Help with fuel pump voltage (have I been misinformed?)
Discussion
As it stands I am struggling to get the fuelling right on my Supercharged Civic Type R (EP3).
My fuel system is currently setup as below
Warlbro 300l/ph in tank pump - Specs here - http://www.glencoeltd.co.uk/walbro-motorsport-upgr...
Sytec rising rate FPR
Fuel rail modified with return, 6mm return line to tank
Standard fuel supply line.
I have been told (which I now think may be wrong) that my voltage at the pump is too low. I have checked wiring, replaced relays and fuses through the system.
When measured yesterday, the battery was charging at 14.5v and the measurement at the pump was 12.1v (see pic below) which is what I have been told is too low..
But I can't see how that can be too low? Surely the system runs at 12v? And the description from the website above says that the voltage for the pump is 12v?
Any help would be appreciated so I can get this sorted!!
My fuel system is currently setup as below
Warlbro 300l/ph in tank pump - Specs here - http://www.glencoeltd.co.uk/walbro-motorsport-upgr...
Sytec rising rate FPR
Fuel rail modified with return, 6mm return line to tank
Standard fuel supply line.
I have been told (which I now think may be wrong) that my voltage at the pump is too low. I have checked wiring, replaced relays and fuses through the system.
When measured yesterday, the battery was charging at 14.5v and the measurement at the pump was 12.1v (see pic below) which is what I have been told is too low..
But I can't see how that can be too low? Surely the system runs at 12v? And the description from the website above says that the voltage for the pump is 12v?
Any help would be appreciated so I can get this sorted!!
Firstly I must stress that I am no expert on this pump but have my doubts over what you have been told.
12v is normally a "nominal" voltage for most auto electrical items as the precise voltage at every service in the car can both go up & down.
Most things for cars work on this nominal 12 volts, which realistically means anywhere from 10 to 15 (ish) should be fine.
Have you (for instance) checked the pump output into a bucket etc for a time of 10 secs to see if you get around a 6th of it's quoted l/min output?
What are the fuelling issues.
12v is normally a "nominal" voltage for most auto electrical items as the precise voltage at every service in the car can both go up & down.
Most things for cars work on this nominal 12 volts, which realistically means anywhere from 10 to 15 (ish) should be fine.
Have you (for instance) checked the pump output into a bucket etc for a time of 10 secs to see if you get around a 6th of it's quoted l/min output?
What are the fuelling issues.
If you were charging at 14+v and you're only getting 12v at the pump you've either got some very poor electrical connections or for some reason there's a few diodes in line, I can't imagine why the latter so I'd guess the former, check the earth are all good and the wiring is large enough for the voltage drop.
As the speed of an electric motor is directly proportional to the voltage applied to it, and the amount of fluid moved by a pump is proportional to the speed of that pump, it should be obvious that "more volts = more fuel" at any given pressure ratio!
Typically, the output voltage for an alternator will be between 13.7 and 14.3 volts, but unless the alternator uses a remote sensing wire (and vast majority don't) that voltage is at the output terminal of the alternator itself. Any given consumer (like your fuel pump) is a lot further "downstream" being behind the main alternator output wire, the high current junction box, the fuse box, at least one relay, and finally, several meters of cable (fuel pump is the other end of the car to the alternator generally) All that upstream system has a resistance, and so it also must have a voltage drop. And as V=IR, the more current you pull, the more the voltage drops at the consumer.
If you want to absolutely maximise pump speed, and hence fuel flow, you need the highest possible voltage at the pump, so i'd suggest replacing the stock pump power feed loom (and possibly even the control relay as well) we something that has a lower resistance (ie, larger gauge wire, higher rated relay etc)
I'd aim to be within 1V of the measured alternator output voltage if you can! Luckily, for a dumb return fuel system and pressure regulator, the highest pump load is actually at idle, so that's easy to measure with the engine idling........
Typically, the output voltage for an alternator will be between 13.7 and 14.3 volts, but unless the alternator uses a remote sensing wire (and vast majority don't) that voltage is at the output terminal of the alternator itself. Any given consumer (like your fuel pump) is a lot further "downstream" being behind the main alternator output wire, the high current junction box, the fuse box, at least one relay, and finally, several meters of cable (fuel pump is the other end of the car to the alternator generally) All that upstream system has a resistance, and so it also must have a voltage drop. And as V=IR, the more current you pull, the more the voltage drops at the consumer.
If you want to absolutely maximise pump speed, and hence fuel flow, you need the highest possible voltage at the pump, so i'd suggest replacing the stock pump power feed loom (and possibly even the control relay as well) we something that has a lower resistance (ie, larger gauge wire, higher rated relay etc)
I'd aim to be within 1V of the measured alternator output voltage if you can! Luckily, for a dumb return fuel system and pressure regulator, the highest pump load is actually at idle, so that's easy to measure with the engine idling........
Thanks MT.
I have considered that I will need to run a new wiring setup. It's just a PITA!
Luckily (I think) the battery is in the boot, so I could run a live from that to a relay to feed the fuel pump?
TBH I may leave this to someone who knows it a bit better, don't want to fry anything!
I have considered that I will need to run a new wiring setup. It's just a PITA!
Luckily (I think) the battery is in the boot, so I could run a live from that to a relay to feed the fuel pump?
TBH I may leave this to someone who knows it a bit better, don't want to fry anything!
Max_Torque said:
I'd aim to be within 1V of the measured alternator output voltage if you can! Luckily, for a dumb return fuel system and pressure regulator, the highest pump load is actually at idle, so that's easy to measure with the engine idling........
Not quite true...as load will go up with pressure and at idle the system will be running near it's lowest working pressure.The 12v at the pump isnt necessarily a problem unless he's actually running out of fuel, but I fully agree there is little reason voltage measured at the pump should not be damn close to system voltage.
Better wiring/connectors are probably required.
Butter Face said:
Done some more testing tonight.
Fuse box - 13.6 volts at idle
Fuel pump relay, 12.8 in, 12.8 out
Fuel pump - 11.9
So seem to be losing volts from fuse box- relay and relay-pump.
Is the stock wiring undersized for the pump? Fuse box - 13.6 volts at idle
Fuel pump relay, 12.8 in, 12.8 out
Fuel pump - 11.9
So seem to be losing volts from fuse box- relay and relay-pump.
My pump is on the other end of the car to the alternator and if the alt is pumping 14.4v then the fuel pump gets 13.8-14v...
PhillipM said:
Is the stock wiring undersized for the pump?
My pump is on the other end of the car to the alternator and if the alt is pumping 14.4v then the fuel pump gets 13.8-14v...
Standard wiring is no doubt fine for standard pump running at standard pressures.My pump is on the other end of the car to the alternator and if the alt is pumping 14.4v then the fuel pump gets 13.8-14v...
While it seems like he has one of the small Walbro pumps....it would seem it is pulling a lot more current then the OEM pump, highlighting volt drop issues.
The OEM pump is perhaps really tiny.
I guess it's lucky he didnt fit one of the bigger pumps they offer...they can draw huge amounts of current !
Butter Face said:
Cheers for all the input.
This pump is sold as a direct fit so I would assume that the wiring should be man enough.
I am going to do a test to see how many amps the pump is drawing. If I can't get any luck I will take it to a local auto electrician next week.
Direct fit...simply means it fit your car and plugs in.This pump is sold as a direct fit so I would assume that the wiring should be man enough.
I am going to do a test to see how many amps the pump is drawing. If I can't get any luck I will take it to a local auto electrician next week.
They have no control over what you use it for or what pressures you ask of it. So in no way can you assume the wiring is up to the job of running a larger pump, in a boosted application...totally different than what it was all designed for.
And to test...just buy cheap clamp meter or if there is a fuse for the pump, one of those crappy things that go in place of the fuse to measure current.
Clamp meter arguably more useful to own though.
eg
http://www.ebay.co.uk/itm/Sealey-Current-Tester-Di...
http://www.ebay.co.uk/itm/New-UT204-DMM-CE-AC-DC-V...
As an update..
We wired the pump to the battery (13.74 volts) and pump was getting 13.34v so all ok there.
Checked the original wiring with no load and all running 13.74v volts. Also check for continuity and no resistance so wiring itself is fine.
As soon as original wiring on the pump it dropped to 11.9v at the pump!
So either the pump is faulty (but I have been told has been tested out of the car and al ok) or just the wiring is not man enough?
My solution is the run a live from the battery to the pump via a relay, the switch for this I will run from the current 12v supply for the pump so I will not be bypassing the existing relays/fuel cut off?
Any thoughts?
We wired the pump to the battery (13.74 volts) and pump was getting 13.34v so all ok there.
Checked the original wiring with no load and all running 13.74v volts. Also check for continuity and no resistance so wiring itself is fine.
As soon as original wiring on the pump it dropped to 11.9v at the pump!
So either the pump is faulty (but I have been told has been tested out of the car and al ok) or just the wiring is not man enough?
My solution is the run a live from the battery to the pump via a relay, the switch for this I will run from the current 12v supply for the pump so I will not be bypassing the existing relays/fuel cut off?
Any thoughts?
some honda's have fuel pump resistor not sure if your has it that would be coorect than - if no load, circut is open so will be 13.7 volt but if you have resistor in-line voltage will drop.. and load applied voltage would drop as you described... from my knowledge mazda rx8 also is eqipped with resitors and 2 relays with one bypassing resistor for higher engine loads
Butter Face said:
I think I have found my own answer, there is a flow chart on the wesbite that shows voltage from 13.2-13.7v, so I am down on where it needs to be. Hmmmmmmmmmmmm
The Walbro pump is taking almost twice the current of the standard Honda pump, so it's not too surprising that the standard wiring is not up the job.Gassing Station | Engines & Drivetrain | Top of Page | What's New | My Stuff