I have a 90 wrangler with a 4.2 litre, .30 over, rv cam and no more than 5,000 miles on rebuild. Pcv system checks out with vacuum in rear port of valve cover, air inlet w/filter in front port of valve cover has suction to bring air in. Compression in cylinders shows 150 psi with quick compression in three cylinders. The other three cylinders compression 130 to 140 with slower build up . When adding oil to cylinders compression in low three cylinders come up to 150. I put a rubber hose on dipstick tube and ran that hose to plastic bottle, drove 10 miles at 45 -55 mph and when returned had 1/4 inch of oil in bottle. What are all the possibilities of problems and what is the cure Thanks in advance for all your thoughts
This may sound funny.. but I had a 8N tractor that did the same thing. It had a couple of cylinders that were a little low on compression after the rebuild. I added a product called "Restore" It took a very short time and all cylinders were the same and it stopped the blow buy. I guess it helped seat the rings that were on the low side.
Just my .02
1995, 4.0, 5 speed YJ, SOA, TC drop, 8.8 swap with 4.10 and LSD, e-grills bumper, 33" BF all terrains on 15" wheels.
has it been doing this since the rebuild or did it just start? are you getting a lot of blow by out the valve cover? the only things other than rings I can think of is the seal on the oil pump spraying oil or overfilling the crankcase.
I have heard of simular problems with high reving v8's and not running a windage shield, but the 4.2 doesn't rev high enough.
It has been getting worse since the rebuild not sure exactly when it started but I thought at first I had a bad oil pan, oil pan gasket, then maybe a rear seal. Replaced all that but of course nothing worked. I checked the oil level by observing and tracking how much oil came out compared to how much I put in. Dipstick seems to be right on to how much oil is in the crankcase. That is and interesting thought about the oil pump I will check that out.
How much vacuum do you think there should be at the pcv valve? Strong where as it's a little tough to remove your finger or just enough so when you plug it you can feel the suction but it's not real strong
it shouldn't be so strong that you can hardly remove your finger but it should be a pretty good draw..I have had the fitting on the intake get clogged..try taking the hose off the intake a run a wire in it to make sure its not trying to clog up..check the vacuum there compared to when you have the hose and pcv valve on and if there is a difference then replace them
I know you said you changed the PCV but perhaps it clogged or was a bad one to begin with try removing the PCV in the rear with the front and then check your pressure if the pressure drops in the front three you know it is the PCV not functioning correctly.
If I am reading your original post correctly.
Sounds like you are doing all the diagnostic things correctly rather than just change parts glad to see or read that.
Let us know
And just so you know I am totally guessing on this but I have seen PCV's be bad right out of the box.
I actually only have one pcv valve in the rear and a breather cap in the front. I am going to check vacuum with hose on pcv filter and then remove and check that. and get a new pcv filter Thanks I will let you know
being that the engine is fairly new I would hope the engine builder did the block correctly and that the rings got worn in ok. I am trying a new pcv filter and have already checked oil level to the amount I have put in and taken out I will let you know what happens
now that you told us that you did not do the rebuild I will feel better about this statement.
It is possible the rebuild was done poorly. The rings should have seated by now you stated 5000 miles. If you have the correct oil amount and the PCV is not plugged and you have the correct size hoses for your PCV and Breather connections they have to be at least 3/8 inside diameter then the rings are not seating because the cylinder walls are scored or deformed or the piston heads are deformed or bad or cracked.
Hate to be the one to say it was truly hoping someone else would share this potentially bad news but at some point someone had to say it.
bad rings could be the problem but the OP said the engine was bored .30 so he would have new pistons. like I posted before if it is blowby you should see it coming out of the valve cover. remove the pcv valve, put your fingers over the hole, if you feel any pressure you have blow by.
I did have blow by in this engine before it was rebuilt. and oil was coming up and into the air cleaner unit. I have checked for any pressure in the valve cover holes but don't feel anything . When the motor is running and I pull the front air inlet I do feel a little suction being created which I think is from the pcv in the rear being hooked up. When I pull the pcv out of the rear I don't feel anything.
yeah it sucks because I took the engine to a ( we have all heard this) reputable shop which has been in business for over 40 years friends and family have all had work done there in the past. There is a real long story to this rebuld . Short story, 1st motor rear bearing went bad in warm up, 2nd motor unspecified knock, this 3rd motor doing the dipstick thing and I have been accused of being every problem that happened even though I asked them how to do every step of firing new motor and break in speeds. So I am out 2,000.00 bucks and they will not honor any warranty because I have been the problem. I would take to court but who knows what lies they would say and how much that would cost. Would rather put the effort into the jeep. Sorry about the venting
So everyone check this out. I removed the breather from the front hole of valve cover, installed the stock air inlet hose that goes to the bottom of air cleaner , still had same problem but less oil out of dipstick tube. So I got back and installed a pcv valve in the hole where the breather was and spliced it with the other pcv valve in the rear . Took it for a ride and guess what, absolutely no oil out of the dipstick tube with the two pcv valves. and I do not seem to be burning any oil as far as sucking through the pcv valves. Only thing I detected a knock between 2800 and 3500 rpm so I guess that is a new problem now to diagnose Thanks for everyone's input here on the forum
Ok so I am little confused by the splice statement. The way I understand how it should work and if I am wrong someone feel free to correct me
But the breather should be attached to the air cleaner and the PCV Should run to the carb or into the intake manifold through a ported vacuum line it is like one large open loop almost wish I could draw on here to show it
So having said all that with Two PCV's you are not getting clean air to pass through and push the gases out through the intake and eventually out the exhaust.
I understand the oil is not coming out the dipstick which in my mind means you have pressure building up to cause that.
So I guess in my mind to finish the diagnostic completely it would make sense to connect up a breather tube to the air cleaner and another breather tube to the other hole and let it vent any where just to see if oil blows out.
Also what size are the lines? You mentioned replacing with stock lines?
When I got rid of the stock air cleaner and replaced with chrome air cleaner I did not want to run hose to bottom of air cleaner for looks I guess. I bought a chrome breather with filter inside to fit in hole in front valve cover hole. Before this it had a 3/8 hose that hooked to bottom of air cleaner with filament to filter air and the hose went right into the front hole in valve cover. As far as the splice I ran a 3/8 hose from the now new front pcv to the rear pcv that is 3/8 hose and both are run to ported vacuum which on mine combines with the vacuum for the brake booster. still no Ideas what might be causing so much pressure in crankcase but now maybe the new knock between 2800 and 3500 is the tell tale sign. Thanks