So I have been troubleshooting this issue with my car not starting up. It will crank but I cannot hear the fuel pump starting up (new fuel pump since I thought that was the issue). I noticed the Check Engine Light is not turning on when key is in ON position. I have checked fuses in footwell and under the hood I swapped relays to see if the EFI relay was the issue but none of them resolved the issue (defrost and i forgot the other one are the same as EFI). I made sure to check with multimeter if fuel pump is getting 12v with key on ON position (I did 12v fuel pump mod so is should be getting it when on ON position) but its getting no power. So i'm starting to think its the ECU. Do you guys have any ideas on what to check/test for? Thanks for the help!

 

What were the symptoms before it wouldnt start up?

 

Remove your ecu and check the caps, sounds like they are leaking.

 

Car would randomly turn off or RPM would drop to the point it would stall out. Also had "bucking" at about 40mph. Before it would not start up the car would take multiple cranks in order to start up.

 

Thanks for the info I will check them out.

 

Check your ignition coils

 

Pulled the ECU and did not find any leaking caps or anything visual that would indicate an issue. Connected everything back up and connected the battery. Still no Check engine light or power to fuel pump......

So to recap these are the symptoms:

No power to fuel pump
Unable to jump FP to B+ because no power on B+
No check engine light when key on ON position

What else can I troubleshoot?

 

So I just checked IGSW (black/orange) pin on ECU and it gets 12v when key on ON position and 0 when off. MREL pin from what I could find is also a black/orange wire so I tested the only other one on the ECU and it gets 0 no matter if key is ON or not. So this seems to be the reason fuel pump is not getting power as MREL sends power to EFI relay. Does anyone have a ECU pinout diagram from SC400s? I could only find SC300 pinouts online. Just want to make sure I was testing the correct pinouts.

*FOUND*



So in fact M-REL pinout is outputting 0v to EFI relay. So bad ECU?

 

Not sure if its your ECU but swap it with another to see if it works or there is a difference.

 

black and orange is power wire. it is routed through your entire harness. there is a FP ECU that you did not check. I have the pin outs and diagram for both, but i am not home. FP ECU is also control by your crank and cam sensors. and those wirings to those sensors are known to get brittle. check voltage at MREL, BATT, +B,
+B1, IGSW, and check your all your GROUNDS. All the Brown wires are your grounds, and located on behind both sides of the heads. and also check the filter grounds coming out from ECU.. LMK how that turns out.

 

Will check grounds as suggested. FP ECU is being bypassed and it should not be affecting the no check engine light and no power to diagnostic port.

 

Are you sure your getting spark and not fuel?

 

Will have to check spark. But not power to fuel pump and CEL light turn on is my main concern right now.

 

I ordered a ECU to see if thats the issue. Lets wait and see : )

 

if you bypass the FP to run when on, then you have a different problem. while you wait spray some flammable brakes parts cleaner into the throttle and then try starting the car. if it still doesnt start then its another problem not related to your FP. becareful when doing this. if it sounds like its trying then check the voltage to your injectors... also like everyone says, check for sparks. IGT1 and IGT2 pins, they are the ones that sends signal to igniter to ignite the coils..