Problem with Blow By - JeepForum.com
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post #1 of 39 Old 08-15-2017, 08:01 AM Thread Starter
CamoX413
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Problem with Blow By

Hey guys so one of the issues I'm having with my Jeep is blow-by. I know some of these Jeeps have been told to have blow by naturally but I never used to notice it on my Jeep. Lately if I lift my factory air box lid I can see oil about to drip onto my air filter from the hose leading to the valve cover. I'm also getting oily residue around each of the plastic elbows on my valve cover.

Can someone tell me why this might be happening and if there's a way to fix it? Does it mean my motor is on the way out?

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post #2 of 39 Old 08-15-2017, 08:14 AM
jeepjeepster
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Sounds normal. Ive always had some oily residue in my air filter box.

Have you checked to see if the PVC orifice is clear?

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post #3 of 39 Old 08-15-2017, 08:31 AM
BorderWalker
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Replace the CCV elbows and grommets. Not a hard thing to do. A PITA if they're old and brittle, but not hard.

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post #4 of 39 Old 08-15-2017, 08:45 AM
HighLonesome
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See if the blowby is excessive, meaning the PCV system can't handle it.

Plug all the holes on the valve cover except the oil fill hole. With the motor running you will feel air coming out the hole. You can use a piece of paper over the hole to view it. Now reconnect the CCV and there should be no air coming out the oil fill hole.

The motor could go a long long time with excessive blowby, but somewhere the compression is going to be down. You could do a catch can.
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post #5 of 39 Old 08-15-2017, 09:20 AM Thread Starter
CamoX413
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Quote:
Originally Posted by BorderWalker View Post
Replace the CCV elbows and grommets. Not a hard thing to do. A PITA if they're old and brittle, but not hard.
I replaced grommets and elbows a year ago. Old ones broke trying to get them out when I painted my valve cover.
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post #6 of 39 Old 08-15-2017, 09:22 AM Thread Starter
CamoX413
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Originally Posted by HighLonesome View Post
See if the blowby is excessive, meaning the PCV system can't handle it.

Plug all the holes on the valve cover except the oil fill hole. With the motor running you will feel air coming out the hole. You can use a piece of paper over the hole to view it. Now reconnect the CCV and there should be no air coming out the oil fill hole.

The motor could go a long long time with excessive blowby, but somewhere the compression is going to be down. You could do a catch can.
I'll try this today but really what does this even tell me? If I have blow by or not?
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post #7 of 39 Old 08-15-2017, 10:16 AM
zjosh93
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All engines have some blow by. Even brand new rings in a brand new bore aren't a perfect seal. (Total Seal gapless rings get close but we are just talking stock stuff at the moment) The CCV is there to suck up the little bit of normal blow by and burn it. So what HighLonesome's test tells you is if there is enough blow by that it overwhelms the CCV. If it there is then it's pushing crankcase gasses and oil through the breather hose and into the air filter lid. Which the fact that you can see oil in there already strongly suggested.

If you never let the engine sit for a long time without running, excessive blow by is a sign the rings are wearing out. A compression test will probably show your cylinders are a bit low. You'll be down a little on power. If it sat for a couple years or so the rings may be just stuck in the ring lands but in that case you'd have so much blow by you wouldn't be wondering about it.

You can drive a long long time with a lot of blow by. It's not great for the engine but it's not catastrophic. It will slowly get worse and eventually will start to cause running issues, but it's not going to blow up.

There isn't really anything you can do short of a fresh set of rings or a rebuild. You'd have to pull the head and mike the bores to see if you could get away with just rings. There are various goops and sludges available at your local parts store that claim to fix blow by but in my experience they are all snake oil.
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post #8 of 39 Old 08-15-2017, 11:27 AM Thread Starter
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Quote:
Originally Posted by zjosh93 View Post
All engines have some blow by. Even brand new rings in a brand new bore aren't a perfect seal. (Total Seal gapless rings get close but we are just talking stock stuff at the moment) The CCV is there to suck up the little bit of normal blow by and burn it. So what HighLonesome's test tells you is if there is enough blow by that it overwhelms the CCV. If it there is then it's pushing crankcase gasses and oil through the breather hose and into the air filter lid. Which the fact that you can see oil in there already strongly suggested.

If you never let the engine sit for a long time without running, excessive blow by is a sign the rings are wearing out. A compression test will probably show your cylinders are a bit low. You'll be down a little on power. If it sat for a couple years or so the rings may be just stuck in the ring lands but in that case you'd have so much blow by you wouldn't be wondering about it.

You can drive a long long time with a lot of blow by. It's not great for the engine but it's not catastrophic. It will slowly get worse and eventually will start to cause running issues, but it's not going to blow up.

There isn't really anything you can do short of a fresh set of rings or a rebuild. You'd have to pull the head and mike the bores to see if you could get away with just rings. There are various goops and sludges available at your local parts store that claim to fix blow by but in my experience they are all snake oil.
Is it a possibility that a hose is clogged up and just needs a cleaning or not likely?
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post #9 of 39 Old 08-15-2017, 12:32 PM
zjosh93
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Originally Posted by CamoX413 View Post
Is it a possibility that a hose is clogged up and just needs a cleaning or not likely?
Pretty unlikely. There are really only two hoses to concern you: the vacuum hose connecting the intake to the rear CCV fitting and the hose from the front breather to the air box. Pretty easy to check them both or cheap to replace if you just want to be sure. I'm guessing the front one is clear enough if oil is getting to the air box. If you want to check the rear all you have to do is pull it out with the engine running and see if there is vacuum at the hole in the fitting. A squirt of carb cleaner would help clean it out if there is some build up but that seems unlikely after just a year since you replaced them.

I did have some kind of blockage once on my front hose but I'm not sure what it was. I blew the hose out and cleared the blockage but never saw the culprit.

FWIW blow by gets worse with RPM so you can have just a little at idle and your CCV works fine and at higher RPM have enough to push into the air box.
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post #10 of 39 Old 08-15-2017, 12:44 PM Thread Starter
CamoX413
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I'll check the hoses just to be sure. I only replaced the elbows and the grommets not the hoses. I do have a bad exhaust leak and I'm suspicious of a bad camshaft position sensor so my Jeep struggles to go up hills sometimes therefore I do have to get on it kind of hard just to get up a hill on the highway

Sounds like a compression test wouldn't be a bad idea either. I've never done it but I just watched a video and it seems pretty simple. Pull the fuel pump relay, take out the plugs, and check compression at each cylinder one at a time and read psi
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post #11 of 39 Old 08-15-2017, 03:12 PM
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[QUOTE="CamoX413;38739489"]I'll check the hoses just to be sure. I only replaced the elbows and the grommets not the hoses. I do have a bad exhaust leak and I'm suspicious of a bad camshaft position sensor so my Jeep struggles to go up hills sometimes therefore I do have to get on it kind of hard just to get up a hill on the highway

Sounds like a compression test wouldn't be a bad idea either. I've never done it but I just watched a video and it seems f

If the camshaft position sensor goes out, it's a no start.
I'd put an oil catch can on the pcv/ccv lines.
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post #12 of 39 Old 08-15-2017, 04:47 PM Thread Starter
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Would a vacuum leak cause a problem with the crankshaft ventilation system?
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post #13 of 39 Old 08-15-2017, 06:21 PM
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A vacuum leak big enough to cause problems with the CCV would cause much bigger problems first.
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post #14 of 39 Old 08-15-2017, 06:30 PM
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With a vacuum leak you're going to have less vacuum pulling through the CCV and less air going into the breather elbow on the front connected to the air box. IIRC on your intake testing you have lower vacuum than many of us in the first place who don't live in "mile high".

I too want to do a compression test on my 96 4.0 sometime. It's my understanding the throttle plate should be pinned open when doing this test. And if I'm going to do a compression test I'm going to do a 'wet test' too. That way it will help pinpoint if valves or piston rings are the main problem. The 'wet test' is on the 2nd page of the below link.

http://troubleshootmyvehicle.com/jee...-compression-1

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post #15 of 39 Old 08-15-2017, 06:35 PM Thread Starter
CamoX413
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Originally Posted by Uniblurb View Post
With a vacuum leak you're going to have less vacuum pulling through the CCV and less air going into the breather elbow on the front connected to the air box. IIRC on your intake testing you have lower vacuum than many of us in the first place who don't live in "mile high".

I too want to do a compression test on my 96 4.0 sometime. It's my understanding the throttle plate should be pinned open when doing this test. And if I'm going to do a compression test I'm going to do a 'wet test' too. That way it will help pinpoint if valves or piston rings are the main problem. The 'wet test' is on the 2nd page of the below link.

http://troubleshootmyvehicle.com/jee...-compression-1
Yep if the gauge I was using was correct then my vacuum is low. I'll probably get another gauge and test it again soon to be certain. I've actually moved since then to West Virginia.

I did watch a video about the compression test on a 4.0 and the guy said to ping the throttle wide open while cranking. I'll try it soon too.

I'm going to get a can of carb cleaner tomorrow and see if I can find any vacuum leaks.
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