Bypassing JZX90 Fuel computer

[JZX083]

Hey guys,
Im currently in the middle of wiring my third 1JZ into MX83 conversion but this time i am using a JZX90 front clip. I have used JZA70 and JZX81 previously. As the JZX90 computer and everything is different to the others i was wondering how some of you guys that have used the JZX90 motor have been bypassing the fuel computer that is usually in the boot.
I have managed to wire the circuit open relay and fuel pump relays to work all ok in the other conversions so im wanting to keep this one the same.
I was thinking maybe a Tacho relay that switches the ground to the circuit open relay???
Any suggestions would be greatful.
Cheers,
JZX083

[bungs]

The FPC (fuel pump controller) pin on the jzx90 ecu switches to ground when the ecu needs the fuel pump to start. So wire this pin to a relay to turn on the fuel pump and you'll be sweet as brudda.

You could probably wire it to the stock mx83 fuel pump relay if you wanted to keep the wiring clean.

[wilbo666]

The FPC (fuel pump controller) pin on the jzx90 ecu switches to ground when the ecu needs the fuel pump to start.

Sorry, no it doesn't.

The FPC pin is PWM (Pulse Width Modulated).

See page 11
http://www.autoshop101.com/forms/h42.pdf

Also if you do not connect Engine ECU pin DI, to +12V (Ignition) then the engine ECU pin FPC does not pulse as it believes there is a problem with the fuel pump ECU.

DI pin is the diagnostic pin from the fuel pump ECU. It is connected to +12V when there is no problem and is open circuit (not connected internally) when there is a problem...

If you connect DI to Ignition power, and use a tachometric relay that is triggered by the FPC output from the Engine ECU to trigger the COR you will be good...

This will also mean that you will get the pre-start fuel pump priming pulse, and the protection of the fuel pump turning off if the engine stalls in the event of an accident.

Tacho relays / Tachometeric relays can be bought, as they are used in LPG conversions (As it sounds like you know ).

Cheers
Wilbo

[bungs]

I stand corrected. I remember browsing around the forums for the answer a while back and reading that the 1j ecu has a pin that switches to ground when the fuel pump turns on and assumed it was the fpc pin. (never assume)

edit: Here's what I was getting confused with: http://www.toymods.net/forums/showthread.php?t=18471

[JZX083]

Thanks heaps for that guys appreciate it.

Wilbo i know on the JZA70 and JZX81 there are two pins from the computer, one for the COR and one for the Fuel pump relay. if i switch the ground of the COR with a tachometric relay from FPC what do you suggest i do with the ground for the Fuel pump relay???

or can i run both grounds for COR and FP relay off of the one tacho relay???

[cambelt]

Theres FP and DI , 1 tells the fuel pump to switch on and the other varys the pump voltage if i recall correctly.
The pulse is only 5 volts out so will have to go thru a tranny to switch yr relay.
Dave

[JZX083]

My Apologies Wilbo,
After having a look at the pdf file you posted and the diagram on page 11 i now understand how you suggested to wire the COR and FPR. Thank you!!!

[JZX083]

Hey guys,

Wilbo,
I managed to get the 5v PWM signal to come on from the computer you wouldnt happen to know the frequencies this signal is sent out at on the different levels???
The reason i ask is im thinking about using this signal through an RC circuit to run a relay to switch the COR ground.
I may just have to get a CRO to measure it!!!
I know it sounds complicated but I'm thinking with the ciruit running correctly i will get all the pre prime and turning off when its suppose to working.
Im not sure if a Tacho relay will work off of this 5v digital signal??? it may work off of the tacho engine output but i didnt wanna do it that way.
Cheers

[cambelt]

When i did this on a 2JZ . i just used the 5 V signal thru a transistor to switch the COR.
As i said i was sure one signal is pump on or off and the other for the pump speed.
Dave

[JZX083]

No worries thanks cambelt,
You dont remember the part number of the tranny do you???
So the Pulse Width Modulated signal doesn't drop off enough to make the transistor drop out then....
Cheers

[wilbo666]

Dave, see picture below




JZX083:
Below is the circuit I used (works well). I used a N Channel MOSFET and an R-C Circuit I don't remember what the frequency was, and it seems I didn't write it down.

On time after FPC signal is lost is around 0.5->1sec from memory (You could work out the approx Frequency from this )

• 1k series resistor
• 470n||470n to GND (I was using SMD)
• 16V Zener diode to GND to protect MOSFET gate
• 1M resistor to GND to ensure gate of MOSGET discharges
• FDC6561AN N Channel MOSFET

I managed to build it on a small bit of vero board and fit it inside the COR.



Cheers
Wilbo

[JZX083]

Wilbo,
Thats excellent thank you very much!!!
Exactly what i was after!!!
cheers for everything guys!!

[chaserbuddy]

sorry for the thread dig but in the circuit you used to supply ground to the COR the what voltage was the 470n||470n capacitor I managed to source a 24v one, does the voltage matter? thanks