PCV Not Functioning - no rear vacuum - JeepForum.com
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post #1 of 15 Old 07-22-2019, 08:32 PM Thread Starter
CJ7Guy1
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PCV Not Functioning - no rear vacuum

I feel like this has been talked to death but, again, I find myself relying on the Jeep Intelligentsia for guidance.

Here's what we're working with:


I'll start by saying EVERYTHING is new -
- front and rear grommets
- PCV check valve (front)
- Straight through elbow (rear)
- All hoses from PCV to T-Connector to "PCV" connector on newer Vapor Canister


The problem - oil in the air cleaner which leads to checking the vacuum pressure at the back of the valve cover, the part that attaches to the air cleaner.

Using Dales amazing site (HERE), the test is simple: with engine at normal operating temp, pull the back elbow off and rig up a vacuum tester.


I get nothing, not a small amount of vacuum, nothing. No matter what the engine speed.

I tried pulling the check valve from the front and having straight vacuum pulling from the front - that worked.

I tried replacing the check valve with another new on and the original old one - nothing.

I tried hooking it up normally and removing the vapor canister PCV hose and covering it with my thumb to test if enough vacuum was going to the PCV check valve with the vacuum tester hooked up to the back - nothing.

Checked the vacuum at the dipstick - nothing.

Cleaned up all of the valve cover, no leaks that I can see from the world's worst gasket - nothing (replaced it less then a year ago).

I have Zero ideas left.

What else can you guys think of - I'm stuck. Ideas?

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post #2 of 15 Old 07-22-2019, 09:13 PM
oldschool74cj5
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hello
have you tried hooking a vacuum gauge directly up to the large port on the carb to make sure you have manifold vacuum at the port? i have a weber so i am hooked directly to manifold vacuum under the carb. but i believe the large port on the bbd carb should be manifold vacuum.


oldschool
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post #3 of 15 Old 07-22-2019, 10:11 PM
CSP
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I'm assuming that your line going out of the PCV valve is going to the charcoal canister.

If that's true, disconnect it from the canister and run it directly to a vacuum source and test again. Eliminate the possibility that your vacuum is cut off at the charcoal canister.
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post #4 of 15 Old 07-22-2019, 10:56 PM
whollsee
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Quote:
Originally Posted by CSP View Post
I'm assuming that your line going out of the PCV valve is going to the charcoal canister.

If that's true, disconnect it from the canister and run it directly to a vacuum source and test again. Eliminate the possibility that your vacuum is cut off at the charcoal canister.
Yes, does the pcv valve go to the carb or the canister? The canister pcv line should tee into the line from pcv valve to carb manifold vac port.

When ever I hear the word 'Jeep' I reach for my wallet.
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post #5 of 15 Old 07-22-2019, 11:16 PM Thread Starter
CJ7Guy1
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Quote:
Originally Posted by oldschool74cj5 View Post
hello
have you tried hooking a vacuum gauge directly up to the large port on the carb to make sure you have manifold vacuum at the port? i have a weber so i am hooked directly to manifold vacuum under the carb. but i believe the large port on the bbd carb should be manifold vacuum.


oldschool
Yes, super strong.

Thanks.
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post #6 of 15 Old 07-22-2019, 11:21 PM Thread Starter
CJ7Guy1
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Quote:
Originally Posted by CSP View Post
I'm assuming that your line going out of the PCV valve is going to the charcoal canister.

If that's true, disconnect it from the canister and run it directly to a vacuum source and test again. Eliminate the possibility that your vacuum is cut off at the charcoal canister.
On my year, 1984, it's a T from the manifold split between Vapor Canister and PCV.

And, yes, I tried to removing the hose from the Vacuum Canister with a vacuum gauge rigged up to the back of the Valve Cover and nothing. Didn't make a bit of difference.

Thanks
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post #7 of 15 Old 07-22-2019, 11:30 PM Thread Starter
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Quote:
Originally Posted by whollsee View Post
Yes, does the pcv valve go to the carb or the canister? The canister pcv line should tee into the line from pcv valve to carb manifold vac port.
Yep, that's right.

Exactly like this:


Thanks
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post #8 of 15 Old 07-23-2019, 04:56 AM
John Strenk
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Quote:
Originally Posted by CJ7Guy1 View Post
...

I get nothing, not a small amount of vacuum, nothing. No matter what the engine speed.

I tried pulling the check valve from the front and having straight vacuum pulling from the front - that worked.
How did you do this? Plugged the vacuum hose directly into the valve cover bypassing the PCV valve? Were you measuring the vacuum on the rear vent at the back of the valve cover?

Quote:
I tried replacing the check valve with another new on and the original old one - nothing.
Did you check to see if there was vacuum on the end of the PCV valve ?

Quote:
I tried hooking it up normally and removing the vapor canister PCV hose and covering it with my thumb to test if enough vacuum was going to the PCV check valve with the vacuum tester hooked up to the back - nothing.
Good idea. Was there vacuum on the hose going to the vapor canister?

Quote:
Checked the vacuum at the dipstick - nothing.

Cleaned up all of the valve cover, no leaks that I can see from the world's worst gasket - nothing (replaced it less then a year ago).

I have Zero ideas left.

What else can you guys think of - I'm stuck. Ideas?


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post #9 of 15 Old 07-23-2019, 06:47 AM
pedal2themetai
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HI I think your over thinking it..
If you are not getting oil pushed out of the gaskets or the breather hose of the PCV and you have vacuum at the PCV , its working fine..... YOUR NOT going to feel or get vacuum out of the dipstick tube.. unless maybe you Plug the filter hose at the back of the motor.
just my .02
good luck
tim
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post #10 of 15 Old 07-23-2019, 07:19 AM
Matt1981CJ7
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Iím curious what ďcheck valveĒ you are talking about.

Edit: After re-reading the original post, I see you are calling the PCV valve a check valve.

As Iíve mentioned several times before, the PCV system on your engine is designed to reverse air flow when the blowby exceeds the capacity of the PCV valve. Thatís why there is a filter element and small oil collection area inside the air cleaner assembly. If you have no vacuum at the rear PCV hose at idle, then itís likely you have too much blowby for the PCV valve to handle. Time for a compression or leakdown test.

Matt
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post #11 of 15 Old 07-23-2019, 10:23 AM Thread Starter
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MODs, this reply came out funky - I'll fix and delete this one in a second...

Quote:
Originally Posted by John Strenk View Post
How did you do this? Plugged the vacuum hose directly into the valve cover bypassing the PCV valve? Were you measuring the vacuum on the rear vent at the back of the valve cover?

I have an extra elbow. Reduced it down to 3/8" and popped it in. I was eliminating anything stupid - valve cover internal oil splash guard not gunked over. Tested if vacuum was there at all - it was and it sucked a bunch of oil out of the little air filter inside the breather. Oh, I've got a clear hose hooked up on the back so I can see oil flowing pretty easy.




Did you check to see if there was vacuum on the end of the PCV valve ? Yep, if I pulled it off (all hooked up correctly and engine running), I could feel vacuum at the bottom of the PCV check valve. If I put my gloved finger over it, the check ball would click in. All working fine.



Good idea. Was there vacuum on the hose going to the vapor canister?
Yes, every time, strong.
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post #12 of 15 Old 07-23-2019, 10:31 AM Thread Starter
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Quote:
Originally Posted by Matt1981CJ7 View Post
I’m curious what “check valve” you are talking about.

Edit: After re-reading the original post, I see you are calling the PCV valve a check valve.

As I’ve mentioned several times before, the PCV system on your engine is designed to reverse air flow when the blowby exceeds the capacity of the PCV valve. That’s why there is a filter element and small oil collection area inside the air cleaner assembly. If you have no vacuum at the rear PCV hose at idle, then it’s likely you have too much blowby for the PCV valve to handle. Time for a compression or leakdown test.

Matt
Yes indeed - the 'PCV' naming is generally for the entire system so I was trying to be specific as to the front valve only.


Reverse flow is fine but ZERO vacuum at the rear (everything nominal) is the problem Matt.

A little oil in the in-breather air filter / oil catch is fine but it was full and leaking into the breather.

If my rings were shot, there would be so many other problems - there should be some rear vacuum in any circumstance.
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post #13 of 15 Old 07-23-2019, 10:37 AM Thread Starter
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John, how do I reply to your reply - when I hit Quote, it only grabs this (below)?

Quote:
Originally Posted by John Strenk View Post
How did you do this? Plugged the vacuum hose directly into the valve cover bypassing the PCV valve? Were you measuring the vacuum on the rear vent at the back of the valve cover?



Did you check to see if there was vacuum on the end of the PCV valve ?



Good idea. Was there vacuum on the hose going to the vapor canister?
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post #14 of 15 Old 07-23-2019, 12:53 PM
Matt1981CJ7
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Quote:
Originally Posted by CJ7Guy1 View Post
Reverse flow is fine but ZERO vacuum at the rear (everything nominal) is the problem Matt.

A little oil in the in-breather air filter / oil catch is fine but it was full and leaking into the breather.

If my rings were shot, there would be so many other problems - there should be some rear vacuum in any circumstance.

Actually, there should be very little vacuum at the rear hose at idle, or at any non-loaded RPM. PCV valves work opposite of what most guys think. They flow the least when the vacuum is highest, and the most when vacuum is lowest. Vacuum is lowest when the engine is under heavy load. You aren't loading the engine when you are just revving it in the driveway.

I know Dales website (Adventures Under the Hood) says there should be 3-5" of vacuum at the rear hose within 15 seconds at idle, but I haven't been able to confirm that in any TSM I've read. The TSM recommends doing a flow rate test on the PCV valve using a specialized testing tool. Then they give the flow rate specifications for each type PCV valves used in different displacements.

Here's the deal, if your engine has excessive blowby, it serves to close the PCV valve even further than it usually is at idle. That could very easily explain why you aren't getting any vacuum at the rear hose.

Why are you so opposed to doing a compression or leak-down test? Wouldn't you rather rule out bad rings than continue chasing ghosts?

Matt
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post #15 of 15 Old 07-24-2019, 06:14 AM
John Strenk
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Quote:
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How did you do this?

Quote:
Originally Posted by CJ7Guy1 View Post
Plugged the vacuum hose directly into the valve cover bypassing the PCV valve?
Quote:
Originally Posted by John Strenk View Post
Were you measuring the vacuum on the rear vent at the back of the valve cover?
Quote:
Originally Posted by CJ7Guy1 View Post
I have an extra elbow. Reduced it down to 3/8" and popped it in.

I was eliminating anything stupid - valve cover internal oil splash guard not gunked over. Tested if vacuum was there at all - it was and it sucked a bunch of oil out of the little air filter inside the breather. Oh, I've got a clear hose hooked up on the back so I can see oil flowing pretty easy.
Quote:
Originally Posted by John Strenk View Post
Did you check to see if there was vacuum on the end of the PCV valve ?
Quote:
Originally Posted by CJ7Guy1 View Post
Yep, if I pulled it off (all hooked up correctly and engine running), I could feel vacuum at the bottom of the PCV check valve. If I put my gloved finger over it, the check ball would click in. All working fine.
Quote:
Originally Posted by John Strenk View Post
Good idea. Was there vacuum on the hose going to the vapor canister?
Quote:
Originally Posted by CJ7Guy1 View Post
Yes, every time, strong.

Quote:
Originally Posted by CJ7Guy1 View Post
MODs, this reply came out funky - I'll fix and delete this one in a second...

Yes, every time, strong.
Quote:
Originally Posted by CJ7Guy1 View Post
John, how do I reply to your reply - when I hit Quote, it only grabs this (below)?



It takes a bit adding quote brackets [ ] and [/ ] after each section.
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