Detonation? RB25DET- Need help asap!

[Kansei240sx]

Hey guys, i usually don't create threads to answer my questions, but im getting kinda stumped here, and i think im on the right path, but i want to know what everyone else's opinions are.

Heres are the mods that i think could contribute to my problems, but not all of them. RB25DETAVC-RSAFC-2Zietronix Wideband Tuned to a stable 11.9 afrStock Fuel pressure regulatorFMICSARD R2D2 Unrecirculated370cc injectorsBrand spankin new NGK Iridium Heat range 6 plugsWalbro 225 LHP 300ZX TT Fuel Filter

Ok, the other week i was having no problems. I would get up to around 12 psi or so and anything past that it would backfire/pop in the exhaust, i looked at the wideband and my AFR's are rich when this happens, im not leaning out,

Now its worse than ever, if my car hits around 10 psi or even gets above 8 or so, its cracks and backfires in the exhaust like crazy.

I thought i had a bad electrical connection, WHICH i did, so i fixed it with a new junction box. I took it for a spin, and took off from around 3500 rpms and the wheels broke loose and rpms shot up to redline and a loud audible backfire from the BEE-R rev limiter which was normal. So i was like... ok cool. So i get to an onramp and do the same thing, except a more stable load with no slipping of tires. Boost would climb up to around .67-69 bar and then if it went higher it would backfire, so i'd let off the throttle and then it would stop and the car would continue to haul *** to redline.

Heres reasons i think this is happening.

Detonation due to running 91 octaneNot high enough fuel pressure due to running stock FPR I dont think it is boost leaks because even with the vent to atmospheric bov, before i had the AFC, my RB would never and has never stalled or bucked from it and or boost leaks. NEVER. It would always run under par with boost leaks or a BOV leak never any kind of popping/backfiring/bucking/hesitation.

Any help would be great, thanks guys.

[Cameron]

well first off, sounds like your running sorta rich, i would first suggest setting the afr back to 14.7:1 to try to see if it was just that you were running to rich..

secondly, trash the SAFC, get a power FC, or do a megasquirt... i have heard to many horry stories from them safc's to want to put one on mine..

[Kansei240sx]

My low throttle map under 20 percent throttle is 15-14.1 afr which is normal.

Hi throttle map being 14.7 under full load is asking to blow your engine. The leanest i'd ever go is 12.5-12.8

The SAFC isnt the problem, and i will never buy a Power FC, there are cheaper methods to get BETTER engine management.

[eh?]

The SAFC isnt the problem, and i will never buy a Power FC, there are cheaper methods to get BETTER engine management. [

Not high enough fuel pressure due to running stock FPR

[Kansei240sx]

stock FPR is what i figured, i did have an ajd fpr but i sold it to a friend who needed it more than i did at the time.

And SAFC wont cause the problem im having right now. I know its not the best thing to use and i dont plan on using it for much longer

Im using a RB20DET NISTUNE ecu with RB25DET translated maps which IMO will be way better than Power FC considering nistune tunes by its self in real time IF you want, and can hold up to 4 different maps. Power FC is too exspensive and Nistune is half the price and can do the same as power FC and more.

To keep this simple, lets not debate about this, but just the problem its self is what i need help with.

[eh?]

Post up a log of a run where you are misfiring. What have you changed since it was tuned? Why are you running a afc when you have a tunable ecu?

[rb25drag]

I think your ECU has retarded your timing not allowing you to get enough spark, Try checking the timing and the spark plug gap, For some reason the RB is the most sensitive motor I have ever worked on about the timing and spark plug gap.

I kinda had the same problem before, It has alot to do with the weather changing too, DO NOT RUN IT 14.00 ANYTHING LEAN unless you wanna purchase a new set of pistons.

mine seems to run perfect around 11.4-11.7 AFR

try backing the boost down to 8 re-tune and bump it from there. Thats how I got mine back to normal, With the AFC you gotta start from scratch again.

[rbosacco]

Zietronix Wideband Tuned to a stable 11.9 afr

Ok, the other week i was having no problems. I would get up to around 12 psi or so and anything past that it would backfire/pop in the exhaust, i looked at the wideband and my AFR's are rich when this happens, im not leaning out,

Now its worse than ever, if my car hits around 10 psi or even gets above 8 or so, its cracks and backfires in the exhaust like crazy.

Heres reasons i think this is happening.

Detonation due to running 91 octaneNot high enough fuel pressure due to running stock FPR

ok use process of elimination. is your car still at 11.9 afr when it breaks up? if so it is not a fueling issue. if your regulator was the problem the car would be going lean, thats just how it works. you would know it being that you have a good wideband. did the car ever run good on 91 octane before? if so and you haven't switched fuels that can't be the problem, if it worked before why wouldn't it work now? so the problem must be something related to spark. have you altered you timing recently? moved your cas? if not when was the last time you put new plugs in? when was the last time you checked your gap? to me, and i don't expect you to listen but i had a turbo integra and over time the gap opened up from just hard use. it did the same crap. what was happening was that my gap was so big that after a certian boost pressure it was blowing out the spark. i regapped them so i could drive home and put new plugs in it and it was back to normal. check your plugs before pulling your hair out just double check the gap. if the car just developed this problem and was totally fine before its probably something simple. if not just start at the plugs and work your way back the system you'll find it. i would start with ignition in my opinion...

did you change or add any parts since it started the misfire?

[Kansei240sx]

Thank you very much sir----^ Your post made alot of sense.

I had a few small boost leaks one at the BOV, and two tiny leaks at the IACV, one was on the screw, and one was on the yellow seal/sticker they use.

I JUST replaced my spark plugs the other night actually with NGK Iridium Heat range 6 plugs. I did not gap the plugs, but if spark is being blown out that would make an immense amount of sense. I was going to say, with a stable afr, and a stuttering motor or backfiring, the spark going out at higher rpms/boost only makes sense.

Soon i will upgrade fuel rails, fittings and a regulator along with 550cc injectors.

Im going to re-gap the plugs and fix the tiny air leaks around the intake manifold and bov. Thanks Richie

[eh?]

which plugs did you install? were they -11'sieBCPR6IEX-11?

[Kansei240sx]

Yes, those were the ones. So i gapped those plugs to .8 instead of 1.1mm as they come in the box and the car ran much better and very hard up to 12 psi or so in higher rpms.

Later as the night went on and i was giving lots of hard runs. It started blowing spark out again, then i looked the maf and some of the pins to the plug had receeded a bit more than likely giving a loose connection. So i monday im ordering a new fuel tank seal for the pump, new Z32 MAF connector and VTC Connector.

If this problem doesnt fix it, i may need to drop a heat range and go to 7's.

[eh?]

Pepboys sells bcpr7iex (no -11) which are .8mm heat range 7 iridiums but you will have to search the boxes yourself.
Modified by eh? at 5:20 AM 10/22/2007

[rbosacco]

sorry man i haven't been on in a couple of days but i do think that you should drop a heat range anyway, just because 91 is kind of a low octane, we have 93 out here in va. and i have 7's in my rb car and haven't had a problem. i'm actually on my same plugs that i used when i did the swap over 2 years ago. probably shouldn't be but it runs fine. and just for reference here's this.



what happens is that a hotter plug will carry heat so long and not cool down fast enough that it can light the mixture off prematurely...