Since last week, I noticed that my Jeep's oil pressure has dropped from 40 to the line below 40 on the stock gauge while at idle. While running, the needle is hitting the line above 40, then when I shift into neutral, brake, downshift, the needle dives to below 40.

My lights (interior and exterior) also dim when I shift into neutral, downshift or brake.

I have a clifford re-built '91 4.0L with RV cam and Jacob's Ignition system. I changed the oil after I noticed the problem, but that did nothing. I remember installing a new oil pressure sending unit when I swapped the engine in about 2 years ago. The engine is a reman and has about 60K on it.

Any tests I can do to find out what is going on? What can I do to fix this?

Is this an indication of my engine going? I have a big trip planned on the 12th and need to know if I can take the Jeep; it's an 8 hour drive to the Outer Banks!

Thanks for your help http://www.stopstart.btinternet.co.uk/sm/notworthy.gif

I would run a mechanical gauge and see what the pressure actually is. Verify that you engine has good OP before looking into electrical issues. Sounds like a bad ground somewhere in the dash.

You need roughly 10psi of OP for every 1000 rpm. So if you are at a light idling at 1000rpm then MINIMUM OP should be 10psi. That is too low for me but it is acceptable. Obviously you can do the math for 2K rpm and up. :D

mine does the same thing, but the oil Pressure gauge on mine drops to zer, then back to about 20 when idled. if my pressure went to zero in reality, i would know it.... try the mechanical guagetho and tell us your findings...

isn't that what the oil pressure is supposed to do? I know mine when its cold the pressure will be up around 60psi and after it warms up will stay at 60 while driveing and drop to about 30 at idle. you gotta remember the engine drives the oil pump and the faster it goes the more oil it pumps and vise versa. Oh yeah, thats with a mechanical gauge

I know the oil pressure drops when you decelerate, but I was particularily concerned #1 because of the drastic drop in iol and volts, but #2 it used to idle at 40 but now idles at the line below 40.

Sounds like I do need to mechanically check the oil pressure.

What is causing the lights to dim and brighten when downshifting/braking/or neutral? Alternator not keeping up? I put a red top Optima in about a year ago and I replaced the alternator when I did my engine swap 2 years ago. Maybe a ground problem?

i BELIVE that it all depends on what kind of oil u put in and how much!!!
here is why: when i bought my jeep 00 TJ my oil pressure was 30-35 idle,
40-50 highway, it was winter time),summer came i switched to syntetic oil from regular and now 35-40 idle, when on highway its 55-60 better said close to 60