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Discussion Starter · #1 ·
I have a rebuilt rb30 bottom end with new rings and bearings. New standard head gasket and an rb25det head.

I have got a misfire from idle and it struggles as you accelerate gently (wideband reads lean as expected due to misfire).

My crankcase breather is just venting to air at the moment with very little smoke at idle, but if I kink this pipe I get excessive smoke from the exhaust on deceleration. It still smokes a bit a idle from the exhaust.

The smoke is more white than anything, but has a slight smell of oil.

I have done the usual search and come to the conclusion its the valve stem seals.

Am I right?

Can bad valve stem seals cause a misfire?

P.s. I have wasted spark running perfectly, fuel pressure and injectors are ok, afm is ok.
 

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Belgium/Netherlands Area Rep
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i thought bad valve stem seals cause blue smoke and oil spitting through the exhaust
dunno bout the misfire tbh
 

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Discussion Starter · #3 ·
I have done some more research and it could be also the fact that I have removed all the pcv plumbing and blocked off the valve at the side of the intake cam cover.

I think I will reconnect it all tomorrow and see what happens.
 

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Look at your breather pipes first and eliminate every possible scenario that way.
If it still persists after that post up here and weel help you diagnose.
 

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possible ringlands and,what do you mean lean as expected because of misfire? yea the crankcase needs to breath
 

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possible ringlands and,what do you mean lean as expected because of misfire? yea the crankcase needs to breath
I would say its because the crank case isnt breathing ted.
But he's deffo going to need to eliminate that though first before doing anything else.
 

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to me it sounds like ringlands as well, have you done a leak down? also the breathers do need re-connecting, if its breathing heavy thats a sign of rings bud...leak down test is my first step
 

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My wideband reads lean because of unburnt fuel due to the misfire.
your logic is mental!have you considered its running too lean and detted and done a piston? it may be the breather problem but what kind of wideband are you nsing?at what rpm load ect does it read lean?
 

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Discussion Starter · #10 ·
The car is lean at idle. I started to map an r33 but while looking at the wrong thing at the wrong time I wrote it off. (too small a turbo too big an engine).

It was not running lean then and I only did 2 km.
No det either.

Now the engine is in a c34 laurel (was a diesel automatic).

The only differences now are

1. Hx35/40 turbo
2. eBay plenum
3. Intake at pod filter is different (that's why breathers are not connected)
 

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My wideband reads lean because of unburnt fuel due to the misfire.
If that's honestly what you think then you need to stop diagnosing things yourself and get to a professional ASAP.
 

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Discussion Starter · #12 · (Edited)
Look it up!

Misfire means unburnt fuel which passes out past the wideband regestering a lean condition when it is actually not a lean condition at all.
 

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iirc they measure the oxygen content of the exhaust,if that were the case then a car running rich and dumping fuel out the exhaust would indicate lean according to your technical expertise
 

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Discussion Starter · #14 ·
Research, research, research.

So far people only want to critisize. If you can't help me don't critisize.
 

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sure whatever you think yourself lad,a misfire is a momentary thing,car should idle round stoich,if your seeing that under load on boost then best of luck,do you know whats causing the misfire?eg coilpacks,whats your definition of a misfire?what part are you from
 

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Discussion Starter · #16 ·
Ok this is getting nowhere.

Misfire regesters lean, don't believe me if you want (check innovative motorsports site all wideband info readily available for those who want to learn).

Wikidpedia- wideband oxygen sensor. It does exactly what it says on the tin measure the amount of oxygen in a gas.

Research helps a lot, making comments about ones train of thought doesn't.
 

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Research helps a lot, making comments about ones train of thought doesn't.
Neither does arsey comments. :rolleyes:

You came on here, a forum, and asked for opinions - you got them. If you don't want the thoughts and opinions of a group of mostly unqualified people then go to a pro tuner.
 

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tdi power
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if its white smoke that would indicate head gasket has gone so its burning water.

and you say to do research to us
 

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Discussion Starter · #19 ·
Ok fair enough I asked for opinions and most people gave them.
But others said my way of thinking was "mental".

I did nothing except respond to someone tell me I knew nothing about o2 sensors.
 
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