So it's a long story I won't get into why here because it is not really relevant. One of those things that just end up happening due to weird circumstance. Anyhow the situation is, I now have all new plugs in my truck. Cylinders one-seven all have new OEM style(Autolite HT15 plugs). Cylinder eight has a new Champion 7989 solid, conventional type ground electrode. All new plugs. One is different make/style. Is this an issue, should I change the one so they're all the same or is it OK to leave it? Why or why not?

 

IMHO, different brand/style plugs could have slightly different temperatures and require different voltages to fire, which can minutely affect timing. If it was my truck I'd want matching plugs in all 8 holes.

 

Swap all 8 out and install Motorcraft SP515's or at least install 1 more HT15.

 

IMHO like driving with 4 tires with the same size but one having a different tread pattern, construction, or model. The vehicle will drive but will you notice a difference???

Purpose of the spark plug is to create a spark, which they all should. They may have different characteristics which may alter your engine performance, but will you notice it and/or significantly affect the performance of your truck???

IMHO, I'd be surprised if you would notice a difference if you swapped #8 out.

 

I apparently ran 6 SP515's and 2 HT15's my last plug cycle. Last shop I used swapped them in to clear a low grade misfire. I didn't have any noticeable issues.

I'd swap # 8 out simply cause I'm not a fan of Champion plugs unless it's going in my lawnmower.

 

My ocd would make me swap the last plug for a matching one. Doubt you would have issues running as is, though.

 

Does it vibrate? No? Then don't worry about it.