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fuel pump won't pump fuel

11K views 137 replies 4 participants last post by  flipit 
#1 ·
Alright,
so first off, I have been surfing the web quite a bit trying to find someone else who has answered the problem I am having, but I can't find one yet, unless it's the simple problem of the fuel pump I bought was shot from the factory, or something about it has to be either EFI or TFI? I didn't dig into that because I don't have a clue in what that means, and since i bought the unit from an auto parts store, I hope they were intelligent enough to give me a proper pump.

so, the problem I am experiencing... My gas tank is on hte floor right now, and the fuel sending unit is sitting on top of it. on the top of the unit, where the wiring harness comes in, on the under side, there are two prongs. hot and sensor.
the hot wire reads 12 volts (11.6 now as the battery is slowly draining) when plain, but when I connect the plug, it is significantly lower.( I'd have to go out and meter for an exact number if you need.) when put the ohms meter on the two plugs, there is no resistance through the circuit, the juice flows through the hot, into the pump, out of the pump, into the sensor, and out of the sensor out towards the gauge.
I really am at a loss here,
I'm hoping it was a very stupid, easily fixed mistake, If you need any pictures I can go out and take them-
Thanks in advance for any help anyone might have.
 
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#4 ·
I did,
this afternoon I pretty much traced all the wires, because when I bought the fuel pump, it was new, so I plugged it in, and didn't have the chance to really test it til now, and of course the gas isn't pumping.
the ground grounds, the hot is hot, and the gauge wire goes to the gauge, It was off by 1/4 tank before the problem, but I'm sure it still functions quite properly.
my real hang up was the sending unit.
right before the sending unit is a "connector" (temrinal, plug something, insert correct nomenclature here) so I unhooked it and checked the three incoming wires. once those were all verified, I checked the ground to it's welded spot on top of the fuel sending unit, and that point, along with pretty much the whole unit, is properly grounded.
This is where it got tough for me, and my far from advanced knowledge.
on top of the underneath of the sending unit, there are two prongs, hot, and gauge. starting at the hot prong, the electrical circuit as I noted, is as follows-
Hot prong~left pump bolt^right pump bolt~sending unit ground point.
(~ is a small clip on wire, and the ^ is like, one is the positive bolt, one is negative, hope that makes sense)
attached to the sending unit ground point is the fuel level gauge, which has a wire coming off of it, going to the gauge prong on top.
so, when I plugged the hot wire into the hot prong, the circuit was completed.
for both-(i thought)
so i thought the gauge was pulling too much voltage, sending the pump down to only 1.6 volts (1.9 with good contact)
I'm kinda new to electrical, I've always enjoyed the mechanical aspect much more,
So,
closer to the evening I finally realized it wasn't the same circuit,
it's some kind of weird thing that i can only presume makes sense in the electrical world.
so i pulled off the fuel pump,
took the two cables, put one on the batterys ground terminal,
and one on the positive terminal.
and there was no pumping sound,
no smoke cloud-
nothing...
so i think either i bought a faulty pump,
or way more likely, I broke it along the way.
so I'll be picking a new one up Tuesday.
I dunno, maybe Monday If I have the time.
and we'll see if a new one fixes all my problems.
 
#5 ·
There are three wires on your pump. One for power to the pump one for the gauge and one for ground. Test it at the battery with some jumper wires IF you know which wire is which.
 
#6 ·
on the pump itself? my pump has two, the hot/power, and the ground. the sending unit has three- well three on top, the ground welds into the top and the other two go through as i mentioned.
 
#9 ·
I think you are getting confused on what you are reading. Laybackman is trying to point it out. When you first turn the key to start the jeep, the ecu supplies power by pulling in the relay for a few seconds and then releases, the pump remains unpowered until you turn the key to start. If you are measuring voltage in the rear without the engine running or the key in the start position then you are measuring the voltage from the guage not the power to the fuel pump. You can jumper power at the relay from pin 30 to 87 in the relay socket with a short piece of wire to supply the pump with the key off.

Also if you are trying to measure any resistance the power to the circuit must be off. That means battery disconnected. If you are reading resistance through windings on a motor then the readings will be a short or very low resistance. The windings are just a long piece of wire.
 
#11 ·
I think you are getting confused on what you are reading.
what I am reading or what he is saying?

Laybackman is trying to point it out. When you first turn the key to start the jeep, the ecu supplies power by pulling in the relay for a few seconds and then releases, the pump remains unpowered until you turn the key to start.
my PO actually hotwired the fuse box, I'm trying to undo it, but I have more to learn before that- but... in all that, my relay does not click when I turn the key, the starter relay clicks, but the [org/blk -hot- wire] (Wrangler Chilton, pg 6-46) has the 12 volts running through it at all times.
so right now, If i go to the back of the jeep, and unplug the connector of the three wires, the hot currently has the 12v up to that point and beyond. the ground, well, is grounded, and the gauge shows continuity....

If you are measuring voltage in the rear without the engine running or the key in the start position then you are measuring the voltage from the guage not the power to the fuel pump. You can jumper power at the relay from pin 30 to 87 in the relay socket with a short piece of wire to supply the pump with the key off
if you are telling me that the 12 volts I am measuring is actually the gauge voltage... then I figured out the problem!
someone (possibly myself) (five years ago) attached that 12 volts to the fuel pump, and put the other cable onto the gauge...
if this is the problem that is really embarrassing.
what a dumb mistake to be made...

Also if you are trying to measure any resistance the power to the circuit must be off. That means battery disconnected. If you are reading resistance through windings on a motor then the readings will be a short or very low resistance. The windings are just a long piece of wire.
for the resistance, I unplugged the two points on the fuel sending unit,
and attached the red meter cable to the left one, and the black to the right.
obviously left and right don't matter, but yes, due to both circuits using the same ground, they in themselves made a full circuit.

Que, I'm really hoping you're right about the circuits, and hopefully they were backward. I've been trying to remember putting the unit in but it's been so long and quick, I don't really remember what happened..
I remember buying the new pump, tossing it in,
and the battery was dead, so we charged it.
we tried to start it but it still didn't start, so we dropped the tank and then my trip was over so I cleaned up and haven't touched it sense.
but maybe, If those volts are only supposed to come in when I start it like your saying, maybe flipping them caused me to fry the pump?
$70 learning mistake if that's it. but i'll take that if it means I can get the engine running again. one step closer to getting back on the road.
 
#12 ·
He hotwired the fuse box? Not sure what you are dealing with!
Here is a link to the Factory manual at Morris:
http://www.jeep4x4center.com/knowledge-base/index.htm

Way better then the Chiltons. Especially in wiring.

Go to P112 on the wiring section:

Pin 1) Blk/Or Ground
Pin 2) DB? Fuel Guage
Pin 3) DG/BK Switched Power from pin 87 of the fuel pump relay
 
#13 ·
He hotwired the fuse box? Not sure what you are dealing with!
yeah, there are two random red wires going into the fuse box, I'm not sure where or what to,
so the plan is/was- to get the jeep to start, and make sure all the electrical components work (or well, the wiring anyways, cause most of it didn't work before anyways) and once I know it works before, I'll just kind of "undo" some things that he did, and redo them in a way that makes sense to me.

Here is a link to the Factory manual at Morris:
http://www.jeep4x4center.com/knowledge-base/index.htm

Way better then the Chiltons. Especially in wiring.

Go to P112 on the wiring section:

Pin 1) Blk/Or Ground
Pin 2) DB? Fuel Guage
Pin 3) DG/BK Switched Power from pin 87 of the fuel pump relay
I hadn't heard of these before, the Chilton works enough to get me by, but yes, I was having a hard time with the wiring,
I just assumed it was something the PO had rigged, cause the DG/BK changes to ORG/BLK right at the connection point i was talking about.
I actually think I am looking at a different manual than you, i went to the online, 93 yj, no wiring systems, so i went to fuel systems, and page 43/66 has a schematic, but i can't read it. i'm downloading the universal right now.
that was a parts manual. oh, haha, scroll down... found it!
okay, so on that schematic on that page, right there.
on that connection in my jeep,
with the key in the off position,
the black green has twelve volts.
the dark blue has 0
and the black orange has 0 (mine looks black pink, but i'll buy black orange.)

all three have continuity and run properly, I see no damage to any wires.
so again, the hot is hot. the ground goes to ground. and the sensor goes to the sensor....
on the bottom connection of that schematic, It doesnt list the colors,
but they change. orange, tan, black, something.......
the hot, stays hot, with all it's voltage, until it goes inside the sending unit,
inside the sending unit there are only two prongs- because the ground is welded on the top.
if I remove the clips from these prongs, they still meter exactly the same. my hot is at 12. my gauge is 0 and continuous.
If I attach the clip that goes to the the fuel pump, the volts drop down to just under two volts.

I feel like i keep reitterating the same thing, even with the manual here now.
all I'm saying is if you need a picture, I'll go out and grab as many as you'd like.

let me know if I'm poorly explaining any part at all.
I really think i just burnt out the fuel pump, but I'd like to avoid doing it again,
so I'm trying to make sure all the wiring is proper...
 
#15 ·
No, you are explaining it. There should be no voltage with the key off. It is wired wrong. The fact that you have 12 there doesn't tell you everything you need to know except that if that was left on the way it was wired you will kill the battery and or the pump. You need to pull the pdc and check the fuel pump wiring at the relay.

Check your fuel pump by jumping power direct to the pump. You have the pump out so take up front and put power right from the battery to it.
 
#17 ·
No, you are explaining it. There should be no voltage with the key off. It is wired wrong. The fact that you have 12 there doesn't tell you everything you need to know except that if that was left on the way it was wired you will kill the battery and or the pump. You need to pull the pdc and check the fuel pump wiring at the relay.

Check your fuel pump by jumping power direct to the pump. You have the pump out so take up front and put power right from the battery to it.
haha, you're killing me Que!
I dont feel like requoting myself, so i'll just say, toaday at 1:14 am-
so i pulled off the fuel pump,
took the two cables, put one on the batterys ground terminal,
and one on the positive terminal.
then at 3:11 pm
I used the two pieces of wire on the unit to test the fuel pump, and I got nothing. and both wires were in good working order, no resistance worth noting.
the bottom line is~

All three wires going into the pump are as mentioned, in working order (except the hot is strangely always hot)
the fuel pump has been "jump tested" and it did not work.
it's broken, malfunctioning, pick a word.
I am not sure what i did to it,
but i would PREFER to not fry it again.
being a college student, I can only afford so many $70 fuel pumps.
so would that constant voltage really be a problem that would break a fuel pump?
I guess i should backtrack.
I bought the jeep in 08, with the wiring in it's current predicament.
I drove it for a year, and then one day, after playing in some mud,
I got towed home. I cleaned up the Jeep, and attempted to fire her up, and it made the clear indication that it was not receiving gas.
I opened the tank and saw a glittered tank- the pump had some how grinded itself and decided not to work anymore.
so I replaced it, and the second one either never worked,
or pretty much instantly broke, I'm not sure i did not get enough time to fully test, now I'm testing all the parts, trying to find out what i can do to make sure the next pump lasts a lot longer than this one has.
Is it actually bad for those 12v to be constant?
or will that just drain my battery?

oh, and thanks for clearing that typo again.
I thought the wide spot was some sort of term,
like the skinny pedal you know?
skinny pedal i get, that one is easy,
but wide spot lost me.
the weld spot is good though,
like I said, the whole ground, grounds.
all along the wire and at the sending unit. it's grounded.
 
#22 ·
Damn! The OP is a real smarty pants. He had the unmitigated gall to post all the pertinent information about his YJ in his profile....How dare he do that!

:rofl: :rofl: :rofl: JK!

I assumed it was a 2.5 or a 4.0 and NEVER thought to check his profile. Doh!! :eek:
 
#20 ·
so, it has been brought to my attention that I missed out some important information-
the engine that needs fuel is a 5.0 HO- from a 95 mustang.
the hot wire is spliced into the main computer, and it is always hot- which it seems is frying my pump,
so the problem is weird because this happened after almost a year of driving, not at first.
and the plan is to try to get that hot wire back on it's original track so that it's only hot when the key is allowing it to be.

I'm off to grab some parts for my Dana 44 and then I have class, should be back in about six hours.
 
#21 ·
He needs to write the fuel pump back to the pdc and wire a switched ignition to control it. It sounds like he has the stock pdc still.
 
#24 ·
The po cut it so part of it is there and part isn't. I think he should use as much as he can. He is going to need help figuring out where the po cut it between the ignition switch and the pdc.

We are definitely on the same page. The only problem I can see is the fuel pump will be on when the ignition switch its turned on because the ECU will not be controlling it....unless we have him wire a kill switch for it.
 
#26 ·
....unless we have him wire a kill switch for it.
I would really prefer, really, really prefer to NOT add extra wires into the mix right now. If i can run out back tomorrow for a bit, I'll take some shots of the wiring set up I have, just to show how hectic it really gets...
 
#27 ·
No extra wires. Right now your pump is not all the time, with a rewire the pump will come off the fuel pump relay. Like I said though, you will have constant power while the ignition its on. The pump is wired to go off if you get into a wreck the engine cutting off will also kill the pump. It's easier to just wire it with the switch ignition. I bet if you can find the wiring diagram for the 5.0 ecu you will find a switched ground pin to control the fuel pump relay. We can wire the switch ignition feed for it but you are going to need to figure out the year for the ECU A's a wiring diagram if you want to wire it in for the ECU to switch the ground.
 
#29 ·
Flipit check on the ecu and see if this wiring diagram matches your ecu and if you have a wire for that pin. If you do then we are going to be able to get you setup real easy.
 
#33 ·
okay, bare with me as I'm not out of bed yet, I will send a picture to visually show what I'm about to explain.
pin 19/the green wire with a yellow stripe- herein referred to as wire 19-
so, if you hop in my jeep now,
and you look inside,
sitting on the A/C is my ECU.
there is a bunch of wires coming out of it,
and out of pin 19 comes wire 19,
a couple inches down wire 19, there is what I call an add-on splice.
if you dunno what that is,
pictures will be here after breakfast.
so, out of the add on splice comes another wire of the same color.
wire 19.5
so this wire 19.5 shoots straight through the firewall,
and in the engine compartment it is attached to an eye terminal.
said eye terminal is screwed into a post,
and the opposing post has another eye terminal,
which conveniently enough is the hot wire going to my fuel pump.
 
#35 ·
Oh and you definitely need to figure out the year of the ecu. The ecu wiring is totally different from the 89 to the 91-93 posted above. Here is the 89
 

Attachments

#36 ·
This is my ECU...



this is the wire, potruding out of pin 19



which makes this a lie



here's my add a splice, creating wire 19.5...

which goes through the firewall onto this terminal board,



which goes all the way to the fuel pump connector.

 
#37 ·
when I removed the top right screw from the terminal board there and metered the eye terminal of wire 19.5, it had 12 volts.
key is in the off and locked position.
if you see the add a splice, there is a connector there, the end of wire 19 is the only hot one on that connecter
 
#38 ·
Which is this plug!



Did you check that green wire for continuity from the plug back to where it ends at the firewall terminal board thingy?
 
#41 ·
this is on the wiring harness, not sure if it helps or not


also, just in case this was missed... My tranny is a borg warner manual.
haha, T-19 mated to a 1345 t case-
just in case any assumptions there were left undiscussed
 
#43 ·
Check your fuse panel under the dash for a blown 10 AMP fuse. It is for your ASD and fuel pump relay.
 
#47 ·
He isn't using the pdc at all for the fuel pump or the asd. That wiring really needs to be straightened out. That block off wires in your pic is an accident waiting to happen. The 12 volt supply makes no sense if it is a stock controller. You need to pull it and try and find id numbers on it. I can help wire around it but if that is a stock controller for a mustang it has to have failed to have power on a ground or you are not reading the right pin on the connector.
 
#48 ·
I agree, the wiring does need to be straightened out,
that's more of a long term goal,
Because of how much work it will take.
I pretty much need to redo all the wiring harnesses,
or at least 90% of them.
also if you look at the wiring terminal i put up behind the battery,
you'll see that the Green wire with a black stripe,
which is the hot wire to the fuel,
goes straight down, very snug against the firewall.
It was guitar string tight before- about three terminals in.
so I moved it all the way to the right just to get it at a straight length with minimal slack.
but wire 19.5 has a bundle of extra wire tied up in case i need more length....

when I pull the battery next time I'll show you the nest underneath it,
He crossed two harness's together and left all the extras just hanging.

but back to the topic-
what do i need to pull to find ID numbers?
 
#53 ·
Okay, so pin connector 19 is dark green with a yellow stripe, so the ECU I have fits the 91-93 pinout that was first linked.
So what I'm seeing is a pink and black cable that is hot at all times, and it goes into the relay, and out of the relay comes wire 19, which goes into the ecu. and over to the fuel inertia switch which I'm not sure that I have, but if i do, that can be another part.
What I'm seeing here is that if i backtrack wire 19, it should go to the relay. We know it doesn't, so the million dollar question... where does it go?
 
#54 ·
The fuel inertia switch is mounted in the dash panel of a Mustang.

A Wrangler uses a roll over valve mounted in the gas tank, The Mustang fuel pump relay is powered by the PK/BK wire.

When the ignition switch is turned to start power goes through the power PCM relay closing the fuel pump relay allowing voltage to travel along the DKGN/YL wire which is probably spliced to the GREEN WIRE in your Jeep fuel pump wiring at the gas tank.

That portion of the DKGN/YL wiring in the Mustang wiring diagram that shows power going through the inertia fuel shut-off switch has probably been eliminated and your green jeep wiring is spliced to it at that terminal board on your firewall
 
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