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Old 12-17-2013, 05:20 PM   #1
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No Power to Fuel Pump! help!

Hello,

I have a 1995 YJ se with 4.0L 5-speed manual.

While cruising down a back country road my YJ cut out and died and would not restart. After towing it back to my garage, I found there was no fuel pressure. After checking all the fuses and relays, I proceeded to remove the tank and replace the fuel pump. After putting everything back together, I still didn't have fuel pressure. I bench tested the old fuel pump on a 12v battery and it worked perfectly fine.

I swapped the horn relay with the fuel relay and the horn still worked but still no pressure.

I checked the connector and plug for the pump and that's plugged in nice and tight.

All the fuses are good and the ground wires are well connected.

Where or what else should I look at? Could the auto shutoff relay be the problem? The computer?

Ignition, starter, and everything else seems to be working perfectly.

Any suggestions would be great, Thanks.

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Old 12-17-2013, 06:18 PM   #2
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The fuel pump relay is powered off of the ASD (Auto Shut Down). Try swapping a different relay in there and see waht happens. If nothing, proble time to pull out the meter and see if you have a bad wire somewhere or a bad ground.

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Old 12-17-2013, 09:05 PM   #3
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I just tried swapping the Horn relay for the ASD (Auto Shut Down relay). Nothing, fuel pump is still not getting power and the horn still works.

I guess its either a bad wire, connection, or the computer???

Any other guess's or suggestions on where I should look?

thanks guys.
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Old 12-17-2013, 10:47 PM   #4
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Check for 12 v at the pump when the key is on? Pull any codes? Bad crank sensor will cause the pump to shut off. I'd start at the ignition and work toward the relay. Then toward the pump.
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Old 12-17-2013, 10:49 PM   #5
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Check for 12 v at the pump when the key is on? Pull any codes? Bad crank sensor will cause the pump to shut off. I'd start at the ignition and work toward the relay. Then toward the pump.
No codes, will the crack sensor throw a code?
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Old 12-17-2013, 10:52 PM   #6
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Yeah. Should. I'd start with ignition wire at the ign switch, check 85 and 86 terminals on the pump relay and 12 v and ground at the pump.
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Old 12-17-2013, 11:03 PM   #7
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Yeah. Should. I'd start with ignition wire at the ign switch, check 85 and 86 terminals on the pump relay and 12 v and ground at the pump.
Terminals 85 & 86 on the relay should read 12V, correct?

If I jump it to terminal 30 should that send power to the pump? If not I'll know I have a wire problem from terminal 30 to the pump or the ground coming from the pump, correct?

Thanks for your help.
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Old 12-18-2013, 01:27 AM   #8
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Subscribed lol
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Old 12-18-2013, 08:45 AM   #9
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85 or 86 should change polarity with the key on. And yes. Jump 30 and it should kick the pump on.
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Old 12-18-2013, 08:46 AM   #10
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Sorry. Jump 30 to 87 and that should kick the pump on.
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Old 12-18-2013, 10:19 AM   #11
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Sorry. Jump 30 to 87 and that should kick the pump on.
Okay, Just tried Jumping 30 & 87 together and nothing happened, Fuel pump did not come on.

With the key off:
30 = 12.5 volts
85, 86, 87= 0.00 volts

With the key on:

30, 85, 86 = 12.5volts
87= 0.00 volts

So this is starting to sound like a wire or ground issue. Sounds like were getting closer to a solution and a fix.
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Old 12-18-2013, 02:23 PM   #12
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Ok. So one of those coils should be grounded. One should be 12v when key is on. They energize and create the magnetic force in the relay to contact 30 and 87. They have to be opposite polarity for the relay to function. I'd guess a grounding issue.

Get a free wiring diagram from autozone.com. Trace the coil wires on the relay and start there. They'll be on the schematic.
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Old 12-18-2013, 03:50 PM   #13
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Here's what I just found,

When I jump 30 to 87 on the fuel pump relay I am getting 12.5 volts at terminal 30. Behind terminal 30 is a Green and Black wire which leads all the way back to the fuel pump. When I hook the volt meter up to the green and black wire at the fuel pump plug it's .75 volts.

I put a test wire going from terminal 30 all the way back to the fuel pump and the fuel pump turn on perfectly.

Conclusion, replace the Green/Black wire. What do you think? I'll give that a try and see what happens
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Old 12-18-2013, 07:33 PM   #14
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That's what I'd do.
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Old 12-19-2013, 12:18 PM   #15
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Not to thread-jack, but you fellas helped me out a lot, but I still need some more lol.

With Fuel Pump Relay removed and jumper wires installed: (Also the Auto-Shutdown Relay is installed)

I have 12v at 30.
I connected 30 to 87 and the fuel pump does come on.

With key off:
Only 30 has power, 85,86,87 are 0v.

With key-on:
30 has 12v
86 has 0v
87 has 0v
85 has 5.8v

Is 85 supposed to have 12v? Where is 85's power coming from? Please tell me it's not the ECM lol.

Also, when I put the meter on 85 with the key-on, the PDC makes this slight clicking noise...


When the Auto-Shutdown Relay is removed, I don't get any voltage to the 85 terminal on the Fuel Pump Relay.

On the ASD slot,

Key off:
30 has 12v

Key on:
12v at 30
12v at 86

That means the ASD slots are correctly powered right?
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Old 12-19-2013, 02:34 PM   #16
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So your fuel pump relay looks like, 86 is ground. 85 is power. Should be 12v. That's probably your issue. 30 will always be 12v.

Every relay works the same. And the numbers are standard. So remember this for future reference.

85 and 86 will always be opposite. 30 dictates what happens to 87 or 87a depending on weather you want the circuit to open or close when the relay switches.

So I'd grab a wiring diagram and figure out where 85 comes from. I used the free one from autozone. I believe it's the ecm. I had a bad fusible link that shorted, burned up the ecm and killed power to the relay and coil. But I also have a 90 with the renix comp. it was easy to rip open and solder. I was stuck going across country so it worked to get me home but I will need to replace the computer.
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Old 12-20-2013, 06:50 AM   #17
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Quote:
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So your fuel pump relay looks like, 86 is ground. 85 is power. Should be 12v. That's probably your issue. 30 will always be 12v.

Every relay works the same. And the numbers are standard. So remember this for future reference.

85 and 86 will always be opposite. 30 dictates what happens to 87 or 87a depending on weather you want the circuit to open or close when the relay switches.

So I'd grab a wiring diagram and figure out where 85 comes from. I used the free one from autozone. I believe it's the ecm. I had a bad fusible link that shorted, burned up the ecm and killed power to the relay and coil. But I also have a 90 with the renix comp. it was easy to rip open and solder. I was stuck going across country so it worked to get me home but I will need to replace the computer.

If I trace back the wire from 85 and find out the the wire is good, that'll leave the ECM. How important is ECM management controlling the fuel pump relay? Can I bypass the ECM and put the fuel-pump on a killswitch? Like, power the pump with 12v continuously and then killswitch the ground?

I am in no mood to be taking apart the PCM, and just by looking online ill be shelling out a couple hundred dollars for replacement. It's one circuit that my PCM could be failing. I don't know what to do now.
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Old 12-20-2013, 10:18 AM   #18
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To be honest, after fixing mine it runs all the time. I had to wire a kill switch to the ign to shut the car off. The computer, I think, just primes the pump when the key is on.
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Old 12-20-2013, 12:02 PM   #19
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To be honest, after fixing mine it runs all the time. I had to wire a kill switch to the ign to shut the car off. The computer, I think, just primes the pump when the key is on.
I'm trying to isolate that part of the circuit with some more wiring checks. When I do a code check I don't get 33 with the ASD or Fuel-Pump Relays installed, so does that mean that the PCM is ok? It's all so confusing lol.

I really appreciate all the help. I'm building another thread for one last troubleshooting method I have an idea for, I'd really appreciate it if you would look over it after I get it posted up sometime tonight. I got pictures this time too lol.
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Old 12-20-2013, 03:05 PM   #20
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Yeah. I had to isolate certain circuits that I knew had power and the one that didn't. Where they met, was obviously bad. I'd assume if its not throwing codes, the ecm will be ok.

The way my computer works is, 12v goes from the key to the computer, as well as battery 12v. The computer sends out 5v to all the sensors. They bounce back resistance info to the computer, which adjusts fuel/air accordingly using the sensors. The comp also receives signal from the crank and cam sensors when the key is on, to prime the pump.

I'd wire a jumper from an ignition wire source like asd relay to the 87 contact on the fuel pump. Problem band aided. Did you make sure the terminals at the wiring into the relays aren't corroded? Ends can cause problems if they are.
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Old 12-20-2013, 04:58 PM   #21
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Yeah. I had to isolate certain circuits that I knew had power and the one that didn't. Where they met, was obviously bad. I'd assume if its not throwing codes, the ecm will be ok.

The way my computer works is, 12v goes from the key to the computer, as well as battery 12v. The computer sends out 5v to all the sensors. They bounce back resistance info to the computer, which adjusts fuel/air accordingly using the sensors. The comp also receives signal from the crank and cam sensors when the key is on, to prime the pump.

I'd wire a jumper from an ignition wire source like asd relay to the 87 contact on the fuel pump. Problem band aided. Did you make sure the terminals at the wiring into the relays aren't corroded? Ends can cause problems if they are.

I did look at the terminals on the relay and the PDC slots, they looked ok but I cleaned them anyway with some No-Flash Contact Cleaner.

For the terminal 85 in fuel pump relay that's only getting 5.8v instead of 12v, I wanted to see exactly where that wire went to, so I took off the PCM connector and checked from the 85 slot to each Pin-Position on the ECM connector until I got a reading. I don't have a wire diagram, so I just went from pin to pin until I didn't get an Open-Line on my multimeter.

I got continuity on pins #9 and #51. (70 ohms on #9 and .3 ohms on #51). #9 is a solid Yellow wire, and #51 is a Orange/Black wire. I'm trying to find a diagram but I think those two are powering the fuel pump relay. Do you think it's ok if I "needle" those wires right from the ECM with the Key-On position? If I get the 5.8v right from there, ill know that my ECM is trash. But if I get 12v, maybe it's something in my PDC that's causing the voltage drop. What do you think?
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Old 12-20-2013, 09:14 PM   #22
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What year and motor?

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