Crank Case Pressure tracking Manifold Air Pressure

Can someone cast their eyes over this.

I've noticed a correlation between crank case pressure and manifold air pressure on my engine.

The CCP is only 90 odd Kpa, compared to the 1500 Kpa peak MAP.

I've been trying to work out where it's coming from. I'm fairly sure it's not blow by as the peak cylinder pressure is going to be massive in comparison.

So somehow the boost pressure is getting to the crank case. Could be a small leak past a seal on the cold side of the turbo maybe???

Am open to suggestions!

90 kpa is about a bar, is that high for breathing? Are you running a PCV valve?

It's absolute, so it's just under atmospheric.

No PCV valve, just an open system. (Atmospheric catch can).

The thing that's confusing me is the way it correlates to MAP. Looks like I'm going to have to go over everything to see if there's a way MAP to be linked into the oil system somehow.

You two have successfully given me a migrane!

Well, if as you say, youre running an open breather and theres no link to the intake system logic dictates that its blow by from the rings...

Where would a turbo cold side leak go? Only to atmosphere

Am I right to think the the CCP is fluctuating between 90.56 and 91 kPa?

Hmmm, yeah so it would appear, just under atmospheric (101.3 Kpa).

I just can't see how the 130 Kpa of MAP I've created in that graph is having such an effect on CCP, yet the massive peak combustion pressure that will be occuring is having no effect at all. Obviously the combustion pressure is only for a very short amount of time, but there's a lot of them!

If I could measure the change that the 150 Kpa is making, surely the peak combustion pressure would be massively pressurising the crank case.

I'm going to conduct a leak down test in an hour or so and log the CCP whilst I'm doing it to see if I can effect....

That is an extremely small pressure fluctuation you are picking up, not even 1/10 of a psi. Without wanting to sound like I'm stating the obvious...is there any way that you could be seeing interference on the CCP signal from the MAP sensor signal?

Have you taken a log in a similar fashion with the CCP sensor hanging free in (for example) the engine bay or inside the car to see if it reads constant?

I suppose it could be signal interference, the wires do end up running in the loom together so I guess it's possible.

Unfortunately, due to the location of the sensor which probably couldn't have been placed in a worse position, (my fault!) there's zero chance of removing it to see what it reads in free air.

I suppose it could be signal interference, the wires do end up running in the loom together so I guess it's possible.

 

Unfortunately, due to the location of the sensor which probably couldn't have been placed in a worse position, (my fault!) there's zero chance of removing it to see what it reads in free air.

Ah I see, so how about something of an opposite approach.... Can you move the MAP sensor feed to somewhere reading simple atmo pressure and try the same test again. In theory the CCP should rise and fall (in line with actual boost) as you plotted above if there is a leak path the the crankcase. If not, that'd make a strong case for interference...

there is very little chance you have perfect cylinder sealing..

so CCP always correlates to MAP..

do you have any leakdown % figures to hand?

to add...

where are you measuring CCP from?

its odd that your managing to pull a vacuum from an open breather...

thhe sensor will read free air without the motor running..

Take that stuff off and stop worrying about it

Smartest bit of advice ive heard all day!

Stop being so anal tony

not really... it is important to measure CCP at high rpm..

excessive CCP causes poor return of oil to the sump.