88 fuel pump circuit

88 auto
It died on trail and only starts then dies again. Ballast is smoking so i think the pump is shorted out and needs replacing. I install a new pump and it starts up but dies after i put it in gear. I check grounds at the motor,head to body,battery to body,and body driver side. all cleaned up but still dies when put in gear or after you torque the motor to make it move.At this point not sure if electrical or fuel pressure. install pressure gauge and find it is losing fuel pressure.still the ballast starts smoking sometimes and it has voltage on both sides. i install a jumper and she runs like a top take it for a ride get a block away and the jumper wire melts in half. now i know there is a short somewhere or bad ground. find short in wire that feeds the ballast where the wire loom runs under the battery thru the header panel over to the driver side. now the short is fixed and she will only start then die again and it will not prime the pump when the key is turned forward only but will turn on the pump when i crank. So i change out the starter relay thinking that the short some how messed up the contacts inside. still only starts then dies but if i jump the fuel pump test terminals it will start and run fine till i remove the jumper then dies. all relays have been tested and found good except for the ASD relay where is it located?
1 Is there multiple grounds for the fuel pump depending what source is telling it to run
2 How many power feeds sources does the fuel pump have
3 where is the ground terminal for the fuel pump or is it grounded only thru the computer and if so where is the main ground for the computer
4 Is the 2 second timer for the fuel pump prime when key is first turned forward a seperate piece or part of the computer program.
:banghead:

Hallo. The pumprelay is supplied by the ignition switch. The relay is activated when the ECU gives a circuit to ground.
A ballast resistor is present, but bypassed when starting. (bypass relay?).
The pump has his own ground (black).
There is no ASD relay , but a Latch-relay in a '88. :wave1:

'92 XJ

You have a short, and it may be through the pump itself.

Use an ohm meter to test the wiring and pump.

i have replaced the pump and fixed the short in the front of the header panel. i can jump the pump and it will run.

any updates? i have a code that says "open or short..." for my fuel pump, i found out about 10 minutes ago.

I have hooked the fuel pump up to a toggle switch and now have no fuel problems

cool, thanks, i wonder if that can be done with a 94? ...one way to find out i guess!

need to get a service manual so you can trace the wires and see if the computer grounds the fuel pump. then go from there..

Sponge Bob said:

I have hooked the fuel pump up to a toggle switch and now have no fuel problems

Click to expand...

Can you provide some details to this? I think I need to do the same thing.

Sponge Bob said:

now the short is fixed and she will only start then die again and it will not prime the pump when the key is turned forward only but will turn on the pump when i crank... ...still only starts then dies but if i jump the fuel pump test terminals it will start and run fine till i remove the jumper then dies.

Click to expand...

Did you replace the ballast resistor after finding the short? That seems like it might be a good idea. Resistors that smoke often are nowhere near their original resistance value afterwards, and usually don't live much longer. As I understand it, the pump is run through the ballast after the engine is started, so it stands to reason that if your ballast resistor is burned out (open circuit) it'll start, then die, and will run fine if you jump the ballast resistor.

Looking at the schematic in my Haynes manual, it looks like a ballast resistor could definitely cause what you're seeing... the fuel pump relay drives the fuel pump through the ballast resistor, either the starter relay or the O2 sensor relay (I think, I can't tell where it's drawing power from, it might be feeding the O2 sensor through the ballast for all I can tell) can shunt the fuel pump past the ballast resistor directly to the battery.

Even after a new starter relay and ballist it still will not run with out a jump wire at the test connector or in stalling a toggle as i have done. toggle is hooked up to the wire that comes from the ballist to the fuel pump. no ballist is hooked up.

with your jumper removed, see if you have power to the ballast resistor immediately after it starts (position the DVOM so you can see it from the drivers seat)

your symptoms sound like a bad fuel pump relay-- it'll start with the B+ latch relay powering the pump for prime, but if the fuel pump relay has failed, you won't receive any power to the ballast once the key is returned to the run position.

a bad ignition switch (electrical part- not the lock cylinder) can cause this too, but 'til you verify the relay is functioning, I 'd say it's less likely.

Thanks i have also replaced all the relays. some times it will prime and if so then it will start and run till the next key cycle. so the switch makes sense plus age and it's fair share of mud and water in the jeep