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Discussion Starter · #1 ·
Hey guys, decided to change my plugs a few days ago and went with the Denso Iridium.. Didnt have any major issues or problems, cleaned everything and everything went back together without any problems. Plugs gapped at 0.028.

Drove the car the last 2 days and it has felt quite good. Also had put in a seafoam treatment in the gas and filled it up.

Well this morning jumped in the car to go to work and started it up. It started up and as it was idling it had a few 'hiccups', like it misfired and the rpms dipped briefly. Thought it was just an early, cool morning 'hiccup' so started to drive out of my neighborhood and within a 1/4 mile it got bad. Very rough idling and very little power. Turned around and had to drive back up a mountain and Hardly could get back up, literally like it was running on 1 cyclinder..

My first thought is this: When I was removing the wiring harness from the coil packs several of the tabs that hold the wiring harness connections onto the coil packs had broken off of the coil packs. I didnt think it was a big deal since when putting the connections back on after changing out the plugs the connections fit on snuggly. The wiring harness also had developed its formed shape and with the engine cover back on thought everything would be held tightly in place. But now I'm thinking this is my problem..
Is it very feasible that because those tabs broke off any vibration would be enough to loosen the connections enough to cause a poor connection between the harness connections and the coil packs? If not what else could it be?
If thats the case then I guess I will just go ahead and order new Bosch coil packs?
 

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Did you ensure you selected the R plugs and not the T5 plugs? By far the most common mistake (my picture, comparing to PO's plug selection):
 

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I also accidentally ran T5 plugs, and got pretty bad hesitation/stumbling and poor mileage. Swapped in the correct plugs and all was well.
 

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Drove the car the last 2 days and it has felt quite good. Also had put in a seafoam treatment in the gas and filled it up.

?
Since your problem did not occur immediately, I'd look to the "seafoam treatment" unleashing crud into your fuel system: change your fuel filter.
 

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Discussion Starter · #6 ·
I'm about positive it was the R plugs. I had gotten them at Advanced Auto parts and it was looked up under the S60 'R' subclassification.. I have my reciept and will call them to get the exact product number for the ones I bought so I can double check that it is correct.

The harness looked fine and didnt see anything wrong with it but will look it over when I take it apart again..

Any opinion on the coil pack tabs that broke off? Could any vibration caused the harness connections to slip off the coil packs enough to cause a poor connection and subsequent misfiring?

The seafoam shouldnt be an issue since I had also run another bottle about a month ago and just wanted to run another one through to get a full clean system. I really dont want to start throwing money into possible things when they dont need to be replaced. Hell I just replaced the fuel filter about a year ago..
 

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I'm about positive it was the R plugs. I had gotten them at Advanced Auto parts and it was looked up under the S60 'R' subclassification.. I have my reciept and will call them to get the exact product number for the ones I bought so I can double check that it is correct.

The harness looked fine and didnt see anything wrong with it but will look it over when I take it apart again..

Any opinion on the coil pack tabs that broke off? Could any vibration caused the harness connections to slip off the coil packs enough to cause a poor connection and subsequent misfiring?

The seafoam shouldnt be an issue since I had also run another bottle about a month ago and just wanted to run another one through to get a full clean system. I really dont want to start throwing money into possible things when they dont need to be replaced. Hell I just replaced the fuel filter about a year ago..
Coil tabs break and IMHO it doesn't affect anything as long as the plug is in snug. Any CEL/codes? That bad of a miss should throw something.
 

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Not OEM? Might be your issue. R's are very touchy when it comes to plugs. Pull one and check the length.
 

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Have you tightened the plugs to the specific torque? If not tightened will cause similar issue. Regarding the coils, go for the original Bosch, don't use aftermarket or used ones. (used ones may last only for couple of thousand miles due to unknown mileage) Also highly recommended the original plugs from Volvo. I've tried different ones in my old S60 and went back to the original ones after 20k miles as the other brand started misfiring. Never had any issues with the factory one.
 

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Also Bosh coils lasts around 120-140k for sure. After that it is just a matter of time, they usually fail on some stage.
 

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Discussion Starter · #11 ·
I spoke with Advanced auto and they said I should probably stick with the OEM as well, so they said if I bring back in the plugs i bought, which had been NGK not Denso, they will swap them out for the Bosch. So I'm going to go that route first and hopefully that will fix the problem.
Another thing thats odd is the NGKs had not been pregapped which I thought they should have been so I had to gap them at 0.028. I hope I didnt change a correct gap, but then again the car wouldnt have run well for 2 days after I had changed them.

If changing the plugs out for OEM bosch doesnt solve the problem then I will consider replacing the coils for bosch and maybe going ahead and replacing the fuel filter as well. I just wouldnt assume any coil would be bad since the car is only at 94k and the fuel filter was changed within 20 or so K..
 

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Another thing thats odd is the NGKs had not been pregapped which I thought they should have been so I had to gap them at 0.028. I hope I didnt change a correct gap, but then again the car wouldnt have run well for 2 days after I had changed them.
Those NGK's are not OEM plugs and likely support different vehicle applications. It's not surprise then that they don't come pre-gapped for the R. I bought my plugs directly from the dealer and they were gapped perfectly right out of the box.
 

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I spoke with Advanced auto and they said I should probably stick with the OEM as well, so they said if I bring back in the plugs i bought, which had been NGK not Denso, they will swap them out for the Bosch. So I'm going to go that route first and hopefully that will fix the problem.
Another thing thats odd is the NGKs had not been pregapped which I thought they should have been so I had to gap them at 0.028. I hope I didnt change a correct gap, but then again the car wouldnt have run well for 2 days after I had changed them.

If changing the plugs out for OEM bosch doesnt solve the problem then I will consider replacing the coils for bosch and maybe going ahead and replacing the fuel filter as well. I just wouldnt assume any coil would be bad since the car is only at 94k and the fuel filter was changed within 20 or so K..
it would help if we knew what cylinder was misfiring. Advanced will be able to tell you I believe they do free scanning. If its just on 1 or 2 cylinders then there is a good change its a coil. Many times if you move a coil the stress from being removed and reinstalled can cause them to fail. Also you might want to invest in a portable OBDII scanner, I have a Bluetooth one for my phone that works really well in a situation like this it was like $10 on amazon for the plug and the app was free, called torque.
 

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Discussion Starter · #14 ·
thanks BrotherMatt I will swap out with Advanced for the OEM bosch on Fri and hope that makes a difference!

That is quite true tystager93 didnt think about that.. I may just go ahead and replace the coil packs since my car is getting to the age and mileage for getting certain routine maintanence work done.
And problem with getting it scanned is it was NOT driveable this morning, I could barely make it back to my house, so I'm not going to be able to drive it somewhere to check codes.
I checked out torque and downloaded it, but I need to get an OBD bluetooth adapter, is that correct?
 

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I checked out torque and downloaded it, but I need to get an OBD bluetooth adapter, is that correct?
Correct. Also, Torque Pro is awesome and easily worth the $5 or whatever it is going for now. Try out the free version you've got first and then you can decide.
 
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