Low voltage to fuel pump, smoking ballast.

Help me out here guys....I just finished the ball joints and putting the front suspension all back together. So then it was time to fire it up....put the key in and..it just cranks....

The last time I ran my truck (efore i did the ball joints) I was heading up a hill and it just slowly died. Tried to start it again and it just cranked. I checked for spark...all good... guages...all good..So i checked the fuel pump and it wasn't turning on. I had a friend bring an external pump...and it still didn't want to turn over. Now I just removed the pump earlier today and checked it against a straight 12v and it ran perfect. So I checked the wiring. I'm getting 7v on the power going to the fuel pump. No change when the key is turned off then back on. So i hardwired the pump to the battery. Connected the sending unit and the jeep fired right up. Less than 30 sec. later the fuel ballast started smoking and was amazingly hot. So I heard about bypassing the ballast. So I just hooked the two wires up. The jeep started then slowly died after melting an extension wire I added so I could relocate the ballast. All of the relays are functioning properly and there are no blown fuses.

What is going on here?? The wiring diagram that I saw shows the power going from ECU to the injectors, to the ballast, to the pump. Could I possibly have a ad ECU?? Pump is good...I have two ballasts so i'm hoping one of them works. Injectors are good..

:helpme::helpme::helpme::helpme:

symptoms point to a bad fuel pump

Pump could be pulling too many amps under load because it's going bad. When engine is cranking it should get 12v and drop down to a lower voltage thru resistor when running. I don't see a spec for max amp draw or ohm reading. You might want to check grounds and voltage thru fusible link > relays > balast resistor.

Agreed with Tom, pump is smoked.

PS:
Your front axle is bent real bad.

GSequoia said:

Agreed with Tom, pump is smoked.


PS:

Your front axle is bent real bad.

Click to expand...

Ok I already have a new pump...i'll give it a shot.


Lol. That's ok. It's still better than a hummer....Even with a bent axle. :viking:

WAIT. I have the pump hardwired through a switch right now. Pump goes on...pump goes off...pump goes on....pump goes off.... I ypassed everything on the fuel cicuit because of the low voltage reading at the pump. Now it gets constant 12v. Did I bypass something that I need?? The wiring diagram doesn't show anything. Just the ballast.

I read somewhere on here that it might be to ASD??? This is the first i have heard of it. What exactly does it do? Cause a complete no start situation with all electrical running, just no fire?? Cause thats were i'm at now... I love my Jeep

ASD = auto shutdown relay

Melting wire says too much load which means pump is toast. A relay won't do that.

So I hooked up the new pump outside of the tank....just to see if anything happens...I wired everything back to the way it was...I checked the voltage to pin6 at the diag connector and there is no voltage when the key is turned on or off. So there is no power on the whole orange line. .. Orange line feeds power to c11 injector feed, and D10 injector feed on the ECU.... pin 6 on the diag. connector...A/C clutch relay...fuel tank unit....latch relay...o2 heater relay... BUT...it looks like all the power comes from the ECU. what tells the ECU to power all of that up???? Ignition? The fsm wiring diagram doesn't show an ASD relay either...

You working on the 88? not sure that has an asd like my 92. I think thats in the pile of fusable links area of a renix...

Peacefrog53 said:

So I hooked up the new pump outside of the tank....just to see if anything happens...I wired everything back to the way it was...I checked the voltage to pin6 at the diag connector and there is no voltage when the key is turned on or off. So there is no power on the whole orange line. .. Orange line feeds power to c11 injector feed, and D10 injector feed on the ECU.... pin 6 on the diag. connector...A/C clutch relay...fuel tank unit....latch relay...o2 heater relay... BUT...it looks like all the power comes from the ECU. what tells the ECU to power all of that up???? Ignition? The fsm wiring diagram doesn't show an ASD relay either...

Click to expand...

The ECU sends a low power signal to the fuel pump relay and that applies the 12v to the pump when it senses the ignition switch being closed. If the motor dies, it turns off the pump for safety reasons.

Beware of running the pump while not submerged. It will overheat real quick and you can ruin it. I've seen a lot of pumps go from being run on an empty tank.

More weird shit.. I get a 12v signal from the out of the fuel relay which then connects to all of the other orange/blk wires. One of the connectors goes to pin6 on the diag connector. There is no voltage on pin6 with the ignition on. Where is the connection made between all of these orange wires? There should be a conjuction of 6 wires going to all of the above mentioned.

And once i hear the pump turn on it will be immediatly shut of.

Peacefrog53 said:

More weird shit.. I get a 12v signal from the out of the fuel relay which then connects to all of the other orange/blk wires. One of the connectors goes to pin6 on the diag connector. There is no voltage on pin6 with the ignition on. Where is the connection made between all of these orange wires? There should be a conjuction of 6 wires going to all of the above mentioned.

And once i hear the pump turn on it will be immediatly shut of.

Click to expand...

Nothing wierd. When you first turn on the ignition it runs the pump for 3-5 seconds and then shuts off until you actually start cranking.

old_man said:

Nothing wierd. When you first turn on the ignition it runs the pump for 3-5 seconds and then shuts off until you actually start cranking.

Click to expand...

But shouldn't that in turn cause a voltage reading at pin6 when the ignition is swithced on? There is nothing.

Only there for the first 3-5 seconds and then when cranking.

Wow. So could a fried relay panel cause some prolems?? All four of them have a melt spot.

But there is voltage on the out portion of the relay.

Is this on the renix rig? I have a spare renix fuel pump if you want to try swapping it in. Give me a call if you want to come grab it, my number is in the recovery thread on the first page.

Looking at the fsm schematic figure 2 fuel pump relay:

Yellow to pin 5 gets power from ignition switch when ignition on (power to relay's coil)

Orange-T to pin 5 ground wire for relay's coil goes to ECU pin A5 when ecu comands pump to turn on it will ground coil for relay contacts to close (ground to relay's coil)

Red to pin 1 12V battery power from fusible link should always be on (12V input)

Orange to pin 4 when contact closes send power to Fuel Pump, c11 injector feed, and D10 injector feed on the ECU, pin 6 on the diag. connector,etc (12V output)

There is a Green-T wire that is spliced into the Dark Green wire which is the signal to crank from start relay to starter solenoid. The Green-T wire sends a 12v signal to the ECU which comands transistor in ECU to ground pin A5 allowing fuel pump relay to close.

I don't see how voltage is controlled to the fuel pump as it's explained in Fuel Pump Description and Operation in the FSM. It looks like its C4 where the wire changes from Orange-Black to Pink-T but there isn't a relay or control to diferentiate when starting or ignition on

so check yellow wire for power when ignition on

12v at red wire

with fuel pump relay pulled out check that you have a ground at Orange-T wire when cranking engine

with relay out put a jumper between orange pin 4 to red pin 1 and pump should run (I would only do it for a moment)

I haven't had to troubleshoot a no start/ no fuel issue but by checking the fsm thats where I would start.

Peacefrog53 said:

So I hooked up the new pump outside of the tank....just to see if anything happens...I wired everything back to the way it was...I checked the voltage to pin6 at the diag connector and there is no voltage when the key is turned on or off. So there is no power on the whole orange line. .. Orange line feeds power to c11 injector feed, and D10 injector feed on the ECU.... pin 6 on the diag. connector...A/C clutch relay...fuel tank unit....latch relay...o2 heater relay... BUT...it looks like all the power comes from the ECU. what tells the ECU to power all of that up???? Ignition? The fsm wiring diagram doesn't show an ASD relay either...

Click to expand...

Even though the fuel pump runs when bench tested it may be turning too slow (low pressure) or pulling too many amps causing a voltage drop so there isn't enough current to fire injectors/ O2 when run with the factory wiring.

A bad ground could cause the wires to smoke but not a low input voltage.