Our old B18c setup with s366 didn't experience missfire problems on high boost level
but when we changed to s372 missfire started to occur on 8 - 9.5rpm @ 28psi - up

timing played from 12-18 degrees
IAT = 22C, C16 Fuel @ 11.5-11.8 AFR
Denso Iridium plugs gapped to .015-.018
OEM distributor and wires

what could be the easiest way to solve this using stock distributor and S300

 

Sounds like it could be plugs....possibly the gab, try an ngk plug

I know on some cars I've done we had to use the ngk #10 for that boost level gapped at .0020

 

Definately try another set of plugs first, and check the cap and rotor as well.

 

ahhh sounds like the same issue i had after i tuned my car last year.

car was tuned mint and did really well on the dyno and street but a week after i noticed if i went on boost on the hwy it would sputter really badly so i would let off right away.

went to the shop and sure as hell needed cap/rotor, plugs and wires.

went back to work and gave her! on the hwy and back to normal.

man was i scared at first and thought i really messed up my motor.

 

already tried another set of bnew plugs still same missfire. cap and rotor are bnew as well.

 

ngk's or iridiums? try the good ole ngk 9's or 10's there alot cheaper!

 

we're using denso iridiums thats what available that time.

 

try ngk's and try another distributor! the ignitor might be going out!

 

just curious. how much hp/boost does our stock ignition can handle before we order an ignition box.

 

we have made passes on the dyno with a stock dizzy at 840 but it broke up a little on the top! me personally i would have a ign. box on everything with over 350 hp but thats just me! but the problem might not be the dizzy itself it might be the ignitor!

 

while driving did your rpm needle every go crazy on you?

 

that could also mean a loose ground....just happened to me.

 

your right or a loose wire on the ignition box but everytime i had that issue it was the ignitor giving me a signal its about to go.


so i guess heres your check list

-cap and rotor
-new wires
-new plugs im on 9's
-check all wires and ignition box ect
-check coil if you use an external coil
-maybe the ignitor in the dizzy is about to go


add to the list guys maybe we can get an answer for this guy

 

Definitly use NGK 9 or 10's. Denso Iridiums should NOT be in that car.

 

Why?

 

yah go with ngk

 

look at the s300 logs if you have clean rpm trace it's the coil if it's choppy the ignitor... or it could be both.... also make sure you dont have something else going on like valve float... but the main culprit of dyno miss fire after the basics are done, cap rotor plug wires and plugs, it is normally the ignitor or coil. also make sure the distributor sub assmbly doesnt have red bearing dust or other signs of issues....

 

I've heard of many people having problems with Denso, let alone Iridiums. Why not run a plug that is tryed and proven like NGK's? 99% of the FI community runs NGK plugs without problems. I'm not saying that their are not other contributing factors as to why this is happening to him, but I personally would start there and see if it helps.

 

I am on a stock dissy but i have a msd ss coil am my car did not like the ngk 10s but i put a set of 7s in it and it was fine.

 

been using denso iridiums for two years now with no problems.

 

here's the dyno...


the green = s366, blue = s372...

as you can see, the blue graph didn't get to rev higher. (thats about 9t only)

we'll try a new dist/ignitor/ngk 9s next time...

btw, this was on 22deg IAT/c16...

what do you guys think this s372 should rev up to? 10t? 9t seem to have narrow powerband...

 

whats the afr doing at the higher rpm?

 

the usual...
11.5-12.0