Strange fuel pump relay issue

[pepe123]

Ok let me start off with it's a 89 240sx hb, with a dohc swap.

Ok what's happening is my fuel pump isn't turning on, I'm guessing because the ecu isnt sending out the ground signal to the egi relay, I had this issue before but then I moved around some wires, fuses and tightes the ecu plug and the pump kicked on, but the other day my battery died and i charged it and now my pump won't prime or go on UNless I bypass the Egi relay but putting wires where the relay connects. I think that's strange. Could it be a break in the black/ pink wire in between the ecu and relay? Also the pump fuse gets power like normal.

[2.5T_/<ouki]

Originally Posted by pepe123

Ok let me start off with it's a 89 240sx hb, with a dohc swap.

Ok what's happening is my fuel pump isn't turning on, I'm guessing because the ecu isnt sending out the ground signal to the egi relay, I had this issue before but then I moved around some wires, fuses and tightes the ecu plug and the pump kicked on, but the other day my battery died and i charged it and now my pump won't prime or go on UNless I bypass the Egi relay but putting wires where the relay connects. I think that's strange. Could it be a break in the black/ pink wire in between the ecu and relay? Also the pump fuse gets power like normal.

It's possible. You should get a multimeter with continuity sound and check to see if the wires have continuity. It's possible the relay is toast, you can possibly try another relay.

[pepe123]

Ya I borrowed a friends relay and same issue, Bo power to pump. By bypassing the relay and it working wouldn't that tell me there's countinity in thd line?

[2.5T_/<ouki]

Originally Posted by pepe123

Ya I borrowed a friends relay and same issue, Bo power to pump. By bypassing the relay and it working wouldn't that tell me there's countinity in thd line?

When bypassing (splicing together) yes it should.

[cotbu]

By adding the jumper wire you confirmed, the 12v wiring to the relay is good, the wiring to the pump is good, and the pump is good. You have to figure out why the trigger is not being sent to the relay. Could be anything from a de-pinned wire to a broken trace. Test the continuity on the trigger wire, and open up the ecu have a looksee!

[pepe123]

I don't have a multimeter handy but I used a check light to poke around on the black pink wire witch is the signal wire right? I hooked on end to the positive terminal on thd battery and then poked the wire,Near the fuse box the light turned on meaning I'm getting the negative signal
Or am I wrong? I opened up The ecu and I looked fine.

[cotbu]

i use a multimeter, there is no continuity to ground on that wire with the key off.
you don't want to send 12v down that wire to the ecu, so disconnect the ecu and see if the test light still lights up

[pepe123]

Ok ima borrow a multimeter tonight and see, ..how
Bad is it to drive it around with the relay bypassed? If I can't figure it out soon I guess I could just get a fuel pump relay kit. To
How do I use the meter to test that line??

[cotbu]

I drove around 6mo with my relay bypassed. The ecu will not be able to control the pump. No 5sec priming function and the trigger for the relay is also used for the AACV IIRC..?!
I didn't have any problems running it like that, but I needed to fix it.

Testing, you want to verify the continuity of the line. The line itself and against the chassis. You can also see if there is voltage on the line, short or whatever.
KOEO see if the ecu sends it to ground, if you don't have a working consult port and consult program you have to be quick or setup a jig.

If you get a chance post picture of the ecu's board top and bottom maybe someone will notice something.

[pepe123]

i used the mutimeter today and got continuity from the relay to the brown plug by the battey, places where the black/pink wire connect . meaning theres no break in the wire, right? im new at using a mutimeter haha...so if thats all good im thinking pin 104 on my ecu,or the ecu itself is messed up. also i opened the ecu again looked on both sides of the board and couldnt see anything wrong.

[cotbu]

Lil confused, so do this for me.
Disconnect the ecu harness , remove the egi pump/fuel pump relay.

  [1]  [2]
   [3][4]

Looking into the relay socket, test pin 1 to pin 104 on the ecu for continuity.
Then de-pin pin104 from ecu plug put the relay back into the socket turn key on, with ecu still disconnect. Touch the wire (104) to ground. the pump should come on.

This means the problem is in the ecu. probably more convenient to replace the ecu than to have it repaired.

Not gonna lie. These test are tedious. And mostly every time the ecu is the problem, but rare cases it cost nothing to fix.

So you could just pop in another ecu, after you determine the cause is not a short in the wiring. usually there are signs of a broken trace or someone says I hooked my battery cables up backwards or I dropped a wrench and blah blabbity blah.

[pepe123]

Ok I'll try that in the morning, thanks so much for all the help, my buddy's letting me try his ecu tomorrow so I'll be able see if it really is the ecu, I hope it is so I can get this fixed easily.

[boyou2]

I got the same problem, but only when the engine is hot, have changed relays, same problem, so I jumped the relay for the moment, until I have time to check it out.

I post to follow.

[NOLAG]

had the exact same problem....its the ecu,the ground pin on our ecu's are somewhat known to go bad..for a while instead of jumping the relay(cause that worked too)i spliced into the ground pin and grounded it directly to the chassis...again no 5 sec prime nor did the ecu control the pump...wich in result fried my pump and screwed up my ecu and tune all together ...so get another ecu man dont make my mistake!! let us know what happens im almost 100% its the ecu

[cotbu]

wich in result fried my pump and screwed up my ecu and tune all together ...so get another ecu man dont make my mistake!! let us know what happens im almost 100% its the ecu

If you like I can tell you why this is false information, but I'll just say fuel pump hard wiring is one of the most common upgrades people do. The most common reason for the ecu to burn out pin 104 is feed back and not properly being grounded when a short happens. I've manually burned traces with test ecu's and I know the path of least resistance. Ok once you remove pin 104 the ecu has nothing to do with the fuel pump any more, and it doesn't care. It just can't cut the voltage. You had a serious wiring problem if you ask me. That's the reason I asked the OP to make sure there is no shorts or the new ecu will suffer the same fate. There is really no reason to ground that pin other than testing, because the relay is all you're controlling. Jumping the relay is a better alternative unless you had a switch involved,for on off testing or security. You could have use another device to trigger that relay but that's on a different level than making my car run!

[Ichiban4]

Originally Posted by cotbu

Lil confused, so do this for me.
Disconnect the ecu harness , remove the egi pump/fuel pump relay.

  [1]  [2]
   [3][4]

Looking into the relay socket, test pin 1 to pin 104 on the ecu for continuity.
Then de-pin pin104 from ecu plug put the relay back into the socket turn key on, with ecu still disconnect. Touch the wire (104) to ground. the pump should come on.

This means the problem is in the ecu. probably more convenient to replace the ecu than to have it repaired.

Not gonna lie. These test are tedious. And mostly every time the ecu is the problem, but rare cases it cost nothing to fix.

So you could just pop in another ecu, after you determine the cause is not a short in the wiring. usually there are signs of a broken trace or someone says I hooked my battery cables up backwards or I dropped a wrench and blah blabbity blah.

I know this is old but I am bumping bc it has good info and I have the same issue.

I've got a similar issue. I recently rebuilt my motor and I think possibly while putting all the wiring back in maybe I created a short or got a broken wire do to bending, twisting ect.

If I jump the relay like in this pic everything works fine.



If I test #1 on your picture to pin 104 I have no continuity, hence why I think it is a break in the wire.

My problem is this, I don't know where that wire runs, I tried tracing it from the ecu and it comes through the fire wall in the loom with all the other wired but the wire coming from pin#1 looks like it runs from the relay box asll the way around the radiator and into the driver side?



Doesn't make sense to me :/

[driftiteasy0313]

i believe it goes the route of your second picture. All the way around the front of the car.