Changing only 4 out of 6 spark plugs

[cj635608]

(skip to the 2nd paragraph for the summary) I just bought a 2007 m35 with 96k miles on it. The car runs great and so far has no issues. I decided to buy the NGK laser platinum spark plugs for it because I figured at 96k they would probably need replacing. My first mistake was not checking before I bought new plugs because once I got the first plug out I noticed it already had NGK laser platinum plugs in it. The plugs that were already in the car looked a little burnt but not horrible, so I went ahead and replaced the 3 "front" plugs on the drivers side. As I was tightening the coil packs down the bolt for the pack furthest back fell into my engine compartment and never landed under my car. I couldn't find it anywhere so I decided to move on for now and go to the other 3 plugs. As anyone who's done this before knows the plugs on the passenger side are a lot harder to access. I finally got the coil pack off the first one and as I went to tighten it back down the bolt holding it on sheared right off flush with the hole so there is no thread sticking out. Discouraged I decided to call it a day and try to locate the bolt that fell earlier. I reassembled and tightened everything else, turned the car on and drove it down the driveway a few times hoping the bolt would fall down from my engine compartment. No such luck.

So now I have 4 out of 6 spark plugs changed and two coil packs that aren't tightened down. Neither of the coil packs seem like they are going anywhere and the one on the passenger side has a wire harness over it that is holding it down anyways. I justified not changing all of the spark plugs because they were the exact same ones just a little darker and not as shiny as my new ones.

Am I screwed? I know I can probably drill the sheared bolt out and buy a new bolt for the other one but is it safe to drive? and did I screw up by changing only 4 of the 6 plugs? The last two were too difficult for me to get to and given my other two coil packs I didn't want to further mess up.

Any advice would be greatly appreciated.

[Ilya]

Hmm...

A bump might jostle the coilpack loose, so I definitely recommend finding a way to tighten them. As for changing only some of the plugs, no, that's fine...albeit I'd never do that. THAT won't hurt it, but not tightening down may lead to lose packs and misfires later.

At this point, I'd probably eat the cost and take it to a shop to have it finished up. I hate tapping bolts out and would never trust myself doing it on an engine related part.

[cj635608]

Thanks for the advice, I made an appointment to get it fixed at a shop. I guess if I can't successfully change spark plugs I'm probably not the right person to extract that bolt.

[Markc]

Sorry about your luck. IMO you have done the right thing by taking it to a shop.
The 2 plugs that you didn't change are likely fine for many thousands of miles, but will not perform the same as the replaced plugs @ some point. This could lead to several issues.
The "floating" coil packs are just waiting to cause trouble.