Missfire On Boost

[EVL-R33]

Im getting a bad missfire on boost at around 4000-5500rpm. My mods are as follows:

Series II RB25DET with:

HKS 2530 turbo @ 20psi

Splitfires + plugs 0.8 gapped

PowerFC

FMIC

Bosch 023 pump

3" Split dump pipe + cat back

Custom exhaust manifold

Stock injectors @ 80-90% duty on 20psi

Hybrid boost controller(which spikes badly)

the most recent thing ive added is a HKS SSQV, can this be the problem? Or is it something else like an air leak?

Im also getting knocking every now and then when i boost it to 20psi(mainly during the daytime in hotter weather), if I reduce it to 1 bar or 14psi there is no knocking or missfires.

Anyone know what the problem could be?

Cheers.

Edited October 27, 2007 by EVL-R33

[zertek]

just curious, are ur internals still standard?

[EVL-R33]

just curious, are ur internals still standard?

yeh stock internals..

[Strik3r]

if hes got the stock injectors at 80-90%, hes only at 220rwkw.. stock internals are fine for that.

1st guess would be that the new BOV is leaking air.. would cause a:f ratios to go mega rich and missfire (as well as lovely black farts out the exhaust). check the tension on the BOV spring. Im not too familiar with the SSQV, but im guessing you have to set the spring tension for the amoutn of boost your running.

either that, or you've made a tiny leak somewhere when installing the BOV, and its letting air out under boost causing the same problem.

[Strik3r]

oh and how much knocking are we talking about here ? audible, or just registering on the PFC h.c ??

@ 20psi, i would have thought that turbo would be pushing somewhere around to 250rwkw or more.. which is way beyond stock injector capabilities ?

[Nathan_G1]

i agree, boost leak through BOV maybe, spark plugs may be shit.....are they iridium or normal copper? how did u re-gap them to .8 you may be blowing out spark. personally id get rid of the BOV its not gonna be much benefit to your turbo or car with your power figures so its a waste of time.

[blv]

im thinking plugs.

i had NGK iridiums and they were terrible, even gapped at .8

now i run NGK V-grooves, cost $18 for the full set and i gapped them to .85

[Adriano]

If its knocking at 20psi only during hot weather, common sense should tell you not to boot it or give it 20 psi when its hot, unless you want a rebuild i the near future

[EVL-R33]

if hes got the stock injectors at 80-90%, hes only at 220rwkw.. stock internals are fine for that.

1st guess would be that the new BOV is leaking air.. would cause a:f ratios to go mega rich and missfire (as well as lovely black farts out the exhaust). check the tension on the BOV spring. Im not too familiar with the SSQV, but im guessing you have to set the spring tension for the amoutn of boost your running.

either that, or you've made a tiny leak somewhere when installing the BOV, and its letting air out under boost causing the same problem.

Thats correct, I am getting 224rwkw at 20psi with the HKS 2530kai.. Oh and I will reinstall the stock plumb back BOV to see if the missfiring stops.

oh and how much knocking are we talking about here ? audible, or just registering on the PFC h.c ??

@ 20psi, i would have thought that turbo would be pushing somewhere around to 250rwkw or more.. which is way beyond stock injector capabilities ?

On a hot day with 20psi im getting anywhere around 90 to 130 registered knocks on the PFCs HC.. On a cool night with 20psi i hardly ever get any knocks..

Does this mean its not tuned correctly or is it normal to get this many knocks on a hot day? I DO have a FMIC installed so too much heat shouldnt be an issue?

Also I have been told by my tuner that this is the maximum flow I can get with the 2530kai, I had it up to 233rwkw with an SAFC II earlier, but with the PFC I have less peak power. I think they changed something in the timing which made the peak power of 233 drop to 224 but the mid range power is heaps better and very responsive.

i agree, boost leak through BOV maybe, spark plugs may be shit.....are they iridium or normal copper? how did u re-gap them to .8 you may be blowing out spark. personally id get rid of the BOV its not gonna be much benefit to your turbo or car with your power figures so its a waste of time.

Spark plugs are iridium and fine I think, I had a mechanic regap them. Splitfires shouldnt be really doing this neither, I just recently had this problem arise so I might reinstall my stock BOV and see if it disapears. If not I might have to check for air/boost/vac leaks..

Edited October 28, 2007 by EVL-R33

[GTR-32U]

I would be getting the car on the dyno and try and replicate the conditions...with summer coming hot now timing would be perfect.Maybe a HKS twin power ignition module may be required...But for the level of tuning you have I wouldnt have thought so....go the dyno dude

[R31Nismoid]

Well was it doing it before you changed BOV? If not, then its a good start one would think.

Also if you havent had it retuned since the change.

More to the point though you probably have a electrical issue.

Just check all the coil connectors etc.

Also the ingition amp pack at the back (if its a SI motor), could be on its way out. Easiest way to test that is get some freeze/cooling spray in can form. when it plays up, give it a hard shot to cool it down, then go for a drive again. If its stopped then its clearly the issue.

[ZILR-34]

manybe by adding a fuel pressure reg would help since ur running Stock injectors @ 80-90% duty.

[EVL-R33]

Well was it doing it before you changed BOV? If not, then its a good start one would think.

Also if you havent had it retuned since the change.

More to the point though you probably have a electrical issue.

Just check all the coil connectors etc.

Also the ingition amp pack at the back (if its a SI motor), could be on its way out. Easiest way to test that is get some freeze/cooling spray in can form. when it plays up, give it a hard shot to cool it down, then go for a drive again. If its stopped then its clearly the issue.

I just recently got the PFC tuned about 3 weeks ago with a GFB atmo BOV, I got the HKS SSQV about 2 weeks ago, so I didnt really drive it around too much to notice any missfiring with the GFB.. And I will change the BOV tonight(once it gets a little cooler) with the stock plumb back and see how it goes..

The motor is an SII btw..

[EVL-R33]

manybe by adding a fuel pressure reg would help since ur running Stock injectors @ 80-90% duty.

Not sure how this would help if the stock injectors are already at 80-90% ??

If I added a FPR wouldnt it still be the same? I think im getting an adequate supply of fuel for the amount of boost im running, the 2530 isnt a much bigger turbo then the stock one, just has better flow rate..