Re: [Amc-list] Idle speed and PCV / Oil Filler Cap Questions ....

[Peter Marano <PMarano@xxxxxxxxx>]

>Message: 1
>Date: Tue, 24 Jul 2007 09:08:07 -0700
>From: Tom Jennings <tomj@xxxxxxx>
>Subject: Re: [Amc-list] Idle speed and PCV / Oil Filler Cap Questions
>	....
>To: "AMC/Rambler owners, drivers and fans." <amc-list@xxxxxxxxxxxx>
>Message-ID: <1185293287.6080.132.camel@xxxxxxxxxxxxxx>
>Content-Type: text/plain
>
>Welcome back!
>
>
>On Tue, 2007-07-24 at 09:04 -0400, greg_taylor@xxxxxxxxxxxxxx wrote:
>  
>
>>Hi all,
>>I have the oil filler cap vent hooked directly to the PCV port on my 
>>Holley carb (360-V8 in '89 GW) and a long tube with a vent filter 
>>stuck into the stock PCV grommet at the back of the intake.  I've run the 
>>Jeep like this for a long time (no PCV valve).  However, I 
>>decided to squeeze off the hose from the oil fill cap to the PCV port on 
>>the carb.  When I did this, the idle dropped by about 200-300 RPM 
>>(it was idling too high).
>>    
>>
>
>The idea behind the PCV is to allow crankcase scavenging by sucking
>crankcase air directly into the intake, but not be such a big "leak"
>that it ruins the idle. The PCV has a weight and a spring, it needs to
>be held vertical (all that I've seen). With high engine vacuum (idle)
>the valve sucks mostly closed; at WOT the spring holds it open and then
>it flows a lot of air. The weight should rattle freely. Sometimes they
>buzz (open/close/open/close/...), that's usually normal.
>
>Without looking at it, I would guess that if the current setup only
>affects idle by 200 - 300 rpm on or off then at higher speeds it's not
>doing a lot of scavenging. That's probably fine on a motor with good
>rings, eg. there's not a lot of ring blowby to scavenge but as the motor
>wears you might notice blowby gas coming out your vent filter.
>
>  
>
>>Does anyone know how critical the PCV valve is on the Jeep?
>>    
>>
>
>I don't know what the science of choosing PCV system "flow" is. My
>hornet (258) is easy to tune with any PCV; my Rambler (232) was a PITA
>to get the right valve. (Symptom was inability to set idle with 'idle
>drop' method, there was no sharp edge). That's an IMPCO CA-125 propane
>carb though.
>
>  
>
>>Also, I'm considering that originally, the oil fill cap had "some vacuum" 
>>to it, since it hooked to the air cleaner,
>>    
>>
>
>Actually that's just a source of clean air; it picks clean air out of
>the big carb airbox. There's probably less than an inch of water of
>vacuum there, and you're right, the PCV got manifold vac, so air goes IN
>the filler neck and OUT the valve cover (six) manifold (eight).
>
>I don't think it matters at all which way the air flows through the
>crankcase; with the 8's it might even help to have it flow INTO the
>manifold and out the filler. It's been a while since I've had a V8 but
>there's a lot of moving oil and mist right under that manifold.
>
>
>The PCV system does affect idle mixture and therefore setting even when
>working right. A few hundred RPM sounds OK, maybe a bit much. 
>
>
>
>  
>
At idle (high vacuum) the flow is fresh air in to the V/8 engine 
crankcase through the oil filter cap (this is the reason for the filter 
media in the cap), out of the engine crankcase through the PCV valve and 
plumbing.  At high power (low vacuum) the flow is reversed somewhat.  
Manifold pressure is near atmospheric flow through the PCV will be very 
small, blow by will exit through the oil filler cap (this is the reason 
the cap will become saturated with oil) and sucked into the intake.

Peter Marano
Kenosha WI
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