Hi there

My first gen rx-7 13b Bridgeport was giving me some problems the other day, basically missing when at WOT. I decided it must be the plugs as they were getting pretty old. The old plugs were NGK B10EG's leading and B9EG's, i know they aren't commonly used but here in South Africa we don't get much choice so all the rotary guys here use those. I went and bought some new plugs (went to 9 L and 8 T this time as I think the 10s and 9s were too cold for street use) . I then went to change the plugs and discovered that the trailing plug on rotor 2 was completely melted. The electrode had almost completely melted away. This was quite clearly the reason my car was running like crap because my megasquirt gets its tach signal from the trailing coil so if this plug wasnt firing it would cut fuel. The strange thing is that the rest of the plugs were all fine. The leading plug in the same rotor was completely undamaged and looked the same as the leading and trailing in rotor 1. They all have a thin blackish layer on them. The question is, is this just a freak occurrence or could there be a problem somewhere? Car has been running strong with no signs of detonation and with the new plugs its running perfectly again . Engine seems to have really run in nicely recently and I just can't keep the tyres hooked up anymore hehe.

Anyways any ideas would be appreciated.

 

i run b9EG all four on my LPG turbo FC and they are a great bang for buck plug

however your issue is you have them back to front
in all NA application mazda use a cooler plug in the trailing than in the leading
( NGK heat range,, larger number is colder )

so the trailing should be the 10 and the leading 9 in your application
if this is prone to fouling you should try 9 and 9
or 9 in trailing and 8 in leading if the wet foul issue persists

 

oops, how did I get that wrong i'm not sure where I picked up the idea that trailing should be warmer. Thanks i'll swap them around and see how things go.

 

For the B9EG plugs, do you gap them? If so, what do you have them at for your L and T.

 

Even with you having the heat ranges backwards, your other rotor should have the same problem but it doesn't. You could have a coil issue. I would swap coils and see what happens while using the same plugs (but new). If you change plugs then you will never know what really happened. Use process of elimination to find the actual fault.

 

ive been running breqp9 in the trailing and rx8 leadings and they look great after a few easy laps