Car: Nissan 240SX

Engine: KA-24 4 cylinder

Siemens Deka 630cc injectors, high impedance

Hall trigger mounted in distributor, sensing a 4 window wheel.

CURRENT 10/21/09, About to install new ecu #2593, this ecu has the 4.7UF 63V cap inside.


I made a new injector harness, and the injectors were replaced with high impedance units. The ECU is still blowing injector outputs.

it turns out the(previous harness)injector relay was also powering the ignition coil(single msd coil) - I forgot to make a note of that

Why are drivers still failing after replacing the injectors and harness?

Maybe the flyback connection from injector common +12v to ec36/23 intermittently (or continuously?) disconnect ?

'''The flyback connection is 100%, I replaced the wire with another new wire, 18 awg, wired it myself, about 2 or 3 failed FETS ago. The grounds were replaced/soldered before that.

Kevin 10/21/09'''

Is it possible that the ecu was damaged before, and now the (previously un-used) injector outputs were compromised?'''

Check that the ECU has at least a 4.7uF 63V foil-type cap inside between flyrail and GND5. All factory ECUs have a green foil type cap since early 2009. This makes it tolerate longer ( ~higher inductance) flyback path or higher inductance injectors. We have not seen blown injector output with this cap. If your ECU is older, and does not have this cap, but blows outputs with your setup, consider adding a cap. We include a 4.7uF 63V foil-type cap free of charge on request.

But it was made to normal standard. Please write in order note next time: use irf640 for injector FETs. With good flyback-connection the FETs should never see overvoltage.

Are there any disadvantages to using irf640? If not, then why are they not the standard, if they are more durable?


1) ECU Installed

Lost a P259 O/P (fan relay)

Lost Inj Ch03 O/P


Move Inj to another O/P

Check Flyback wire, check grounds, all check OK.

Improve/clean engine to chassis grounds.


Lost Inj Ch04 O/P

Re-do Grounds (changed crimps to solder)


Replace Flyback wire from 20 awg to 18 awg

Replace loose resistor box terminals


Lost Inj Ch05 O/P


Lost Inj Ch00 O/P (new cylinder this time)


Replaced injectors with high impedance Siemens 630cc.

Build new injector harness, flyback wire and relay near ecu - all good conections.


Lost Inj Ch01 or Ch02 O/P (have not seen the car yet)



ECU #2168 (Order #3255)

Car ran well every day for a week.

Then, one day the Fan output(P259 Ch01) stuck ON, and later, it lost fuel Injector Ch 03 (Pin 20)

I changed the fuel Injector to Ch04, and the Fan to P259 Ch6.

I checked the GND5 connections, they measure 0.1 Ohm between them. Main Ground is 12 awg wire to engine block.

I checked the Flyback wire. The Flyback wire is ran to the 12v input to the Honda resistor box. The resistor box has a common 12v supply, then branches out to the 4 injectors.

Also, I added a wire from the Ignition output (IGBT 20) to the car's OEM Tachometer.

Today, the ecu lost the Injector Ch04 driver

I did three things at the same time to fix it (had no other choice, I do not have any spare FETs left!) -

1) Replace Honda resistor box (with another one that was in a running Honda, the box from the car was put into the running Honda and it is still running.

2) Replaced 20awg flyback wire with an 18awg flyback wire. The 20awg flyback wire was previously tested with a battery and a string of light bulbs.

3) The Honda resistor box had no connector, instead used ECxx terminal pins, pushed onto the resistor box terminals and strain relieved. This time we found the correct connector and installed it.

I (thought) #3 was the problem.

Last week, the ecu lost another FET.Again on cyl #2.

I am going to replace the injector harness, I cannot think of anything else to do. Is it possible that these other FETS were compromised earlier, and the failure was bound to happen anyway?