Flow/pressure/resistance is just like an electrical circuit - The pump provides pressure and the 'load' draws flow. If the pump can't cope with the flow then the pressure will drop.

Current draw relative to pressure and flow depends on the pump type. An impeller pump will provide a relatively steady pressure and the current draw will go up as you draw more flow. A vane / gear etc. type pump tends to provide a steady flow and current draw goes up as you increase pressure. Either way - when you go on boost the flow goes up and pressure goes up (maintained at a steady figure above manifold pressure) so you will draw more current on boost.

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If at first you don't suck seed, try drier grain.

Carried out a few more tests tonight..

I fitted a new earth cable direct from the pump to the battery, it was going through the chassis but i haven't noticed any difference by doing this.
with the diagnostic FP and B+ bridged and the fuel pump disconnected in the boot im seeing the same voltage as the battery.
When i reconnect the fuel pump this voltage does drop lower than the battery voltage, surely this is always going happen though?

The fuel pump draws 7~Amps at idle/normal driving and goes up to around 8.5~Amps on boost, this does seem a little lower than what Walbro shows, this is in keeping with what you mention above.
i have noticed that walbro list two 255LHR Fuel pumps, normal and High pressure, of course i can not for the life of me remember what one i have?

It turns out the two DVM's that i have been using read around .1v different to each other, the lower reading being the one i have been using to read Fuel pump voltage, all of todays voltages are taken with two good DVM's.

I have come to the conclusion that the fuel pump and battery have a difference of .3V (using two accurate DVM's, which i think is OK?

The Fuel pump does not drop below 13Volts now and i would say drops to around 13.20V when on boost?
Resistance of the fuel pump is 0.6 Ohms, this sounds about right to me.

I can only assume that the ECU is taking its power from under the bonnet somewhere, closer to the alternator, which is why im seeing 13.6 Volts once up to temperature.


Thank you once again for all your input

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Steve Gillies
ST-165 88 UK

www.GT4-Play.co.uk

I have noticed that the battery voltage is dropping as revs/boost rises, at the same rate as the fuel pump.

Is this a normal phenomenon?
Water injection, priming pump, injection duty cycle and fuel pump all kick in and draw more?

Having fitted the Alternator rear cover back on this hasn't altered the voltage drop at the ecu as the car gets up to temperature.

I have also noted voltage dropping at the ecu when lights and heaters are switched on while driving along.

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Steve Gillies
ST-165 88 UK

www.GT4-Play.co.uk

Yes voltage will drop a bit as revs rise, as you say injectors run for a longer time pump will have to start actually working to try and shift and maintain pressure .
Of course as lights n heater etc go on voltage will drop. The alternator can only supply so much power.


--
Darryl

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--

Darryl

Evening... Having purchased a recon Alternator from TCB I'm actually seeing slightly less voltage than my older unit!?!?
Do brush's take some time to wear to the armature to work 100%, a little like brake discs and pads?

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Steve Gillies
ST-165 88 UK

www.GT4-Play.co.uk

I appear to of gained a Whine from the new alternator too!?

http://youtu.be/zqt7QqrCtfA

My old Alternator was quiet!?

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Steve Gillies
ST-165 88 UK

www.GT4-Play.co.uk

The voltage out is set by the built in regulator unless a fault causes it to be lower. There is some production tolerance on this.

_________________
If at first you don't suck seed, try drier grain.

Thanks for the reply, What's your thoughts on the whining noise from the Alternator?
It's very noticeable when driving and is louder when the Alternator is under more load, lights on etc

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Steve Gillies
ST-165 88 UK

www.GT4-Play.co.uk

Have you tried pinpointing the noise with the old screwdriver 'stethoscope' trick Steve? A while ago I made the mistake of over-tensioning the drive belt and as a result knackered the air-con compressor bearing which then started making a whine type noise. Bit of a rookie error I know and its unlikely in your case but just thought I'd mention it.

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Don
GT4DC Chairman
1994 Toyota Celica GT-Four ST205WRC JDM 269bhp @ 0.9bar
1994 Toyota Celica GT-Four Special GT 590bhp @ 1.8bar
1989 Van Diemen RF88/89 Formula Ford 1600
2008 Nissan Patrol GU 3.0L ZD30DDTi 154bhp

Hi Don I haven't done that actual test just yet but have a look at this other video below.

Keen to know what voltage you guys are seeing at the battery and ecu once the car is up to temperature.

Thanks for your input Don.

http://youtu.be/0yEjF9X23TI

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Steve Gillies
ST-165 88 UK

www.GT4-Play.co.uk

Seems very wrong to me.

I had a replacement alternator from the same place, it seems to be fine but did require modification to fit so certainly wasn't perfect.

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GT4DC Events Co-ordinator
1996 ST205 UK

So from the second video it sounds like the alternator is only whining under load so it would indicate that either the alternator bearings are the source or perhaps the extra load is causing the belt to slip on the pulley. If you vary the drive belt tension you could eliminate the belt/pulley as the cause then you will know for sure its in the alternator. Alternatively borrow another alternator to see if the noise disappears!

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Don
GT4DC Chairman
1994 Toyota Celica GT-Four ST205WRC JDM 269bhp @ 0.9bar
1994 Toyota Celica GT-Four Special GT 590bhp @ 1.8bar
1989 Van Diemen RF88/89 Formula Ford 1600
2008 Nissan Patrol GU 3.0L ZD30DDTi 154bhp

Mike- No noise from your Alternator from Cornwall?

I slackened the belt off to the point that it squeaked upon start up an no change.
The previous alternator was silent as a mouse!

It must be the Alternator at fault.

_________________
Steve Gillies
ST-165 88 UK

www.GT4-Play.co.uk

is there a warranty on it?

_________________
Don
GT4DC Chairman
1994 Toyota Celica GT-Four ST205WRC JDM 269bhp @ 0.9bar
1994 Toyota Celica GT-Four Special GT 590bhp @ 1.8bar
1989 Van Diemen RF88/89 Formula Ford 1600
2008 Nissan Patrol GU 3.0L ZD30DDTi 154bhp

It was one if the selling pitches that it came with a 12 month warranty.

So, who is going to tell me what voltage there battery in the boot is showing once EVERYTHING is up to temp?

_________________
Steve Gillies
ST-165 88 UK

www.GT4-Play.co.uk