Rb25det Fuel Pump Ecu/wiring Problems

[paddles]

Hi guys,

Apologies if this is in the wrong section - couldn't see a section for electrical questions...

Anyway, we have recently purchased a 260z with rb25det (standard ecu) as an unfinished project. The only real running problem remaining is that the fuel pumps are not getting power - with a battery pack applying 12v to pumps the car will run no problems.

Now I'm attempting to work out why the pumps arent getting power.

For reference, I'm working with the wiring diagram found here:

http://www.meggala.com/rb25detenglish.html

Based on this diagram, I believe that the fuel pump relay is triggered by the ecu switching to ground at pin 18 of ecu. Since constant +ve is supplied to pin 1 of fuel relay (check out bottom left of diagram) I figure this is the only way the relay can be triggered. Is this correct or am I way off the mark?

With battery connected, ignition on, I'm getting +12v at pin 1, 2 and 3 (not 5).

At one stage I removed the fuel pump relay from its socket (creating an open circuit) and I still had +12v at both pin 1 AND pin 2 of the relay. I can see why 1 would have +12v but why oh why would pin 2 of relay have 12v?

The only conclusion I can draw is that perhaps I have misunderstood the diagram and the ecu supplies the 12v for switching the FP relay.

Any help/suggestions would be greatly appreciated!

Please let me know if more info is required.

Cheers,

Paddles

[paddles]

Also when should hte ecu trigger the fuel pump?

I assume the pump should be active when ignition is switched on to build pressure prior to cranking the motor?

[PM-R33]

Yep correct, ECU will trigger the relay giving power to the fuel pump when key is turned to ignition. Therefore if you aren't getting any power when the key is on igniton i'd be looking at how you have set up the wiring to that relay.

Not to sure how the pin out puts should be connected though, but im sure some one will have some knowledge on here.

[paddles]

Thanks for your input!

Here's a Van Gogh-spec diagram of how the relay is currently wired if its any help. Although this wiring was completed before we got the car so it's a case of trying to work out what has and hasn't been done as we go!

with ignition on Im getting +12v at pins 1, 2 and 3 but not at 5. So this leads me to believe the wiring isn't faulty and either the relay is faulty or perhaps the ECU isnt switching the relay for some reason.

Any ideas why the ECU might not switch the relay? Is there maybe some signal it must receive from another source (say an ignition feed?) before it will switch the pump on? Ie. one of the ecu feeds has not been connected or something? Although that may be farfetched as it runs fine with pumps hardwired...

[blind_elk]

Is the ECU "alive" when you turn the key to ON?

In general, ECUs switch to earth (rather than provide power). But the ECU needs to be ON to know to do all this. What happens if you ground pin 1 with IGN ON?

[chrissso]

Just had a quick look at the diagram and it looks like you have 1 and 2 mixed up.

[paddles]

Is the ECU "alive" when you turn the key to ON?

In general, ECUs switch to earth (rather than provide power). But the ECU needs to be ON to know to do all this. What happens if you ground pin 1 with IGN ON?

The car will run if pumps are hotwired so ECU is 'alive' then yeah? (sorry not too sure what you mean by 'alive'; do you mean it is receiving power?)

What is Pin 1? I don't have the ECU pinout diagram on me at the moment... What should/shouldnt happen when I ground it?

Just had a quick look at the diagram and it looks like you have 1 and 2 mixed up.

I thought power could go through either way?

Although thinking about it I suppose if current went through the coil the wrong way round it may push/pull the switch the wrong direction due to an inverted magnetic field...? You may be on to something... I'll give it a crack anyway

Thanks muchly for the help guys!

Edited October 2, 2008 by paddles

[116.hks]

yeah mate doesn't matter what way the current flows through the windings. its just a coil of wire. if you have can supply power to the fuel pump and it runs then the computer has power to it. either you don't have the trigger out of the computer correct or you have a faulty relay. just check with a test light that there is a negative prime feed from the computer. it will only be on for a couple of seconds. from memory the fuel pump trigger feed is a black with pink trace. not to sure on the 25 motor but thats what it is on the 32's. (pretty sure. lol)

[KiwiRS4T]

Hi guys,

Apologies if this is in the wrong section - couldn't see a section for electrical questions...

Anyway, we have recently purchased a 260z with rb25det (standard ecu) as an unfinished project. The only real running problem remaining is that the fuel pumps are not getting power - with a battery pack applying 12v to pumps the car will run no problems.

Now I'm attempting to work out why the pumps arent getting power.

For reference, I'm working with the wiring diagram found here:

http://www.meggala.com/rb25detenglish.html

Based on this diagram, I believe that the fuel pump relay is triggered by the ecu switching to ground at pin 18 of ecu. Since constant +ve is supplied to pin 1 of fuel relay (check out bottom left of diagram) I figure this is the only way the relay can be triggered. Is this correct or am I way off the mark?

With battery connected, ignition on, I'm getting +12v at pin 1, 2 and 3 (not 5).

At one stage I removed the fuel pump relay from its socket (creating an open circuit) and I still had +12v at both pin 1 AND pin 2 of the relay. I can see why 1 would have +12v but why oh why would pin 2 of relay have 12v?

The only conclusion I can draw is that perhaps I have misunderstood the diagram and the ecu supplies the 12v for switching the FP relay.

Any help/suggestions would be greatly appreciated!

Please let me know if more info is required.

Cheers,

Paddles

You say you have a standard RB25DET ECU but in fact there are many. In my Stagea (1997 RB25DET - what is known in skyline circles as a series 2 engine) the fuel pump relay is triggered by pin 13. See:http://www.skylinesaustralia.com/forums/index.php?act=attach&type=post&id=31087

[blind_elk]

Can you hear / feel the relay click on/off when you switch ON/OFF?

Use an ohmmeter to confirm 0 ohms (or at least open circuit) between pins 1, 2.

Remove the wire from pin 1 and just connect an earthed cable to the pin 1 on the relay, with IGN ON. You should hear the relay click, and the pump start working.

[paddles]

Thanks for the help guys, issue #1 solved!

Sorry blind_elk I misread your original post - I thought you meant take pin 1 of ecu to ground (not pin 1 of relay) Doh!

For reference, the relay was clicking when ignition was switched on - but no power was getting through the switch side.

So I did as blind_elk suggested and took pin 1 of relay to ground and I was getting 12v to pump! So this suggests the ecu may not have been switching the relay yeah?

Anyway I removed the additional earth wire and inverted the current direction through the coil side of the relay, nothing... So connected it back up the way it was originally and tadah it works!

So overall teh wiring is exactly how it was in the beginning - leading me to believe that perhaps the relay was dicky and wiring it up backwards (or perhaps due to additional earth) released the switch... Or something...

The relay will now turn on for about 4 seconds every time ignition is switched on. This is the ecu turning on the pump to prime, correct?

Anyway, I'm a tad confused, and have decided that a dicky relay was the culprit... Unless anyone has a better (read: more educated) synopsis?

Although now we've found that both the low and high pressure pumps are rooted.. Huzzah... Any suggestions as to a good replacement high pressure pump? Currently running an external unit - I believe it is a VL unit.

Thanks again for the help guys!!

[KiwiRS4T]

Thanks for the help guys, issue #1 solved!

Sorry blind_elk I misread your original post - I thought you meant take pin 1 of ecu to ground (not pin 1 of relay) Doh!

For reference, the relay was clicking when ignition was switched on - but no power was getting through the switch side.

So I did as blind_elk suggested and took pin 1 of relay to ground and I was getting 12v to pump! So this suggests the ecu may not have been switching the relay yeah?

Anyway I removed the additional earth wire and inverted the current direction through the coil side of the relay, nothing... So connected it back up the way it was originally and tadah it works!

So overall teh wiring is exactly how it was in the beginning - leading me to believe that perhaps the relay was dicky and wiring it up backwards (or perhaps due to additional earth) released the switch... Or something...

The relay will now turn on for about 4 seconds every time ignition is switched on. This is the ecu turning on the pump to prime, correct?

Anyway, I'm a tad confused, and have decided that a dicky relay was the culprit... Unless anyone has a better (read: more educated) synopsis?

Although now we've found that both the low and high pressure pumps are rooted.. Huzzah... Any suggestions as to a good replacement high pressure pump? Currently running an external unit - I believe it is a VL unit.

Thanks again for the help guys!!

You may be right with pin 18 but I have two different pinouts/wiring diagrams that say pin 13 for fuel pump (including one thats colour coded b/p). One says nothing for pin 18 and the other puts pin 18 among the lights and switches for overdrive on/off!

So if you replace your pump and all is well then you are OK -- if not, time to check out pin 13.

[paddles]

Forgot to thank you for that pinout diagram kiwirs4t, cheers! Does the diagram accurately represent the location/shape of the plug to the ecu? I notice with the pin diagram I've been working off (link below) the plug shape and number of outlets is an exact match to the plug/ecu in the car. The alternative diagram seems to have a much different plug shape - is this a valid way of telling the two apart?

Either way I believe the wiring issue is sorted now as the relay is turning on for 4 seconds when ignition is switched ON and for that period of time I'm getting a 12v supply to the pump! I guess now all I can do is replace both pumps and see how we go.

Pinout diagram:

http://wiki.r31skylineclub.com/images/thum...ECU_Pinouts.jpg

[KiwiRS4T]

Forgot to thank you for that pinout diagram kiwirs4t, cheers! Does the diagram accurately represent the location/shape of the plug to the ecu? I notice with the pin diagram I've been working off (link below) the plug shape and number of outlets is an exact match to the plug/ecu in the car. The alternative diagram seems to have a much different plug shape - is this a valid way of telling the two apart?

Yes that's right. Looks like your ecu is an earlier model than mine and the ones i have been looking at. How much power are you planning to make? Why do you need two pumps? These are very popular:

Bosch 044 660hp fuel pump

This Bosch 660hp pump is commonly called the "044" Bosch Motorsport fuel pump. This is a K-Jetronic style pump and doesnt mind pumping at much higher than normal fuel pressures. Approx 270L per hour flow rate at 3 bar fuel pressure. More methanol tolerant than most other EFI pumps.

Price:

document.write(getProductPrice("$","\,",2,".",false, true, 7,"inc GST within Australia","inc GST within Australia","International Orders",1,true));$250.00

document.write(getPriceInfo(7,"inc GST within Australia","inc GST within Australia","International Orders",1,true));inc GST

[paddles]

Ok sweet, thanks again! Looking to keep the motor standard for now, maybe a wee bit of extra boost later. Running a low pressure lift pump into surge tank from which the high pressure pump feeds; as the 260z tank can't be good in terms of fuel surge.

[BigC1988]

I have about the same problem. I wired the RB25 harness in my R32 and everything was fine. I started it a few time so there was no problem there. Yesterday I hooked everything up (intercooler piping, radiator ect) and the car didn't start. No I see that my fuel guage is just hanging (it's WAY below empty). Today I checked to see if it is getting power at the fuel pump plug and nothing. What could this be?

I remember I had the same problem at first but one day it just fixed its self.