[mchez]

Hi all

I've got something that's throwing me for a loop so I figured I would see what you guys think.

I decided to change my plugs in my 2011 E90 335i since I have no idea when they were changed last (bought the car a few months ago). So I drove from my house to my dad's house so he could help out and because he had the plugs. We got the old plugs out with little difficulty and immediately noticed that the plugs that were in the car were for the N54. This is easily noticeable because of the different tips of the plugs (N54 plugs have a tri-tip end and the N55 plugs have a single tip end). This brought out some concerns as to how properly the car was maintained before I got it, and I was in awe that the car ran with the N54 plugs in.

Regardless, we took all the N54 plugs out and put in new Bosch ZR5TPP33S plugs pre-gapped. We got all 6 in there, torqued them down, fired it up and it ran great. However, when the car was put under load there were misfires on cylinders 3 and 6 (read from Carly OBD2 bluetooth adapter) and a plethora of other misfire codes. We found this to be odd because it was a textbook job; changing out spark plugs isn't that hard. Nevertheless, we took apart the cowling again hoping to see a loose connection somewhere but could find nothing wrong.

From there we thought the plugs weren't gapped right. After inspection of all the plugs we found that the plugs were not gapped at 0.032" (which is what the box says the plugs are supposed to be gapped to), but rather 0.028". After multiple attempts at different gap sizes both bigger and smaller over a 2 day period, we gave up and put in the old N54 plugs thinking that would still work. When we installed the plugs and started the car we got the same issue- misfires on multiple cylinders. At this point we were defeated and confused as to why the plugs that were working the day before were not working again. Clearing the codes and starting the car again yielded no progress.

Today we took the car to the dealer and told them what happened. They seemed just as confused as we were and told us they'd look into it. A little while later they told us that the plugs they used worked just fine and that seemed to be the issue. We had the dealer put in new plugs for $550 (!!) and we went on our way.

Their reason as to why their plugs worked and mine didn't? They said the tool we used must have been seating the plugs incorrectly. I think that reason is total crap as the tools we used were used to put on plugs on many cars including some E92s with N54s.

What are your thoughts? Has anyone dealt with their car not liking any plugs after install? Clearly something we did wasn't right, but I'm having a hard time coming up with anything we did wrong.

[TemjinX2]

did you use a torque wrench to torque to the correct tq number? Thats the only thing i can think of some of your coil backs are starting to go bad. Its usually recommend you change your plugs and coils together.

Maybe you had bad luck and got a bad set of spark plugs.

I literally did the same thing you did, i ordered oem spark plugs and swapped them out and didn't have any problems. Only difference is, i used a tq wrench to tq to the correct tq number.

[mchez]

Originally Posted by TemjinX2

did you use a torque wrench to torque to the correct tq number? Thats the only thing i can think of some of your coil backs are starting to go bad. Its usually recommend you change your plugs and coils together.

Maybe you had bad luck and got a bad set of spark plugs.

I literally did the same thing you did, i ordered oem spark plugs and swapped them out and didn't have any problems. Only difference is, i used a tq wrench to tq to the correct tq number.

Yep. Can't remember what the torque spec was. Maybe 23NM/17 FT LBS if I recall correctly. It would be one heck of a coincidence if my coils went bad when I changed the plugs but I guess stranger things have happened. It's worth considering. Thanks for the reply!

[TemjinX2]

Originally Posted by mchez

Yep. Can't remember what the torque spec was. Maybe 23NM/17 FT LBS if I recall correctly. It would be one heck of a coincidence if my coils went bad when I changed the plugs but I guess stranger things have happened. It's worth considering. Thanks for the reply!

Maybe just bad luck...sounds like you did everything correctly. I'd recommend you at least keep one coil pack as back up if not gonna replace them anytime soon.

[Bullcitybmmer]

Originally Posted by mchez

Yep. Can't remember what the torque spec was. Maybe 23NM/17 FT LBS if I recall correctly. It would be one heck of a coincidence if my coils went bad when I changed the plugs but I guess stranger things have happened. It's worth considering. Thanks for the reply!

I'd replace them just to be safe, especially if you're concerned about the prior maintenance on the car. I don't think it's crazy to think that something might have gotten tweaked on one or two of them after they've been yanked out and plugged back in a few times. They're a little bit more expensive than just swapping the plugs out, but you should be able to get a full set for less than $150 from FCP Euro with a lifetime warranty.

To your original post though, when I first tuned my N55 I put in a set of NGK plugs that I bought from amazon. On the first trip down the highway with more than half throttle it misfired like crazy and went into limp mode. I took it to my indy shop and had them run a ton of tests, and they couldn't find anything. I bought another set of the same plugs from a more reputable source, swapped them out, and everything was peachy. My mechanic and I just figured that one of the plugs might have been bad. Bosch/NGK/etc make millions of spark plugs, stuff happens, sometimes you might just get a dud. Sucks you had to sink $500 in at the dealer though.

[Pladi]

Ill tell you my theory. I went to hell an back tring to fix random cold start misfires with N55.

What i learned:

- These engines are very finicky with coils/spark voltage distribution. I believe the DME adapts to a certain voltage distribution for the amount of load that it senses for each cylinder. Load changes based on temperature and spark plug gap and condition of the plug. So long story short is RESET adaptations. Never adjust new park plug gap. 0.028 gap will not cause misfires.. should not. I would put new n55 plugs and dont touch them just install them torque them. Reset adaptations go for a drive. Long drive. Monitor things. Misfires should settle.

[mchez]

Originally Posted by Bullcitybmmer

I'd replace them just to be safe, especially if you're concerned about the prior maintenance on the car. I don't think it's crazy to think that something might have gotten tweaked on one or two of them after they've been yanked out and plugged back in a few times. They're a little bit more expensive than just swapping the plugs out, but you should be able to get a full set for less than $150 from FCP Euro with a lifetime warranty.

To your original post though, when I first tuned my N55 I put in a set of NGK plugs that I bought from amazon. On the first trip down the highway with more than half throttle it misfired like crazy and went into limp mode. I took it to my indy shop and had them run a ton of tests, and they couldn't find anything. I bought another set of the same plugs from a more reputable source, swapped them out, and everything was peachy. My mechanic and I just figured that one of the plugs might have been bad. Bosch/NGK/etc make millions of spark plugs, stuff happens, sometimes you might just get a dud. Sucks you had to sink $500 in at the dealer though.

Coils are definitely on the top of my list now. Thankfully those are even easier than plugs. Perhaps bad plugs are more common than I thought.

[mchez]

Originally Posted by Pladi

Ill tell you my theory. I went to hell an back tring to fix random cold start misfires with N55.

What i learned:

- These engines are very finicky with coils/spark voltage distribution. I believe the DME adapts to a certain voltage distribution for the amount of load that it senses for each cylinder. Load changes based on temperature and spark plug gap and condition of the plug. So long story short is RESET adaptations. Never adjust new park plug gap. 0.028 gap will not cause misfires.. should not. I would put new n55 plugs and dont touch them just install them torque them. Reset adaptations go for a drive. Long drive. Monitor things. Misfires should settle.

I was wondering about a reset procedure of some sort. The longest drive I went on the misfire and reduced power mode was no more than 2 miles. I did drive about 15 miles on the N54 plugs in reduced power mode to take it to the dealer and it never 'reset'. I wonder how long the process is, if it exists.