Air pressure under oil filler cap?

[Coolguy@18]

Hi guys, I have a diesel and trying to solve a EML issie.

 

I have noticed that if I remove the oil filler cap or dip stick there is NO change in engine tone.

 

If I remove the oil filter cap there is a LOT of air pressure behind it?

 

It's enough where if I twist it undo with engine on it will lift the cap off.

 

I am sure there is ment to be a vacum where if I lift the oil filler cap off there should be some suction??

 

Any idea or can u guys remove you oil filler cap and see if yours does the same?

[Guest]

My 06 1.9PD is the same, blowing oil out if I remove the cap.

 

Normally I would suggest excessive piston ring blowby especially as it seems to have little engine braking which I've always found diesels have.

 

I've checked my vacuum check valve and it seems fine.

 

From the looks of what's on YouTube it seems to be par for the course for VAG diesel engines of this era.

[xman]

Pcv valve blocked?

[Coolguy@18]

Hi guys, ok so if I remove the pcv pipe engine seems to run a little better.

 

If I use my hand to block off the plastic tit to the pcv valve it's ok for a short while, if I hold my hand over it for more than 30 secs then remove my hand it will blast out LOT of compressed air, it's like the build up is a LOT.

 

A thought a pcv is to suck only and not have volume of air being forced though?

[Coolguy@18]

Hi guys, any one had chance to remove thier oil filler cap while engine is running to see of they do have air pressure??

[xman]

10 hours ago, Coolguy@18 said:

 

A thought a pcv is to suck only and not have volume of air being forced though?

 

Pcv is to allow excess pressure from crankcase/cylinder head and feed the oil contaminated air back into the inlet pipework before the turbo to be burned off in an ECO friendly way. It has a one way valve to stop air being drawn back into the crankcase.

[Coolguy@18]

14 minutes ago, xman said:

 

Pcv is to allow excess pressure from crankcase/cylinder head and feed the oil contaminated air back into the inlet pipework before the turbo to be burned off in an ECO friendly way. It has a one way valve to stop air being drawn back into the crankcase.

That's correct, the hose from the pcv valve is connected to the intake hose from the intake manifold which will cause neg pressure (vac), this should then suck the gas from the gasses in the rocker (That came from the sump) back into the manifold to be burnt off etc.

 

My question is most engines have a ballance of pressure close to 0, the pcv will then operate causing a slight vacuum to draw the gasses out, and normally if you remove the oil filler cap the engine will hunt a little (as vac loss and extra air enter intake etc) but you should feel a slight vac from the oil filler cap once removed.

 

This one is blowing and if I cover up for 30 secs and release my hand it will shoot out a huge amount of compressed air, this can't be right?

[Rustynuts]

Always positive crank case pressure when you take the oil filler cap off. It has been on all my diesels for the past 30 years at least.

[Coolguy@18]

19 minutes ago, Rustynuts said:

Always positive crank case pressure when you take the oil filler cap off. It has been on all my diesels for the past 30 years at least.

Yes there will be positive pressure but I am worried about the amount that's all.

 

If I take my hose off from the pcv and hold hand over nipple, after 3 secs let hand off it just out so much air, seems too much and my MAF reading is very high

[Rustynuts]

It might help to state what actual engine you have so people can make a valid comparison.

[SuperbTWM]

On 26/01/2019 at 18:45, Coolguy@18 said:

Hi guys, I have a diesel and trying to solve a EML issie.

 

I have noticed that if I remove the oil filler cap or dip stick there is NO change in engine tone.

 

If I remove the oil filter cap there is a LOT of air pressure behind it?

 

It's enough where if I twist it undo with engine on it will lift the cap off.

 

I am sure there is ment to be a vacum where if I lift the oil filler cap off there should be some suction??

 

Any idea or can u guys remove you oil filler cap and see if yours does the same?

 

Why would the engine note change? and why would there be any suction?

 

Diesels do not generate any vacuum to be able to get any part of the engine below atmospheric pressure.

 

Sounds like normal to me, if its a PD engine then the vacuum pump discharges air into the top of the engine also which doesn't help.

Edited 27 January, 2019 by SuperbTWM