410 replies to this topic

[LukeFranky]

Now I need a new PCV valve. Any one got one or know where to get one?

[Jimbo]

Surely REPCO would have something?  There's tonnes on eBay which are in Aus.

It's hard to say that it will fix your problem, but it's likely a step in the right direction. Even if it doesn't, you can rest assured it's something you have fixed that needed to be done?

[cowie165]

Jimbo, you're a smart dude

[duncanm]

So your crank case breather is just a single line from the outlet, straight to the back of the intake tract?

I'm not entirely sure (waiting for someone else to chime in), but at idle, wouldn't the ECU be tuned to account for the volume of air coming from the crank breather with the PCV open?

Closed system. Doesn't matter how much air flows.

At idle, air will be drawn into the manifold strongly, which means air will flow intake tract -> heads -> crank -> manifold.

lack of PCV shouldn't screw the MAF numbers -- it'll should just give you no crankcase ventilation.

[Jimbo]

I thought that was the case, though wasn't sure with later models.

[duncanm]

mmm -- on second thought.. it WILL screw with the amount of air available at idle.

Blocking the PCV will mean the idle mixture is probably all out of whack... IACV (idle air control) may be maxxed out.

certainly a suspect for throwing codes at idle.

The previous link given http://www.obd-codes.com/p0171 does mention PCV problems.

Bingo Jimbo.

[Jimbo]

Well, best he can do is get that all plumbed back to factory spec and hope it improves. Fingers crossed the issue goes!

[duncanm]

yes -- first suspect is anything not stock.

 

I'm not sure it pulls idle air through the PCV -- idle vac may not overcome the spring -- but all that bodged venting is a good starting point.

[LukeFranky]

Here's some engine bay pics.

The blue vac line with the filter in it goes to a boost gauge in case you are wondering.

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[LukeFranky]

How much vacuum should I be seeing at idle in the manifold?

[duncanm]

Mine pulls 20 inHg (68kPa)

[cowie165]

Mine pulls 20 inHg (68kPa)

 

Mine too.

 

Luke is that a RevD engine? Have you checked your vac setup against the pics in the Guide to Twin Turbo thread? Some of the blue lines seem to go in unusual directions, but mine in RevC

[LukeFranky]

Mine is at 16 inHg at idle. Rolling with throttle shut it pulls 20 inHg.

I just ordered new intake gaskets.
Oh yeah, it's a Rev D. I'm fairly sure the vac lines are correct, although a little messy.

[duncanm]

mmm - you said you put spacers on the manifold. Twice as many opportunities to have a leaking gasket.

Try spraying some carb cleaner around the gaskets when idling.. see if the idle changes, indicating a leak.

[Matt]

yes -- first suspect is anything not stock.
 
I'm not sure it pulls idle air through the PCV -- idle vac may not overcome the spring -- but all that bodged venting is a good starting point.

PCVs ive seen dont have any type of tensioned spring in them....simply a ball bearing that rolls down to block the hole

So on boost the bearing gets pushed hard in to the hole, stopping your crank from seeing boost pressure

And in vacuum the ball is let off the seat and allows ceankcase vapour to leak past

[LukeFranky]

I've already tried the carb cleaner trick. No idle change. I've ordered new gaskets anyway.

 

I will put the new gaskets and plumb in a new PCV in when all the bits arrive. I also bought longer bolts for the intake manifold so I can tighten them just that little bit more.

 

Then I'll test again and pray...

 

Thanks everyone.

[RX25SE]

Mine pulls 20 inHg (68kPa)

 

 

Mine too.

 

 

Mine is at 16 inHg at idle. Rolling with throttle shut it pulls 20 inHg.

 

Your variance may not just be a vacuum leak. Incorrect valve clearance (too tight tappets) or cam timing out can also cause this. Obviously, a vacuum leak test is the simplest to do first. Even poor ignition timing or mixtures can effect manifold vacuum.

 

Closed throttle over run will always pull manifold vacuum down.

[LukeFranky]

Opps, I said this was a Rev D. It is actually Rev E.