I am new here and I am learning as I go. I have just bought a 1998 Cherokee Classic, from a not really reputable dealer, for what I feel was a deal. I can't seem to get the lift-gate open, and the oil pressure gauge seem to drop down very low when I let off the gas and come to a stop at a sign or a light. The pressure seems to jump right back to an even level when we are in motion. Is that normal?

I can't answer to the liftgate...perhaps others will know.

The oil pressure- any engine noises when the pressure drops low?
There are two ways to approach the problem:
1) Attach a mechanical gauge to the sender port and see what you really have for oil pressure, or
2) Clean the sender oil passage in the filter adapter(pipe cleaner, small wire tie) and just replace the sender.
They fail by reading low at idle, or by reading extremely high....and they do fail somewhat frequently.
If you still have low readings after that...get the mechanical gauge and check.

I had a similar problem with the liftgate on my '99. Sometimes if you pull on the handle several times it will open. If not, crawl in the back and pull the panel out as much as you can to get a hand in there and manually open the gate. Then, with the gate open, remove the panel and adjust the mechanism so it will open when you pull the handle. Sometimes they just get off, for some reason. Wish I had a picture from when I fixed mine. Good luck.

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1999 Cherokee Sport, 4.0L

Oil pressure fluctuation is absolutely normal. The important question here is what does the oil pressure gauge read?

Below is the oil pressure spec. for the 4.0 engine. If you are in this range, you are fine.

If you are not in this range, I agree with Radi that it would be a good idea to "verify" your true pressure by temporarily installing a mechanical oil pressure gauge where the oil pressure sending unit resides. Many parts stores will rent you this tool inexpensively.

*Not less than 13 psi at HOT idle

*Between 37-75 psi OVER 1600 rpms