Tuesday, February 14, 2012

AE86 Tech #86-25: GZE Resistor

 I've notice quite a few 4AGZE powered cars that never use the fuel pump resistor, then again many setups imported from Japan never come with them.  Even an online harness builder opts to leave out the often ignored option.  It doesn't affect start up nor getting from point a to b.  Though some sensitive drivers will notice that driveability is a bit annoying at times. While others who may be a bit numb when it comes to driving have no clue of what's going on or maybe they just don't care.
The resistor is similar to in theory to the kenne bell boost a pump contraption.  During off boost driving, idle and cruise, the relay is activated and redirects voltage to a resistor dropping voltage slightly.  This in turn reduces fuel line pressure, leaning out the mix.  But as you lay down the law and unleash the boost of the SC12 supercharger, the relay turns off and redirects full power directly to the fuel pump for maximum line pressure.

Borrowed and cropped from club4ag
 Even the Japanese 4AGZE engine diagram shows the fuel pump resistor and relay.  If the option was bypassed, the resulting higher pressure adds a bit more fuel during cruise and idle.  This leads to crappy gas mileage and a car that has a bit of hesitation during quick throttle acceleration.  These effects are more pronounced when using a higher than normal fuel pump.  Cars with stock pumps may not be overly affected by this issue.  But then again you shouldn't be using your stock pump with boosted engine to begin with, very naughty.

 Since dark blue didn't have one, and they're usually difficult to source, I opted to use a resistor/relay setup from an FC3S turbo.  That's Mazda RX7 Turbo II to those aren't familiar with Japanese automotive chassis speak.

Pulled down the circuit opening relay so I can modify the fuel pump wires.

Since I really don't like cutting up the GTS spec harness, a crime for those who do, I opted to remove the terminals.  So the harness can be returned back to stock and look like nothing ever happened.

Even used the same color wire, nice to have a large bin of unused wires, so tracing wires for diagnostics would be a snap.

This part is where some of you will need to be creative since the harness I received was setup with the adapter plug.  So it made things go much easier.  All I had to do was to solder the wire to the harness plug. Scrounging in the wire bin, I found a wire with the correct ecu pin I can plug into ECU body plug.  This will be the relay wire.   

To test the system to see if it's working, you'll need to attach a fuel pressure gauge.  With an assistant to start the car, watch the fuel pressure gauge.  At start up the fuel pressure will be high on the high side then it will drop a few psi when at idle.  Since dark blue is not in a state to be started up yet, you'll need to use your imagination to picture what I have described.  Sometimes a couple beers helps. Cheers

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1 comment:

Aquariuns said...

can you tell me the value of the resistor that you used?