Blow-by with good compression?
#1
Newbie
Thread Starter
Join Date: Feb 2011
Location: Kelso, WA
Posts: 4
Likes: 0
Received 0 Likes
on
0 Posts
Year: 1989
Model: Cherokee
Engine: 4.0 L, IL 6
Blow-by with good compression?
`89 Cherokee, 4.0 I6, Just did a compression check. Cylinders were between 138 and 150 psi. Which seems quite good to me! When I pull the PCV valve, or take off the Oil fill cap, I have puffing blow-by! Could this be bad valves? I`m not seeing any water in the oil, and am not losing any coolant. I`m new to these Jeeps, so I have lots to learn. Also, Oil pressure when cold runs around 45 psi, after warm up at an idle it drops to around 15psi. Is this enough oil pressure at an idle? I know it should be around 37psi at 1600 rpm, warm. Any and all help will be appreciated. . Thanks.
#2
CF Veteran
Join Date: Nov 2010
Location: In the middle of Minnesota!
Posts: 5,804
Received 99 Likes
on
88 Posts
Year: 1999
Model: Cherokee
Engine: 4.0
*Are you actually using oil (IE: having to add?)
*A little puffing with the oil filler cap off is not unusual
*Your compression is good (120-150 with no more than a 30 psi variation between cylinders)
*Oil pressure of 15 psi at HOT idle is fine. The spec is no less than 13 psi at HOT idle.
*Do you have any evidence of oil in the air filter box? That is very common with the 87-90. It can often be managed or eliminated by replacing the grommets and hoses that are installed on the valve cover.
Here is a pretty good thread that explains the CCV (crank case ventilation) system and its weak points. There is no PCV valve on the 4.0 Jeep.
http://www.cherokeetalk.com/forum/f8...d-blowby-5870/
*A little puffing with the oil filler cap off is not unusual
*Your compression is good (120-150 with no more than a 30 psi variation between cylinders)
*Oil pressure of 15 psi at HOT idle is fine. The spec is no less than 13 psi at HOT idle.
*Do you have any evidence of oil in the air filter box? That is very common with the 87-90. It can often be managed or eliminated by replacing the grommets and hoses that are installed on the valve cover.
Here is a pretty good thread that explains the CCV (crank case ventilation) system and its weak points. There is no PCV valve on the 4.0 Jeep.
http://www.cherokeetalk.com/forum/f8...d-blowby-5870/
#3
Newbie
Thread Starter
Join Date: Feb 2011
Location: Kelso, WA
Posts: 4
Likes: 0
Received 0 Likes
on
0 Posts
Year: 1989
Model: Cherokee
Engine: 4.0 L, IL 6
Hey TJ, Thanks for the info and the link to the CCV system! I`m headed out to check the smaller line that goes to the intake manifold. Make sure it`s not plugged. The other line that goes to the airbox, does have a pcv valve in it now, and it still will accumulate oil and have a small drip towards the airbox. Should this fitting just be an open 90deg. fitting going to the airbox, so that air can be sucked into the valve cover?
#5
Newbie
Thread Starter
Join Date: Feb 2011
Location: Kelso, WA
Posts: 4
Likes: 0
Received 0 Likes
on
0 Posts
Year: 1989
Model: Cherokee
Engine: 4.0 L, IL 6
Cleaned out the small line to the Intake manifold, it was plugged solid! Now I have NO visible blow-by, and also got rid of the PCV valve that someone had installed. Engine seems to be running better, with possibly fewer oil leaks, due to a reduction in inside block pressure. Thanks again for the info TJ ! Still need to change out the Rear Main Seal and pan gasket.
#6
CF Veteran
Join Date: Nov 2010
Location: In the middle of Minnesota!
Posts: 5,804
Received 99 Likes
on
88 Posts
Year: 1999
Model: Cherokee
Engine: 4.0
Cleaned out the small line to the Intake manifold, it was plugged solid! Now I have NO visible blow-by, and also got rid of the PCV valve that someone had installed. Engine seems to be running better, with possibly fewer oil leaks, due to a reduction in inside block pressure. Thanks again for the info TJ ! Still need to change out the Rear Main Seal and pan gasket.
Replacing all of the CCV hardware and a thorough cleaning of the valve cover is always a good idea here. It isn't that expensive ($45 or so for the grommets and hoses) and isn't a tough job to perform.
Now get on that rear main seal and pan gasket!
#7
Senior Member
Join Date: Jan 2011
Location: N. IL
Posts: 801
Likes: 0
Received 1 Like
on
1 Post
Year: 2000
Model: Cherokee
Engine: 4.0
Cleaned out the small line to the Intake manifold, it was plugged solid! Now I have NO visible blow-by, and also got rid of the PCV valve that someone had installed. Engine seems to be running better, with possibly fewer oil leaks, due to a reduction in inside block pressure. Thanks again for the info TJ ! Still need to change out the Rear Main Seal and pan gasket.
Search oil filter adaptor
Trending Topics
#8
Newbie
Thread Starter
Join Date: Feb 2011
Location: Kelso, WA
Posts: 4
Likes: 0
Received 0 Likes
on
0 Posts
Year: 1989
Model: Cherokee
Engine: 4.0 L, IL 6
I`ll check the oil filter adapter first. I bought the O ring already when I picked up the Rear Main Seal and Pan gasket. I was thinking that might be contributing to the oil leakage. Thanks for all the help TJ and DaddyCat.
#9
Senior Member
Join Date: Jan 2011
Location: N. IL
Posts: 801
Likes: 0
Received 1 Like
on
1 Post
Year: 2000
Model: Cherokee
Engine: 4.0
Good Luck and you're welcome
Thread
Thread Starter
Forum
Replies
Last Post
shelby5041
Stock XJ Cherokee Tech. All XJ Non-modified/stock questions go here
39
11-07-2015 01:22 AM
Ye Ol' Cherokee
Stock XJ Cherokee Tech. All XJ Non-modified/stock questions go here
8
10-09-2015 10:29 PM
Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)