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Old 01-03-2018, 02:02 PM   #1
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Default Upgrading Fuel Pump Relay

I've blown several fuel pump relays, and it's probably well past time to upgrade the relay and wiring. After researching on the site I found several references to this being done, but haven't found a "hold my hand and tell me exactly what to do" kind of writeup.

I found this direction:
Quote:
Originally Posted by Savington View Post
Bypass the OEM fuel pump relay, and wire a new 30-40A relay and dedicated 30-40A fuse directly from the battery to the fuel pump. If you are running a DW300 you can probably get away with going through the OEM connector, but if you are running a Walbro 450, you definitely will be drilling holes in the fuel pump hangar and running new 10awg wire through isolated lugs.
I was hoping for a little more clarification before I manage to blow myself up. Any specific relay/connectors/wire I should be buying? What am I cutting? What am I connecting new wire to? Sorry for being dumb, I'm just terrible at electrical and not finding a lot of clear instruction, maybe I'm just making this more difficult than it really is.


2000 Miata
DW300 fuel pump
Return fuel system
3 dead fuel pump relays
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Old 01-03-2018, 03:12 PM   #2
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Take the easy route and get the Deatschwerks hardwire kit. Super cheap, and super simple. its like 40 bux. I've installed em, super easy to work with.
comes with a fused power wire, and all the wires are 12awg (overkill, but that's a good thing)
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Old 01-03-2018, 03:19 PM   #3
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I think I have an unused DW hardwire kit laying around that I won't be using.. I'll have to check
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Old 01-03-2018, 03:20 PM   #4
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to answer the other questions:
you run 1 wire from battery to pump (super duper easy in a Miata). You ground 1 wire. You then either splice into the power/signal wire to the OE pump hanger (not ideal, but works just fine), or run a dedicated 2 wires to the actual pump (ideal) like spendington did

we're talking 30min to an hour tops to do all this, or 2 hours if you're old and slow like me
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Old 01-03-2018, 04:33 PM   #5
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Yes! So glad I asked now. I had no idea they actually offered a hardwire kit that definitely helps.

Also found this:


Just to make sure I've got it correct: *edited*
1. Splice new relay signal wires into stock signal wire.
2. Connect ground to chassis
3. Connect power to battery

Thanks so much for the help. I ordered the hardwire kit. I'll try to get some pics and maybe turn this into a productive thread for someone in the future.

Last edited by pdexta; 01-03-2018 at 05:21 PM.
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Old 01-03-2018, 04:43 PM   #6
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It's 1 signal wire that you cut and connect each end to relay wires. (scenario1)
Or run the relay signal wire to the pump directly and then another dedicated ground from pump to chassis. (scenario2).

You probably don't need scenario 2 for your power level, but it doesn't hurt ...
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Old 01-03-2018, 04:55 PM   #7
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I assume that means the stock relay remains in place? You're just adding the 2nd relay that will handle power to the pump?
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Old 01-03-2018, 05:10 PM   #8
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Yes. And it shouldn't fail anymore because it won't be overdrawn like crazy. (unless of course you have other issues)
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Old 01-06-2018, 08:50 PM   #9
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There's no need to keep the OEM relay, bypass it and use that wire to trigger the new relay.
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Old 01-08-2018, 08:38 PM   #10
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I got the DW hardwire kit in and wired it. It works, tune is about a point rich now so the pump seems like it's getting more voltage now. The kit came with this diagram:



Here's what I did:
Connect red wire to the battery
Ground black wire to the car
Cut the red/blue power wire (on my 2000 Miata) where it goes to the fuel pump
Connect the yellow wire to the end of the red/blue wire that goes to the fuel pump
Connect the blue wire to the other end of the red/blue wire that goes to the stock fuel relay

This allows the stock fuel pump relay power wire to be the signal wire to the new relay. Kind of redundant relay wise, but it should eliminate load on the stock relay and it was a super simple install. As I understand it this is the method 18psi was suggesting. I'll report back if anything catches fire.
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Old 01-09-2018, 12:20 AM   #11
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That DW kit looks so crusty. Those relay sockets dont hold up over time, resistance increases on the spade connectors built into it and eventually they melt. Honestly it looks exactly like the fog wire wiring kit you can get at autozone for 20 bucks and it comes with a free super craptacular rocker switch. Its not hard, buy a real relay and some real (TLX) wire and dont suck. It'll cost like $50 to do it with not **** parts. If you end up needing "stage 2" like if you have a 450E85 or something you'll have to hunt through the couple of our build threads that bought real bulk head connectors to not catch on fire and die.
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Old 01-09-2018, 01:05 AM   #12
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Old 01-09-2018, 12:43 PM   #13
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I've always had good luck with Eastern Beaver (the company). He seems to find all the nice high quality OEM stuff as far as connectors, relays etc I've used several of the 20 AMP Matsushita (Panasonic) relays and they have the bigger 40 amp also. Might be a little pricey and ships from Japan but he's spent a lot of time finding some of this stuff so I don't mind supporting him. I always stock up on a ton of terminals, shrink tube, etc when I order from him. Lots of useful info on his site too. It's all JDM too bro so it's got to be the best right? I do sort of like the look of that Delphi stuff too though..

Relays
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Old 01-11-2018, 04:34 PM   #14
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The power and ground wires are 12ga...what gauge wire should be used for the actual 4 wires on the relay itself?
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Old 01-12-2018, 05:14 AM   #15
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In case this helps others, I believe this is “scenario 2” as referenced above. See pic.
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Upgrading Fuel Pump Relay-39dda967-903f-4018-a757-f6deab758c8d.gif  
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Old 01-12-2018, 11:41 AM   #16
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Yup, thank you.
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Old 01-12-2018, 06:40 PM   #17
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Stupid/noob question, what is the consensus about fused relays in such applications?

Amazon Amazon
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Old 01-12-2018, 08:53 PM   #18
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Quote:
Originally Posted by pdexta View Post
I got the DW hardwire kit in and wired it. It works, tune is about a point rich now so the pump seems like it's getting more voltage now. The kit came with this diagram:



Here's what I did:
Connect red wire to the battery
Ground black wire to the car
Cut the red/blue power wire (on my 2000 Miata) where it goes to the fuel pump
Connect the yellow wire to the end of the red/blue wire that goes to the fuel pump
Connect the blue wire to the other end of the red/blue wire that goes to the stock fuel relay

This allows the stock fuel pump relay power wire to be the signal wire to the new relay. Kind of redundant relay wise, but it should eliminate load on the stock relay and it was a super simple install. As I understand it this is the method 18psi was suggesting. I'll report back if anything catches fire.
I did a similar wiring job a year or two ago and it's worked fine. My stock FP relay is triggering a pair of 50A relays to run my twin pumps, and it's never failed to do that. I did run 10 gauge wire and bulkhead fitting as I measured too much voltage drop with smaller wire for my pumps.
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Old 01-12-2018, 09:26 PM   #19
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Can anyone here give a "for instance" on what you consider good relays for this application? I am using 50A ones I bought from radioshack partly because they are so ubiquitous and easy to get if/when they fail.
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