Fuel pump wire off battery in trunk?
Fuel pump wire off battery in trunk? Hi everyone,
A couple times in the past I have heard my in-tank Walbro 255 fuel pump change pitch when little things are done that add electric load, like stepping on the brakes. The power wire for my pump is the little one that current performance added when the harness was modded and its about 20ft long. I've been looking at the hotwire kit but think its kind of silly to buy that when I have my battery sitting less than 3ft away from my fuel pump.
Worried about my fuel pump dieing from low voltage; I'm thinking of pulling power straight from my battery. I figure I could use the current power wire to energize a new relay and use a fuse to protect it all. I'm wondering if this is a bad idea that might lead to problems though. I'm not that strong in the electrical department so someone please chime in and let me know if this is a good/bad idea. Also, anywhere to get a nice little 1 fuse/1 relay block that I could mount in my trunk nicely?
Thanks,
A couple times in the past I have heard my in-tank Walbro 255 fuel pump change pitch when little things are done that add electric load, like stepping on the brakes. The power wire for my pump is the little one that current performance added when the harness was modded and its about 20ft long. I've been looking at the hotwire kit but think its kind of silly to buy that when I have my battery sitting less than 3ft away from my fuel pump.
Worried about my fuel pump dieing from low voltage; I'm thinking of pulling power straight from my battery. I figure I could use the current power wire to energize a new relay and use a fuse to protect it all. I'm wondering if this is a bad idea that might lead to problems though. I'm not that strong in the electrical department so someone please chime in and let me know if this is a good/bad idea. Also, anywhere to get a nice little 1 fuse/1 relay block that I could mount in my trunk nicely?
Thanks,
TECH Regular
Joined: Feb 2012
Posts: 491
Likes: 128
From: Newberg, OR
Hella makes a 4 prong relay with a mounting tab that has a fuse holder built right in. Its really a nice piece I use one on my Holley fuel pump on my El Camino as well as on the head light circuits. They run about $15 but I don't know a part # I've always just talked with the parts counter guy at the local speed shop (not chain) to figure it out. A nice plus is they have lasted for 10 years unlike the cheap little black relays I've also used.
Jessica
Jessica
The changes in pitch are normal. That is just alternator output voltage fluctuations with changes in load. Even a volt or two of fluctuation will cause that.
It wouldn't hurt to run the fuel pump off the battery but there may be no reason to believe you need to. If you have the pump fused properly than that will protect against a true low voltage condition.
It wouldn't hurt to run the fuel pump off the battery but there may be no reason to believe you need to. If you have the pump fused properly than that will protect against a true low voltage condition.
Mine's hot-wired direct from the battery, less than 2 ft of wire and it still changes pitch. Here's a clip of my wiring diagram, it has an "on-off-on" switch under the battery so I can switch the pump completely off or on in addition to normal running. I've labelled the other wires off the FP relay so you'll see they are not important to the FP itself.
The available voltage for the whole system changes when you add load. It doesn't matter how short the cable is, the voltage will still drop a little when you hit the brakes or turn on the headlights (causing a change in pump speed/pitch). As long as the wiring itself isn't causing excessive resistance, I'd leave it alone.
Check voltage drop across your pump power wire (and the ground as well). If its over a few tenths of a volt, you should change your setup.
Check voltage drop across your pump power wire (and the ground as well). If its over a few tenths of a volt, you should change your setup.
Mine has the harness "keyed" power line run to a relay. The fuel pump is connected to battery hot and only comes on when the key is turned. The relay came from a wrecked bmw (free) and had the schematic printed right on it.
Thanks for all the info guys. I have been meaning to check the voltage drop whenever I'm under the car next but want to have an idea to fix it should there be a substantial drop found. Just seems to me that the power wire is really long and really small so I figured a shorter run can only help the situation.
78Elky: I think I found the Hella "fused relay" its just what I am looking for, thank you.
S10xGN: any reason why you decided to wire your fuel pump with automatic and manual controls?
Thanks again
78Elky: I think I found the Hella "fused relay" its just what I am looking for, thank you.
S10xGN: any reason why you decided to wire your fuel pump with automatic and manual controls?
Thanks again
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Thanks for all the info guys. I have been meaning to check the voltage drop whenever I'm under the car next but want to have an idea to fix it should there be a substantial drop found. Just seems to me that the power wire is really long and really small so I figured a shorter run can only help the situation.
78Elky: I think I found the Hella "fused relay" its just what I am looking for, thank you.
S10xGN: any reason why you decided to wire your fuel pump with automatic and manual controls?
Thanks again
78Elky: I think I found the Hella "fused relay" its just what I am looking for, thank you.
S10xGN: any reason why you decided to wire your fuel pump with automatic and manual controls?
Thanks again
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