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Walbro 255 fuel pump

  • Crombie
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20 Mar 2020 19:35 #38501 by Crombie
Walbro 255 fuel pump was created by Crombie
Installed one of these the other day, ended up blowing fuses on the road in dangerous areas, I read at 40 psi it produces approximately 7 amps, IACV, Alternator regulator, and ECU is on the same circuit as the fuel pump, does anyone know what gauge wire is on a Honda CRX fuel pump wiring? its a 10 amp fuse for the whole circuit. The main relay consists of 2 relays in effect, one for the fuel pump, but watched Paul Danners video on the main relay, and says Honda uses a resistor in the main relay to lower voltage for some reason. I was able to do 15 to 20 miles before it blew and and the wires are loose onto of the fuel tank, so can't be a dead short

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22 Mar 2020 08:45 - 22 Mar 2020 08:47 #38540 by Andy.MacFadyen
Replied by Andy.MacFadyen on topic Walbro 255 fuel pump
7 amps is on the money for a fuel pump the only ones I know that take less are diesel systems with two pumps plumbed in series.
However I would double check the correct fuse size 10 amps is a much lower current fuse than I would expect in fuel pump power circuit 20a or 25a or 30a is more typical the lowest I have encountered is 15a. Fuel pumps take much higher current on start up and also spike if they have an intermitten open.

I don't think the wire to ECU is a power wire but more likely be just a sensing wire to confirm the relay is closed pump is powered up same goes for the alternator sensing wire

" We're trying to plug a hole in the universe, what are you doing ?. "
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Last edit: 22 Mar 2020 08:47 by Andy.MacFadyen.
The following user(s) said Thank You: John Curtis

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22 Mar 2020 09:18 #38542 by John Curtis
Replied by John Curtis on topic Walbro 255 fuel pump
Fuel pump circuits and their fuses are generally at least double the fuel pump amps. More accurately is that the fuel pump should not draw more than 55% to 60% of the fuse rating or it will kill the fuse.

Thinking out loud always helps me in the process.

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22 Mar 2020 09:32 - 22 Mar 2020 09:32 #38543 by Tutti57
Replied by Tutti57 on topic Walbro 255 fuel pump
Yep, and keep in mind that when current goes through that circuit, there is a good spike right away before the pump starts turning.

You said yours ran for a bit before blowing, but still something to consider for the future.

Nissan Technician
Last edit: 22 Mar 2020 09:32 by Tutti57.

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22 Mar 2020 16:01 #38554 by Crombie
Replied by Crombie on topic Walbro 255 fuel pump
Thanks for the responses, some great information there. Yeah it seemed to be a spike of some sort, happened the first time when giving it more throttle, I attached a few pictures. The power and ground going to the pump is under the seat, but the pump itself is further back, (attached picture of my fuel tank) so theres more wiring. I put a 15a instead of the 10a, and its been fine now, just concerned that I will melt wires or cause a fire. Very thin wire it seems to use, but that's what Paul Danner said about the reason they used the main relay to use thinner gauge wire. I didn't think Id have a problem with it drawing too many amps for the fuse, but then I saw the IACV on there and other items. Cheers Andy I think the ECU wire from the main relay is to command the pump on initial prime? thanks for the other comments saying about the fuse capacity. I might have to wire in a separate relay and fuse, but to do it correctly Id imagine I'll have to drop the tank down again to get to all of the wiring. My friend said I could put a relay in there then I could run off 10amps, but on here it seems to indicate that 15 would be the lowest on its own circuit 50% of 7 amps 10.5a
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22 Mar 2020 16:26 #38555 by Crombie
Replied by Crombie on topic Walbro 255 fuel pump
yeah the 2nd time, I was coming off a 60mph road, on a roundabout that goes onto various fast roads, cut out, put the hazards on (about 11pm in the dark, had trucks not paying attention coming into the filter lane, i jumped over into the passenger seat, my phone was dead, so I tried getting enough charge into it to use the light, ended up using the light off my go pro as I couldn't see nothing lol, changed the fuse to the 2nd 10a then nursed it back

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23 Mar 2020 14:32 #38567 by Crombie
Replied by Crombie on topic Walbro 255 fuel pump
we fitted a relay and inline fuse to one of the (optional) connections at the fuse box, the power wire had 19 strands, so it can handle 15a I think we worked it out at, there;s a 10amp fuse inline, I worked it out at 10.5 amp with that 50% buffer or whatever the correct term is. See how it goes, but so far so good

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23 Mar 2020 16:16 #38572 by Crombie
Replied by Crombie on topic Walbro 255 fuel pump
I read John Curtis's reply wrong, saying not use 50% of the fuse rating, so that be 70% of a 10 amp, will double check that wire rating again and if its ok fit a 15a, that be about 45%.

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