Constant 12 volt fuel pump supply

[Disturbed1]

what are your guys opinions about doing this on a 7mgte - i here theere mixed response from my research. but i get a few stumbling issues and stalling issues with my cars setup, want to know if this is a worth while mod

[slide86]

so when ignition is on there is 12v supply? or even with the igintion off?

the pump has constant power when the ignition is on anyways......you dont want it to be running when the engine is off.

also its a safety issue, if you crash and the pump stays running, it will pump fuel everywhere. very dangerous and chances of fire are very high

[Mr Ed]

Ive got my pump wired to run constant 12v with IGN. Power thru a 30amp fues and relay off the IGN circuit.

Only downside I can think of the danger of having the pump continue to run after the fuel line has been severed and pumping fuel out everywhere cos it keeps going regardless of engine running or not.

You can fix this by wiring it through a relay with an oil pressure switch. You may need to include a little time delay circuit to give oil pressure a few seconds to build up when you start the car. This is what Im planning to do with mine once the immediate requirements are done.

[roadsailing]

i take it he means that standard the pump runs at, say 6 volts below a certain power/boost level then runs at 12 volts above that power/boost level.

running a fuel pump off the ignition is (no offence to anyone) a really stupid idea.

and you don;t need a circuit opening relay to do it properly either.

the oil switch is a good method for cars that don't have EFI, but any EFI toyota should have an "engine running" signal that you can use to trigger a relay.

if you use an oil pressure switch, you just have another fuel pump relay that is triggered from the START signal, that way you wont be turnong over the engine till it builds oil pressure.

[BigWorm]

Um, I think he's refering to the fact his fuel pump runs at a lower voltage at idle (8 or 9 volts I think?)
then switches up to the full 12V after a certain revs/load. Not having it running flat out all the time, which would run your battery flat pretty quick.....

I'd be interested to hear the claimed benifits of this mod too, I've heard people have had problems that could be related to too much fuel at idle after performing said mod, but havn't heard any concrete evidence?

[Mr Ed]

Um, I think he's refering to the fact his fuel pump runs at a lower voltage at idle (8 or 9 volts I think?)
then switches up to the full 12V after a certain revs/load. Not having it running flat out all the time, which would run your battery flat pretty quick.....

I'd be interested to hear the claimed benifits of this mod too, I've heard people have had problems that could be related to too much fuel at idle after performing said mod, but havn't heard any concrete evidence?

Too muc fuel at idle is because the stock regulator isnt big enough to cope with the extra fuel of a larger fuel pump which is what people usually have when bothering to muck around with the circuitry. You dont get this problem with a stock pump.

Yes the voltage is 9v and switches up to 12v once the revs get up a bit, this is too reduce noise at idle not to prevent fuel surge.

On a big turbo car that still has the fuel pump set to swtich only to full power at X revs you can get problems because the boost pressure surges up quicker than the fuel pressure, fuel rail pressure drops and AF leans out then pistons start melting.

Common on big single JZA80s which often run big turbo setups on fairly stock cars.

Ive done it on mine as the 2JZ ECU doesnt have a simple switch over like my old 1G one did. The 2JZ ECU sends a signal to a seperate computer that controlls the fuel pump voltage. I didnt have this computer (its in the boot and I bought a halfcut) so I had to wire my own fuel circuit. Theres no point in having headaches over wiring up a custom dual voltage circuit as I dont care about noise.

However, there isnt any point on doing it on a completely stock car.

[Mr Ed]

the oil switch is a good method for cars that don't have EFI, but any EFI toyota should have an "engine running" signal that you can use to trigger a relay.

Mine doesnt.

if you use an oil pressure switch, you just have another fuel pump relay that is triggered from the START signal, that way you wont be turnong over the engine till it builds oil pressure.

I forgot to mention the START signal in my post before before, thanks.

[roadsailing]

yours didn't have a circuit opening relay?

you could use the two voltage outputs to control 2 relays (or one if you got tricky) and have your fuel pumps switch off when the engine stops

[Draven]

I've done this mod to my JZA80 (to eliminate it as a possible cause of prior problems). There has been no change in the running of the car at all - no overfuelling at idle or anything... that said, why are you planning on doing this?

[Disturbed1]

i have a few hesitation provblems and slight stumbles whilst driving, i dnt have no vac cleakls or notinging and alot of yanks claim that this is a common prob when running safc and aftermarket fuel pump ... weather its tru or not. ..

my car also stall sometimes with dying revs even though the idle is set at 1500 RPM!!!! dont know why

ill post up a pic of my afr datalog for u to have alook at .. there a deep trough at about 3200 rpm which i cannot adjust

[Draven]

I'd like to know why your idle is at 1500 for a start

[nick.parker]

I agree that its a big safety issue and out of the question to run the pumps full time. No matter how unlikely something seems it has happened to somebody...On the 4AGZE the fuel pump runs when cranking, or when the AirFlowMeter swtich is closed (when there is airflow). Some Fords and others also have a special switch that opens when the car experiences a rapid deceleration (atleast a head on - not sure about side impact) this could be worth investigating too if anyone wanted an extra safeguard..I think some old triumphs have this too (even the carby ones - Stag). Modern cars probably tie fuel pump control in with airbag deployment / impact detection.
Cheers, Nick

[Disturbed1]

hopefullyy u guys can understand the plots... as u can see there is a distint trough which im unable to smooth out whilst engine is comming on boost not sure if its related but it running a steady 12volt rather then the flucctating 9-12 volt was recomenc=ded by u peers i will give it a go and see if it helps my causes

[Disturbed1]

I'd like to know why your idle is at 1500 for a start

\
cause if its any less 1000-800 it will die instantly>> every time after backing off accel

[Mos]

Older setups have a relay ("Fuel Pump Relay") that changes over a set of contacts. This introduces a (very short) period where the pump is not getting any power at all. Some claim this can cause a dip in fuel pressure (something that I personally do not believe but haven't done any testing to disprove).

Newer setups run a fuel pump ecu, as already discussed, with no "easy" way of removing the "feature".

There are some intermediate setups that modified the fuel pump relay wiring slightly to ensure the fuel pump always gets power, even during the swithing time - it shorts out the resistor rather than switching circuits. The early setup is easily modified to the intermediate version.

Now to answer the question ... I remove the fuel pump resistor and relay on most engine swaps I'm involved in, unless specifically asked to leave it in. None of the vehicles in question suffer any sort of problems with overfueling at lower rpm ranges, as evidence by many dyno runs with afr measurement.

Mos.