Fuel Pump Issues... AGAIN

[moozieman]

My fuel pump has never run correctly in my 1977 280z. Currently, I get no voltage coming off the wires leading up to the fuel pump when I crank. I swear I've read voltage off those wires before, but one day during the process of rebuilding, it just stopped. So what i've done is hard wired the pump to the battery with a switch in the middle and that's it. Is there any problem with this method? I just flip the switch and let the fuel pump run while running the engine. Ideally, I would like to fix this. I've read things about the fuel pump safety switch getting stuck and cutting off power. Is there anything else I could look into? How would I test this switch?

[Patcon]

Somebody should reply with an answer on the diagnosis but direct wiring a fuel pump is not a good idea. At the very least, I would add an inertial kill switch in case of accident. Sitting inside a Molotov cocktail never sounds like fun!

[superlen]

Here is a quick guide to how that FI relay works.

First some notes:

N1- The FI relay (FIR) actually has two physical relays in it (call them X1,X2).

N2- X1 provides power to the fuel pump and the air regulator (both the pump and regulator +12V feed are connected together directly INSIDE the FI) When X1 fires, your pump should spin and your air regulator should have power. (remember this note for later when we debug the circuit)

N3 - X2 provides power to the ECU, the Dropping Resistors, and the AFM air flow switch(which incidentally is also one of the items that can fire X1 to make your pump run) This is also the safety switch that if your engine dies, your fuel pump turns off. Caveat: 78 and later they replaced the airflow switch with an oil pressure switch. Both offer the same exact function, just a different method of determining when the engine is NOT running.

N4 - X1 (which again will turn on your pump) gets it's signal and is fired by one of two methods. The AFM switch we just mentioned in Note3 & the start signal (CRANK) from the ignition switch. Either input will fire X1 and you should have a running fuel pump (as well as +12V feed to your air regulator)

N5 - Datsun wiring harness for the EFI is fairly easy to traverse as Datsun conveniently printed the wire number in light white or light yellow numbers. If I refer to W36 it means the wire with number 36 written on it. Many times, but not in all case, when W36 terminates at a connector, the connector will have "36" stamped in it as well. For example, the AFM connector & the ECU connector. Somewhat UN-convenient is the fact that most all of the wires are green. ?

-- Lets debug a little.

1 - If the pump isn't working, it can be one of the following: No power feeding X1, no signal telling X1 to turn on, or the power being routed through X1 is not reaching the pump.

2 - Remember Note2 where we said the air regulator and pump power are tied together. The air  regulator is right on top of the engine and super easy to reach and test with a meter. So the first step is to pull the air regulator connector, locate W48. Probe it with a multimeter and see if it has power when you CRANK the engine and/or push the AFM flap in. If you get 12V there with either of those tests, you know X1 is working, and the problem is downstream of the FIR with the wiring from W74 exiting  FIR to the pump, or the pump itself.

3 - If you don't get 12v with those tests, jumper 12v to W48 and you should hear the pump run. This will confirm your wiring to the pump is good and we are in fact chasing down a problem that is in the relay or power to the relay. IMPORTANT: The air regulator connector also has W34 which runs to the ECU. The ECU grounds this wire to turn on the air regulator. If you mistakenly jumper 12V to this wire you will be shorting 12v to gnd through the ECU!!! Don't guess, double check which wire you are working with. If you are worried, just unplug the ECU.

4 -   If it is the relay, move on to ensuring that power is reaching the relay properly. This is a little more difficult as the relay isn't the easiest to get to.

5 -  Before the next few tests, you need to confirm that the FIR is getting a good ground. It comes in on W72. Place the ground side of your meter on W72 at the relay and the pos side on the +12V and make sure you read +12V on the meter. If not, check the ground connection of W72.

6 -  With the key OFF, measure voltage at W73 at the relay. It should be 12V.  If not, check your fusible links.

7 -  With the key OFF, measure voltage at W70 at the relay. It should be 12V.  (The schematic shows direct from battery, but I believe it is coming from a fusible link as well) I'll confirm later..

8 - With the key ON (but not cranking), measure voltage at W71 at the relay. It should be 12V. If not, check the ignition switch.

9 - With the key ON (but not cranking), measure voltage at W39/W10 or W43. All should be 12V. If not, X2 inside FIR isn't working.An easy way to reach W39 is at the AFM plug.

10 - With the key in the START position, we are back up to Step 2.

 

Len

[moozieman]

On 10/10/2019 at 10:11 AM, superlen said:

Here is a quick guide to how that FI relay works.

First some notes:

N1- The FI relay (FIR) actually has two physical relays in it (call them X1,X2).

N2- X1 provides power to the fuel pump and the air regulator (both the pump and regulator +12V feed are connected together directly INSIDE the FI) When X1 fires, your pump should spin and your air regulator should have power. (remember this note for later when we debug the circuit)

N3 - X2 provides power to the ECU, the Dropping Resistors, and the AFM air flow switch(which incidentally is also one of the items that can fire X1 to make your pump run) This is also the safety switch that if your engine dies, your fuel pump turns off. Caveat: 78 and later they replaced the airflow switch with an oil pressure switch. Both offer the same exact function, just a different method of determining when the engine is NOT running.

N4 - X1 (which again will turn on your pump) gets it's signal and is fired by one of two methods. The AFM switch we just mentioned in Note3 & the start signal (CRANK) from the ignition switch. Either input will fire X1 and you should have a running fuel pump (as well as +12V feed to your air regulator)

N5 - Datsun wiring harness for the EFI is fairly easy to traverse as Datsun conveniently printed the wire number in light white or light yellow numbers. If I refer to W36 it means the wire with number 36 written on it. Many times, but not in all case, when W36 terminates at a connector, the connector will have "36" stamped in it as well. For example, the AFM connector & the ECU connector. Somewhat UN-convenient is the fact that most all of the wires are green. ?

-- Lets debug a little.

1 - If the pump isn't working, it can be one of the following: No power feeding X1, no signal telling X1 to turn on, or the power being routed through X1 is not reaching the pump.

2 - Remember Note2 where we said the air regulator and pump power are tied together. The air  regulator is right on top of the engine and super easy to reach and test with a meter. So the first step is to pull the air regulator connector, locate W48. Probe it with a multimeter and see if it has power when you CRANK the engine and/or push the AFM flap in. If you get 12V there with either of those tests, you know X1 is working, and the problem is downstream of the FIR with the wiring from W74 exiting  FIR to the pump, or the pump itself.

3 - If you don't get 12v with those tests, jumper 12v to W48 and you should hear the pump run. This will confirm your wiring to the pump is good and we are in fact chasing down a problem that is in the relay or power to the relay. IMPORTANT: The air regulator connector also has W34 which runs to the ECU. The ECU grounds this wire to turn on the air regulator. If you mistakenly jumper 12V to this wire you will be shorting 12v to gnd through the ECU!!! Don't guess, double check which wire you are working with. If you are worried, just unplug the ECU.

4 -   If it is the relay, move on to ensuring that power is reaching the relay properly. This is a little more difficult as the relay isn't the easiest to get to.

5 -  Before the next few tests, you need to confirm that the FIR is getting a good ground. It comes in on W72. Place the ground side of your meter on W72 at the relay and the pos side on the +12V and make sure you read +12V on the meter. If not, check the ground connection of W72.

6 -  With the key OFF, measure voltage at W73 at the relay. It should be 12V.  If not, check your fusible links.

7 -  With the key OFF, measure voltage at W70 at the relay. It should be 12V.  (The schematic shows direct from battery, but I believe it is coming from a fusible link as well) I'll confirm later..

8 - With the key ON (but not cranking), measure voltage at W71 at the relay. It should be 12V. If not, check the ignition switch.

9 - With the key ON (but not cranking), measure voltage at W39/W10 or W43. All should be 12V. If not, X2 inside FIR isn't working.An easy way to reach W39 is at the AFM plug.

10 - With the key in the START position, we are back up to Step 2.

 

Len

I appreciate the help and the thorough answer. Im confused as to which numbered terminals I should be looking at. You say W48? I'm not seeing any numbers. Are they on the connectors? I assume im doing something wrong. And where exactly should I be touching the meter leads? I tested by connecting them to the two contacts on the air meter plug. I never read any voltage, even when I was lifting the door in the afm.

[superlen]

W48 would indicate Wire 48. *Most* of the time wire 48 would end up a terminal on a connector and the connector will have '48' stamped in it, but this isn't always the case so it is a bit confusing. However, '48' is printed on the green wire...very small in faint yellow or white. ?

It's best to work with the wiring diagram printed out in front of you and follow W48 to where it connects. W48 runs to the Air regulator as well as the fuel pump so do this:

1. Locate the two position plug on the air regulator. Note this is the auxillary air regulator, NOT the Airflow Meter (AFM).

2. Unplug it from the regulator. Forget about the regulator now. We don't care about it, it's just an easy place to find W48.

3. Look at the two wires going to the plug and find the one with 48 printed on it.

4. Take your voltmeter (make sure it's on Volts scale if multimeter). Black lead on bat ground., Red lead on Bat Pos. It should of course read 12V (just testing that your meter is working)

5. Now move the red lead to W48. It shouldn't read any volts.

6. Now turn the ignition key to crank. What does you meter read? It should read ~12V. (A helper is handy here)

7. Now take of the air intake boot in (front of AFM) so you can push your finger in their and push the flap open a bit. Read your meter again, it should read 12volts with the flap being pushed open, 0volts when flap is closed.

Post back your voltage readings and we can keep tracking it down. Not the fastest of methods, but we can figure this out.

 

 

Len

 

[Zed Head]

The relay numbers are pressed in to the fiber board bottom of the relay.  Very difficult to see, but they are there.  Sometimes the stamping is not too sharp.  Bright light and good eyesight help.

[moozieman]

22 minutes ago, superlen said:

W48 would indicate Wire 48. *Most* of the time wire 48 would end up a terminal on a connector and the connector will have '48' stamped in it, but this isn't always the case so it is a bit confusing. However, '48' is printed on the green wire...very small in faint yellow or white. ?

It's best to work with the wiring diagram printed out in front of you and follow W48 to where it connects. W48 runs to the Air regulator as well as the fuel pump so do this:

1. Locate the two position plug on the air regulator. Note this is the auxillary air regulator, NOT the Airflow Meter (AFM).

2. Unplug it from the regulator. Forget about the regulator now. We don't care about it, it's just an easy place to find W48.

3. Look at the two wires going to the plug and find the one with 48 printed on it.

4. Take your voltmeter (make sure it's on Volts scale if multimeter). Black lead on bat ground., Red lead on Bat Pos. It should of course read 12V (just testing that your meter is working)

5. Now move the red lead to W48. It shouldn't read any volts.

6. Now turn the ignition key to crank. What does you meter read? It should read ~12V. (A helper is handy here)

7. Now take of the air intake boot in (front of AFM) so you can push your finger in their and push the flap open a bit. Read your meter again, it should read 12volts with the flap being pushed open, 0volts when flap is closed.

Post back your voltage readings and we can keep tracking it down. Not the fastest of methods, but we can figure this out.

 

 

Len

 

I really do appreciate your help! I'll look into this and get back next time i'm at the garage.

[moozieman]

23 minutes ago, superlen said:

W48 would indicate Wire 48. *Most* of the time wire 48 would end up a terminal on a connector and the connector will have '48' stamped in it, but this isn't always the case so it is a bit confusing. However, '48' is printed on the green wire...very small in faint yellow or white. ?

It's best to work with the wiring diagram printed out in front of you and follow W48 to where it connects. W48 runs to the Air regulator as well as the fuel pump so do this:

1. Locate the two position plug on the air regulator. Note this is the auxillary air regulator, NOT the Airflow Meter (AFM).

2. Unplug it from the regulator. Forget about the regulator now. We don't care about it, it's just an easy place to find W48.

3. Look at the two wires going to the plug and find the one with 48 printed on it.

4. Take your voltmeter (make sure it's on Volts scale if multimeter). Black lead on bat ground., Red lead on Bat Pos. It should of course read 12V (just testing that your meter is working)

5. Now move the red lead to W48. It shouldn't read any volts.

6. Now turn the ignition key to crank. What does you meter read? It should read ~12V. (A helper is handy here)

7. Now take of the air intake boot in (front of AFM) so you can push your finger in their and push the flap open a bit. Read your meter again, it should read 12volts with the flap being pushed open, 0volts when flap is closed.

Post back your voltage readings and we can keep tracking it down. Not the fastest of methods, but we can figure this out.

 

 

Len

 

I was by myself when i tested this afternoon, so i did not try cranking it, but I did open the afm flap and for some reason, still read 0.00 V.

[superlen]

Ok, so no voltage there with flap open...so the FI relay is NOT routing 12V to this wire. Lets see if the relay is getting power to it.. If it doesn't get 12V fed to it properly, it can't pass it along to the fuel pump. (Note: I'm assuming that crank isn't giving you 12V either - you still should test that).

-- snip from above

Test 5 - Confirm that the FIR is getting a good ground. It is grounded by W72. Place the black lead of your meter on W72 directly at the relay and the red lead on a known good +12V and make sure you read +12V on the meter. If not, check W72 and find where it gets grounded. Make sure it's getting a good ground. Without the ground, the FI Relay has no chance of working. You can also put your meter in ohmeter mode and measure the resistance between W72 (again right at the FI Relay terminal) and Battery ground..Ideally it should be 0, but anything under 1ohm on your meter is ok.

Len

[moozieman]

On 10/18/2019 at 6:55 PM, superlen said:

Ok, so no voltage there with flap open...so the FI relay is NOT routing 12V to this wire. Lets see if the relay is getting power to it.. If it doesn't get 12V fed to it properly, it can't pass it along to the fuel pump. (Note: I'm assuming that crank isn't giving you 12V either - you still should test that).

-- snip from above

Test 5 - Confirm that the FIR is getting a good ground. It is grounded by W72. Place the black lead of your meter on W72 directly at the relay and the red lead on a known good +12V and make sure you read +12V on the meter. If not, check W72 and find where it gets grounded. Make sure it's getting a good ground. Without the ground, the FI Relay has no chance of working. You can also put your meter in ohmeter mode and measure the resistance between W72 (again right at the FI Relay terminal) and Battery ground..Ideally it should be 0, but anything under 1ohm on your meter is ok.

Len

I was able to work on it a little over the weekend and heres what I found... I tried jumping 12v straight off the battery and into W48 and when I did this, I finally began reading voltage on the fuel pump wires in the cabin! So I know that the error is before this. What would be my next item on the agenda? Also, what would I do if i shorted 12v through the ecu? My buddy whos helping me said he saw "sparks" which can only mean bad things. If it was shorted, would it just blow a fuse? After I thought that I might have shorted it, I quickly moved the wire over to W48 and still successfully read 12v. Therefore, the circuit is still being completed. Hopefully I didnt mess anything up too bad. The 12v was only in contact with W34 for a split second. Idk if that makes any difference.

Edited October 29, 2019 by moozieman

[superlen]

Well...we aren't making fast forward progress, but any information is good information. ?

Q1) When you jumped 12v from the battery to W48 and you read voltage "in the cabin"..are you talking about the wires behind the passenger seat going to the fuel pump , or the wires under the dash near the relay, or someplace else? "In the cabin" doesn't help me any in debugging. If your fuel pump was still connected, 12V direct to W48 and you should hear it run.

Q2) Did you confirm the gnd getting to the FIR as outlined in Test 5? If not, that would be my next step. We need to confirm if the relay connects W48 and W73 when the key is in 'START' position or the flap is open.

As for the ECU short...if you shorted to W34 you're probably fine. You would see sparks as W34 is connected to gnd inside the ECU. I might recommend again to unplug the ECU before doing any of these tests. It doesn't need to be plugged in at all to diagnose the FI relay.

It would not blow a fuse if you shorted 12V (that was directly connected to your battery) to W34. It would just be a dead short...there's no fuse in your connection. It could burn a trace on the ECU if left on long enough and with a good connection. I really doubt you did that so, don't worry. You can test by just hotwiring the fuel pump on and try to start the car.

Len

[moozieman]

9 minutes ago, superlen said:

Well...we aren't making fast forward progress, but any information is good information. ?

Q1) When you jumped 12v from the battery to W48 and you read voltage "in the cabin"..are you talking about the wires behind the passenger seat going to the fuel pump , or the wires under the dash near the relay, or someplace else? "In the cabin" doesn't help me any in debugging. If your fuel pump was still connected, 12V direct to W48 and you should hear it run.

Q2) Did you confirm the gnd getting to the FIR as outlined in Test 5? If not, that would be my next step. We need to confirm if the relay connects W48 and W73 when the key is in 'START' position or the flap is open.

As for the ECU short...if you shorted to W34 you're probably fine. You would see sparks as W34 is connected to gnd inside the ECU. I might recommend again to unplug the ECU before doing any of these tests. It doesn't need to be plugged in at all to diagnose the FI relay.

It would not blow a fuse if you shorted 12V (that was directly connected to your battery) to W34. It would just be a dead short...there's no fuse in your connection. It could burn a trace on the ECU if left on long enough and with a good connection. I really doubt you did that so, don't worry. You can test by just hotwiring the fuel pump on and try to start the car.

Len

Im with my car right now. Luckily, the short doesn’t appear to have affected anything. Thank god! I going through your instructions now. I'm looking at the wiring leading up to the efi relay. I'm not reading anything off of W72. I have my multimeter on the battery and on W72. And when i say in the cabin, I mean under the passenger seat

Edited October 29, 2019 by moozieman