1993 SR20 240SX: Fuel pump fuse keeps blowing

Post by **S14Dorikin** » Thu Jul 27, 2006 2:14 pm

I've got a post on here for the problem but figured I'd try here. First off, the car is a 1993 240SX Hatch and has a S13 Blacktop and a Walbro 255 fuel pump. The car starts and runs perfect for a while, but after a while the fuel pump will pop the 30amp fuse like nothing. I tried re-grounding the fuel pump, no change. I bought a new walbro, still nothing. I was gonna try re-wiring the fuel pump to the fuse box with a thicker gauge wire because I think the stock wiring might not be able to handle it, while I'm at it I'm gonna bypass the fuel pump relay as well. I wanted to get a 2nd opinion and maybe a description on what color wires are what from the fuel pump. Thanks.

Post by **elwesso** » Thu Jul 27, 2006 3:10 pm

very odd..... the walbro has to be pulling too much amperage... The only way to know for sure is to measure the amperage at the fuse and compare it to what a stock one does.....

Post by **elwesso** » Thu Jul 27, 2006 3:14 pm

read this thread and compare it to yours...

zerothread?id=40019

The Q45 fuel pumps are similar to the 240s, and should be similar amperage.. if its blowing a 30a fuse, you have a big problem....

A 10a fuse should be in there from the factory, right?

If your amps are really high and then it just goes over the 30 mark, you know whats going on, the fuel pump just draws way too much power.... If it stays around where it should be, and spikes, you have a wiring problem...

Post by **vancouverbc** » Thu Jul 27, 2006 6:37 pm

fsm is in my signature

Post by **vancouverbc** » Thu Jul 27, 2006 6:39 pm

red is positive. blue is negative.

Post by **S14Dorikin** » Thu Jul 27, 2006 7:10 pm

Ok, so what would it be...an exposed wire or just the wires aren't handling the power...When checking the wires above what should I look for and should I go through upgrading the gauge of the wire? Thanks.

Post by **S14Dorikin** » Thu Jul 27, 2006 7:15 pm

Oh, and if I run around on low boost it seems to do fine for a longer period of time. But the higher I turn up the boost the faster it blows, if not immediately.

Post by **cturbo28** » Fri Jul 28, 2006 8:17 am

I have ran into a simular issue with blowing the fuel pump fuse. The car i fixed had a problem with the wiring by the battery which has the fuel pump (black & pink ) wire. This persons issue was caused by his battery moving around and shorting out the FP wire hence blown fuse.

This was on a s13/SR20DET/walbro.

I would check for any cut wires.

hope this helps.

Post by **S14Dorikin** » Fri Jul 28, 2006 1:49 pm

*Condition Update*

Today I rewired the Fuel pump so that I bypass the fuse box and relay. I used the info provided by the FSM and cut the white/purple wire from the fuel pump to the harness and connected it to a 12 gauge wire which I ran to a toggle switch (12V 35Amp). I grounded the switch to the nut that holds the E-brake. I ran another 12 gauge wire from the switch to the battery with an in-line fuse in between which I used a 20amp fuse for now. I also unplugged the Fuel pump relay (EGI Fuel) and the Fuel pump fuse from the engine bay. Basically its hardwired to the battery by passing the black/yellow wire that provides power from the relay. I made a diagram below.

Now heres the dilema. When I flip the switch the fuel pump turns on and I start the car. But now the idle drops low, like 700-500rpm and almost bogs out but goes back to 1000rpm. When I press the accelerator it bogs and then revs to the throttle I apply.

What I found out NOW, after doing all this wiring, is that the black/yellow wire from the relay also goes to the Air regulator. Hmmmmm, I wonder. Sorry, I'm a newb to wiring and hate messing with electronics. I was also rushing a bit so I missed the whole Air regulator I guess...

So what do I have to do to get the car running straight now?

Post by **elwesso** » Fri Jul 28, 2006 2:33 pm

the fuel pump does not run at full speed all the time, you are probably flooding it.. The fuel pump shouldhave an adjustable speed controller, that you bypassed.

Post by **S14Dorikin** » Fri Jul 28, 2006 3:19 pm

Ok, well how can I regain the use of the controller while keeping my new setup. I'm trying to use the thicker gauge wire to keep it from blowing the fuse, lol, if its not one thing its another. I cant find anything on the pump controller in the FSM or online.

Q #1: Where is the controller located and how can I wire it into my setup so the car will run fine?

Q #2: About the air regulator...does it have anything to do with the way the car is currently running or is it fine?

Post by **vancouverbc** » Fri Jul 28, 2006 4:43 pm

For safety reasons, it is not appropriate to bypass fuses or relays in a fuel related circuit. I would not change the gauge of wire, either.

The computer(terminal 104) regulates when the fuel pump is on by supplying ground to the relay ,so you cant bypass the relay(it is essential). The air regulator supplies extra air when the car first starts or anytime when temperature thermistor(type of sensor) indicates a cold temperature.In other words, the ar increases the idle when car is cold.

High amps in a fuel circuit raises safety issues. I would check the connections you have made. Make sure they are soldered. Look for loose wire or oxidized connections.
Modified by vancouverbc at 9:32 PM 7/28/2006

Post by **S14Dorikin** » Fri Jul 28, 2006 7:09 pm

Ok well with that said, I made sure I would be able to return to the stock wiring by leaving enough wire to backtrack.

So if rewiring with higher gauge and bypassing the fuse and relay is "bad" then how can I fix the blowing 30amp fuel pump fuse problem while running on the stock wiring?

My mechanic and I are stumped and have no idea where to go from here, and the fact that its a JDM engine, with an Aftermarket Standalone ECU, and an Aftermarket Fuel pump doesn't help much. Honestly this car is turning into a major problem, I have friends with the same setup and no problems occur whatsoever, so I have no where to look for advice or answers.

Post by **vancouverbc** » Fri Jul 28, 2006 10:39 pm

I didnt notice the SR20 part. I've talking about the ka24de. Walbro 255 works with the ka24de which has a 10 amp fuse so it cant draw more than 10 amps. I've never heard of a 30 amp fuel pump fuse. Is that the stock fuse? I couldnt find any electrical diagrams for an sr20.

Post by **S14Dorikin** » Sat Jul 29, 2006 2:04 am

I was just mentioning that it is very odd that it is drawing so much power that it is blowing 30amp fuses. I was using a 20amp originally, but I put a 30amp to get a little more drive time, but it turns out those are popping as well, so I need to find the problem or else the car is just gonna sit.

Post by **S14Dorikin** » Sat Jul 29, 2006 4:12 am

Ok, I think I made a breakthrough here. Yesterday when I rewired the fuel pump and it kept bogging and picking back up I did not have a fuse or relay plugged into the fuse box. This morning I plugged in the fuel pump relay and a 15amp fuse like factory. The car ran fine, for a while. After running back and forth through my dads parking lot it started bogging again like yesterday, first thing that came to mind was I blew the 15amp fuse, and I did. But wait...I bypassed the fuse box all together when it comes to the fuel pump...so...I'm thinking something else that works on the same circuit must be blowing the fuse.

This is where I'm at and I will be trying to find the culprit. If you have any ideas that can help, let me know. Starting to feel better about my problem now.

Post by **S14Dorikin** » Sat Jul 29, 2006 4:57 am

In the FSM I see the Ignition switch (B/R wire) as well as the fuel pump relay (B/W wire) both meet at the 15amp "Fuel pump" fuse. I also notice after the fuse pops, both the EGI and EGI pump relays are considerably hot compared to the others in the box.

Is it possible that the ignition switch is blowing the fuse? The only thing that confuses me is that the car will start and run for a while.

Uuuuh! One step at a time...
Modified by S14Dorikin at 9:02 AM 7/29/2006

Post by **vancouverbc** » Sat Jul 29, 2006 11:37 am

The ignition swtich has it's own 30 amp fuse. If the fuel pump fuse goes, it most likely has to be the fuel pump or circuit. Dont bypass a fuse because you will damage the circuit components. If the fuse blew,fuse was still in the circuit. Probably parallel, so fuel pump would still blow it.

Wiggle wires and see if you can trigger short. relays getting hot is pretty normal. Switch the fuel pump relay with one with the same colour and see what happens.

Modified by vancouverbc at 2:51 PM 7/29/2006

Post by **S14Dorikin** » Sat Jul 29, 2006 12:24 pm

I've changed the relays with same results. Tried wiggling the wires and found no short. Man this is aggravating. Thinking about just getting a new harness and have a shop do it all over.

Post by **180fan** » Sat Jul 29, 2006 5:08 pm

just out of curiosity, did you solder the connections at the pump or did you crimp?

Post by **S14Dorikin** » Sat Jul 29, 2006 6:38 pm

crimp

Post by **vancouverbc** » Sat Jul 29, 2006 7:59 pm

Crimping is notoriously problematic. The crimped connections would be the first thing to check. Also check connectors and the connections at the relay and the fuse. The next step would be to take multimeter and test for high resistance(ohms) in the wiring. You have to have the power off and disconnect anything connected to computer or gauges. You could also test for voltage drop(dc volts) but power has to be on and the computer has to close the fuel pump relay. Both tests should be left to someone with experience.

Post by **S14Dorikin** » Mon Aug 07, 2006 1:57 pm

Ok, brought it to a local performance shop, they rewired the fuel pump with a relay so its on its own circuit...drove fine...but then, it started idleing rough out of nowhere and dropped to 100rpms and then back to 1000rpms...at one point it dropped and the car died, so i had to pop the clutch in 2nd to get it back on. I know the Air regulator (IACV) is on the same circuit as the fuel pump and goes to the same fuse as the fuel pump. So could the IACV have been the problem the whole time and was shorting out the fuse thus shutting off the fuel pump because it was blowing the fuse for both of them? If I replace the IACV should it stop blowing the fuse is what I'm asking....thanks.

Post by **vancouverbc** » Mon Aug 07, 2006 3:35 pm

Sounds like the performance guys did not wire the relay right. It has to be connected to the computer. the computer regulates the fuel pump by supplying ground to the fuel pump relay when computer wants fuel pump on.

Is your car still blowing fuses? The air regulator could be blowing that fuse. The air regulator supplies air when the engine is cold ie when you first start the engine. it is remotely possible that the temperature sensor is malfunctioning and the air regulator is coming on and off. doubt it. A working air regulator bumps the idle up to around 1200 for the first few minutes car is running and then it closes and idle comes down to normal idle.

I'm assuming the SR20 is similar to the 1991-1994 240sx on these issues.You could unplug the air regulator to see if that stops fuse from blowing.(assuming fuse still blowing)

Sounds like your idle issue is caused by the computer not being in the fuel pump circuit.
Modified by vancouverbc at 6:45 PM 8/7/2006

Post by **S14Dorikin** » Mon Aug 07, 2006 4:59 pm

It was blowing fuses before it was rewired. The pump was hooked up to the ecu the way it should have been, but still was blowing the fuse. The way they wired it was so it operates on its own circuit with a relay and directly to the ecu. After they rewired it, the fuse will still blow but the car will still run. So I'm suspecting the Air regulator since its on the stock fuel pump circuit and is the only thing left that runs through that fuse, plus I hear your supposed to change those anyways when you get a fresh swap because they go bad, theres no telling if the previous owner replaced it or not, won't know until I take off the manifold and take a look-sie.

When I drive the car, everything is fine. Just after the fuse blows, the idle will drop to 100rpms when I'm at a stop light or press the clutch, and will pick bacl up to 1000rpms, but sometimes will die out...like I said. Fuel seems to be fine, Air is what I worried about.

Post by **vancouverbc** » Mon Aug 07, 2006 7:53 pm

If the fuse is blown, the air regulator is not operational. You would only have problems when the car is cold. Not sure why you would have idle problems. I have not seen the wiring diagram for the sr20 so maybe the iacv-aac valve is in the affected circuit.

The air regulator only does anything when the car is cold. Unplug the electrical connector to ar and see if the fuse still blows and if the idle is weird. If you want to know if the air regulator is open or closed, squeeze the hose that supplies air to it(from air filter). sqeeze the hose that branches off to ar. the other branch goes to iacv.
Modified by vancouverbc at 12:39 PM 8/8/2006

1993 SR20 240SX: Fuel pump fuse keeps blowing

1993 SR20 240SX: Fuel pump fuse keeps blowing

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