How to Test ECU?

[pearlwhiteS14]

I was driving the car last week and it worked fine. When I went to start it today it only turns over and no fire. I think it is the ecu but not sure. I unpluged the ecu and checked to see if it was getting power at the plug and it was fine. The light in the ecu is off when the ignition is on. Is there a way I can check the ecu before I go out and buy a new one. THanks

[nissanguy13]

Double check the screw that you turn to pull the codes from the ecu. Make sure that it isn't turned the wrong way/partially turned

[pearlwhiteS14]

When I check that screw what position should it be in? And the red lit is not on at all, what is that screw for?

[racepar1]

That screw is quite a bit more complicated to set correctly than most people think. I think there is like 6 functions you can select. If you didn't turn it then DON'T SCREW WITH IT!!!!!!!! If you did turn it when you removed the ECM then get a factory service manual. As far as why the car won't start there are a million things that I would suspect way before I got to the ECM. Check for the basics first: spark, fuel pressure, and injector pulse.

[idlafie]

That screw is quite a bit more complicated to set correctly than most people think. I think there is like 6 functions you can select. If you didn't turn it then DON'T SCREW WITH IT!!!!!!!! If you did turn it when you removed the ECM then get a factory service manual. As far as why the car won't start there are a million things that I would suspect way before I got to the ECM. Check for the basics first: spark, fuel pressure, and injector pulse.

Actually, the 6 position only apply to the ECU's on an 89-94 S13 - those ECU's are OBD I. Judgind from Pearl's screen name, I'm assuming he has an S14. The ECU's on 94 1/2 thru 98 are OBD II or OBD II compliant. Putting the S14's ECU into Diagnostic Mode are alot easier than the OBD I's.

To retrieve the codes on OBD II ECU's, turn the ignition to ON, turn the diagnostic mode selector on the back of the ECU fully clockwise, wait 2 seconds, then turn the mode selector fully counter clockwise. The check engine light should begin to flash and repeat. The long flashes are the first two digits of the code and the short flashes are the last 2 digits. The codes are all four digits long. 0505 (5 long, 5 short) means it's all clear.

You'll need a Factory Service Manual to determine what the problem is. Chances are it could be a bad ground wire causing your NO RUN problems. You'll need to trace everything down if your ECU is good. Electrical shorts are usually a pain in the ass to diagnose. Good luck!!!

Hope this helps..
ID