Currently troubleshooting a fuel related issue.

Jump in and turn the key to on - initially there is no fuel pump priming noise before startup.

With the key left on after a few minutes you'll eventually hear the fuel pump relay rapid clicking for something like 10-20 seconds straight or soo and then the clicking stops and the normal expected fuel pump prime noise is heard.

Until this long series of clicking comes and stops with the anticipated prime noise finally the jeep will then finally start! Until then it only cranks over (yes it has spark).

I've replaced and cleaned all ground wire points in engine bay and even added one from neg to block. Verified harness connector at fuel pump is clean and making good connection. Replaced and cycled relays on fuse block with no difference. Battery is new as well as i thought my old one just wasnt handling the initail draw for startup. Once its gone through the click cycle to prime then key off and back on and all is well.




soo what say you?

 

I'd check:

Fuel Pump Relay (is this the source of the clicking?)

Fuel pump (apply 12v direct to see if it runs)

Ignition Switch (does everything else work?) Yellow wire provides power to lot's of stuff including FP relay. FP relay grounds through the ECU.

 

Yes its the fuel pump relay that clicks.

Yes I've applied 12v directly to fuel pump and it works when done, even done this via the terminal on the fuse block

Everything else works like normal via the key turn

 

I've also traded out my ignition switch from another jeep without this issue and there is no change

 

here is a few ideas

1) Grab a small roll of 5A wire (very thin), I like red, remove relay and insert bared ends into the 3 relevant slots, insert the relay.
A test light (best) or multimeter can be used, and you will be able to externally monitor what is occurring with respect to 12V at each relay pin (clues)

2) using a pin, solder up a "backprobe" . This can pierce wires or be pushed into the back end of connectors, same deal

3) Inspect the PDC female slots with bright light and mag glass (do this 1st)

4) Carefully unbolt the PDC and lift it up to examine the underside. You might find something is dodgy, burnt, cracked etc etc

5) Report your findings !

 

I've done a hot lead to the fuel pump relay terminal for its power and the hot lead powers the pump at contact - this got me thinking though about the ground, I could also tap into the ground side of the relay to eliminate a grounding issue for that relay.

I'll give this a whirl ^^ and update after

 

A relay takes MINIMAL power to activate...thats why we use them. Power to the pump or pump ground is irrelevant. For the relay to"cycle clicking" means you are losing power or ground to the relay coil which has nothing to do with the pump unless someone has messed with the wiring. You list many vehicles..which one are we talking about so I can check the wiring prints

 

95 xj harness setup

 

Yes of course.

My best bet is on option 4

 

Is the Fuel Pump relay the only one clicking, (cycling) or put your finger on the ASD relay..power to the coils of both the Fuel pump and ASD comes from ignition switch to splice 5124. The ground for the ASD coil and the fuel pump relay coil are both grounded in the pcm 51 ASD relay control. If only the fuel pump relay is the issue then the power splice to the fuel pump might be bad or the ground splice might be bad. If both click then find the common interface points

 

I have noticed the ASD may be clicking as well (have not physically put my fingers on it during the process to verify) I actually figured since i still have spark during this ordeal the ASD relay isnt as much suspect. But i see your point with how they joint togethor for power/ground.

My adhd is fighting me on reading those wiring diagrams, (i cant zoom and have clear detail atm, im also not the most fluent with wire diagram on command) am i looking for a physical wire splice for them or are we talking pcm board is potentially the issue?

 

It would be a physical connection on the wiring harness but if both are clicking it could be either the power in or the. Ground out

 

I had to post photos of the prints which don't enlarge well. I will try again to download actual diagrams which will enlarge better

 

Start with simple checks that are easy to perform. The first test is to remove the ASD relay, turn the ignition on and probe (use a meter or a test light) the ASD relay socket terminal 21 for power. The coil voltage to both the Fuel Pressure Relay (FPR) and the ASD relay are supplied directly from the ignition switch, drawing from fuse 6? (the scan isn't clear.) Check this fuse. Actually the FPR coil and ASD are wired in parallel so they share the same voltage supply (wire A21) and ground source from the PCM (wire K51). If you are missing 12V at the ASD relay coil more than likely the FPR will be missing it also. I would test the FPR socket the same way as the ASD to be sure. It looks like the FPR socket terminal 8? (scan is unclear) should have 12V for the coil.

If you have solid voltage at the ASD and FPR then you must have a grounding issue to the PCM. You can probe the relay sockets for ground by attaching your positive probe to battery plus and probe the socket with your negative probe. If you are using a test light then which probe you use is irrelevant. Check all wiring and connections from the relay to the PCM for breaks. Back probing both sides of sockets can really speed up the process. Hopefully you find a corroded connector. Worst case would be no ground from the PCM. That could mean replacing the PCM. Did you check grounding to the PCM?

Don't throw expensive parts at this issue. It's a pretty straight forward diagnostic problem that is more than likely to be a wiring issue.

 

Thanks
This was just the explanation i needed, i havent gotten back into the garage yet but your description is precisely what I'm doing potentially friday/this weekend