Rb25 Miss Fire

[methz]

hey im trying to hunt down a miss fire in my rb25det

the car is a stock rb25det making 470rwhp at 26psi

last 3-4 weeks its been getting bad, now its time 2 do something about it.

basically the car from cold will start up and run on 5 cyclinders for first 10secs then clear up and run fine.

i can drive around off boost and it will run fine. As soon as i give the car a hard time and thrash it, i can pull up and on idle its back to 5 cyclinders.mind you it runs perfectly fine under load/boost

ive narrowed it down to cyclinder 6 which is the cyclinder not firing.

ive tried new injectors,coilpack wiring harness etc

injectors have been cleaned etc and new seals.

ive done a compression test and its good came back with 150-155 from 1-6

anyone else got any ideas? some ppl ive talked to think its lifter problem in cyclinder 6?

Edited September 6, 2011 by methz

[Randon_I_Am]

the car is a stock rb25det making 470rwhp at 26psi

[SargeRX8]

Simon is making 500+hp on a stock motor? Misfiring could be caused by many things but it seems you've tried the basics. I will be keeping an eye on this thread to see how it progresses. Keep us posted. What I would suspect is the spark plug or coil back. Next would be wiring. Next would be CAS(could be playing up?) Sounds electrical to me. My car had similar symptoms on startup. It would sound like its missing a cylinder or even two and after a few seconds they all kick in, my spark plugs were on their way out. Try gap your plugs closer see if that gets rid of the misfire.

[The Mafia]

470rwhp, 26psi out of a stock engine?

Leak down test on cylinder 6 please.

[methz]

plugs are about 500kms old bk7re always used them.

leak down test might be on the cards then, might ask my tuner 2 perform this.

yes 26psi thru gt35r on a stock rb25. i dont always run this boost. only turned it up for a dyno day not long ago.

running 1.75bar atm.

[Lithium]

At that power level I am assuming normal 98 pump gas? Simon is getting away with it on an ethanol mix, petrol would probably be a bit much for the crap fuel we get in this part of the world

+1 on compression test.

[methz]

yes pump 98 bp ultimate

car has been on big boost and 400hp for a few yrs now.

ive done 2 compression test's and both came up fine 150-155 across all 6.

leak down i have not done, i dont even know someone with the right tool 2 do it.

[boostn0199]

Have you had a look at the CAS could also be slight sign of it playing up by causing a miss.

[methz]

I will try another CAS tnite and see how that goes.

going 2 try another ecu aswell.

[Aleckr33]

Sounds like the cas mate.. mine kept dropping to 5 cyl due to broken cas

[DVS JEZ]

Try a CAS and see. Just borrow a mates one if possible.

Have u upgraded the valve springs?

Does the engine tick when its misfiring?

Any smoke?

Do a compression test when it starts to misfire if u can. Maybe a valve seat issue

[methz]

Gonna try new CAS 2morrow morning.

Valve springs are stock

only ticking noise is from the injectors, as far as im aware

no smoke at all.

ill get it 2 run on 5 and do a compression test then and see wot it comes up with.

yeh my tuner thinks a lifter or valve or something along those lines in cyclinder 6

[DVS JEZ]

Thats my thoughts exactly