1989 Cherokee 134000 miles 4.0 liter Lorado 4wd automatic. I have owned this XJ for 28 years. Stock. No start about 3 months ago. After testing the fuel pump and driving it with power, I found the relay was bad by jumping the relay connector with a paperclip. I could hear the fuel pump come on and could hear the fuel rail pressure up by the hum it made. I replaced the relay and it started fine for 2 months. Same thing, a no start one morning. Checked the relay again and swapped it out. Still did not start. I jumped the relay at the connector and I could hear the fuel pump and the fuel rail hum. A thread stated that I should check the ground behind the dipstick tube. I did , cleaned the everything including the negative cable and both grounds and the post on the engine. It started fine, for a month. This has happened again. No start in the morning. Ran fine the evening before. No fuel pump unless I jump the relay connector. Any ideas where I should start now before I start checking bad wires and pcm?

 

It may be a bit different going back to an 89, but on the control side of the fuel pump relay I believe the + is usually provided (ultimately) by the ignition switch, and the ground is provided by the PCM. Which kinda equates to (ignition on/start (TRUE) + PCM alive (TRUE) = fuel pump relay control closed (TRUE)).


Makes me wonder if the ignition switch circuity that runs to the fuel pump relay is sometimes not closing properly causing the fuel pump relay to remain open.


Most techs would probably start at the fuel pump relay and try to determine definitively which item is dropping out (control side voltage, control side ground, or load side voltage). Using something like a relay buddy (Lisle tools).

 

Have you bypassed ballast on driver fender.

 

Have you seen this ....http://www.lunghd.com/Downloads_and_...ion_manual.pdf

 

Have you tested the relay itself? Or are you just jumpering across it to get voltage to the pump?

 

The hose in the tank could be bad, or the pump itself. test the fuel pressure.