I have a 2006 Ford Mustang V6 4.0L. I just purchased these Bosch 6715 platinum spark plugs and installed them. I took them out because I noticed air was coming out of the spark plug socket. When I inspected them when they were out these plugs were bent. What could be the issue? I'm going to buy standard Motorcraft copper plugs to replace these $3.00 plugs.

Bent electrode

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  • 2
    Welcome to the site. What car and engine are you having trouble with? If you give us the details, we may be able to give you a specific answer. It is very possible you were given the wrong plugs.
    – CharlieRB
    Dec 20, 2017 at 20:56
  • UPDATE During my lunch break I purchased 6 Motorcraft spark plugs and gaped them to .054 and replaced the Bosch. The issue has now been solved in Bank 1. But now I am having an issue with weak acceleration and I can hear air leaving from Bank 2. Maybe I did it too rushed and didn't tighten them in Bank 2, maybe I left a cable slightly unplugged, I don't know. I have to fix this after work or else I won't be able to get home.
    – go.surf13
    Dec 20, 2017 at 22:03
  • @CharlieRB I have a 2006 Ford Mustang V6 4.0L. The plugs Bosch are "compatible" with my vehicle but no way will I ever use them or recommend them to anyone else with the same vehicle. I am currently resetting my ECU (disconnecting the negative terminal from the battery) so that it can read the new plugs. And before I connect the battery cable I will inspect Bank 2 spark plugs and ensure they are fitted properly.
    – go.surf13
    Dec 20, 2017 at 23:51
  • Did you get to compare the plugs that worked with the Bosh ones? It would be interesting to see the side-by-side of the thread end of the plugs. Wonder if the Bosh plugs were mislabeled.
    – CharlieRB
    Dec 21, 2017 at 15:12
  • Just from visually inspecting the Bosch and Motorcraft plugs I noticed that the Bosch electrodes "looked" and seemed like a "softer" metal. I didn't compare them side by side so I can only say by what I saw when I was installing the new ones.
    – go.surf13
    Dec 21, 2017 at 16:47

2 Answers 2


I think the only reason that would happen is that the plugs are just a little too long for your head and they have been impacted by the piston. Compare these to other models for your car and check the length. Since it's only bent a little, I doubt any serious damage was done, but certainly double check that you get the right parts before installing new plugs.

I also just noticed that there is no washer on the top of that plug. I'm use to seeing a washer there, and a missing washer could make the plug sit too low. So, that's another possibility.

  • Yeah none of the 6 plugs came with washers. But I'm only having issues on the bank 1 (passenger side). I sealed the air by using Teflon tape around the threads and that stopped the air from coming out. The engine runs fine (I ran it to 100 mph) last night. The only issue I'm dealing with is that it shakes at low speeds such as driving through a fast-food drive thru.
    – go.surf13
    Dec 20, 2017 at 20:47
  • Well, teflon tape isn't really rated against the heat and pressure of 1000's of explosions per minute, so that's not the right thing to use. It could just be that the rotation of those plugs is enough to cause contact, and the ones that don't have an issue are rotated just right. I'd go to a different parts store and get an OEM style plug and compare it to the new ones. Compare the length, the seat, and the threads. All of those can vary and cause the issues you see.
    – JPhi1618
    Dec 20, 2017 at 20:52
  • I know Teflon isn't the best to create a seal on engines but it did stop the P0171 code (running lean). So Teflon did help.
    – go.surf13
    Dec 20, 2017 at 21:06
  • Plugs should make a tight seal - if there is air coming out, they've got the wrong thread. As @JPhi1618 says, Teflon tape isn't the right thing to use!
    – Nick C
    Dec 21, 2017 at 10:10
  • Whether they have the wrong thread or not doesn't resolve my situation. The plugs are labeled as "compatible" for an 06 Mustang V6 4.0L. And as the quote goes. "If it's stupid and it works, it's not stupid". Teflon tape has proved to me that it sealed the air escaping the plugs in Bank 1.
    – go.surf13
    Dec 21, 2017 at 16:48

The plugs have a tapered seat so don't need a sealing washer, but the length overall from the seat to the electrode is critical. You need to check against the ones you removed - if, of course, you still have them.

The other concern is the apparent damage to the threads or have you applied some sort of sealant / lubricant...

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