bobbylx

So, hopefully this will be an easy one. On a Renix 4.0 (not sure about HO) there is a vacuum line that runs from the rear of the valve cover to the intake manifold.

Does anyone know what function this serves? And, is there any harm in leaving it off?

Reason I ask, I was doing to maintenance on the Jeep today and noticed that vacuum line was noisey. I could actually hear a suction type noise coming from the line. I cut a new piece to make sure there was no leak, nope, just a noisy hose.

So for kicks and giggles I pulled the hose off at the intake with it running. My idle actually got more smooth and the throttle responded a tad better. This was with both end wide open, not capped off. Anyone experience something like this? Or should I just leave it hooked up and forget about it?

freegdr

Its our version of pcv its a leave it hooked up.

5-90

The 6-242 uses CCV to relieve crankcase pressure due to piston ring blowby, not PCV (actually, CCV is common on most PFI engines with a "dry" manifold - the idea of a PCV vavle was as a check valve in case there was a backfire burning through the intake, it could blow gaskets in the crankcase.)

CCV will have two lines - one to allow fresh air IN to the engine, one to draw blowby gasses (which still contain fuel) OUT of the engine. These are usually spread pretty far apart - like opposite ends of an inline engine or opposite cylinder banks, or thereabouts.

And, PCV/CCV is one of a very few emissions-reg-mandated devices I can actually agree with - all it does is loop unburned fuel back into the intake stream for another go. Plug it back in, make sure the orifices are clean (you may need to change the grommet, you should be able to find it at NAPA,) and alles gut!

bobbylx

Thanks. Makes perfect sense, the front hose draws air in, back one recirculates it into the intake.

And it is hooked up, I wouldn't leave it off unless I knew it was harmless. Now, to piggyback on this question. Is there a size spec for the rear hose? Mine were dry rotted so I replaced them all during the engine swap. But I have no idea was size the original was. Mine may not be allowing enough air flow or something?

freegdr

Green circled area what should be there...

5-90

Airflow is metered by a sized orifice in the grommet - the hoses are effectively immaterial. I've patched those lines with various sizes of vacuum hose with no ill effect - just try not to ream out the orifice oversized (I'm not sure what it would do, I've not had occasion to find out. Why screw with it if it's working?)

rawk krawler

I had to open up my front one because I couldn't find an oem fit, using a rear one was causing crankcase pressure, spitting oil out of my dipstick. Once bored out it now runs great.

cruiser54

To the OP:

Make sure that white plastic orifice and the hose are clean and clear. Carb cleaner will work fine.

bobbylx

Thanks for all the info. Now I remember what was going on with that.

See before pic below. PO used a peice of black heater hose, and stuffed it into the valve cover, then he put an elbow on it and a small chunk of red hose, and allowed it to vent into the engine bay.

I'm pretty sure when installing the new engine I grabbed a generic elbow and grommit from the parts store. Anyway, I'll just make sure I get the correct one and leave well enough alone.

Before



After

DFlintstone

That one from the manifold to the rear needs the correct fitting with the 2.6 mm orifice, or it will be a vacuum leak and kill your mileage. (if the map reads low vacuum it will think you have your foot in it). It's there to guarantee flow through the crankcase.

The front should be large...like 1/2 inch, free to vent, designed to go to to the air cleaner. If it can't vent, like rock crawler says crankcase pressure can make it **** all over, including out the rear main seal.

cruiser54

Renix Vacuum Harnesses
The vacuum harness that attaches to the front of the valve cover and includes the grommet/fitting, and is called the front harness, is Napa part number BK 715-1367
　
　
The vacuum harness that is closest to the air cleaner, EGR etc, and is called the rear harness, is Napa part number BK-715-1366.
　
　
The tube from the rear of the valve cover to the intake manifold is part number 715-1365.
　
　
Revised 09-11-2012

Carteale97

hey! I had a question for you! Im missing my ccv/pcv hoses on both and i can see where the front one goes but im having really bad crankcase blowback from the rear pcv that just has an air filter on it and im just trying to figure out exactly where the rear pcv valve hose goes onto the i take manifold!

DFlintstone

Look at the photos in post #9. Top front end of the intake.