1992 4.0 HO issues

Ok, so my girlfriend said her jeep was acting wierd and making noise. I asked her what was going on, and here's the story so far: Well its got 200,00+ on it and it seems to be ok until the other day when she notice her oil pressure dropping at idle. Well, come to find out her dad had put a cleaning solution in with the oil to help clean some carbon out of the block. I've heard thats supposed to make the oil a little less thick, is that true ? Could that have been the problem there ? anyway ....
Now the engine has a knock in what sounds like the top of the engine. I'm not experienced with jeeps very much, so I'm not sure what to do about it. I've heard these jeeps are notorious for knocking and running anyway, though. After changing the oil and putting in some Lucas oil addative there's no problem with oil pressure but the knock is still there. Also, there is a possibility the engine could have been over filled with oil (girl owns it remember) when I changed the oil, I changed the air filter too. It needed it, apparently one of the lines from the top of the valvecover going to the air filter box had filled with oil and spilled oil into the air filter box, covering most of the filter with oil. The body is in great shape, and this girl is pretty darn attached to this jeep. Should I rebuild the engine ? How long can I wait to rebuild the engine ? Am I overreacting ? I need input guys. Thanks in advance.

Tim

Lots of question here – lets give it a try.

First, if the “cleaning solution” was a standard engine flush, that would thin the oil out. The containers usually say not to run the engine above an idle and for only 10 or 15 minutes.

If it was something else, then I would have no idea unless you could provide a brand name and maybe look at the instructions on the bottle.

If the knock is from the top of the engine, then you are likely hearing noise from the valve train. That could be the lifters, camshaft, rockerarms, pushrods or even a worn tip on the valve stem. Being as it started after the oil was doctored, I would suspect a sticky lifter but who knows what you would find when you get in there.

You can confirm the noise source and identify the valve location by removing the valve cover and running the engine at an idle. If you have a mechanics stethescope great otherwise push down on the moving rocker arms one at a time and listen for a change in the sound. Or you could roll up a sheet of paper into a cone and listen with the large end at your ear to each rocker arm at the push rod or valve ends.

The oil in the air filter is likely the result of the hose to the PCV valve being restricted. Pressure builds in the crankcase and pushes the oil into what should be the in take for the PCV. Replace or clean the hose and the PCV filter and replace the PCV valve.

Unless the engine is running poorly, has high oil consumption or a proven low oil pressure problem, I would just look into the upper engine noise for now and keep an eye on the performance and oil pressure.

I think I’ve addressed all the concerns you raised.

Hope this has helped.

JD

Ok, I'm not terribley knowledgable about valvetrain and whatnot, but I want to learn. I have a mind to get a friend of mine to help me do a top end rebuild of this engine (4.0 I-6). How long can it wait before I find time for the rebuild (assuming the jeep gets driven almost every day) ? Could you point me to a website or place where I could learn about the valvetrain and possible know better how to identify the problem specifically and correct it. Her parents want her to junk it and buy another one, so I might get it at a good price :iceslolan and I've been wanting to get my hands dirty with a rebuild anyway. Thanks again guys.

Tim

Check eBay, you should be able to pick up the shop manual for that year which will have all the information you need.