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View Full Version : rb25 missing at higher rpms/done a lot of research


feito
02-14-2012, 11:52 PM
Im not the type of person who likes to just go on asking for help with any little problems that comes out, but man this thing's getting to me. Im dealing with the rb25det higher rpm (around 5k) missing/skipping problem which apparently is a common problem. Well I've done a lot of research and have tried different methods/repairs and so far nothing!!
Here's the list of what i have
98 240sx se
Rb25det s2 5spd all stock
fmic
am performance downpipe
apexi power intake air filter
apexi 85mm exhaust with hollowed out cat
greddy type s bov
new bkr6e gapped to .028
aem wideband (bought brand new, around 11's at wot when it starts acting)
circuit sports 255 fp (heard its the same as walbro..)
z32 fuel filter
10psi (problem still there on 7 psi)
everything done by me including wiring

I read about the coils breaking/arching at higher rpm's and people using different methods to avoid/repair this problem consisting on covering the coils with some kind of insulator such as silicone or flexane94, well i went with the flexane, tried my best and i think i did good with the exemption of one, only 'cause that stuff dries faaaast!!
Here's a pic:
http://i1081.photobucket.com/albums/j341/andres14oj/IMG_20120201_192952.jpg
Oh yeah, this was after i gapped down my plugs from .031 to .028. They look that healthy, here's a pic
http://i1081.photobucket.com/albums/j341/andres14oj/IMG_20120205_172801.jpg
Well the missing didnt stop with the flexane lol, i kinda regret it after reading that this is bad for coils 'cause it can worsen overheating issues..
I had read about putting elect tape around the boots and decided WTH! It comes off anyway, so i gave it a try today and still nothing, problem still there.
Checked the grounds on every single coil and they all get the same signal.
Did a boost leak test the right way with 14 psi, nothing.
Adjusted my tps according to fsm
Adjusted my timing with a timing gun to 15. Unfurtunately it was an old gun and i had to do the spark plug wire trick. At 15 the cas was almost all the way clockwise and compared to some pictures that i found here and decided to centered it. Its probably the gun not working properly.
Now i dont think it could be a tooth off on the belt 'cause besides that problem the engine feels really strong before it starts skipping.
I know it has nothing to do with my o2 sensor.
I read on nico about a guy that found out his problem was some little restriction on the turbo intake pipe. On my stock rubber intake pipe, i had to cut about an inch or a bit less to be able to fit my filter next to the reservoir: I cut it right in the middle where it was the straightest and spliced it together using about 1 1/2" of intercooler pipe and two clamps. Now im leaning towards that idea and will either get another unmolested stock intake pipe and find a way to make it fit or get one of those silicone ones.
My dad has mentioned that maybe my cas is worn out and cant keep up with higher rpm's, any way to check this? He says it doesnt feel like a miss, rather like the whole thing goes on n off. He also said that maybe the t-belt goes loose at higher rpm's as if the tensioner can't support it. I havent replaced either one of these since i got it.
Any input on this guys? I would really hate buying new coils or/and a cas and still have this problem.
Thanks

feito
02-15-2012, 05:20 PM
C'mon guys, someone's gotta have some input on this

AS240
02-15-2012, 05:25 PM
I had the same problem and tried all the remedies that you tried. I even swapped out the CAS with another one. nothing ever helped. I just saved up and did the ls2 coil swap. it was worth every penny.
my CAS is almost all the way clockwise at 15deg too.

feito
02-15-2012, 07:02 PM
yeah, i still want to believe its my coils, its just that i've read so much about this problem that im almost convinced that's my problem

AS240
02-15-2012, 09:12 PM
It is mostly likely your coils. there's only so much you can do to try to make them not crap out. The tape and flexane helped me for a couple months, but the miss eventually came back. I would highly recommend changing to lsx coils or the gm wasted spark setup instead of dropping $500 on splitfires or yellowjackets that will eventually do the same thing. And because you have a series 2, the lsx coil swap is soooo easy. best mod i have done to my rb so far imo

redline racer510
02-15-2012, 11:31 PM
I can bet you that your coils are bad or are about to go out. A cas would cause ignition problems regardless of rpm. The coils start missing when the resistance becomes too high, high temperatures doesn't help.

bvr463
02-16-2012, 01:13 AM
ive had the exact same problem before and sometimes still do.

my hood dont seal good, so when i rains hard and my car is parked for couple days water leaks in under the hood, drips done right on coil cover and leaks all into my coils and spark plug(thats one cause of it) Before this happend i had to replace my coils and it all went away, but if you have a hairline crack inside the coilpack, at normal driving it will be fine until you hit boost, then you will start sputtering.

Hope this helps

RBPOWERED240
02-16-2012, 02:33 AM
sounds like i had the same symptoms. but i was running 18psi of boost on a 35R. i took it to the dyno and the graph showed some sort of issue after 5k rpms. it would break up. I swapped out my stock coils for splitfires, and after driving it it feels like a whole new monster. i would recommend swapping out the coils.

redline racer510
02-16-2012, 03:14 PM
Would definitely recommend splitfire coil-packs work pretty good.

feito
03-12-2012, 11:08 PM
turned out to be a bad maf. Replaced it with a good one, problems gone! Revs beautifully all the way to 7k! Now im just a little concern about my afr's being a bit on the lean side. Thanks for all your input

smoked240
03-12-2012, 11:58 PM
Nice! That's awesome its fixed. I had the same problem but it was a vacuum leak. Now I'm having some weird problem that just started. If my car is under 70c it will run terrible and basically you give it gas and it loses all power and shuts off then comes back. Tonight it died twice. Now if its 71 it will run awesome and pull nice. I don't know what it is haha