PROBLEM #1 - Im having some issues with the gas guage in my 88 YJ 4.2L. Its not working is the problem....lol When the truck is off the guage reads nothing, when turned on it goes over full. Now I know this is a wiring issue and a bad ground. Now my issue is im new to jeeps (my wifes) and im not sure as to where the harness/fuel pump is grounded if anyone can clarify this for me before I just drop the tank to check it out.

PROBLEM #2 - Just curious as to how the vaccume in the 4x4 works. The light stays on as if the 4x4 is engaged even in 2wd but the fork on the axel is not engaged. Up over 1500 the light stays off because the vaccume level is high. The truck has plenty of vaccume and engages on occasion but is tempermental. If I shift it into 4x4 (high or low) and pull the green vaccume line off the axel it engages right away or rev it over 1500rpm it will engage every time. Is there some sort of pressure type switch that these vaccume lines go to and could that be whats malfuntioning? Thank you

 

Check out this site here it's a breakdown of the complete fuel system

 

also,you can check the tabs on the rear of the instrument cluster,make sure there's good contact.
but,to me,it sounds like a bad ground or wiring problem.After checking the cluster,I would drop the tank & inspect.
By bad ground I mean either the harness/connector has oxidized(green substance),or it might be grounded on the tank itself-depending on the model. looks like you'll be dropping the tank.

 

Hey im haveing the same issue, My fuel gauge is reading REALLY full all the time on my 1990 YJ I have also noticed that the batt gauge and oil presure arent working either. Im on the lookout for a bad ground and trying that damb flex circuit board cleaned up to work.

Does anyone know how to get it off the inst cluster? and if and were i can get a new one. The one i have has been jumpered, so that the clock will work ( a trace lifted)

Thanks

 

To answer your question 2. Some of the yj's and xj's have a vacuum switch that indicates whether you are in 4wd or not, should be on the passenger side inner fender if memory serves correctly. The vacuum lines sometimes get clogged and sometimes the switch gets clogged with crap.