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      I had misfires in cylinders 2 and 4 for the burnt exhaust valve in cylinder 1. Do a compression test.
      05 XC70, 16 XC60 T5, 19 Tundra

    9. #7
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      Maybe unplug the MAF and see if the car returns to a steady idle? I've read this is a way to determine if you're having MAF issues...but then again if the MAF was causing problems, maybe you'd have gotten a code in VIDA? Hope you solve this bugger!

    10. #8
      Senior Member ScottishBrick's Avatar
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      Deff do a compression test
      2003 V70 T5 - Mystic/Graphite - M56LK - 211k - K24/Greens/Do88/Quaife/SMF/P2R Clutch/DW300C/H&R/Bilstein TC/316mm & 308mm Brakes - SteveO Tuned
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    11. #9
      Junior Member josephku's Avatar
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      Thanks for the suggestions everyone. The idea of a burnt exhaust valve makes me nervous but definitely want to rule that out. Iíll do a compression test when I get home.

      Before I do that Iíll try unplugging the MAF just to see if that makes any difference, only takes a second anyway.

      I donít think the VVT would be causing this though, I would imagine VIDA would have a code related to timing if that was the case, but you never know..


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      2006 XC70 (236K) - Silver/Black --- Hella 500FF Driving Lamps | IPD Skid Plate | Yokohama Geolandar A/T G015 | Too Many Antennas | Utility/Micro-RV Build
      2004 S80 T6 (126K-148K) - Black/Black - RIP

    12. #10
      Senior Member ZZZZZZZ's Avatar
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      Did you swap #1 coil AND plug with another cylinder? Might be worth a shot. Then swap coil with another and leave plugs in place. Not 100% out of the realm that the new parts have flaws if everything was running great before Saturday.
      Quote Originally Posted by josephku View Post
      Thanks for the suggestions everyone. The idea of a burnt exhaust valve makes me nervous but definitely want to rule that out. Iíll do a compression test when I get home.

      Before I do that Iíll try unplugging the MAF just to see if that makes any difference, only takes a second anyway.

      I donít think the VVT would be causing this though, I would imagine VIDA would have a code related to timing if that was the case, but you never know..


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      2007 Passion Red/Gobi VRgt; 2005 Silver/Beige Leather S60 2.5T AWD; 2002 Silver/Off black leather V70XC
      Past: 1999 Tropic Blue/Green/Oak leather V70 (NAa); Mom traded 1975 Maroon/Maroon leather 164E

    13. #11
      Junior Member josephku's Avatar
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      Quote Originally Posted by ZZZZZZZ View Post
      Did you swap #1 coil AND plug with another cylinder? Might be worth a shot. Then swap coil with another and leave plugs in place. Not 100% out of the realm that the new parts have flaws if everything was running great before Saturday.
      I actually did not try swapping them, but Iíll give that a try tonight seeing as Iíll be doing compression tests anyway.

      I forgot to mention too, that over the past month or two when the engine is under a load, there is sometimes (not that often) a single hesitation, then everything is back to normal. Never had a CEL or anything for that. And on the drive up to NY, I noticed a new slight vibration (again, under load) that was only noticeable on the highway when accelerating.


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      2006 XC70 (236K) - Silver/Black --- Hella 500FF Driving Lamps | IPD Skid Plate | Yokohama Geolandar A/T G015 | Too Many Antennas | Utility/Micro-RV Build
      2004 S80 T6 (126K-148K) - Black/Black - RIP

    14. #12
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      How much oil does your engine burn? My was consuming about 250 ml/1k miles for years and then shortly before death ramped up to 400 or more.

      Upon engine disassembly I found that the combustion chambers were covered in a thick layer of semi-hard scale-like deposits. It seems that the deposits were flaking off, chunks were caught between valves and seats from time to time. Valves were not closing properly, were overheating and the chunk of death finally caused a burn.

      Also the camshaft-tappet thermal gaps in some cylinders were near zero. And the piston rings are definitely worn out - they measure 0.75-0.85 mm gaps at the bottom of the cylinders. The bearings were good, cylinder sleeves wear is not abnormal, everything is straight.

      The reason the engine died is that I had to to replace valve stem seals and adjust the gaps at 150k. Or overhaul the engine at 200k. At 220k it died. I did some things, like new turbo, always working PCV, extra oil catch can, new oil cooler, new pan gaskets, etc, but never had anything done to the head.

      I will also switch to a European-spec oil that does not have that much ashes in it. Don't care about super-long OCI, in my cars the OCI is 5k or twice a year.
      05 XC70, 16 XC60 T5, 19 Tundra

    15. #13
      Junior Member josephku's Avatar
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      Quote Originally Posted by vtl View Post
      How much oil does your engine burn? My was consuming about 250 ml/1k miles for years and then shortly before death ramped up to 400 or more.

      Upon engine disassembly I found that the combustion chambers were covered in a thick layer of semi-hard scale-like deposits. It seems that the deposits were flaking off, chunks were caught between valves and seats from time to time. Valves were not closing properly, were overheating and the chunk of death finally caused a burn.

      Also the camshaft-tappet thermal gaps in some cylinders were near zero. And the piston rings are definitely worn out - they measure 0.75-0.85 mm gaps at the bottom of the cylinders. The bearings were good, cylinder sleeves wear is not abnormal, everything is straight.

      The reason the engine died is that I had to to replace valve stem seals and adjust the gaps at 150k. Or overhaul the engine at 200k. At 220k it died. I did some things, like new turbo, always working PCV, extra oil catch can, new oil cooler, new pan gaskets, etc, but never had anything done to the head.

      I will also switch to a European-spec oil that does not have that much ashes in it. Don't care about super-long OCI, in my cars the OCI is 5k or twice a year.
      I don't know exactly, but I would say it consumes about 1/2 qt. per 2000-3000 miles, at least after doing the PCV system. But it does vary with the driving I am doing, mountainous driving seems to burn about 2x as much oil, and when I went up Pikes Peak a couple years ago I went through almost a quart just in that day, which was pretty weird.

      That would make sense if a chunk of something prevented the valve from seating properly. We'll see, I'm going to do compression tests today, yesterday was way too rainy.

      I've been using European-spec (Castrol 0W-40) and always do my oil changes at 5k miles, but who knows about the previous owners..
      2006 XC70 (236K) - Silver/Black --- Hella 500FF Driving Lamps | IPD Skid Plate | Yokohama Geolandar A/T G015 | Too Many Antennas | Utility/Micro-RV Build
      2004 S80 T6 (126K-148K) - Black/Black - RIP

    16. #14
      Junior Member josephku's Avatar
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      Exclamation

      Ok so I did compression tests on all cylinders, looks like we have a problem.

      Cylinder 1 0 psi
      Cylinder 2 130 psi
      Cylinder 3 96 psi
      Cylinder 4 138 psi
      Cylinder 5 162 psi

      So obviously Cylinder #1 doesn't have any compression, but the rest of them are not even close to each other (except 2 and 4).
      2006 XC70 (236K) - Silver/Black --- Hella 500FF Driving Lamps | IPD Skid Plate | Yokohama Geolandar A/T G015 | Too Many Antennas | Utility/Micro-RV Build
      2004 S80 T6 (126K-148K) - Black/Black - RIP

    17. #15
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      So you have the same problem with a burnt valve. And about same mileage! My engine died at 221k miles.

      I would say, only cylinder #5 has a good compression, which is strange, because 4 and 5 are chronically overheated and underlubed in this engine.

      Welcome to the engine rebuilders club! If you need your car quick, I'd say buy a donor engine, swap it. Take your time to do a quality rebuild of your blown one.
      05 XC70, 16 XC60 T5, 19 Tundra

    18. #16
      Junior Member josephku's Avatar
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      Quote Originally Posted by vtl View Post
      So you have the same problem with a burnt valve. And about same mileage! My engine died at 221k miles.

      I would say, only cylinder #5 has a good compression, which is strange, because 4 and 5 are chronically overheated and underlubed in this engine.

      Welcome to the engine rebuilders club! If you need your car quick, I'd say buy a donor engine, swap it. Take your time to do a quality rebuild of your blown one.
      Hey it's not dead yet, still got me home But yeah it was a good run, of course this happens right after I put a lot of money/time into other parts of the car, but that's always how it goes. It is strange that there is so much variance between the working cylinders' compression too, do you think this could all be from valves that aren't seating right? I guess I don't really understand why the valves burn, and I want to make sure it doesn't happen again if I have a valve job done.

      I don't need my car to be on the road immediately, as much as I would like it. So I'm bringing it to Rolling Motors to have them do a valve job and replace any bad valves, but it looks like it's going to be a good wait. I just don't have the spare time right now to take on a project like that. I do wonder how the condition of the bottom-end is though..

      At least I have a truck to drive in the meantime.
      2006 XC70 (236K) - Silver/Black --- Hella 500FF Driving Lamps | IPD Skid Plate | Yokohama Geolandar A/T G015 | Too Many Antennas | Utility/Micro-RV Build
      2004 S80 T6 (126K-148K) - Black/Black - RIP

    19. #17
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      I would replace piston rings and deglaze cylinders at minimum. Maybe do rod bearings while you're there. Piston rings are bad at this mileage, they are soft and worn, with large gaps a few times over the specified wear limit.

      Cylinder walls wear - it was OK in two engines I took apart. Only deglazing was needed. Crankshaft bearings were good on both engines. Bottom end is more sturdy than the head in this engine.
      Last edited by vtl; 10-19-2020 at 06:57 AM.
      05 XC70, 16 XC60 T5, 19 Tundra

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