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Changed spark plugs, now getting new misfires

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catchmeifucan652
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Changed spark plugs, now getting new misfires

Post by catchmeifucan652 » Fri Feb 22, 2019 5:45 am

My 2009 S60 was running just fine until I decided to replace the plugs, with NGK 6962 plugs. I am now getting misfires on cylinders 1 and 2, with misfire codes on them, as well as "random multiple misfires." It runs rough at idle and you can feel the misses if I rev to 2k. Here's what I've tried:

- Disconnecting the coils from 1 and 2 make no difference to the engine roughness. Disconnecting 3, 4, and 5 almost makes it quit.
- Swapping coils 1 and 5 makes no difference, the miss stays in #1 and cylinder 5 runs just fine. Presumably the same for coil #2.
- I pulled the coils out while running and verified that there is a spark on both coils 1 and 2
- I put the old plugs back in cylinders 1 and 2 and get the same result
- I checked the wiring harness for pinching or chaffing and didn't find anything.
- I cleared the codes on the ECU and restarted. It seems to run normally for 15-20 sec until the idle comes down it starts missing and the codes and CEL come back. I cannot tell if there is a soft miss at first before the computer starts cutting fuel to 1 and 2, or if it's 100% normal at first.

How did I mess this up so badly? I only was doing this for routine maintenance with no other issues observed. What do I do next?



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Re: Changed spark plugs, now getting new misfires

Post by 93SCMax » Fri Feb 22, 2019 5:57 am

Welcome to the forum,
I'd start by swapping coils from #2 to #5 to confirm that coil #2 is good. If it is, it appears you have eliminated the coils as the problem.

If coils are good, I'd suspect wiring to #1 and #2, or grounding at #1 and #2. When you install the coils in #1 and #2, make sure the bolt is tight and clean (no rust). Also clean the head mating surface, this is where you make your ground.

Try this and see what happens. Good luck.



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Re: Changed spark plugs, now getting new misfires

Post by abscate » Fri Feb 22, 2019 9:21 am

The coils need to be grounded with the M6 screw to work reliably - don't pull them off while running.

How old are the coils? It is possible they have pooped out while handling them. If you removed the harness to them, it is also easy to mix up the plugs - they have to be right.

100k is the accepted lifetime on the PM (no failure in street) model for coils


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Re: Changed spark plugs, now getting new misfires

Post by catchmeifucan652 » Fri Feb 22, 2019 9:48 am

Thanks for the replies. I'm hoping that grounding is my issue, I'll try to correct it later today.

Yes, I had wondered if I wrecked the coils pulling them out, in fact the coil boot dislodged on at least one of them. However the fact that coil 1 works in a different cylinder has me scratching my head. The coils are original, 175k miles, so if I have to replace then it won't be a huge loss.

Found this thread where someone solved their misfires by correcting coil grounding. https://www.matthewsvolvosite.com/forum ... hp?t=80363



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Re: Changed spark plugs, now getting new misfires

Post by abscate » Fri Feb 22, 2019 10:13 am

If you have the coin, put 5 new ones in, sell 4 of the five as tested working spares, keep one as a spare.


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Re: Changed spark plugs, now getting new misfires

Post by catchmeifucan652 » Fri Feb 22, 2019 7:50 pm

No luck with ensuring good ground from the coil grounding bolts. Behavior is exactly the same. Also, I checked coil #2 and it's definitely working if I swap it to a good cylinder. Seems likely that I have a grounding issue with my wiring, or something with the ECU. I'm pretty close to calling triple A to get it to a shop.

Since the "bad" coils work in other cylinders, they are okay, right? I'm willing to order new ones, but I don't want to wait 4 days and find out that it wasn't the problem.



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Re: Changed spark plugs, now getting new misfires

Post by chrism » Fri Feb 22, 2019 10:20 pm

NGK 6962 have those “V” Power electrodes. I’m not so sure they really work well in Volvo’s. I would have used BKR6ES (NGK 6364).



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Re: Changed spark plugs, now getting new misfires

Post by precopster » Fri Feb 22, 2019 10:39 pm

I've used 6962s religiously on the turbos with no issues. Mine have almost 38K kilos on them on the 2001 T5 and about 20K on our XC90 2.5T and need a re-gapping on the T5 but aren't worn yet and burn cleanly.


Current cars:2002 XC70, 2006 Ssangyong Rodius (Stavic), 2006 XC90 2.5T, VW Transporter 2.5TDI

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Re: Changed spark plugs, now getting new misfires

Post by abscate » Fri Feb 22, 2019 11:25 pm

Check for the 12 V feed to the coil. That’s the last gasp. They all get the same 12v feed and the ECU grounds each coil /plug To fire them individually.

Take a good look at the coil connector and make sure all the pins are clean and bright and are in the right place in Theva socket.

That’s about all that’s left. Last resort. Unseat and reseat theECM, you need the removal tool for that.


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Re: Changed spark plugs, now getting new misfires

Post by precopster » Sat Feb 23, 2019 3:27 am

Last week a 2004 XC70 rolled in with a blown fuse and shorted coil pack wiring. I can't recall the fuse number but it was one of the tiny ones under the hood and it was 20A. That loom was so fused on cylinder 2 that the coil pack had overheated and melted.

Most of the split tubing was in reasonable condition but beneath that most of the wiring was splitting badly, especially where the wires were curving to reach the coil packs. On cylinder 4 there was about to be the same disaster if I hadn't caught it and wrapped the wiring.

The mechanics who sent it my way said that the wire with the pulse was arcing to the positive due to no insulation. I feared the ECM would be fried.

The fused wires were the positive and negative leads.

I was really surprised as the wiring on my 2000 build P2 V70 T5 is quite good though I have wrapped it twice with new split tubing since purchase.
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