Renix used to cutout, now it's dead

[87manche]

ok, so I started at the tank and checked every connector for continuity. Then I unplugged the connector under the drivers side bucket and put my meter on the big orange pin. I grounded my meter to the seat bolt harness bolt. Turned the switch and got that same .3v that I got at the pump. So I don't think it's a ground issue with the pump. I'm about to pull the ECU and check all of those connections. I realy think it has something to do with wires in the engine compartment though.

 

[langer1]

Jumping 30 to 87 should make the pump run. 87 should be orange, it is spliced under the air box and changes to orange-black. It then goes to the bulkhead connector and changes to pink on it's way to the pump.

 

[Flatspins]

Been on the phone with my lil bro and we've narrowed it down to this:


Good 12v power at latch relay
Connections to fuel pump ok
No 12v power at fuel pump relay

Jumpered 12v from battery to 30 on fuel pump relay, pump turns on and works
Jumpered from 30 on latch relay to 30 on fuel pump relay, pump works

Looks like no 12v power to red wire input to 30 on fuel pump relay, thought latch relay and fuel pump relay fed from same red wire with fusible link, but apparently not because latch relay has power, but fuel pump relay doesn't.

Anybody know where the red wire on the fuel pump relay gets 12v power from to power fuel pump?

 

[langer1]

Been on the phone with my lil bro and we've narrowed it down to this:


Good 12v power at latch relay
Connections to fuel pump ok
No 12v power at fuel pump relay

Jumpered 12v from battery to 30 on fuel pump relay, pump turns on and works
Jumpered from 30 on latch relay to 30 on fuel pump relay, pump works

Looks like no 12v power to red wire input to 30 on fuel pump relay, thought latch relay and fuel pump relay fed from same red wire with fusible link, but apparently not because latch relay has power, but fuel pump relay doesn't.

Anybody know where the red wire on the fuel pump relay gets 12v power from to power fuel pump?

My FSM says the orange fuseable link.
My 87 renix FSM show a seperat fuesable link for the fuel pump but don't give the color.

 

[Flatspins]

So does mine, but he's physically looking at the wiring and there's no connection between the fuel pump relay and the red wire with the orange fusible link. The only red wire from the fuel pump relay goes to the ecu and provides battery power. We can't find the connection between the orange fusible link to the latch relay to the fuel pump relay.

 

[langer1]

So does mine, but he's physically looking at the wiring and there's no connection between the fuel pump relay and the red wire with the orange fusible link. The only red wire from the fuel pump relay goes to the ecu and provides battery power. We can't find the connection between the orange fusible link to the latch relay to the fuel pump relay.

The wire going to the ECU is the ground.

 

[langer1]

So does mine, but he's physically looking at the wiring and there's no connection between the fuel pump relay and the red wire with the orange fusible link. The only red wire from the fuel pump relay goes to the ecu and provides battery power. We can't find the connection between the orange fusible link to the latch relay to the fuel pump relay.

The only other place it could come from then would be the ignition switch.

 

[Flatspins]

Found the power splice. Jeep in it's infinite wisdom ran the power wire from the starter relay (orange link/red wire) all the way to the ECU where the red wire connects from the fuel pump relay to provide battery power to the ECU and spliced the two together in the ECU connector.
Once we figured that out, bro started tracing the wire back to find why we had no power and discovered an awesomely redneck engineered wire splice between the two red wires. Apparently this was a problem before and the po didn't even bother to use solder or splices or anything, just good ole duct tape.
I'm sure he'll be on later to thank you guys, but thanks for the help.

Josh

 

[87manche]

Odd theory, but since it's what happened on my 88 XJ when it had fuel pump problems it's worth a shot: does the jeep ever try and catch while you're turning the key to Start, then die when it's in Run? if I'm remembering correctly the Start circuit feeds power to the fuel pump through a bypass circuit (orange/black maybe?) off the starter solenoid... so it'll work fine while starting and then just cut off the second you let go of the key.

also... trace back the wires under the diagnostic connector and see if you have a big 5-red-wire splice under the coolant bottle there. mine was completely corroded into green powder, causing intermittent and eventually zero power to several ignition-powered circuits, including the fuel pump.

ok, so that spaghetti mess of wires was indeed there. Looks like a PO had fixed it once, but it wasn't done right. I've got to go to the parts store and get somering terminal connectors to make fusible links out of my inline fuse holders. The running theory is that the corrosion on the duct taped, twisted together with no solder splice cuased the voltage to drop, so the current skyrocketed and toasted the fusible link. I did get power to the fuel pump through the relay, I just need the stuff to wire it up right and I'll be back on the road.
thanks for all the help people, I really appreciate it. I would have never thought to open up the wire loom and look for a splice there. I think that I made it worse when I flushed the coolent last weekend

 

[87manche]

IT RUNS!!!!
Well, I wired up a few inline fuse holders with ring terminals to replace all of my iffy fusibl links. Jeep runs now, but I've got the cutout still. Now instead of cuting out and coming back it just pops the fuse. What's the current capacity supposed to be on that circuit? I had a 30A fuse in the holder, do I have a problm with the something drawing excessive current, or do I really need a bigger fuse for that circuit? Until I figure it out I just won't go WOT

 

[langer1]

IT RUNS!!!!
Well, I wired up a few inline fuse holders with ring terminals to replace all of my iffy fusibl links. Jeep runs now, but I've got the cutout still. Now instead of cuting out and coming back it just pops the fuse. What's the current capacity supposed to be on that circuit? I had a 30A fuse in the holder, do I have a problm with the something drawing excessive current, or do I really need a bigger fuse for that circuit? Until I figure it out I just won't go WOT

What color was the fuse link?

 

[87manche]

the orange fuel pump relay link. I found somewhere on the forum via search that it's supposed to be a 15A circuit, but @ WOT above 3K RPMs I'll pop the fuse. I've been considering going to the yard and pulling the fuse block from a newer cherokee and retrofitting it into the MJ.

 

[langer1]

the orange fuel pump relay link. I found somewhere on the forum via search that it's supposed to be a 15A circuit, but @ WOT above 3K RPMs I'll pop the fuse. I've been considering going to the yard and pulling the fuse block from a newer cherokee and retrofitting it into the MJ.

Just replace the fuseable link with a new link. Fuses don't work well there.
A fuseable link is used for a reason. Get some wire the same gauge as the old link and make a new ones. Standard fuses react to fast so just put it back like it was.

 

[87manche]

will do then.

 

[langer1]

What happens is little spikes in current that last for only milliseconds will blow a fuse but not a fuseable link.

 

[87manche]

I think I'm just going to live with not having WOT until I can just upgrade the entire engine electrical system.
In the plans:
A set of 5-90s wires.
A PDC from a newer cherokee with maxi-fuse block.
New wires wherever needed in the harness.