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Electric fuel pump works when hooked directly to battery but not to original leads

No wires have breaks harness looks good no dry wrought. If I ran a new lead Where should I run it from or should I run a switch?

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Many shade tree guys will tell you run a switch and direct wire. This is not a good answer. The circuit includes an oil pressure switch which kills the pump in the event of an accident, to prevent the pump from running and feeding gas to a possible fire. There is also a bypass to supply juice while cranking. Fix it right! Check fuel pump fuses (sometimes two) and fuel pump relay.

Posted on Mar 27, 2015


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My new fuel pump only primes when wired direct?

Well you need to get out the DVOM - digital volt ohm meter an check for battery voltage at the fuel pump relay ! if you replaced it you saw the holes it plugs into in the relay / fuse box ? Put you volt meter on the 20 volt scale , hook the black lead to the battery negative or a good engine ground an take the red lead an touch - don't stick it in an spread the terminals . Two of the holes should have battery voltage ,if not check the EEC power relay ! If you find voltage at two holes change the meter to ohms , leave the black connector on a good ground an touch the red to the two holes left , one should be open or OL on the meter , this is the control side from the engine computer . the last hole should show a few ohms resistance , this is down through the wiring to an through the fuel pump to ground . You have two different wiring circuits , control an load side , load side being power to the fuel pump an control side is power an the engine computer supplying a ground energizing the relay closing the contacts in the relay sending battery voltage to the fuel pump. Test don't guess !

May 25, 2015 | 1987 Ford Ranger

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Car was running in driveway then just stopped. fuse was blown. replaced fuse ran for 5mins, fuse blew again. replaced fuse ran for 10mins fuse blew again. replaced fuel pump, car ran for three days then...


i am assuming that the fuse you are replacing is the fuse for the fuel pump, then replacing the fuel pump did solve ur problem for 3 days.

did you check again the fuse of the fuel pump? if it is blown again, try looking at manual to see if you are putting the right fuse. is the fuel pump that you put in is an original pump for the car or a replacement pump?.

if it is a replacement pump, kindly check the label and if you can find out what rating of fuse it is using then use that fuse rating for that particular pump.

another case could be another defective pump...could be a factory defect...

you can compare resistance of windings of pumps to find out if they have problems.

another thought could be if there is a return line on your fuel system..if this is clogged and building up a pressure on the fuel line, then this could cause a problem on your fuel pumps.

i hope i was able to solve ur problem,

pls rate me,

tnx drcool

Jul 28, 2008 | Suzuki XL7 Cars & Trucks

1 Answer

I found no power going to driver side switches.(I disconnected original yellow hot lead) Where would the original wire be going that it may have corroded and lost it's connection?

A lot of time the feed wire breaks inside of the body to door harness. Look inside the black flex tube. I bet its there you find the trouble.

Mar 04, 2015 | 2007 Chevrolet Uplander Cargo

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Could I run a electric fuel pump on my 1998 Cadillac deville?

if it did not have an electric fuel before then the installation of an electric pump is a relatively easy process. If you have an electric pump already fitted but it has failed then remove it and install the new pump in its place. Take care to check all wires, fuses and relays and any pressure sensors for correct operation. Remove and blank of the opening for any mechanical pump on the engine
For new installation select an easily accessible place under the vehicle that can be protected from flying rocks and road debris. Run a power wire (red colour) from the run side of the ignition switch to the relay ( to be fitted ) near the battery or in the engine bay. Run this wire through an inline fuse close to the ignition switch to protect the circuit. attach to a coil actuation terminal of the relay.( look at the base of the relay for terminal identification. Run a black wire from the other side of the coil actuation pin on the relay to earth. Normally the same bolt that mounts the relay. Run a red wire capable of carrying 20 amps directly from the battery terminal through an inline fuse ( close to the terminal) to a power pin on the relay. Run another red wire from the outlet power pin on the relay to the electric pump. . Run an earth wire from the pump to earth.
This is a basic electric circuit for the installation of the pump. If there is a requirement for a pressure regulator or pressure sensor to control the pressure or pump operation , that control wire will be connected in series into the wire from the ignition switch so that when the pressure is reached then it breaks the circuit to the relay from the ign. switch and the pump will stop operation until the circuit is again completed. When the ignition switch is off there will be no power for the pump

Oct 09, 2014 | 1998 Cadillac DeVille

1 Answer

Fuel pump testing

Yes the gray wire goes from the relay to the pump, and the black wire grounds the pump.
I should tell you running the tank dry kills the pump. The pump uses liquid gasoline to cool and lube the pump. Running low on gas makes the pump work harder and hotter. Never run an electric pump below 1/4 tank of gas.
While you have the pump out you should fix the gauge too if you can.

May 28, 2013 | 1999 Chevrolet S-10 Pickup

1 Answer

98 z24 parked the car went out next day. Engine turns over but won't start. Ran the fuel pump direct and it runs. Disconicted the battery for 20 minute and stell nothing all fuses good and relays .

if the car runs when you feed the fuel pump directly then you have a fuel pump relay problem,no good or bad connection.if the fuses are good then its possible the relay may not be sending a signal(voltage) out to the pump to run or it is but there`s a wiring problem from the relay to the don`t say how or were you feed the pump.if you feed the pump using the spade connector for the pump feed in the wiring harness under the hood then the problem could be were that wire splices off back to the relay.i don`t think its the pcm not getting the signal while cranking or the check engine light would be on,as the pcm uses this to turn on the fuel relay to turn on the pump.

May 03, 2011 | Chevrolet Cavalier Cars & Trucks

1 Answer

Fuel Pump wiring

If I understand right, I would say the normal ground for the pump is bad.
"I am guessing the pump uses a ground source to start." well, just the normal ground like for any motor, you have the power wire (gray) to the pump, then the ground wire for pump, does it branch off near the tank and find a ground? Or does it go into the tank connector and then routed back somewhere through the wiring harness? Anyway, it has to go to ground somewhere. You have the wiring right it sounds,. just make a good ground source, or find the original ground and repair it.

Mar 14, 2017 | 1999 GMC Sierra

6 Answers

I replaced fuel pump on a 2000 Silverado a week ago and it works till now. WHen key is on there is no power going to the fuel pump. Also the wire has light dirtyness to it. I had a extra power source and...

i think you answered your own question on if its the pump itself. if you had an extra power source hooked up and it worked then that tells you that is good.. i would try replacing the battery (whether its the problem or not it needs a new one to run anyway.) Think Logically. when you turn that key not only is the fuel pump looking for power. so is the starter the ignition control module. dash lights Daytime running lights if your truck has them and umpteen sensors are begging for power too. someone is the low man on the totem pole and with the fuel pump being the farthest away i would guess thats it.

Electricity is lazy. it takes the shortest path to ground. If it can go through this sensor to get to ground easier than running through the fuel pump then its going to.

one thing that might work (i haven't tried this i just spun this idea off the top of my head) is hook your truck up like your going to jump start it and try to start it and see if that second battery gives it that little extra umph to start.

Oct 28, 2009 | 1999 Chevrolet Silverado 1500

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No power from wiring harness to fuel pump on 2000 s 10

on the drivers side left rear frame next to bumper bracket there is a ground for the fuel pump make sure it is not cut or rusty . the 4.3 has a oil sending unit at back of intake it controls fuel pump . oil sensor tells the computer to give power to fuel pump.

Apr 11, 2009 | 2000 Chevrolet S-10

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