Two very odd issues w/ 96 2.5L 2wd cherokee

Okay fellas, lets see if you guys can lend me an idea or two here. First issue just popped up yesterday while I was driving around. The jeep just shut off. I noticed that when I got out of the vehicle that the fuel pump was no longer running even though the key was in the run position. I immediately checked spark and there was a plenty. So I figured maybe the fuel pump relay took a dive. I swapped out the fuel pump relay with the AC clutch relay and still nothing. The vehicle turns fine and has fuel. I pull out my handy dandy test light and see that the power and ground for the fuel pump is still in the relay slots so I throw in a jumper wire just to see if the pump kicks on. Sure enough it does, so I put the key back in the ignition and start the jeep up and it runs just as smooth as ever and I get it back home before yanking the jumper back out and start trouble shooting. I'm stumped so far....all grounds test good, and there is no apparent wires that are worn. Another odd thing that has plauged the jeep since my ownership is that the fuel level gauge always reads on E, the coolant hand always stays on the coldest reading (although when I ground out the wire running to the sensor it jumps all the way to hot just like it's supposed to), and the oil pressure gauge pegs all the way out on start and will return to the lowest setting when the ignition is cut off. Could these two issues be related back to the ECU? Am I going to have to dig hard to find a microscopic break in a wire? Could it be the ignition switch? (doubtful of the switch considering that everythings else works perfectly BUT the mentioned gauges and the fuel pump relay) Any help is greatly appreciated!

C'mon guys...Tore into the wiring harness and found that all the ECU engine grounds and power wires tested fine. Any ideas?

I have lots of ideas, but my wife won't let me try them!

Could the fuel pump issue be related to your ASD relay?

I think the oil pressure is a bad sender, that is how mine acted until I replaced it.

The water temp sender is a single pole sender, and if there is too much thread sealer on it then it won't make a good ground to the head.

joe_peters said:

I have lots of ideas, but my wife won't let me try them!

Could the fuel pump issue be related to your ASD relay?

I think the oil pressure is a bad sender, that is how mine acted until I replaced it.

The water temp sender is a single pole sender, and if there is too much thread sealer on it then it won't make a good ground to the head.

Click to expand...

Doubtful on the ASD relay. I swapped that one out for a known good relay as well and still had the same problem. I'll check the water temp sensor connection just to make sure there is no resistance between the sensor body and the engine block.....the engines connection to ground is excellent.

I don't remember if the newer models have the fuel pump ballast resistor, but that could explain your problems.

I don't believe there is one on the returnless system vehicles. Just from what I've gathered the system puts out full pressure once the jumper is in the fuse box and I think the ballast resistor just deals with the constant +12 of the pump and would affect rail pressure....aka I'm still lost as to these issues. I really don't want to have to replace the ECU, but it's looking more and more like it. Any more ideas fellas?

I ordered some new sending units for the oil pressure and the coolant temp gauges as I noticed that the one I have for the coolant has a black connector and is strictly for a "dash light". The oil pressure sender is just jacked and old so the new guy should fix it right up. I gave my fuel tank a motivated kick or three and the fuel level gauge now works to a little above half a tank when it's full up. I suppose I may need to yank that bad boy out and give it a good cleaning and ohm it out to see if it's still within spec. I'll get those sending units installed and hopefully post up a positive update with the gauge functionality. Still stumped as to the weak ground signal for the fuel pump relay. It's problematic, but I think I may just go ahead and pull the trigger on a new ECU from the dealership as my mother-in-law has been working there for about 20 years and I get a MEAN discount. ($310 for a reman without a core.) gimme some more ideas if you guys have any. Also, does anyone know if the center consoles between the four doors and the two doors are the same? I'm wanting a better condition replacement since this is my daily and I like to keep my toys fairly nice.

Not sure on the console. I think teamcherokee.com was recently still listing some new consoles as available, and I have seen a number of them listed on eBay.