My fuel pump on my 1988 325i will not come on, I checked for power at fuel pump, no poer at pump, both wires reading as a ground. but can turn pump on with power probe. checked fuel pump fuse. fuse good, checked relay, found relay not cycling replace relay. relay has constant 12 volts and key on 12 volts but no ground. if i send ground to relay with power probe fuel pump turns on. back traced green wire with red stripe to pcm, pcm was sending battery voltage. checked for grounds going to pcm all 3 are good. Then I sent ground to green/red wire with power probe to back of pcm and fuel pump turns on. replaced pcm, still sends poer to green and red wire. Is there something else that tells the pcm to send ground and close relay? Thank You [email protected]

Does vehicle engine turn over. If yes, then pay attention to fuel system. Check for good power and ground at fuel pump connector. If no power check fuel pump fuse, relay and for open wires (power, ground) to fuel pump.

Not sure what you are using as a ground when checking voltage. If you check at the connector you should have 12 volts at the blue wire with the red stripe (red prong on volt meter) and you can check putting the ground/black prong on your volt meter on either one of the black wires on the connector. When turning the key just to the on position you\'re only going to get full power for about 2 seconds unless you\'re turning the engine over. If you\'re not getting full voltage try putting the black prong (leaving the red one from meter on the terminal that has the blue wire with the red stripe) using a good ground on the body of the vehicle (the black prong from meter). Now if you\'re getting the voltage you need then you need to trace the black wire(s) to where they are grounded out on the vehicle and clean/tighten and repair the ground as well as making sure you are getting zero continuity from where the ground is on the body to the connector at the fuel pump. A bad ground will cause weak power. These are also the 2 wires you need to apply direct power (on the pump side of the connector) in order to check the pump as you asked. Since there are 2 black wires at the connector, if you have direct power to the blue and red wire and put your ground on one of the black wires and it doesn\'t run, than try using the other black wire (or where it would be on the terminal of the connector...pump side) at the connector because that would mean you are testing the wrong ground wire for the pump itself. If your ground is good down there and it turns on when applying direct power than it could be a number of things but the 2 most common would be the fuel pump relay or the air flow meter/sensor. Start with check power and ground and direct powerfirst. If the pump is working when putting direct power and your grounds are good then further testing needs to be done of course. I\'ll be happy to help you with further testing if needed like checking the relay and/or air flow meter. You will need an ohm meter for further testing. I hope I was detailed enough for you to understand the testing needed at this point and I hope I was able to help

If relay worked when placed in another vehicle you must have a wiring problem. trace wires from fuse block to relay checking for corrosion or short.

have you check for power to the main fuel relay ,it is near the ECM. it also poers the ECM up. if no power is coming from it then the ECM will not ground the secondary fuel relay to transfer power back to the fuel pump.

You have lost the ground input to the gas gage. Its the black wire coming from the fuel pump connector at the fuel pump. Either the wire is broken or the input to the body control computer is broken, thus creating high Resistance on the input wire. The computer will think the tank is full, a shorted wire would indicate lo Resistance and read empty. Locate the fuel pump connector and jumper the black wire directly to the body (ground) and turn the key to run, check gage. If reads normal the wire is broken betwwen fuel tank and its ground location.

POWER GOING TO FUEL PUMP NOT TO FUEL PUMP.YOU CAN BUY AND REPLACE FUEL PUMP WIRES SEPERATELY.SOUND LIKE OLD WIRES HAS A OPEN CIRCUIT OR POOR GROUND.

First make a set of jumper wires and jump the pump from the battery and see if it works. If it runs its the relay or the ECU,or the ignition switch.
Remove the relay and test it for B+. Then jump the terminals and see if the pump runs. If pump runs and you got B+ up to this point its the relay.
However,if no B+ at the relay means ECU not giving relay the turn on signal..
While wearing a ground wrist strap check out ECU Grounds and B+ wires for continuity from Ignition switch and other areas of interest (use shop manual)
either the switch is not telling ecu to send message to relay to turn on the pump or someone in this circuit has gone bad.

How to Replace a Fuel Pump

Parts:
1. Fuel Pump - $51.16



DELPHI, ELECTRIC FUEL PUMP -- Meets Or Exceeds OEM Quality, Matches The Genuine Fit And Function

Tools:
1. 3/8 in. Drive Ratchet
2. Floor Jack
3. Multimeter
4. Jack Stand Set
5. Flat Head Screwdriver
6. Mallet Hammer
7. Socket Set

Steps:
Step 1 * Locate the fuel pump.
o Tip: Safety Tip:Always wear safety glasses when working on your vehicle. Wear other personal protective equipment (PPE) when necessary, for example latex gloves or safety shoes.

Step 2 * Have a friend turn the key to the“ON” position while you listen for a high pitched hiss/whine coming from the electric fuel pump.
o Tip: If the fuel pump is located in the fuel tank, you can open the fuel cap and listen to hear the fuel pump. The fuel pump should run (priming the system with fuel) for a couple of seconds. Once it stops, you should be able to start the vehicle.

Step 3 * If the fuel pump does not make a sound (run and prime the fuel system) check to see if there is a fuse that supplies power to the fuel pump and check its location.
o Tip: Check the owner’s manual for location of the fuse box and fuel pump fuse.

Step 4 * Once you have found the location of the fuel pump fuse, remove the fuse from its housing and check to see if it is blown.
o Tip: A blown fuse will usually have a metal strip connecting both tabs that“blows out” (the wire looks as if it has been chopped in half or broken).

Step 5 * If you noticed that the fuse was blown, replace the fuse with a new fuse of the same amperage and repeat step 2.

Step 6 * If the fuel pump now works, you do not need to replace it. However, you will need to find what caused the fuel pump fuse to blow. We strongly recommend that this is done through a certified shop, unless you have the tools and knowledge to test electrical systems and diagnose more in depth problems.

Step 7 * If the fuse wasn’t blown, it should be checked for power and ground at the fuel pump. If there is power and ground present then you will need to replace the fuel pump.
o Tip: On most vehicles you may need to lower the fuel tank to access the power and ground leads for the fuel pump.

Step 8 * Siphon or drain as much fuel as possible from the fuel tank. Disconnect any possible fuel lines from the fuel tank.

Step 9 * Remove any retaining straps or bolts holding the fuel tank to the frame.
o Tip: You may be able to access the fuel pump from the bottom of the back seat or the trunk of the vehicle.

Step 10 * Using a digital multi meter, turn the key to the“ON” position and check for power at the fuel pump. Touch the negative lead from the DMM to a good ground and the positive lead of the DMM to the power cable at the fuel pump. You should have a reading that is equal to battery power. If you do not have a reading at all, you will need to inspect the power side of the fuel pump.
o Tip: With the ground lead of the DMM still connected to a good ground, touch the power lead to the positive side of the battery, to each side of the fuse, and again to the fuel pump. Wherever you notice the voltage reading goes from battery voltage to 0 you will need to replace whatever wires and fuse are in between.

Step 11 * If you have noticed that the power and ground being supplied to the fuel pump are both good, then you will need to replace the fuel pump.
o Tip: To check for a good ground, place the negative lead from the DMM to the ground side of the fuel pump, and the positive lead of the DMM to the positive side of the battery. If the reading on the DMM is battery voltage then you have a good ground.

Step 12 * Remove any retaining rings or bolts that hold the fuel pump in the fuel tank.

Step 13 * Remove any electrical connections or fuel lines connected to the fuel pump. Replace the fuel pump.
o Tip: If equipped, inspect and replace strainer as needed.

Step 14 * Use reverse procedure to install fuel pump and assemble all components back to their original state.

Step 15 * Start the vehicle to verify repairs.


Good job (remember rated and comment this help).

How to Replace a Fuel Pump
DIY & Save up to $219.24 (Complexity: Hard / Time: 3.2 hours)

Parts:
1. Fuel Pump - $140.07

Tools:
1. 3/8 in. Drive Ratchet - $7.55
2. Floor Jack - $145.54
3. Multimeter - $247.13
4. Jack Stand Set - $36.93
5. Flat Head Screwdriver - $3.14
6. Mallet Hammer - $6.83
7. Socket Set

Steps:
1 Locate the fuel pump.
- Tip: Safety Tip:Always wear safety glasses when working on your vehicle. Wear other personal protective equipment (PPE) when necessary, for example latex gloves or safety shoes.
2 Have a friend turn the key to the“ON” position while you listen for a high pitched hiss/whine coming from the electric fuel pump.
- Tip: If the fuel pump is located in the fuel tank, you can open the fuel cap and listen to hear the fuel pump. The fuel pump should run (priming the system with fuel) for a couple of seconds. Once it stops, you should be able to start the vehicle.
3 If the fuel pump does not make a sound (run and prime the fuel system) check to see if there is a fuse that supplies power to the fuel pump and check its location.
- Tip: Check the owner’s manual for location of the fuse box and fuel pump fuse.

4 Once you have found the location of the fuel pump fuse, remove the fuse from its housing and check to see if it is blown.
- Tip: A blown fuse will usually have a metal strip connecting both tabs that“blows out” (the wire looks as if it has been chopped in half or broken).

5 If you noticed that the fuse was blown, replace the fuse with a new fuse of the same amperage and repeat step 2.
6 If the fuel pump now works, you do not need to replace it. However, you will need to find what caused the fuel pump fuse to blow. We strongly recommend that this is done through a certified shop, unless you have the tools and knowledge to test electrical systems and diagnose more in depth problems.
7 If the fuse wasn’t blown, it should be checked for power and ground at the fuel pump. If there is power and ground present then you will need to replace the fuel pump.
- Tip: On most vehicles you may need to lower the fuel tank to access the power and ground leads for the fuel pump.

8 Siphon or drain as much fuel as possible from the fuel tank. Disconnect any possible fuel lines from the fuel tank.
9 Remove any retaining straps or bolts holding the fuel tank to the frame.
- Tip: You may be able to access the fuel pump from the bottom of the back seat or the trunk of the vehicle.

10 Using a digital multi meter, turn the key to the“ON” position and check for power at the fuel pump. Touch the negative lead from the DMM to a good ground and the positive lead of the DMM to the power cable at the fuel pump. You should have a reading that is equal to battery power. If you do not have a reading at all, you will need to inspect the power side of the fuel pump.
- Tip: With the ground lead of the DMM still connected to a good ground, touch the power lead to the positive side of the battery, to each side of the fuse, and again to the fuel pump. Wherever you notice the voltage reading goes from battery voltage to 0 you will need to replace whatever wires and fuse are in between.

11 If you have noticed that the power and ground being supplied to the fuel pump are both good, then you will need to replace the fuel pump.
- Tip: To check for a good ground, place the negative lead from the DMM to the ground side of the fuel pump, and the positive lead of the DMM to the positive side of the battery. If the reading on the DMM is battery voltage then you have a good ground.

12 Remove any retaining rings or bolts that hold the fuel pump in the fuel tank.
13 Remove any electrical connections or fuel lines connected to the fuel pump. Replace the fuel pump.
- Tip: If equipped, inspect and replace strainer as needed.

14 Use reverse procedure to install fuel pump and assemble all components back to their original state.
15 Start the vehicle to verify repairs.

Hope helps with this (remember rated this help) Good luck.

You have a short to ground.What that means is,you have a power wire...............that is grounding on the vehicle somewhere,or possibly back in the fuel pump.The fuel pump theoretically could be shorted internally causing the problem.It also could be a wire or wires back where you were working possibly got pinched.Disconnect negative battery terminal until problem is solved.