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I have a Haltech Elite 2500 I'm in the process of building the wiring map for. I'm wondering about some of the oem ECU functions, and if it would make sense to replicate them with the 2500.

Fuel pump ecu - E10(A) pin 22 to fuel pump ecu F15
This outputs a 0-5V (I think) PWM signal to the fuel pump ecu to change the pump voltage from 9V to 12V. Helps with not heating the fuel as much with lower-load conditions, which sounds like a good thing. Most people just wire the pump directly to +12V and be done with it, but if one has the output available, why not use it ?

If NOT using that functionality, I think the way to just give +12V to the pump is to unplug the fuel pump ecu and jumper from pin 1 to pin 2. Then, the pump will just be on full-bore when the master-relay is on (key is ON position).
252783


Fuel Pressure Up vsv V6 - E9(B) pin 73 to vsv V6
This is used to switch the fuel pressure regulator reference from manifold pressure to atmosphere during startup. This way the regulator reference sees a higher pressure (atmosphere) than the manifold which would be under vacuum, so it keeps the fuel pressure a bit higher.

http://www.mkiv.com/specifications/ncf/ncf93/ncf068.jpg
http://www.97supraturbo.com/Trouble Codes/P0001 Fuel Pressure Control.pdf

Looking through the Haltech ECU software it seems that the Cranking table under the Fuel tables can do sort of the same thing, albeit by providing just more fuel rather than adjusting fuel pressure. That gives more fuel, but won't help if there's vapor lock going on due to a hot engine.

Removing should be simple. Just replace the vsv and two hoses with a single hose from regulator to intake manifold.

Electrical Load signal - E10(A) pin 15 to Diode D8
This is a voltage available that indicates the amount of electrical load coming through the 10A fuses MIR-HTR and Panel. As there's more load on the electrical system, more drag on the alternator, so the ECU can compensate with higher rpm etc. Much like how the AC Request signal is treated - when it's up, there's more load on the engine.

While the Elite 2500 has an Electrical Load function, it's a digital signal, on/off. Not an analog voltage, so can't really use the signal directly. That said, one could build a table(s) to monitor that signal as an analog voltage and make fuel/ignition/etc adjustments accordingly. The Toyota engineers knew what they were doing and put that in there for a reason, but it seems like most people who've gone single and/or standalone don't replicate this function. My gut feel for this is ... meh.
 

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I always PWM the primary fuel pump on TT cars. Takes 5 seconds to setup. (9v/12v)

The Fuel pressure VSV can be removed because it can be replaced by good tuning.

For electrical load, most newer ecu's have very good PID algorithms that can be tuned to compensate for this. I do use the AC request to add duty cycle when requested.
 

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Discussion Starter #3
Cool, that's kind of what I thought. Any chance you could share some of your tables ?
 

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Does anyone know if the ECU harness is wired the same for 6-speed and automatic cars ? I have a 6-speed, and there are some pins for the auto that would come in handy to re-purpose if they were there ...

For example, E9(B) pin 24 is the auto transmission temp sensor. That connector has the signal on pin 2, and general signal GND on pin 1. If it was there, and the connector just ... hanging, that would be nice to re-purpose.
 

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If your car is a 6 speed it will not have wires for auto only parts.
 
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