Fuel Pump Issues...

First off, let me say hello and thanks for the chance to blab to other people that might know better than me. It's always good to see other ideas on certian subjects. Anyway, Here is the situation. I have a 94 cherokee 4.0 with a temper. If you try to start it any time, it takes forever and a day to start. I began ripping out ideas and started testing junk for fun, but what I figured out is that the fuel pump relay doesn't even trun on until about 30 seconds after the key was turned to the run position. I switched the relay with another one from the box with the same numbers, but it made no difference. Can someone give me an idea? It's not helping my battery in the cold weather. Thanks, and let me know if you need anymore details. Mike

Welcome!
Many XJ owners have experienced the long crank issues with their jeeps. Several possibilities.
First, the fuel pump only runs for a second or two when you turn the key on, so you won't hear it running after that until the engine starts, or til you turn the key off and on again. Normal.
There is a check valve in the fuel pump that is supposed to prevent fuel pressure from bleeding back into the tank when you turn off the key. This valve often goes bad; you can replace an otherwise good pump, or install an in-line check valve in the gas line to prevent back flow.
Also be suspicious of your ignition switch, and change the fuel filter.
Anyone else with more ideas...? I think there was also an issue about a leaky hose inside the tank, on the pump itself??
Good Luck!

I second the check valve comment. That is exactly what happened to mine. You could put a gage on it and it would go to almost no pressure in less than 2 minutes. I don't know the exact spec...

Well thanks for the ideas, but the problem is that the pump doesn't even trun on until 30 seconds later or so. Then it runs for a few seconds and you can start the truck normally. I don't understand why the pump isn't getting the power from the system until 30 to 50 seconds after the key is turned on. All the thoughts you gave have to do with things that would be problems if the pump worked. But thanks again anyways. Mike

Sounds like maybe a bad fuel pump, getting ready to die. How many miles on your XJ ?

Another good point, but the second the relay gets power, the fuel pump starts, you can hear the relay click when it turns on. Obviously I have enough time to get out and stand in front of the truck to hear it. She's only pushing about 115000 miles.

That's an odd symptom all right. Have you experimented to see if cycling the ignition switch makes a difference? In other words, does it always take the same time before starting? Assuming it's consistent, the first thing I'd do is put a test light or voltmeter on the relay socket to determine whether or not it's getting the signal in the first place. Terminal 86 should be at +12 volts with ignition on. If the PCM (engine computer) is getting its signal out, terminal 85 should be at ground potential. So if 86 is 12 volts to the chassis, but not to terminal 85, you know the problem is in the PCM or between it and the relay. If terminal 86 is not at 12 volts, look for a wiring fault. If there is a good 12 volts between terminals 85 and 86, then the correct voltage is reaching the relay. Terminal 85 shares a line with terminal 85 of the automatic shutdown relay, running to terminal 51 on the PCM. Terminal 86 taps into a common positive line that feeds many other components, all fed through the ignition switch.

The switch portion of the relay is between terminal 30 and 87. 30 should show +12v with the relay removed, and the relay should switch +12v to terminal 30, which is the supply to the fuel pump. The fuel pump is grounded at the tank end. If the relay is getting its juice, try another relay, or start tracing back toward the pump. If you bridge between 30 and 87 the fuel pump should start right up.

Some people (including me) have had problems with bad splices in the wiring harness causing voltage drops and other odd symptoms, so it's worthwhile to go through the pertinent wiring carefully with an ohmmeter if voltages aren't up to par.

Pin 87A on the relay is not used, by the way.

Looking at the schematic I notice that the fuel pump relay seems also to supply the positive voltage to the heater on the oxygen sensor, and I wonder if some problem with the sensor heater or its wiring might foul up fuel pump operation.

Good luck!