So I'm just about done with my ancient project but need help to finish it. Turns out my engine won't fire up due to a missing ground to the fuel pump/relay box. I turn the key and get and you can't hear the pump turn on. At the fuel pump relay I have 2 powers and only one ground, the other pin I have nothing. I jumped it with a wire and it started right up. Checked Alldata and Mitchell but cant find a clear diagram, any help people. Thanks.

http://www.nicoclub.com/FSM/240sx/91-94/EC.pdf

Page 135.

If you're missing a pin at the relay, check the wire colors and figure out what's missing. It's probably the wire to the ECU, which is a ground complete. The ECU grounds the relay, which activates it, and turns the fuel pump on. What you described just sounds like the wire to the ECU is gone.

Check the wiring under the relays to see where the wire was put or cut off. It just sounds HIGHLY suspicious that someone would pull just that wire.

Thanks dude. The pin and wire are definitely there, because when I jumped it it fired up. Also I noticed the top of the fuel sending unit is badly rusted and the connections look horrible. I bought one from a fellow Nico user yesterday. Once I receive it I will install and play with it. BTW: I did the harness a long time ago, is it possible I might've done something wrong there or perhaps I caused a break in the wiring while tugging on the harness trying to get it through the firewall?

do you have a walboro, and you might as well hardwire it while your at it

This issue is actually very common. (Both of my S13s have had it.) With both of my cases it was just as Bart said. It's the ECU connection. I don't think it's your wire, though. It's more than likely, your actual ECU. You can do one of the following:

1) Hardwire it. (Deatschwerks sells kits on their website.) - I did this with my first S13
2) Jump the relay. - I did this with the one I drive now

I priced together my own kit at Napa for about 15 bucks cheaper plus I didn't have to pay shipping

idahotuner wrote:I priced together my own kit at Napa for about 15 bucks cheaper plus I didn't have to pay shipping

You should put the details in a thread.

Hey guys I just saw your posts. This is interesting, so IF I hardwire it I no long have to fix the connection problem correct? Is this something you really want to do? I mean safe wise?..

It's recommended for high horsepower builds, as it's rare for the fuel pump to actually get the full 12v from factory connections. The hardwiring kit I used tapped into the factory wiring so it turned on/off with the key, but it got it's power directly from the battery so no voltage drop.

Thanks. Do you know of a guide to do this? I came across the ka-t.org hardwire guide but the link doesn't work.

tEknoS13 wrote:Thanks. Do you know of a guide to do this? I came across the ka-t.org hardwire guide but the link doesn't work.

I'm pretty sure deatschwerks has instructions for it on their site...

/e Nevermind.. I thought they had it in PDF format. I do know that if you order their kit, it comes with instructions.

Ok Kool. So this In a sence will bypass the factory wiring and just have power directly from a power source(battery). Even though you kinda answered already, I just want to make sure that I don't have to fix the problem at hand now. It seems kinda obvious that I DON'T if I'm bypassin the factoy system. thanks for your patience man I'm just not great at all with wiring

tEknoS13 wrote:Ok Kool. So this In a sence will bypass the factory wiring and just have power directly from a power source(battery). Even though you kinda answered already, I just want to make sure that I don't have to fix the problem at hand now. It seems kinda obvious that I DON'T if I'm bypassin the factoy system. thanks for your patience man I'm just not great at all with wiring

It's what I'm here for. You're 100% correct from with your first line.
Wiring isn't hard, just tedious. It's as simple as connecting 2 pieces together. I just recommend you always use solder and heat shrink instead of crimp connectors.

I found this in another forum... What do you make of this? Seeks easy enough.


"find out the size of the fuse is for the fuel pump, get an inline fuse holder.

simple 4 wire relay, constant power with fuse holder in it, ground to a chassis source, 12v switched wire to 12v ign on (can use the one where the radio is) and then run the trigger wire to the fuel pump".

I can see this working but, the ecu sends ground to the pump right. So if I turn the key forward the pump won't shut off after a few seconds like it should.

Nevermind. The ecu signal wire will also be eliminated since bypassing right...

The EGI relay already supplies direct power to the pump. Just fix the issue in the wiring, and it'll work fine. The only other system that would get power from that circuit is the IACV-Air Regulator, but it doesn't exist on an SR.

Grab a Service Manual and look up EC-135, EC-141, and EL-6.

Hijacker, I know I should just fix the issue BUT I will have over 300whp and I've already seen countless threads about hardwiring the fuel pump. To think those wimpy old wires can rob the pump of voltage at high rpms scares me. So, I'm going for a hardwire.

Let us know how it runs!

Of course, now I'm curious how much voltage drop is actually occurring on the system. I'm doing up some custom harnesses, and I might consider running a thicker gauge wire in the harness if the drop is a bit excessive. Doing some quick number crunching and assuming a few things (like wire length based on chassis dimensions in the FSM and amperage of the pump at 40 psi being 8.5A) I'm getting around a 1.3V drop over the system on a 16g wire. A 12g is much better since it only shows a .5V drop.

I really need to get a multimeter back there and check it out and verify the current load of the pump as well as voltage drop of the wires.

Flip side of it all though is that there are plenty of 300+ RWHP cars out there using walbro pumps on factory wiring with no fuel starvation at all.

Sure ill post to see how it works out. Yea there are plenty of people with large power numbers and still using factory wiring BUT not a lot of them are aware of this issue. I know I wasn't until a couple of days ago. Now to see if I got this all right...

At relay terminals:

85: chassis ground
86: signal (ignition)
30: battery power with inline fuse holder (20 amp)
87: to fuel pump white and purple wire?

If for whatever reason I'm not getting my ground from the ecu, can I just tap the wire from the pump connector into the relay 85 terminal as well? Or will the pump stay on at all times?

For what it's worth, my car has not been dynoed, but I'm running a setup that should easily break 400+whp... (GT3071R .86AR), and I'm nowhere near starving for fuel at WOT at 7k+ rpms. (In fact, I'm running 10-11 AFRS) I'm still on factory wiring.. All I did was jump the relay.

I reran my numbers, btw. I'm getting between .3 and .6V drop over the circuit now. Dunno what changed in my numbers. Still need to actually measure the drop properly instead of running couch electrician calculators. One thing to remember is that the pump is designed to run at 12v, but most alternators put out around 13.5v. The difference is to allow for voltage drops along the circuits.

I found the problem!!!!!!!! Upon ripping wiring looms apart I found the culprit. Black and pink wire to brown connector near battery was not properly connected, butt connector broke. Peeled wires, twisted them together (temporary fix), turn key, and buzzzzz!!!!!!! So effing happy!!!! I had just bought relay, wires and all necessary hardware for hardwire lol. Still, I think imma go for it just for safety measures.

PyR0NiAk wrote:

idahotuner wrote:I priced together my own kit at Napa for about 15 bucks cheaper plus I didn't have to pay shipping

You should put the details in a thread.

well i was doing two fuel pumps what i did was go to the DW web site and see what was included in there kit when to napa and bought it lol.
depending on where your battery is you may only need one thing of wire

15' of 12ga SLX spec red power cable
5' of 12ga SLX spec black ground cable
30 amp in-line fuse
40 amp automotive relay
4-lead relay socket with pigtails

then wire it in like this

85- white/purple wire from chassis harness side
86- ground to chassis
87- white/purple from pump
30- from battery with fuse inline

then take the blue/red wire from the pump and ground that to the chassis.

this is what mine looked like when finished





sorry it took so long to get back to this thread

Finally got around to testing the pump voltage. Mine is at 11v give or take. Not ideal, but it's to be expected with 20 year old wiring.

Personally, unless I were to see that number drop below 10 and saw a depreciable drop in fuel pressure at WOT, I wouldn't bother. But that's just me.

Works for me. Anyway I need your help guys, I'm just about fed up with this damn car. Frustration is not enough to describe how sick I am with this damn thing. So I fix the fuel pump issue, cool. Now this bastard won't start to save its own life. I crank it and it floods of gas. I already lifted the fuel rail to check if injectors are dumping fuel and nothing they are fine. I have spark on all 4 plugs. I spoke to Martin from Enthalphy and he gave me all the tests, MAF sensor, fuel rail/injectors and nothing. I guess he too has given up because he told me what I can do is send the ecu back to him so he can plug it up to another car with similar mods and see if it fires up. It's weird because I had a 62 ecu and I got it to start once by shooting starting fluid directly into the throttle. Now I have an e5 ecu I bought from a Nico user, that's the one Enthalphy tuned for me and it won't start for s**t. Someone help!!!!!!!! Please!!!!!

Coolant sensor? I've seen the wrong one installed cause over rich nostarts.

What's your fuel pressure set to as well?

I've actually been seriously thinking about that coolant temp sensor as I've heard this is somewhat of an issue. I asked Martin about it as well and he claims he doubts it would have anything to do with it. As far as fuel pressure I don't know, don't have a gauge to it and I don't have an adjustable one, its oem. Faulty fpr maybe? Martin told me that with his tune I wouldn't need to touch anything with the fuel...

I've seen plenty of no starts due to the coolant sensor. S13 Type X and S14s have different sensors from S13 redtops IIRC. A buddy of mine had a JWT tune give him over rich issues because he used a later blacktop sensor. Swapped it for a redtop, and it fired right up.

Well to be honest I have the oem sensor that car with the engine set. Kinda dumb in my part. You know is possible that since I have a redtop my ecu is sending out wrong fuel readings? Also e5 ecu's are from a black top correct?