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Vents on valve covers...

A

AboveNBeyond

NAXJA Forum User
Location
Northern AZ.
Hello all,
I have a 96 motor with a 89 Renix system...

On the valve cover of the 89 there was only one breather and it went to the intake manifold (direct vacuum)

On the 96 the valve cover has 2 breather holes...

On mine now One is just blocked off, and the other is going to the manifold directly but I winder if that is the best way??

The reason I ask is because with the hose connected to the manifold the engine is idling a little high, if I disconnect it and plug the manifold the idle comes down and she purs like a kitten... but I have no crankcase vacuum relief... What is the best way to relieve the crankcase pressure? Leave the vacuum directly connected to the manifold? Are there any better options?

BTW: I do not have the stock airbox anymore.
 
All the 4.0 valve covers come with an inlet for fresh air, and an outlet for the vacuum that draws air through the block to the intake, it's called CCV, Crank Case ventilation. The inlet is normally connected to the air box, low vacuum area, dirty side of the air filter, and the the other hose connected the engine intake manifold, directly, but with a 2.2 mm metering orifice to limit the air flow rate bypasing the IAC and throttle body butterfly.

If there is a larger tube than 2.2 mm, with no orifice it can cause a high idle, but it does need an air inlet to the valve cover. A leaking valve cover gasket can act as the inlet!

There are many places where excess air can sneak in, intake manifold gasket, loose bolts, throttle body gasket, loose vacuum lines...etc.
 
AboveNBeyond said:
Hello all,
I have a 96 motor with a 89 Renix system...

On the valve cover of the 89 there was only one breather and it went to the intake manifold (direct vacuum)

On the 96 the valve cover has 2 breather holes...

On mine now One is just blocked off, and the other is going to the manifold directly but I winder if that is the best way??

The reason I ask is because with the hose connected to the manifold the engine is idling a little high, if I disconnect it and plug the manifold the idle comes down and she purs like a kitten... but I have no crankcase vacuum relief... What is the best way to relieve the crankcase pressure? Leave the vacuum directly connected to the manifold? Are there any better options?

BTW: I do not have the stock airbox anymore.
Click to expand...
You have an 89' RENIX with a 96' engine
With everything connected as (your) normal, use unlit propane torch.
If idle goes up there's a leak you need to fix.

Keep the line, it scavenges the harmful gasses out of crankcase.
The orofice at rear of Valve Cover should be 2.6mm (confirmed87'), excessivly oversized could simulate vac. leak, or not sealing line properly.
You should unplug the opening at the front of V.C. and at least use a filter, most people "plumb" it back in after the filter for fresh clean air.
 
Last edited:
Ecomike said:
The inlet is normally connected to the air box, low vacuum area, dirty side of the air filter,
Click to expand...
I hope NOT.
Bearings LOVE dust, try it!



Better yet, don't

Metering orofice size should molded onto it.
 
Harlee&Tahoe said:
You have an 89' RENIX with a 96' engine
Click to expand...

Yup and it rocks, I love the extra power!!

Harlee&Tahoe said:
With everything connected as (your) normal, use unlit propane torch. If idle goes up there's a leak you need to fix.
Click to expand...

I already found that I have no leaks, and that this tube is causing the leak... and from an above post I now see why, it has a hose about the size of a sharpie, anyways when I cap it the motor idles perfect.[/quote]

Harlee&Tahoe said:
Keep the line, it scavenges the harmful gasses out of crankcase. The orofice at rear of Valve Cover should be 2.6mm (confirmed87'), excessivly oversized could simulate vac. leak, or not sealing line properly.You should unplug the opening at the front of V.C. and at least use a filter, most people "plumb" it back in after the filter for fresh clean air.
Click to expand...

I will start with the 2.6mm hose, I know the one on there now is to big now... thanks.
 
2.6mm hose will be too small.
The hose size isn't the problem, air is getting in somewhere.
The orofice is supposed to be a metered vac. leak.
You have a leak at the V.C. connection or bored out orofice.


I already found that I have no leaks, and that this tube is causing the leak
Click to expand...
 
Harlee&Tahoe said:
2.6mm hose will be too small.
The hose size isn't the problem, air is getting in somewhere.
The orofice is supposed to be a metered vac. leak.
You have a leak at the V.C. connection or bored out orofice.
Click to expand...

Is the orifice the brass nipple the vacuum line slides onto? Is that where it is metered? Because the vacuum line between the brass nipple and the cover vent has been replaced.
 
Ecomike said:
All the 4.0 valve covers come with an inlet for fresh air, and an outlet for the vacuum that draws air through the block to the intake, it's called CCV, Crank Case ventilation. The inlet is normally connected to the air box, low vacuum area, dirty side of the air filter, and the other hose connected the engine intake manifold, directly, but with a 2.2 mm metering orifice to limit the air flow rate bypasing the IAC and throttle body butterfly.

If there is a larger tube than 2.2 mm, with no orifice it can cause a high idle, but it does need an air inlet to the valve cover. A leaking valve cover gasket can act as the inlet!

There are many places where excess air can sneak in, intake manifold gasket, loose bolts, throttle body gasket, loose vacuum lines...etc.
Click to expand...

Good catch guys, Correction, use the clean side of the air filter for the CCV supply air.

One of the FSMs I ran across listed a 2.2 mm orifice for 87, and a later version listed a 2.6 mm orifice, 89 IIRC. I think the hard black tubing is between 2.5 and 3 mm, perhaps 3 mm OD, and 2.6 mm ID, so in that case the tubing acts as the orifice. You can either use the small tubing as the orifice, or larger tubing with a restriction fitting inline of about 2.6 mm to get the proper flow rate. I have done both with the same good results.
 
I'd go slightly larger than stock, so it doesn't get crapped up with CC vapors.
With a 2.6mm line you may acquire blow-by.
Or better yet CC pressure pushing oil out any weak seal since fresh line is plugged
(VC,RMS,Oil Pan, Crankshaft FMS, Timing Chain Cover seal).
That could get messy. It would be great before lift kit though.

For my 87, a 2.6mm orifice is used.
Which I was debating opening up to 3mm to alleviate my blow-by issue,
until I made a catch can to keep the air filter clean.
(I run a lot of WOT here in the Sierra Nevada Mtns. 7-8000 ft. passes)

I just eyeballed against a ruler and OD looks to be 7mm, and ID 5mm.
You will not get the same flow from a long 2.6mm ID line,
like sucking air through a long hose.
 
I have found that anything larger than 2.6 mm will let it suck oil into the intake manifold, and also raises the idle causing a high idle, on the two Renix Jeeps I have running.
 
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