No power to fuel pump

AARONMCD

MEMBER
1995 JEEP WANGLER YJ
150,000 MILES

4.0 L motor
Manual transmission
20 gallon tank

Would just crank (it started and stalled after a second a few times making me think a fuel problem was present)
Fuel relay clicked, fuel pump fuse is good, battery was good
Swapped relay with starter relay and no change, swapped with the relay that's in the fuel circuit (automatic shut off? No change either)
Checked fuel pressure at rail, there was none
Fuel filter was not very old, and there were no obvious leaks
Fuel pump was not priming
I dropped the tank and took apart the fuel sending unit
Put 12 VDC on the pump and it functioned

When the key is on (during the first 2 seconds, no voltage at the fuel sending unit harness, however there are 7 volts at the fuel gauge sensor pin

I jumped the relay (the high current one.30 I believe) to 87
There is 12 VDC at the fuel harness when the pins are jumped
The fuel relay still clicks when the key is just turned on

Ideas would be appreciated

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Tuesday, August 14th, 2012 AT 7:04 PM

21 Replies

SATURNTECH9

MECHANIC
30,870 POSTS

So while cranking is there power to both sides of the fuel pump fuse?

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Tuesday, August 14th, 2012 AT 7:33 PM

HMAC300

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Seeif your automatic shutdown relay is stopping it from getting power it could also be the pcm not sending power to relay

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Tuesday, August 14th, 2012 AT 7:34 PM

AARONMCD

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18 POSTS

I just checked to see if I had spark, and I do
While cranking I was getting about 11 volts on both sides of the fuel pump fuse

How do you want me to check the automatic shutdown relay? And the PCM?
Thanks everyone

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Tuesday, August 14th, 2012 AT 7:39 PM

HMAC300

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48,601 POSTS

The blue/yellow wire goes to relay see if it gets voltage or not

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Tuesday, August 14th, 2012 AT 7:41 PM

AARONMCD

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18 POSTS

I checked the 3 pins on the autoshutdown relay and they have voltage
The 4th obviously wouldn't have voltage without the relay
I'm unsure how to check that wire?

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Tuesday, August 14th, 2012 AT 8:06 PM

HMAC300

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That wire probably is the ground. But see if it goes to the fp relay if not you have a bad wire or connector someplace.

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Tuesday, August 14th, 2012 AT 8:07 PM

SATURNTECH9

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Hey hmac300 doesnt the power go thru the fuel pump relay then thru the fuel pump fuse on that one?Because they have power thru both sides of the fuse. So that would mean the relay was working?I dont have a wire diagram in front me iam not home so I cant check that myself.

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Tuesday, August 14th, 2012 AT 8:34 PM

AARONMCD

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18 POSTS

I'm confused guys

What and how would you like me to do?

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Tuesday, August 14th, 2012 AT 8:56 PM

HMAC300

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48,601 POSTS

See if the darkgrn/black wire going to fp is getting power then check the blk/orange wire near dist, that is ground, and seeif its making good contact. There is a fuse in fuse block fuse 5 tht goes to asd relay and fuse 1 in powr dist box, make sure both of those are ok. Those are for the relays I still think it's a shortsome place.

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Tuesday, August 14th, 2012 AT 10:12 PM

AARONMCD

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18 POSTS

All fuses In the power distribution center are good

I still don't know what you mean about the wires
What do you mean by dist? (Distributor or power distribution center?)
Should I remove the power distribution center?

Thank you

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Tuesday, August 14th, 2012 AT 10:33 PM

HMAC300

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There is a DARK GREE/Black wire to power the fuel pump, check to see if power goes through it to the pump and check the ground by the DISTRIBUTOR. Do not pull the power distribution center.

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Tuesday, August 14th, 2012 AT 11:58 PM

AARONMCD

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Ok, so, you mean the 3 pin harness where the fuel pump plugs into?
There was no voltage unless I jumped the fuel pump relay
I'll check the ground tonight

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Wednesday, August 15th, 2012 AT 12:40 AM

HMAC300

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Ok if you have to jump the relay tehre is problem there, either the pcm isn't telling the relay to turn on or the auto shutdown relay isn't sending a signal

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Wednesday, August 15th, 2012 AT 12:42 AM

AARONMCD

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How would I proceed then?

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Wednesday, August 15th, 2012 AT 1:01 AM

HMAC300

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Well recheck your fuses and see if the fuel pump relay is getting turned on. It's one of the previous answers I gave you. Also check fuse 21 in power dist box, the 96 is wired a little different and this may be closer to that. But it still leads to pcm or auto shutdown relay that turn on the fuel pump relay.

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Wednesday, August 15th, 2012 AT 2:19 PM

SATURNTECH9

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Aaronmcd what model jeep is this?Iam trying to find a wire diagram to see whats going on here.

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Wednesday, August 15th, 2012 AT 3:42 PM

AARONMCD

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As I said in the first post, it's a 1995 jeep wrangler (YJ) SE (the 4.0L model)

I am going to recheck everything today

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Wednesday, August 15th, 2012 AT 4:13 PM

YJFANATIC

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I have this exact same problem. Did you ever come up with a solution? '92 YJ 4.0 no power to the pump with switch on, 7 volts on middle prong of the pigtail at the tank, but can run 12V directly to the pump and will run.

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Saturday, October 13th, 2012 AT 3:14 PM

KHLOW2008

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41,815 POSTS

Igniton switch on would only provide power to the fuel pump for a brief period, 2-3 seconds, for priming the system.

The 7 volts is for the sending unit.

Remove the fuel pump relay. Ensure you have battery voltage at terminal # 1. Use a fuse wire to bridge terminals # 1 and # 4 and if fuel pump does not work, you have an open circuit between the relay and fuel pump. Fuelpump circuit works on a rather high current flow and opens in circuits are often due to overheated terminals at connectors.

Btw aaronmcd had tried swapping relays, did you do that? Symptoms and even faults can be similar but the cause or source could be different.

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Saturday, October 13th, 2012 AT 8:21 PM

YJFANATIC

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I am completely out of ideas on a solution for this fix. I have tried everything I know to test and diagnose my problem, and the Jeep still isn't running. Everything up to this point has led me to believe that the PCM is bad. I previously had a '94 wrangler that had this same problem. Running down the road one day and instantly lost power to fuel pump. The PCM was bad. I'm guessing that's what is wrong with this one. Any ideas would greatly be appreciated.

What I know:
1. Fuel pump is good (12V) connected to it and it runs.
2. Fuel gauge wire (tan/blk) has 7 volts on it and gauge itself is pegged full.
3. Ground is good.
4. When key is initially turned on, both the fuel pump and the ASD relay "click" and then there is an additional "click" immediately following, which I'm assuming is the ASD relay killing the power.
5. The jeep will run with the fuel pump wired directly to the battery, so I'm assuming the crankshaft sensor is good as well as any other sensor that could normally prevent the Jeep from starting or cause the ASD relay to kill power.
6. There is no check engine light on whatsoever and when I flash codes (ignition on-off, on-off, on-off), the only codes showing are 12 and 55, so not displaying any trouble codes.

I have literally tried EVERYTHING to fix this problem.
Anybody have any ideas?

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Monday, October 29th, 2012 AT 2:42 PM