How to diagnose malfunctioning fuel pump system

[g6civcx]

Disclaimer
This thread was started in an effort to address common fuel pump questions. Zilvia.net and the author not responsible for content or misuse.

Always maintain a fire extinguisher meant for gasoline on hand, and do not smoke.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Background
If you suspect that you fuel pump is malfunctioning, symptoms can include impossible to start and you have verified that you have spark, fuel starvation, inoperative fuel pump, etc. The purpose of this article is to restore your fuel pump system to OEM specfications.

Go to zeroyon.com and download a copy of the FSM for your year 240SX. I will cover the DOHC S13 in this article. SOHC and S14s are similar.

Go to autozone.com and read the information available there on repair information. Select your vehicle from the choices available and look in the repair info section. They provide some basic information as well as some diagnostic and repair guidelines.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Tools
* Multimeter - a good, high quality multimeter tool should be used to diagnose electrical problems. You can get one from any electrical supply store. I will not cover how to use a multimeter. Follow the instructions on the package or search google for directions.
* Screwdrivers and sockets - to remove trim panels.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
System Description
Look at the following picture for general system description. It's self-explantory.

The fuel pump itself is located in the fuel tank. There is an access panel located in the trunk compartment, near the US-right passenger side. This is where the blue fuel pump harness will be.

Let's walk through how the stock fuel pump control system works.

1. Battery power is supplied via the E22 harness at the positive battery terminal.
2. Power passes through the fusible link located in Relay Box A located near the battery.
3. Power then travels to the ignition switch. When the ignition switch is turned to the ON position, power travels to the 15A fuse located in Relay Box A.
4. Power then travels to the fuel pump relay, also located in Relay Box A.
5. The fuel pump relay has 4 pins. 2 pins are connected to ignition power as described in #4. One pin goes to the ECU. One pin goes to the fuel pump itself.
When ignition power is available, the ECU can activate and deactivate the fuel pump. The fuel pump relay is normally open, i.e. no current flows to the fuel pump under normal conditions. To activate the fuel pump, the ECU draws current through the relay and the relay lets power flow to the fuel pump.
6. Fuel pump relay connection travels to the ECU through the firewall and to the ECU harness.
7. Fuel pump power travels to the fuel pump via the Super Multiple Junction (SMJ) located in the US-left driver side kick panel. It then travels via the body harness to the back of the trunk compartment.

Here are pictures of the locations of the various components.

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Preliminary Check

Have someone turn the ignition to ON. Listen for a faint, high-pitch noise as the fuel pump primes for several seconds. If you hear it, your fuel pump is getting power. If you continue to have problems, suspect a faulty fuel pump that is unable to maintain pressure or you have a leak somewhere in the fuel system.

Check your fusible link and fuse pump fuse. Inspect and replace as necessary. Sometimes a fuse can appear intact, but is in fact blown. Use your multimeter and measure for continuity between the two terminals of the fuse. If continuity doesn't exist, replace the fuse.

Check your fuse pump relay. Remove the relay. When you look at the pins of the relay, each pin is labeled with a number. Use a paper clip and jumper the 1 and 3 terminal on the wiring. If your fuel pump comes on with ignition, you have a bad relay.

Check the engine harness that runs under the US-left driver side front fender. This is common on 240SXs that has been lowered. The best way is to reroute this harness to the engine bay to avoid problems.

This is my friend and fellow Zilvia poster holding the harness.

You should relocate this harness to the engine bay like so.


These are the most common points of failure. Check them thoroughly. If you can't find anything, you will have to track down broken wires.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Fuel pump check
Turn the ignition off and go to the trunk compartment. We will be working around this area to see if the fuel pump is getting power. PLEASE MAKE SURE YOU DO NOT SMELL FUEL. If you do, fix it immediately. Working with your multimeter may expose some sparks. Make sure you do not smell fuel.

For information about the fuel pump, including how to change it, read this article: http://www.zilvia.net/f/showthread.php?t=94575

Credits to the author for his contributions. This is him holding the fuel pump. You will be looking for that blue harness.


Go find that blue harness and disconnect it. We will be working with the side on the fuel pump. Use your multimeter and check for continuity between the two wires going to the fuel pump. This harness is labeled 'C' in the circuit schematic.

What you're looking for is broken wiring somewhere in the fuel pump itself. If you do not get continuity, make sure you're checking the correct wires. If there's still no continuity, there is a broken wire or the fuel pump itself is defective. You can use bjorkluv's writeup to remove the fuel pump and repair, or look at the wires for damage.

If the fuel pump has continuity, we will go to the harness on the side of the body harness. We will be checking for power and ground.


Start by checking for continuity between terminal a and body ground. This is see if your ground wire is good. If you don't have continuity, follow the ground wire and repair the broken wire.

Now check for continuity between terminal c and pin 3 of the fuel pump relay. This checks to see if the wire described in #7 above is not broken. You will need a long wire to connect these 2 terminals. If you have no continuity, track down the broken wire and fix it.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ~~~~~~~~~~~~~
ECU check

Check for continuity between pin 2 of the fuel pump relay wire harness and pin 104 of the ECU. Please note that this is the KA ECU. If there is no continuity then you need to fix this broken wire.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ~~~~~~~~~~~~~
Relay harness check
Turn the ignition to ON. Check pin 2 and pin 3 of the harness individually for current. Ignition power should be delivered to these 2 pins when the key is turned to on. If ignition power is not present in both of these wires, track down the broken wires and fix them according to the schematic.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ~~~~~~~~~~~~~
Remaining items
If you still don't get power, track it to the fusebox and check the pin on the fuse pump fuse that supplies power.

If you still don't get power, you may have a faulty ignition switch or broken wire through the engine harness that runs under the front US-left driver side fender, as described above.

If all wires are intact then suspect the ignition switch and its wiring from the battery and the fusible link.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ~~~~~~~~~~~~~

Ignition switch failure is not that common, but could be possible, especially on cars that have been converted from auto to manual.

If all else fails, start tracing power from the battery and follow the circuit schematic. Go through the circuit one wire at a time and see how far power can be found. Look for the broken component and see if you can fix it.

This is a little complicated after looking through the obvious parts. Just be patient and learn how to read a wiring diagram. It'll also help if you learn a little about how electronics work.

Good luck!

[jdm_s14_zenki]

good job on the write up! probably a good idea to archive this one. i think we need more write ups like to for solutions to common, and uncommon problems. that would make zilvia a dope ass forum :]

[Dutchmalmiss]

Is there a way I can check if my pump is not only working, but working to its limit? For example, at WOT, and at full boost, it sounds like it's not getting enough fuel, and sounds like some sort of click sound.

I just want to know if it's my injectors, fuel pump, regulator, etc.

Thanks

[Slidin240Wayz]

Fuel Pressure gauge?

[projectRDM]

^ Bingo. Inline gauge, takes 60 seconds to install.

[Black Dawg]

Is there any way we can get this thread updated with pictures? I know it says that there's pictures of the components but they don't load anymore. The site they were hosted on is down or just doesn't load on my computer.

[g6civcx]

I really don't have a choice. Free Web hosting only lasts for a period of time and Zilvia attachments have size limits.

[driftermic]

Hey, how's it going, I need some help man I installed a brand new walbro fuel pump, an for about an hour it worked fine an it was quiet but after that hour it started making a loud whining noise, now it makes the noise as long as the car is running an it affects the way the car runs it starts to die after a short time what i do is pull over an turn it off an I wait a while then I start it back up an runs perfect for a while an then turn it off again a wait, what do you thing might be the problem? also i changed the other fuel pump I had because it was also whining an i checked the fuel pressure an it wasnt good, any help would be greatly appreciated thanks.

[g6civcx]

Originally Posted by driftermic

what do you thing might be the problem?

Could be any number of causes:

bad pump
bad ground
bad fuel pump relay
bad ECU
bad fuel pickup
clogged fuel line
bad fpr?

Sorry but you will have to check everything.

[90blacktop]

m....m..mm..m.

[Adam496]

I intended to make a new thread but somehow i ended up responding to this one. Since im not a premie and can't delete it i am wondering if anyone can help me out. I have a s14 with a redtop swap and i am having a problem getting the fuel pump to prime. When i test the relay, it is only giving off 5 volts at prong 1+3. So is there anything that would cause the relay to be giving out voltage lower than the battery or is the relay on its way out. ECU is from a working car and battery is fine.

[MarkShasti]

Originally Posted by g6civcx

Disclaimer
This thread was started in an effort to address common fuel pump questions. Zilvia.net and the author not responsible for content or misuse.

Always maintain a fire extinguisher meant for gasoline on hand, and do not smoke.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Background
If you suspect that you fuel pump is malfunctioning, symptoms can include impossible to start and you have verified that you have spark, fuel starvation, inoperative fuel pump, etc. The purpose of this article is to restore your fuel pump system to OEM specfications.

Go to zeroyon.com and download a copy of the FSM for your year 240SX. I will cover the DOHC S13 in this article. SOHC and S14s are similar.

Go to autozone.com and read the information available there on repair information. Select your vehicle from the choices available and look in the repair info section. They provide some basic information as well as some diagnostic and repair guidelines.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Tools
* Multimeter - a good, high quality multimeter tool should be used to diagnose electrical problems. You can get one from any electrical supply store. I will not cover how to use a multimeter. Follow the instructions on the package or search google for directions.
* Screwdrivers and sockets - to remove trim panels.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
System Description
Look at the following picture for general system description. It's self-explantory.

The fuel pump itself is located in the fuel tank. There is an access panel located in the trunk compartment, near the US-right passenger side. This is where the blue fuel pump harness will be.

Let's walk through how the stock fuel pump control system works.

1. Battery power is supplied via the E22 harness at the positive battery terminal.
2. Power passes through the fusible link located in Relay Box A located near the battery.
3. Power then travels to the ignition switch. When the ignition switch is turned to the ON position, power travels to the 15A fuse located in Relay Box A.
4. Power then travels to the fuel pump relay, also located in Relay Box A.
5. The fuel pump relay has 4 pins. 2 pins are connected to ignition power as described in #4. One pin goes to the ECU. One pin goes to the fuel pump itself.
When ignition power is available, the ECU can activate and deactivate the fuel pump. The fuel pump relay is normally open, i.e. no current flows to the fuel pump under normal conditions. To activate the fuel pump, the ECU draws current through the relay and the relay lets power flow to the fuel pump.
6. Fuel pump relay connection travels to the ECU through the firewall and to the ECU harness.
7. Fuel pump power travels to the fuel pump via the Super Multiple Junction (SMJ) located in the US-left driver side kick panel. It then travels via the body harness to the back of the trunk compartment.

Here are pictures of the locations of the various components.

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Preliminary Check

Have someone turn the ignition to ON. Listen for a faint, high-pitch noise as the fuel pump primes for several seconds. If you hear it, your fuel pump is getting power. If you continue to have problems, suspect a faulty fuel pump that is unable to maintain pressure or you have a leak somewhere in the fuel system.

Check your fusible link and fuse pump fuse. Inspect and replace as necessary. Sometimes a fuse can appear intact, but is in fact blown. Use your multimeter and measure for continuity between the two terminals of the fuse. If continuity doesn't exist, replace the fuse.

Check your fuse pump relay. Remove the relay. When you look at the pins of the relay, each pin is labeled with a number. Use a paper clip and jumper the 1 and 3 terminal on the wiring. If your fuel pump comes on with ignition, you have a bad relay.

Check the engine harness that runs under the US-left driver side front fender. This is common on 240SXs that has been lowered. The best way is to reroute this harness to the engine bay to avoid problems.

This is my friend and fellow Zilvia poster holding the harness.

You should relocate this harness to the engine bay like so.


These are the most common points of failure. Check them thoroughly. If you can't find anything, you will have to track down broken wires.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Fuel pump check
Turn the ignition off and go to the trunk compartment. We will be working around this area to see if the fuel pump is getting power. PLEASE MAKE SURE YOU DO NOT SMELL FUEL. If you do, fix it immediately. Working with your multimeter may expose some sparks. Make sure you do not smell fuel.

For information about the fuel pump, including how to change it, read this article: http://www.zilvia.net/f/showthread.php?t=94575

Credits to the author for his contributions. This is him holding the fuel pump. You will be looking for that blue harness.


Go find that blue harness and disconnect it. We will be working with the side on the fuel pump. Use your multimeter and check for continuity between the two wires going to the fuel pump. This harness is labeled 'C' in the circuit schematic.

What you're looking for is broken wiring somewhere in the fuel pump itself. If you do not get continuity, make sure you're checking the correct wires. If there's still no continuity, there is a broken wire or the fuel pump itself is defective. You can use bjorkluv's writeup to remove the fuel pump and repair, or look at the wires for damage.

If the fuel pump has continuity, we will go to the harness on the side of the body harness. We will be checking for power and ground.


Start by checking for continuity between terminal a and body ground. This is see if your ground wire is good. If you don't have continuity, follow the ground wire and repair the broken wire.

Now check for continuity between terminal c and pin 3 of the fuel pump relay. This checks to see if the wire described in #7 above is not broken. You will need a long wire to connect these 2 terminals. If you have no continuity, track down the broken wire and fix it.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ~~~~~~~~~~~~~
ECU check

Check for continuity between pin 2 of the fuel pump relay wire harness and pin 104 of the ECU. Please note that this is the KA ECU. If there is no continuity then you need to fix this broken wire.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ~~~~~~~~~~~~~
Relay harness check
Turn the ignition to ON. Check pin 2 and pin 3 of the harness individually for current. Ignition power should be delivered to these 2 pins when the key is turned to on. If ignition power is not present in both of these wires, track down the broken wires and fix them according to the schematic.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ~~~~~~~~~~~~~
Remaining items
If you still don't get power, track it to the fusebox and check the pin on the fuse pump fuse that supplies power.

If you still don't get power, you may have a faulty ignition switch or broken wire through the engine harness that runs under the front US-left driver side fender, as described above.

If all wires are intact then suspect the ignition switch and its wiring from the battery and the fusible link.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ~~~~~~~~~~~~~

Ignition switch failure is not that common, but could be possible, especially on cars that have been converted from auto to manual.

If all else fails, start tracing power from the battery and follow the circuit schematic. Go through the circuit one wire at a time and see how far power can be found. Look for the broken component and see if you can fix it.

This is a little complicated after looking through the obvious parts. Just be patient and learn how to read a wiring diagram. It'll also help if you learn a little about how electronics work.

Good luck!

Thanks a lot for your Guidance .They are really helpful in my work.I am owner of Jay's Auto Service auto repair shop.We offer a wide range of auto repair services including Tires change,breaks,shocks,alignment,suspension,ac service etc.and these type of forum helps me a lot.