Replaced Valve Cover Gasket now engine runs very rough.

[AnotherOldJeepGuy]

I just replaced my valve cover gasket today.  I had a lot of oil leaking, but the engine ran fine.  Now I need HELP!

 

I cleaned up the area where the gasket goes so it looked pretty clean both on the engine and on the old valve cover.  Now the truck runs very rough, sounds like it has a bad exhaust, and quickly fills my garage with what I believe is probably carbon monoxide!  There was a hose that I broke, I believe it is a vacuum hose of some kind.  It split as I tried to remove it it out of the valve cover.  It split into only two pieces, that part outside the cover and the part just inside the cover.  I was able to pull out the piece that stayed in the cover with needle-nose pliers.  When it came out it also cracked the plastic pipe at the other end.  I temporarily taped it back together, and set the other in in the hole, but it is not held in tight. 

 

The only other thing I see is a piece of plastic pipe that seems to go nowhere at one end, that is, I can't see anyplace to connect it.  The other end is up by the firewall.  My guess is this pipe has been open for a long time, but I can't prove it.

 

I can't see anything else that looks touched, and the two things I mentioned above don't seem to be large enough trouble to totally mess up the engine running, but, they are the only things I can see and the truck is running very rough now.

 

The vacuum hose assembly is available so I'll replace it, but is that hose enough to cause what I have described?  If not, any other ideas what has happened?  I can't imagine how a valve cover gasket replacement messed up the engine, but something did!

 

[Ωhm]

You ain't going anywhere with that MAP sensor hose disconnected. Should connect up at the base of TB. Look for the other missing end. What's that green thing laying on the heat shield?

[AnotherOldJeepGuy]

19 minutes ago, Ωhm said:

You ain't going anywhere with that MAP sensor hose disconnected. Should connect up at the base of TB. Look for the other missing end. What's that green thing laying on the heat shield?

Looks like that green thing is part of a latch.  I have hunted but can't see anything to attach that plastic hose to, perhaps someone can post a picture where it goes when it is connected.

[Ωhm]

This shows the general area where the vacuum hose goes.

 

 

 

 

That broken tab (green) can/will cause problem later on. Take note.

[AnotherOldJeepGuy]

Found the connection!  Running normal now, thanks.  I guess I'll tie wrap the connection with the broken tab so it won't wiggle loose.

[schardein]

I just read through this post. I have a couple suggestions.

It sounds like you intend to replace the fresh air hose, that is the large hose that connects to the front opening in the valve cover.  It is part of the Crankcase Ventilation (CCV) system.  That is where fresh air is drawn into the engine.  

I would also remove and carefully inspect the thinner hose that attaches to the rear hole in the valve cover.  That is the vacuum side.  It uses a "metered orifice".  That metered orifice looks to be white or off-white and plugs into the rubber grommet in the valve cover.  Carefully wiggle that out, and disconnect the other end at the intake manifold.  Then make sure the line is clear.  Blowing through it is a good test.  It's common for the orifice to be clogged with carbon.  If it is, your CCV system will not work as intended.  If it is clogged, soak the orifice in a solvent (brake clean, carb cleaner, PB Blaster) and use something like a paper clip to carefully break up the carbon and clear the orifice.

 

The connector for the MAP sensor (green plastic) can be replaced.  The connector is relatively inexpensive.  https://www.rockauto.com/en/catalog/jeep,1989,cherokee,4.0l+242cid+l6,1179929,electrical-connector,manifold+pressure+(map)+sensor+connector,2597

 

Rather than cut and splice the factory wires, I would de-pin the old connector.  Working one wire at a time, de-pin one wire from the old connector, de-pin the corresponding wire on the new connector, and place the old free wire in its new home in the new connector.  Work through the other two.  You'll need a special tool to de-pin the weatherpack connector.  There are many choices, here is one:  https://www.amazon.com/Weather-Pack-Terminal-Extractor-Tool/dp/B0040CRUNO/ref=sr_1_12_sspa?crid=3W3YW97MYOIWC&dib=eyJ2IjoiMSJ9.-guaGmIeFsBVVD4lcyjMg9is5378Y3SzA7C2yoU-Cr7YnIGdbKl8Ds_4rdCzmh86862Jv4GhEgRSdxCXpJJD63Q0KG_4fcpSdkJpWe6fvLg.AeY6QI9by4LhAzS2SZPvta_7buxqbLPpYJ4z8IuMlvw&dib_tag=se&keywords=12014012&qid=1731885133&sprefix=12014012%2Caps%2C283&sr=8-12-spons&sp_csd=d2lkZ2V0TmFtZT1zcF9idGY&psc=1

[AnotherOldJeepGuy]

Thanks for the suggestions Greg.  Yes I was planning to replace the larger hose since the grommet came apart at the valve cover and now it's just setting there.  But I didn't know about the common carbon build-up in the smaller one, I'll see if I can carefully remove it and clean it out.  Or I might just replace it along with the other since it's only $15 at Napa.  I am a little afraid to try and replace the grommet there at this point since it may fall apart like the front one when I try to pull it out, and having just put on the new valve cover I'd hate to have to do it over again if half of the grommet fell inside.  Here's where hindsight comes in, should have replaced that when the cover was already off!  I'm pretty handy with my soldering iron so I might skip the de-pin plan, but I'll give it some thought!

 

There's a lot of other lines I'd like to replace, the plastic ones are so brittle that they tend to break if you even  look strongly at them.  But several of them seem to disappear into the obis, or through the firewall, and I don't know what it would take to fish new ones in, and then I don't even know if these molded lines are even available, so I am holding off on that project.

 

GM

[schardein]

I meant to mention something about that larger hose.  That is where fresh air enters the engine.  It is filtered (clean) air from the air cleaner box.  Rather than replace the hose, you could put a rubber grommet in the hole in the valve cover and use a regular filtered breather, similar to the one here:

https://www.amazon.com/Moroso-68813-Valve-Cover-Breather/dp/B000COO04Q/ref=sr_1_20?dib=eyJ2IjoiMSJ9.-KT67FQuWZXFt3jiLhwuU1EMQJ5i9DVNYDj8av5dds5gcv66t7cIxgTBtaAj1jo3SGVSTOzLXyeNdUNhay0AxcBJ7C1PokbgsltLl6k7ih2zwvIJdBOvYiL9Srzm5hWTtAR58bWZedQmvtvqvQUjVMsl3vblBFlEAA1LimKkmCcS7KmTdGKXMyS1OGdTIdoQCcdTDSbgIdGb0e026KRUaiSaOEayX9ppcxwOzNu2-mw.yedWFLeHlP2ZN4Txy9R4p39xrdwYQcT93rxnCOm0LP8&dib_tag=se&keywords=VALVE+COVER+BREATHER&qid=1731937903&sr=8-20

 

This is just one example, there are a bunch of different designs that do the same thing.  You would just need to match the grommet to the valve cover and the breather to the grommet to make sure it all worked together.  And make sure it fits under the hood.  And cap off the nipple on the air cleaner box.

Personally, I would prefer to keep the factory setup if the parts are still available.  

[AnotherOldJeepGuy]

12 hours ago, schardein said:

I meant to mention something about that larger hose.  That is where fresh air enters the engine.  It is filtered (clean) air from the air cleaner box.  Rather than replace the hose, you could put a rubber grommet in the hole in the valve cover and use a regular filtered breather, similar to the one here:

https://www.amazon.com/Moroso-68813-Valve-Cover-Breather/dp/B000COO04Q/ref=sr_1_20?dib=eyJ2IjoiMSJ9.-KT67FQuWZXFt3jiLhwuU1EMQJ5i9DVNYDj8av5dds5gcv66t7cIxgTBtaAj1jo3SGVSTOzLXyeNdUNhay0AxcBJ7C1PokbgsltLl6k7ih2zwvIJdBOvYiL9Srzm5hWTtAR58bWZedQmvtvqvQUjVMsl3vblBFlEAA1LimKkmCcS7KmTdGKXMyS1OGdTIdoQCcdTDSbgIdGb0e026KRUaiSaOEayX9ppcxwOzNu2-mw.yedWFLeHlP2ZN4Txy9R4p39xrdwYQcT93rxnCOm0LP8&dib_tag=se&keywords=VALVE+COVER+BREATHER&qid=1731937903&sr=8-20

 

This is just one example, there are a bunch of different designs that do the same thing.  You would just need to match the grommet to the valve cover and the breather to the grommet to make sure it all worked together.  And make sure it fits under the hood.  And cap off the nipple on the air cleaner box.

Personally, I would prefer to keep the factory setup if the parts are still available.  

Good input.  If the OEM wasn't available good to know there is a convenient backup plan.  Surprisingly, the full assembly appears to be available in 2 piece, where I would only need the end half.. https://www.napaonline.com/en/search?text=vacuum harness&referer=v2, and it is actually cheaper that the example aftermarket you noted, go figure!

[AZJeff]

Virtually any of the hard plastic vacuum/vent lines on a 30 yr old MJ are going to be super brittle, and they will crack if you even look at them wrong.😁

 

if you want to fix this once and for all, I recommend replacing all the hard lines with appropriate sized rubber or silicone tubing.

[AnotherOldJeepGuy]

Well it seems the more I "fix" the more problems I get.  At the beginning of this thread the problem was the disconnected hose for the MAP sensor that caused the truck to run VERY rough.  Once this was reconnected it ran normal.  Although the original task of replacing the valve cover gasket damaged hose connecting at the front of the valve cover I ordered the new assembly from Napa I linked earlier.  This assembly came with all new hoses to the left (the "New" side in picture 1).  1 of these was the new hose to the valve cover.  2 of these were short loop backs, and the 4th was from the assembly routed below the large corrugated hose from the air cleaner box to something just to the other side under the hose (pic 2).  The kit also included an additional new hose which I installed also.  For access I removed the large hose from the air cleaner,  and also disconnected one electrical connection. 

 

Now with all of this in place, the truck once again runs rough.  Not nearly as rough as the original failure caused by the MAP sensor being disconnected, but still rough and it ran smoothly before this (*once, before this new assembly was put in but after the MAP sensor issue was resolved, when I stopped somewhere the idle was higher than usual but returned to normal when I restarted).  The new connections match the old ones, the MAP sensor is still connected (I checked again), so what happened?

 

The only other thing I did was attempt to remove the small hose to the back of the valve cover to try to clean it, but it was not willing to come loose at the engine side so the original is still there same as it was before.

 

[AnotherOldJeepGuy]

Oh I also put in a new cap where you add oil to replace the old one that was very loose because the gasket was worn out.