Thread: raised the boost to 12.5 lbs and now im missfiring?

At 11 psi the car runs fine at wot up to redline. Now i raised the boost to 12-13 psi and it miss fires pretty much from 4k to 7500rpm. Do I have to regap the plugs when i raise the boost? or am i maxing out my injectors(370's at 4bar) and maf(stock sr20 bored out). I trap at 111mph on 11psi, but I wanted to go a wee bit quicker and now its miss firing at this boost level? any ideas?

What plug gap are you running?
What do your AFR's look like?

I wish i could remember that as i set it last year, and i dont know about the afr's as its a jwt ecu and ive never checked it, so i would hope it would have stayed at whatever the tune was set at for this set up

Check your gaps. You may be blowing out the spark. It could also need a bit more fuel pressure.


Also just a little food for thought. You should always give the car a once over before you go giving it more power.. Juts some advice.

at only 12psi on a gtir t28 you shouldnt be blowing the spark out unless your gap is crazy big, hell i run a spike of 19psi on my t25 it falls to 12 by 5500 and it doesnt misfire one bit. by the looks of it you might be making too much power for your fuel setup. if your running 3bar fuel pressure/ stock then your probably making too much power and possibly detonating because of it. check your gaps. and i take that back because you have s4's i guarantee your making way too much power for you fuel setup and going lean, very dangerous. You need to upgrade man. I will be throwing on an S15 Dual
BB T28 and running 17psi on it but my injectors will be upgraded to 520cc @4 bar fuel pressure. More than enough but not too big. Its going to make crazy power. And especially looking at your 111 mph trap speed your power is up there. Thats just about what i trap.

mine does the same thing. At first it was just my fuel system (fuel pump) but now i blew my head gasket so misfiring is bad.

well it doesnt missfire back down at 11psi which is what i thought odd, i check the gap on the plugs and i had it set at .30. The jwt ecu is supposed to be 4 bar set up. you guys think i just need bigger injectors and a maf?

if you are using the stock maf thats your problem, its maxing out, they max out at 250whp, at 11psi you were probably a little over 250 but not enough to cause problems, 1.5psi more and there you go, thats worth probably an additional 15-20whp so yeah, enough to make that voltage on the maf go way too high causing the problem. Change your setup or leave it at 11psi. There is not much else you can do. The S4's make serious power for t28 cars. You will be surprised. I guerantee your setup was maxed out at 11psi. Plain and simple

Sounds good man, im actually hoping to get a z32 maf for free from someone with a failed swap, trust me i know about the s4's, after i got done breaking them in, changed the oil, and went for a spin, i about crapped my pants, my trap went from 105 at 9psi to 111 at 11psi and s4's

He said hes running 4 bar with a bored maf, that should be good up to 290hp....