Engine crank...no start...no power to fuel pump....

[blodi]

"what does 'up' mean?"
I meant whatever measurement on my electrical tester is displayed while I have it set to diode mode to test for continuity. I am not sure what it is measuring exactly. I'm not fully electronically literate.

"When you jumpered the green / black terminal to the black / yellow terminal of the relay that connects to the fuel pump relay you caused current to flow through the main FI relay isolation diodes and main FI relay fuel pump circuit relay coil to the fuel pump. This would be a high resistance path and the pump would not have been running very fast."
It sounds like it's running at full speed, but I am not certain.

"Have you tried jumpering the green black terminal of the main FI relay to ground with the ignition on? If so, did the main FI relay operate - the internal relay in the main FI relay that supplies the fuel pump circuit should energize when the green black wire is connected to ground. This would then apply 12v to the black / yellow wire which supplies the fuel pump relay."
Just tried this....the relay clicks once when I make the connection with the igntion switched on...but no change as far as fuel pump powering up or anything...and still no start.

"As a cautionary note, the main FI relay has three black / yellow wires connected to it. When you talk about the black / yellow wire, I assume you are talking about the black / yellow wire that supplies the fuel pump relay. "
yes, sorry I meant the black yellow wire that goes to the fuel pump relay.

 

[Old Guy]

I have a 2000 and I think the main relay is slightly different than it is on the early model cars like yours so I had to scrounge around to find a pinout. I hope I have the right diagrams. I have attached the internal wiring and pin connection for the main relay (#1) and what should be the pinout for the relay socket (#2 ).

Disconnect the relay from the socket and measure the voltage to ground on pin #5 in the relay socket. It should be a black / yellow wire. With the ignition switch in the run position you should be getting +12v on pin #5 . If you don't get +12v, then fuse #2 is blown, you have an ignition switch problem or a broken wire upstream of the relay. If you have +12v on pin #5 , then placing a jumper between pin #5 and pin #7 (pin #7 is the black / yellow wire to the fuel pump) should cause the fuel pump to run. This is what the relay does when it gets a ground connection on the green / black wire. It connects pin 5 to pin 7 to energize the fuel pump.

If you are getting 12 v on pin #5 with the ign sw in the run position, and the pump starts up when you jumper #5 and #7 , connect your voltmeter between pin #4 in the socket and ground (pin #4 should be a black / white wire which is connected to the start position of the ignition switch). Have someone turn the ignition switch briefly to the start position (briefly because you don't want to be cranking away on the starter motor) and you should measure +12 v on pin #4 . If you don't measure +12v you have a problem with the ignition switch in the start position or a wiring problem back to the ignition switch.

If all of the above checks out as good, put the relay back in the socket. Connect your voltmeter between pin #7 (the black / yellow ) fuel pump wire and ground. With the ignition switch in the run position, jumper pin #8 (the green / black wire) to ground. The relay should click, you get 12 v on pin #7 and the pump should start up. If the relay doesn't click or it clicks and the pump doesn't start up the relay is the likely culprit. If this works out, leave the voltmeter connected to pin #7 and have someone turn the ignition switch briefly to the start position while you connect pin #8 to ground. You should again get +12v on pin #7 and the pump should start. If this doesn't happen, then the relay is likely faulty.

(update - the very last step with grounding pin 8 and turning the ign sw to start can be a bit convoluted. I might skip it. If things are still not working out I would go to the test procedure for the main relay.)

If the tests suggest the main relay is at fault, I suggest you carry out the test procedure for the main relay to confirm that the relay is faulty. If you go to page 11-103 of the on-line version of the fuel system section of the service manual (I think I found this on the link to Dali's site), there is a test procedure for the main relay. It is a bit involved; but, it can confirm whether the relay is faulty.

 

[ftuhy]

I meant whatever measurement on my electrical tester is displayed while I have it set to diode mode to test for continuity. I am not sure what it is measuring exactly. I'm not fully electronically literate.

Diode mode in an continuity tester applies enough voltage (through a relatively high resistance) so that current will flow through a typical diode. If measuring a circuit that contains a diode you will see a different resistance value (or current value, depending on the meter) if you reverse the leads to the meter(because, as you probably know, diodes pass current in one direction and block it in the other direction). If the circuit was purely resistors (including, for example, the resistance of the wiring harness) the resistance value would be the same with the leads normal or reversed. Note that if there are dissimilar metals or corrosion in the circuit, you might also see different resistance values with the meter leads reversed.

 

[Old Guy]

Frank raises good points. I prefer to use the ohmmeter function on my Fluke meter to do continuity testing. As an observation, never use a continuity tester or ohmmeter on circuits that might be energized. At best you will get flakey readings and at worst you will melt your tester or do other damage.

If you do try to test the main relay by measuring continuity between terminals, keep in mind that there are internal isolation diodes. An ohmmeter or diode test function will give different results depending on how the leads are connected because of the isolation diodes. If you reverse bias the diodes with the tester (connect the red lead to the cathode side of the diode) it will show a very high resistance or open circuit, even though the diode and circuit are good. If you are not up on your anode and cathode stuff, switch the leads to see if you get the same measurement in both directions. Only necessary when working on circuits that have diodes.

 

[blodi]

Ok, again, you guys are awesome.

I made some progress tonight, but not quite there.
The update so far...

#5 pin was not getting and voltage at all. I went and checked the #2 fuse and somehow in all of this checking and rechecking..I had placed it into the usually empty #3 slot...so that wasn't helping anything. I then tried again and #5 pin was getting full 12v.

I then jumpered #5 to #7 and yes, the fuel pump came on with the ignition. I then tried with the main relay back in place....nothing.

I then moved on to the #4 pin...I was not measuring any voltage when switching on the ignition or trying to start. I then found where the white/black wire came out of the main wiring harness and to the EMS at the D21 pin....and it was broken! I tried holding the two ends of the wire together, but I still wasn't getting any fuel pump. So, when I get some time I'll go back out and solder the wires together.

However, I should mention I tried just measuring voltage at the wire that was coming out of the EMS and wasn't getting a reading. So, like I said...made some progress here tonight...but not there yet. Old Guy, your process there was a huge help.

 

[Old Guy]

I then moved on to the [URL=http://www.nsxprime.com/forum/usertag.php?do=list&action=hash&hash=4]#4 [/URL] pin...I was not measuring any voltage when switching on the ignition or trying to start. I then found where the white/black wire came out of the main wiring harness and to the EMS at the D21 pin....and it was broken! I tried holding the two ends of the wire together, but I still wasn't getting any fuel pump. So, when I get some time I'll go back out and solder the wires together.

Pin #4 in the relay socket should be a black / white wire, not a white / black wire. The wire from pin #4 goes back to the ignition switch, not the EMS

 

[blodi]

Pin [URL=http://www.nsxprime.com/forum/usertag.php?do=list&action=hash&hash=4]#4 [/URL] in the relay socket should be a black / white wire, not a white / black wire. The wire from pin [URL=http://www.nsxprime.com/forum/usertag.php?do=list&action=hash&hash=4]#4 [/URL] goes back to the ignition switch, not the EMS

Sorry, I meant black/white...not white/black. According to the wiring diagram you posted first...the black/white wire does go to the ecu and I tested the broken wire at the wiring harness to the #4 socket and it is connected.

 

[Old Guy]

You are correct - my error.

The wire from pin #4 goes to the starter cut relay and also goes to the EMS (don't know the pin #). If the blk/wh wire to the EMS is broken, the EMS is not getting the signal that you are trying to start the car which would definitely bugger things up.

The blk/wh wire gets its +12v start signal from the starter cut relay. Your starter cut relay is working because your starter motor is working so you should be getting 12v on the blk/wh wire when you engage the starter! There is a 7.5 A fuse (fuse #7 ) between the starter cut relay output and the main FI relay. That fuse could have blown if the broken blk/wh wire shorted out against the body. Check to make sure that it is OK.

 

[blodi]

Ok, I fixed the broken wire, which actually when I got some light on it was a Green/black wire...so not related. Sorry....it was dark out there.

I checked fuse 7...it was fine.

I then checked voltage from the black/white wire at the EMS harness and then with the relay plugged in from inside the terminal on the relay...both read ~9.5V when cranking the starter. So, the relay is getting the voltage from the ems via the black/white wire. It is not a full 12v...but it is something.

I'll give your last test a shot if I warm back up enough to brave it again tonight or tomorrow night.

 

[blodi]

Alright, some interesting findings tonight. I tried the old main relay again just to check and see if it would work with the changes so far (fuse, broken wire)....it did not.

So..I did the final test with the ignition to run, not start. When I jumpered ground to #8 ...I did hear a click...but no voltage and no pump. Then as I was moving the main relay to remove my volt meter the fuel pump came on. I was able to replicate this several times. With no volt meter connected...jump the ground to #8 til it clicks (which was instantly) then remove the jumper and wiggle the main relay a around a bit and eventually the fuel pump would come on...until I wiggled the main relay more then it would shut off.

So...it seems like a bad connection either at the plugs or in the main relay. I looked at the pins on the main relay and the plugs and they all look normal. I do have a new main relay coming Friday. So I can try that then. Maybe tomorrow or before I can just see about inspecting the connections a bit more.

 

[Old Guy]

The fuel pump should only come on while pin #8 is connected to ground. It wasn't clear if you still had pin 8 connected to ground while you were wiggling the relay around and the pump started. If you got the pump to start without pin 8 connected to ground, that is a bad thing since you would have to have wires shorting together for that to happen. If you had pin 8 connected to ground and the wiggling caused the pump to start, that is better. Either the relay has a broken internal connection or perhaps one of the contacts in the relay socket is loose or broken.

 

[blodi]

I did not have #8 connected to ground when the pump started. I would jump it for a split second for the relay to click, then pull away the jumper and then by moving the relay around it would start up the pump. If I didn't move it or do anything after removing the jumper the relay would eventually click again after maybe 15-20 seconds. If it did the 2nd click I could not get it to power the pump.

So, again, jumping it would immediately get the relay to click "on" and it would stay on for 15-20 seconds without being jumped...then it would click "off". Only during the time while it was clicked "on" could I move the relay and get it to power up the pump. When the pump would come on it would stay running and not just prime.

 

[Old Guy]

That is beyond bizarre!

When you ground pin 8, the relay should close (click). When you remove the ground on pin 8 it should immediately open, not stay closed for 15 - 20 seconds. Even if it was getting a ground from the EMS it should not stay closed for that long. On the stock ECU, the ECU will put a ground on pin 8 for 2 seconds when you first turn the key (prime the fuel system). It will open the ground and then reapply the ground once you start cranking the engine and the ground will stay connected if the engine starts. The AEM EMS may have slightly different timings; but, I don't think it would be a lot different. I have absolutely no clue why your relay is staying closed for 15-20 seconds after you remove the temporary ground on pin #8 .

You say the pump stays running, not just the 2 second prime. If the engine is not running, Pin #8 should not be getting a ground signal from the ECU. You have to have something internal in the relay or the socket that is providing the ground or shorting to supply the pump. I would try the test procedure for the relay set out on page 11-103 of the service manual. You could use a 12 v lantern battery to do the test out of the car. In fact, a 9 volt transistor radio would probably be adequate to test energize the relay coils.

If the relay checks out OK, considering that you already had one broken wire to the EMS, perhaps inspect the harness and look for other broken or chafed wires. Also, closely inspect the socket for the main relay and make sure that all the individual connectors are properly seated, that there are no broken wires and that there is nothing bridging between the connectors. Beyond that, I have kind of shot the wad in terms of suggestions as to what to test.

I am inclined to think the your ECU might be OK and that with the test results you have got so far the problem is with the main relay, its socket or the wiring to the socket; but, I would have thought that the problem would have showed itself by now!

Good luck with it!

 

[blodi]

Tell me about it! I think tonight I'll pop the cover off my old relay and see if it does the same thing. I was going to take a video of it, but you understand exactly what I'm saying.
Yes, normally my EMS primes the pump for 2 seconds just like the OEM ECU before start up. I think my EMS is fine too since I've used another generously loaned to me by other local prime members and am getting the same results. So, it either is that both of my main relays somehow went bad...or the connections to the relay or wire are somehow bad.

I should also mention I tried to start the car while the pump was going and I as soon as I turned the key to start the relay would click "off"/open and the car would not start.

I was thinking of popping the pin connectors out of the harness and connecting them directly to the the relay to see if there is any change. I wish I had that new main relay coming sooner than Friday! Not that I am driving anywhere this time of year, but man this is perplexing!

 

[Old Guy]

The run and start circuits for the fuel pump circuit in the relay are separate. Pin #4 goes to +12v (from the start contact on the ignition switch) and the ECU needs to re apply the ground on pin #8 to energize the relay and close the contact supplying the pump during the start sequence. When you turned the key from run to start whatever sneak circuit energizing the pump disappeared and the normal sequence that would energize the relay supplying the pump did not happen.

Remove the pins out of the socket as a last resort. With the exception of Deutche brand sockets which are designed with a connector release mechanism in the socket, my experience is that the connectors are never very secure in the socket body after reinsertion unless you re terminate with a new connector.

 

[blodi]

Ok, more fun tonight.

I tried the same test on my old relay...and it functioned more "correctly" when I jumped pin 8 to ground it would click on and instantly run the fuel pump and when I removed the jumper it would instantly click off and the fuel pump would shut off. It had none of the moving it around made a difference nonsense of my "new" relay.

I just now brought the relays inside and with a 7.2v RC car battery did the following test I found....

"1. Remove the main relay.
2. Attach the positive battery terminal to the #4 terminal and the negative battery terminal to the #8 terminal of the main relay. Then check for continuity between the #5 terminal and the #7 terminal of the main relay.
a. If there is continuity, go to step 3.
b. If there is no continuity, replace the relay and retest.
3. Attach the positive battery terminal to the #5 terminal and the negative battery terminal to the #2 terminal of the main relay. Then check for continuity between the #1 terminal and the #3 terminal of the main relay.
a. If there is continuity, go to step 4.
b.If there is no continuity, replace the relay and retest.
4. Attach the positive battery terminal to the #3 terminal and the negative battery terminal to the #8 terminal of the main relay. Then check for continuity between the #5 terminal and the #7 terminal of the main relay.
a. If there is continuity, the relay is OK.
b. If the fuel pump still does not work, go to harness test.
c. If there is no continuity, replace the relay and retest."


The step 2 and 4 test worked on both of my relays. The step 3 test...neither relay had continuity. So.....does that make sense? Interesting they both are the same exact way.

Sigh, the new relay can't get here soon enough!

 

[BTL3.0]

Can you borrow the relay from your friend whom loan you the ems, to try?

 

[Old Guy]

Your test #3 should be:

3. Attach the positive battery terminal to the #6 (not #5) terminal and the negative battery terminal to the #2 terminal of the main relay. Then check for continuity between the #1 terminal and the [URL=http://www.nsxprime.com/forum/usertag.php?do=list&action=hash&hash=3]#3 [/URL] terminal of the main relay.

When you are doing the test with the relay out of the socket, try wiggling the relay terminals (or shaking the relay) and see if the test results change. I have had non automotive devices that would test OK when disconnected and then fail to operate when installed. The force of the socket on the device connectors was moving something in the device side causing the connections to open intermittently. Drove me nuts trying to diagnose the problem.

 

[blodi]

Can you borrow the relay from your friend whom loan you the ems, to try?

I could've and should've grabbed it as well while I was there. But, i do have a new one coming tomorrow regardless, so I'll just wait.

Your test #3 should be:

3. Attach the positive battery terminal to the [URL=http://www.nsxprime.com/forum/usertag.php?do=list&action=hash&hash=6]#6 [/URL] (not [URL=http://www.nsxprime.com/forum/usertag.php?do=list&action=hash&hash=5]#5 [/URL]) terminal and the negative battery terminal to the [URL=http://www.nsxprime.com/forum/usertag.php?do=list&action=hash&hash=2]#2 [/URL] terminal of the main relay. Then check for continuity between the #1 terminal and the [URL=http://www.nsxprime.com/forum/usertag.php?do=list&action=hash&hash=3]#3 [/URL] terminal of the main relay.

When you are doing the test with the relay out of the socket, try wiggling the relay terminals (or shaking the relay) and see if the test results change. I have had non automotive devices that would test OK when disconnected and then fail to operate when installed. The force of the socket on the device connectors was moving something in the device side causing the connections to open intermittently. Drove me nuts trying to diagnose the problem.

Ah, ok, the instructions I found were just general honda main relay instructions. I'll test #6 tonight. It will be hard to test/shake the relay since I had to have my wife hold the tester in place while I hooked up the battery...I need more hands

- - - Updated - - -

Just tried #6 and #2 and I did hear both relays click. I couldn't check continuity as well since I don't have my 2nd set of hands at home yet.

Should I try this main relay harness test next if my new main relay tomorrow doesn't fix it? Do I replace #5 with #6 in these instructions as well?

MAIN RELAY HARNESS TEST

1. Keep the ignition switch in the OFF position.
2. Disconnect the main relay electrical connector.
3. Check for continuity between the BLACK wire (pin 2) in the connector and body ground.

Fig. 33 Main Relay Harness Test (pins 1 and 2)
Click the image to open in full size.

Fig. 34 Main Relay Harness Test (pins 2 and 5)
Click the image to open in full size.

4. Attach the positive probe of the voltmeter to the YELLOW/WHITE wire (pin 1) and the negative probe to the BLACK wire (pin 2).
a. Battery voltage should be available.
b. If there is no voltage, check the wiring between the battery and the main relay as well as the ECU fuse (15A) in the main fuse box.
5. Attach the positive probe of the voltmeter to the BLACK/YELLOW wire (pin 5) and the negative probe to the BLACK wire (pin 2).
6. Turn the ignition switch ON.
a. Battery voltage should be available.
b. If there is no voltage available, check #14 fuse and the wiring from the ignition switch to the fuse box, and the wiring from the fuse box to the main relay.
7. Attach the positive probe of the voltmeter to the BLUE/WHITE wire (pin 4) and the negative probe to the BLACK wire (pin 2).

Fig. 35 Main Relay Harness Test (pins 2 and 4)
Click the image to open in full size.

Fig. 36 Main Relay Harness Jumper Test
Click the image to open in full size.

8. Turn the ignition switch to the START position.
a. Approximately 10 volts should be available.
b. If there is no voltage check the #2 (10A) fuse and the wiring between the ignition switch and the fuse box, and from the fuse box to the main relay.
9. Connect a jumper wire between the BLACK/YELLOW wire (pin 5) and the YELLOW/BLACK wire (pin 7).
10. Turn the ignition switch ON.
a. The fuel pump should work.
b. If the fuel pump does not work, check the wiring between the main relay and the fuel pump, and the wiring from the fuel pump to the ground (BLACK wire).

 

[blodi]

Ok, I just tried the above harness test and tried both #5 and #6 wherever it said to do #5 . I tested the harness this way and then plugged in my "old/not weird" main relay without the cover on it and conducted the tests from the terminals inside to see if there were any spots where it wasn't getting the right signal.

Everything checked out perfectly. So...unless it's the main relay (coming tomorrow)...I truly don't know anymore.

 

[Old Guy]

I have attached a .pdf copy of the relay and harness test procedure for the early version NSX. You can use it to confirm whether your procedure was the same.

 

[blodi]

Thank you! I'll give it a whirl if the new relay doesn't do the trick tonight.

 

[blodi]

Got the new main relay. No change. So....I guess I'll test the harness as shown in the attachment above. But, I am really stumped now. Maybe I'll check downstream from the main relay again too.

 

[ftuhy]

Have you looked at the pins in the connector on the cable that goes to the relay? Perhaps one of them is spread open a little and not making good contact?

 

[blodi]

Have you looked at the pins in the connector on the cable that goes to the relay? Perhaps one of them is spread open a little and not making good contact?

I did that harness test with the relay plugged in/cover off and tested from the pins inside the relay, so I know it's getting the proper signals. I'll bust into it again tomorrow maybe, although, it's supposed to be a high of 4 tomorrow, so I dunno how much time I'll want to spend out there. :/