PCV valve or sensor - JeepForum.com
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post #1 of 17 Old 02-25-2020, 06:53 AM Thread Starter
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PCV valve or sensor

First post. New to me 86 CJ7 258 is getting blow by from oil breather. The PCV rattles and slips up and down as designed, but oil is ending up on the valve cover. I just installed an aluminum valve cover as the old plastic one was just running out. My question is, what is this sensor/valve in-line from Carb to PCV? Is it necessary? I suspect it’s some kind of sensor or emissions thing, but I just replaced the line, unplugged it and pulled it out. Haven’t driven yet to see if it fixed it, but am getting 18.5lbs of vacuum at idle.

Final question, I am also getting a very small amount of oil dripping from the transmission bell housing area, which could be the rear main seal. I mean about 5 drops after each ride on the concrete. Could the crank pressure that obviously exists based on blow by on valve cover also be causing a rear main seal leak? It’s not running out, so it makes me believe it’s possible it’s under pressure and that may be another weak link susceptible to leaking.

Thanks in advance!

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post #2 of 17 Old 02-25-2020, 07:29 AM
Matt1981CJ7
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The item in your hand is called a PCV solenoid. AMC did a recall on that part, which eliminated it all together. You don't need it.

Is the fresh air intake side of your PCV system hooked up correctly? Here's an easy test from Adventures Under there Hood

"To test the system, pull the breather tube from the rear of the air cleaner and plug a vacuum gauge into it. With the engine running, there should be 3 to 5 inches of vacuum within 15 seconds."

If the system tests out, it may be time for a compression or leak down test. How many miles are on this engine?

Rear main seal leaks are just a fact of life with AMC engines. It's not likely that blow-by is causing the RMS to leak.

Good luck,

Matt


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post #3 of 17 Old 02-25-2020, 07:32 AM
John Strenk
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Factory actually eliminated that and just uses a regular PCV valve.

PO must of missed the recall...

It's a solenoid valve, not a sensor of any kind. It could block the PCV valve from working if it got stuck closed.
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post #4 of 17 Old 02-25-2020, 07:33 AM
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missed it by that much....
That's what I get for spending time looking for diagrams...


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post #5 of 17 Old 02-25-2020, 07:44 AM
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If you recently changed the valve cover and the leak started soon after you need to retorque it. A leaking valve cover is often confused with a rear main leak. Always look at the last thing you did before assuming the worst. Leaks caused by excessive pressure will always seek the weakest point. Also clean the rear of the engine so residual oil won't continue to drip.

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post #6 of 17 Old 02-25-2020, 07:45 AM
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post #7 of 17 Old 02-25-2020, 08:49 AM Thread Starter
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Quote:
Originally Posted by Matt1981CJ7 View Post
The item in your hand is called a PCV solenoid. AMC did a recall on that part, which eliminated it all together. You don't need it.

Is the fresh air intake side of your PCV system hooked up correctly? Here's an easy test from

"To test the system, pull the breather tube from the rear of the air cleaner and plug a vacuum gauge into it. With the engine running, there should be 3 to 5 inches of vacuum within 15 seconds."

If the system tests out, it may be time for a compression or leak down test. How many miles are on this engine?

Rear main seal leaks are just a fact of life with AMC engines. It's not likely that blow-by is causing the RMS to leak.

Good luck,

Matt
Good info here! Thanks for the clarification on PCV Solenoid, it's removed. I guess I'm not clear on the fresh air intake side question. The valve cover breather filter is just a Mr. Gasket Push-in type filter, and it isn't clogged, and seems to flow in and out unrestricted (Though the filter still has oil on it from the previous blow by. I completed the Vacuum test on the breather port, and got no vacuum at idle or WOT. The engine is running really good, and though I have only had it a month or so, was told by PO that he had the top end rebuilt a couple of years back. The overall engine has about 106K miles, but the rebuilt TE only has about 10K. I don't have a compression test kit, but am sure I can rent one and test that though at this point, It's not my main concern.

Regarding the RMS being a fact of life, "I reject your reality, and substitute my own" . I cannot stand a leaky vehicle, and will figure it out somehow. I was hoping pressure build up in the Crank might find its way to RMS, but maybe not.

When I originally purchased it, it was leaking everywhere, rear end, front end, valve cover, etc. I am now down to 5-6 drops coming from the transmission bell housing area, and am working that next.

Thanks for the help!
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post #8 of 17 Old 02-25-2020, 08:54 AM Thread Starter
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Quote:
Originally Posted by bob4703 View Post
If you recently changed the valve cover and the leak started soon after you need to retorque it. A leaking valve cover is often confused with a rear main leak. Always look at the last thing you did before assuming the worst. Leaks caused by excessive pressure will always seek the weakest point. Also clean the rear of the engine so residual oil won't continue to drip.
Thanks for the info Bob, and while I'm new to CJ's I am not new to wrenching, and agree with your sentiment on checking the last thing first. I didn't go down the road of history with the leaks Iv'e already encountered and resolved, but the valve cover was the first major leak I resolved. The engine previously had the cheap plastic valve cover that was leaking because it couldn't be tightened, and it was leaking bad! At that point, I thought that was my only engine leak, and it was as you said running down the rear of the engine and onto the inspection plate. I have replaced and cleaned the engine, and now only see the oil leaking from or around the weep hole on the inspection plate, so I'm afraid it is the RMS.
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post #9 of 17 Old 02-25-2020, 09:24 AM
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Be sure to buy new grommets for your valve cover PCV connections to tighten up the fit to eliminate the leaking oil as well. Also make sure your oil fill plug is super tight and not contributing. All those rubber parts shrink over time. I had the same issue regarding oil on the valve cover and quite a bit of dripping off the bell housing under the Jeep when parked. Turns out my oil fill plug was loose and running oil all over the valve cover and that's what was dripping. Oil was running down the back of the motor because of the downward angle, and air movement.

Once I tightened all that up my oil drips almost completely disappeared, and my valve cover is nice and dry.

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post #10 of 17 Old 02-25-2020, 09:26 AM
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If you are not getting vacuum at the breather port, with the solenoid removed, then your PCV valve is probably sticking.

I'm not a fan of the stand alone push-in type PCV filters because the PCV system is designed to flow air in BOTH directions, depending on driving conditions. That fact inevitably leads to oil fouling of the push-in type filters, and will ultimately mist your whole engine with oil. That's why the factory routed the fresh air intake thru the air cleaner assembly, so those oily vapors are routed back thru the intake and burnt.

Matt


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post #11 of 17 Old 02-25-2020, 09:45 AM Thread Starter
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Quote:
Originally Posted by Matt1981CJ7 View Post
If you are not getting vacuum at the breather port, with the solenoid removed, then your PCV valve is probably sticking.

I'm not a fan of the stand alone push-in type PCV filters because the PCV system is designed to flow air in BOTH directions, depending on driving conditions. That fact inevitably leads to oil fouling of the push-in type filters, and will ultimately mist your whole engine with oil. That's why the factory routed the fresh air intake thru the air cleaner assembly, so those oily vapors are routed back thru the intake and burnt.

Matt
I'm not opposed to changing it, just was there when I bought. However, the OEM air filter housing is no longer in place and the Carb had been replaced for Motorcraft 2150, so where do I get the fresh air intake from?
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post #12 of 17 Old 02-25-2020, 09:56 AM Thread Starter
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Quote:
Originally Posted by Matt1981CJ7 View Post
If you are not getting vacuum at the breather port, with the solenoid removed, then your PCV valve is probably sticking.

I'm not a fan of the stand alone push-in type PCV filters because the PCV system is designed to flow air in BOTH directions, depending on driving conditions. That fact inevitably leads to oil fouling of the push-in type filters, and will ultimately mist your whole engine with oil. That's why the factory routed the fresh air intake thru the air cleaner assembly, so those oily vapors are routed back thru the intake and burnt.

Matt
I was hoping the PCV was bad like you suggested, but as you can tell in the below, I’m getting good vacuum through it. Weird that there is no vacuum at the breather hole. The new valve cover came with all new grommets, so old grommets aren’t the issue.
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post #13 of 17 Old 02-25-2020, 12:58 PM
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Your aftermarket air cleaner may, or my not, have a place to connect the PCV intake on the bottom side of the air cleaner assembly.

Did you test the PCV valve at idle? If so, you should NOT be getting "good vacuum" thru it. You should be getting minimal vacuum thru it at idle. The PCV valve opens up more under conditions of low manifold vacuum. It works opposite of what some guys think. High vacuum should virtually close the PCV valve.

Matt


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post #14 of 17 Old 02-25-2020, 10:46 PM Thread Starter
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Quote:
Originally Posted by Matt1981CJ7 View Post
Your aftermarket air cleaner may, or my not, have a place to connect the PCV intake on the bottom side of the air cleaner assembly.

Did you test the PCV valve at idle? If so, you should NOT be getting "good vacuum" thru it. You should be getting minimal vacuum thru it at idle. The PCV valve opens up more under conditions of low manifold vacuum. It works opposite of what some guys think. High vacuum should virtually close the PCV valve.

Matt
Yes. I tested the PCV at idle, and was getting 18-20lbs of vacuum. That sounds right to me, but maybe I’m wrong. More throttle should equal less vacuum, right? Are you saying I should have less vacuum at idle and the PCV is bad?
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post #15 of 17 Old 02-26-2020, 01:51 AM
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Oh boy, does that bring back memories.........
Here is the rub.....
That solenoid helped to get the idle down.....without it, you tend to draw too much air if everything else is not perfect.

I spent a lot of time fixing leaks....like the diaphragm on the evap canister.

The 258 is a great little engine.....even better when you put fuel injection on it.


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