too bad the gap cant be adjusted. but i don't think an all stock car should be having issues regarding plug gap and weak spark. I still dont know how a lack of spark can cause preignition knock.

i dont think i have carbon buildup, because the engine is literally a new replacement from mazda, not a rebuild.

I don't particularly like reproducing the sound it makes, it scares the crap out of me.

THIS is good to know, i was just about to start digging into the car to check when i read this.

Could a partially clogged stock downpipe cause this? the car seems to lack a lot of power in the top end of the rev range. 5000+.

 

I've seen people have similar issues with a plugged cat.

Seeing as yours is USDM and has both the pre cat in the downpipe and the second cat it could be that one or both are getting clogged up. Its easy enough to check, or swapping on an after market cat less downpipe never hurts anyway.

 

Would be nice if you had a PFC and could log the knock. Know anyone who could loan you one for a just cause?

 

I'll be installing a 3" downpipe in the next week or so. I'm hoping its just that.

I don't know anyone in my area with a power FC. but changing the computer would probably change or mask the issue wouldn't it? especially if the map didnt work with my car.

 

Changing the ecu could do a number of things. But generally when ppl install the PFC a lot of the weird quirks that the rotaries tend to have go away like the 3800 hesitations and such. Also you could pull timing, and log the knock to see if that truly is what you're hearing. If its audible your knock levels would read really high on the PFC.

 

The plan is go to full stand alone in the spring anyway. Microtech with custom harness and 350rwhp tune with 14-15 psi.

i hope my downpipe cures it in the meantime. i'll also be doing a fuel filter replacement and relocation. and I may check the sock in the tank also, but from what i am reading the sock doesn't cause issues very often at all.

 

Stock precat is out, man its heavy compared to the stainless one. just gotta get some header wrap so i can put it back in!

 

Well, i got the new downpipe in, but unfortunately i broke the o2 wire reinstalling it. i'll have to get another o2 sensor..

good news is, i can't hear any knock anymore. and boy did it wake the car up!

 

eeeexcellent