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Fuel Pump Wiring & Control System Modifications

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stuka
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2014/08/26 19:41:13 (permalink)
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Fuel Pump Wiring & Control System Modifications

I am planning to upgrade my pump to the walbro 450 lph. On inspection the wiring and heat shrink to the cradle and pump looks in good condition, not brittle or anything. From reading posts over the years I see people always recommending to upgrade the wiring as well. Why is this? Is it really needed if the factory wiring is in good condition?
 
Also, I have been told modifications are required to the fuel pump resistor pack to run the aftermarket pump. Does anyone has a link to information on this?
 
Thanks
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    stuka
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    Re: Fuel Pump Wiring & Control System Modifications 2014/08/28 06:40:59 (permalink)
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    anybody get information on this?
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    kojab
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    Re: Fuel Pump Wiring & Control System Modifications 2014/08/28 07:46:15 (permalink)
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    A Fuel pump that delivers more fuel usually draws more power.  If the factory pump wiring is of a size that does not match the amperage of the new pump the wiring should be changed (bigger diameter).  A voltage drop can occur across the inadequate wiring causing the pump to run slower.
     
    How good the factory fuel pump wiring is I don't know but you can do your own test. Factory fuel pump first then new pump.
     
    1) Put a battery charger on your battery to try and simulate the the vehicle is running/driving.
    2) Link the fuel pump relay so pump is continuously running.
    3) Measure voltage across pump.  Ideally you want the same voltage as you have across the battery.
     
    If your battery is in the boot even better as its close to the fuel tank.  Run bigger cable direct from battery to new pump with new relay triggered by existing pump wiring.
    post edited by kojab - 2014/08/28 08:05:49

    92' SW20 3SGTE   GEN2 GT Hardtop Holden Ls1 ECU
    87' AW11 3SGTE   Delco EFI ECU & 21 psi boost
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    78' KE55 L67        Delco EFI ECU
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    robk
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    Re: Fuel Pump Wiring & Control System Modifications 2014/08/28 09:58:45 (permalink)
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    kojab
    If your battery is in the boot even better as its close to the fuel tank.  Run bigger cable direct from battery to new pump with new relay triggered by existing pump wiring.

    In the SW20 the battery is in the front of the car, the fuel pump is just behind the gear shifter under the centre armrest/tunnel, and the fuel pump relay is at the back of the car.
     
    Pat:
     
    There is a 'circuit opening relay' and a 'fuel pump relay'. The 'circuit opening relay' (FC pin on factory ECU) must be activated for the fuel pump to run at all. The 'fuel pump relay' (FP or FPR pin on factory ECU) determines whether the fuel pump resistor is in series with the fuel pump or not. The factory ECU activates the fuel pump relay when a higher fuel flow rate is required.
     
    Many people bypass the fuel pump relay and remove the fuel pump resistor, so the fuel pump runs at full speed all the time.
    Here are some reasons for retaining the fuel pump resistor setup:
    - Reduce wear on the pump
    - Reduce the required flow capacity of the fuel return line
    - Reduce fuel heating
     
    The main reason for bypassing the fuel pump relay and removing the fuel pump resistor, is to simplify the wiring.
     
    That's just one part of the story.
    The other thing, as Richard mentioned, is that you may want to consider the adequacy of the factory wiring.
     
    On my car I did the following:
    - I bypassed the fuel pump relay, then removed the fuel pump relay and fuel pump resistor. 
    - The fuel pump output from my Adaptronic ECU controls the 'circuit opening relay' only. 
    - I cut the factory wiring to the fuel pump, at the access hole below the ash tray which is only about 1 foot away from the fuel pump. 
    - I installed a new relay under the dash with a 30A fuse, and extended/re-routed the factory wiring to that new relay to trigger it. 
    - I ran a beefy power cable from the battery to one of the switch contacts on the new relay, and another wire from the other contact back to the fuel pump. 
     
    post edited by robk - 2016/03/11 09:55:30

    There is an extensive build thread for my car here: http://www.mr2australia.com/mr2play/tm.aspx?m=18316
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    MCT_MR2
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    Re: Fuel Pump Wiring & Control System Modifications 2014/08/28 22:57:18 (permalink)
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    Rob pretty much covered it, but the only bits I will add to it as to why people also remove the factory system is:
    - The system is generally 20 years old (or older) and doesn't work as well as it used to, and
    - Once the vehicle has been modified from stock, the system does not always switch over from factory
    - Big fuel pumps like the walbro 400+lph pumps, and the 300lph+ pumps from other makes require better voltage and current than the factory pump wiring can provide. You will generally find a 1-2v lower than battery voltage at the pump through factory wiring, which in big pumps, can be 50-100lph less flow.

    On a side note, usually with a big pump, it is usually the fact that the reg will struggle to bypass enough fuel at idle, rather than the size of the return line. Whether or not this is a problem can be easily checked with a fuel pressure gauge.

    '88 MR2 4AGTE W/ EFR6258

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    more to come......
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    stuka
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    Re: Fuel Pump Wiring & Control System Modifications 2014/08/29 06:41:56 (permalink)
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    all that makes sense thank you. i have upgraded all fuel lines to -6AN and also the FPR to accept the -6AN fittings. Im keen to know whether you reckon I should replace the wiring to the actual fuel pump cradle outside tank and within tank as this will be a pain due to the stock connections in this area
    #6

    MCT_MR2
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    Re: Fuel Pump Wiring & Control System Modifications 2014/09/01 09:10:48 (permalink)
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    Pat, for the wiring inside the tank (cradle wiring) I generally would worry too much about that wiring, as most people can cause more harm than good with that area (wrong kind of heatshielding, poor quality crimps, soldering etc).

    I would just upgrade the wiring after the connector that passes through the service panel under/in front of the shifter assembly.

    Keep the earth wire short, ground it with an eyelet nearby, and clean the paint under it for a good ground.

    Use something like 4mm auto cable (also known as 1.84mm2 ((refers to the area of actual wire)) for the power side. Run a pump like that on a 15a fuse, maybe a 20a. You could try running a relay triggered by the factory fuel pump wiring, that way it would only prime when you key on and not start running flat out.

    Those pumps will usually draw 8-12a while running, but there is always a spike when they power up or down.

    You could also use 3mm auto cable/1.13mm2, as it is rated to 30a, whereas 4mm is rated to 50a.

    '88 MR2 4AGTE W/ EFR6258

    224.6KW @ 20PSI

    more to come......
    #7
    stuka
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    Re: Fuel Pump Wiring & Control System Modifications 2014/09/03 19:32:38 (permalink)
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    Thanks for the reply Nathan. What are your thoughts on the pump connector on the photo attached? I was thinking of just doing away with the connector and soldering the pump wiring to the OEM wiring and sheathing with chemical resistant shrink wrap.
     
    #8
    MCT_MR2
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    Re: Fuel Pump Wiring & Control System Modifications 2014/09/03 20:45:23 (permalink)
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    Hey Pat,
     
    That should be fine. Those connectors are designed to minimise the chance of corrosion of the pins, but they are very bulky and awkward, and you often have to remove them (also, depending on the supplier, they supply the pump without the other half of the connector.) I generally prefer crimping over soldering, but there is nothing wrong with soldering.
     
    I find raychem DR-25 doesn't always hold up with E85, I usually use ES-1 glue lined heat shrink. Whatever you use, make sure the wiring is secured in a way that if the heat shrink does degrade, the wires can't short together, or the positive against the pump bracket.
     
    I see you got the pump switched over from the smaller one.

    '88 MR2 4AGTE W/ EFR6258

    224.6KW @ 20PSI

    more to come......
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    stuka
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    Re: Fuel Pump Wiring & Control System Modifications 2014/09/04 18:59:42 (permalink)
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    Yes Dylan at Gorilla Industries sent me the right pump straight away.
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