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Discussion Starter #1
Can a of you electrical gurus edumucate me on the fuel pump operation?

When you put the key in the ignition and switch it to ignition on, it comes on for a few seconds then turns off until the engine is cranking then stays on when the engine is running...

What tells the fuel pump when to run and when the engine is running or not?


Reason for asking is the 2gr is requiring a 12V with ignition on but engine not running, and 0V when the ignition is on but running... trying to figure out how to wire up the fuel pump (and starter too) off the lotus multifunction relay pack so I can keep the immobilizer and whatnot.
 

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I don't know of a good way of getting that output without your own circuit. The ECU controls the fuel pump. I had to build a circuit to allow the IC fans to come on ONLY when the engine is running.
 

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Most new cars have both....e.g. Turn off lights/radio when cranking... And have a signal wire for what you are asking for....car alarms often require this configuration so they don't sound when driving....anyway I don't think the lotus has this anywhere. If it does I want to know.....
 

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Pretty sure it's pressure in the rail - it comes on when it drops below a certain value, hence why it comes on when you start it, as the system is de-pressurized between runs. I think?
 

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Discussion Starter #5
That's kind of what I was thinking too, wonder if anyone knows for sure. Does it run variably as the engine runs or just on/off?
 

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The fuel pump is turned on by the ECU (via the multi-function relay), also the circuit loops through the immobilizer. It runs for a few seconds on "key on" (not driven by fuel pressure) and resumes once the crank position sensor shows the ecu a minimum rpm signal.
 

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Discussion Starter #7
Hell… so I guess the only way to run it is off of the 2gr ecu and just cut the pump connections to the multifunction relay?
 

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Hard to say without seeing the pinout and wiring schematic for the ecu you plan on using. I would think the fuel pump signal would be similar to the Lotus ecu (usually a sink to ground)
 

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Discussion Starter #9 (Edited)
Ok an FYI to anyone else looking for info on it:

Lotus ECU wise:
For the fuel pump relay in the multifunction relay block-

12V signal in - Ignition signaled 12v -> Fuse Fuse F13 -> splice AD (basically 12v when ignition on) to relay signal in
Ground signal in - 160 BP 0.5 wire straight to ECU (basically ECU controlled ground signal) relay ground
12V source for pump - 12v from stud -> Fuse R1 -> relay voltage in
12V out to pump - 126 P 2.0 wire -> inertia switch -> immobilizer -> fuel pump

So basically in order to control the fuel pump without the Lotus ECU while still maintaining the immobilizer, it looks like Im going to have to provide a grounding signal from the 2gr motor when the pump needs to be on OR ground the grounding signal, and use a 12v signal.

Could be wrong though if the immobilizer gets a signal cutting the voltage going to the pump. Working on figuring out what signals it now.

For the 2gr wiring (in case anyone is interested)

lotus Ign voltage --- relay --- 2gr FC ecu wire
Ign Off: ...........0v--relay---0v ->pump off
Ign On eng off:.12v--relay--12V -> pump off
Ign On Idle: .....12V--relay--0v -> pump on

Im not sure if that runs it when cranking though.. guess that's on the 2gr ecu signal whether the FC signal wire puts out 12V when cranking... I would assume so since it says Idle :shrug:
 

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Yes it should be running when cranking so that it can spit fuel in at the proper pressure.
 
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