You can't GAP these plugs, they are done already from Bosch. If you attempt to GAP them you can damage the Firing PIN.

 

Yep, don't fool with them. I've only had an issue one time when I ordered them online and the electrode was visibly damaged. Wasn't worth the shipping to return it, but made me run to the local parts store anyway.

 

Thanks

 

Did you ever put these plugs in? If so what is your experience with them?

 

You can definitely gap iridium plugs and absolutely should test the gap of any plug, new or otherwise. However, you must use pliers on the outside of the electrode and pull away from the body rather than the tried and true method of a flat screwdriver prying the electrode away from the tip. Place the plug in a vice and use a ball peen hammer to gently tap down to the gap required. Use an old school set of flat paddle gapping gauges.

Iridium is a very soft metal in these applications and they don't want you manhandling them or running one of those horrific circular gap tools between the electrode and tip, it will thin the iridium layer very quickly as it's a soft, rare and expensive metal.

https://www.gearbest.com/other-instruments/pp_009809805954.html?wid=1433363&currency=USD&vip=4444999&gclid=EAIaIQobChMI_cv-j7j33QIVgVh-Ch3njAL1EAkYAyABEgJrVfD_BwE

 

I know when I installed this set my car immediately started to misfire & my Engine light kicked on. So either something else was going on or they were not GAP correctly from the manufacturer, put my original Mazda plugs back in & worked like normal.

 

Don't believe it when plugs say they are pre-gapped. I've only installed spark plugs once, and bought some of those Bosch plugs that claimed to be pre-gapped. Well I measured with my feeler gauges and they were nowhere close to the gap they said they were. Buy a $5 set of feeler gauges and get the gaps correct. If you use poorly gapped plugs you will get worse fuel economy and misfires. Seriously, if you're going to DIY don't cheap out, do it right.

 

I replaced my OEM plugs with the same Bosch 9621 plugs. I never gaped them and the engine has no issues with them, and have used them for at least half a year, engine runs the same as with the OEM plugs. Maybe YMMV. Based on some other threads on this forum some gen 3 ran good with Bosch, shit with NGKs, and vice versa.



/Necropost.