I've read that N/A and TT ECUs are interchangeable but are AT and MT ECUs interchangeable as well?

Will having the wrong computer in there cause it for the computer not to turn on when the key is turned on (assuming there are no problems with the ignition)?

I have a 90 N/A MT Fed and the computer in there is for a 90 N/A AT Fed. When I turn on the key I get no power it seems like to the computer. The main power supply and ground circuit is as should be, as well are the relays and fusible links. I can't think of anything else that can be wrong besides that.

Any thoughts?

 

The ECU & engine have to match; ie M/T engine with ECU for a M/T

 

You've read wrong. You cannot interchange NA and TT ECUs. (That's actually flat out absurd - the TT ECU has fuel maps for boost conditions, the NA ECU does not.)

Auto ECUs can be used in manual transmission cars, but not the other way around. (I believe you could use a manual ECU to power on the systems in an auto car, but it wouldn't drive because the transmission wouldn't have the proper information. The manual car would drive just fine with an Auto ECU, though [it'd simply ignore the transmission data].)

If you have a known working ECU in and aren't getting power with the key in the on position, it's not the ECU.

 

ok that doesnt really matter anyways since my car is n/a and the computer is n/a. so it should work right? what else could cause it not to power on? ive checked all power into the ecu and all grounds as well as per the nissan service manual. the only thing weird i found was that the ignition switch wire (pin 45) going into the ecu grounds with the key off and has battery voltage with the key on. the manual confirms that it should get battery voltage with key on but says nothing about with the key off.

 

It doesn't really matter what it's supposed to do with the key off - that's not when you're having problems. As long as it's doing what it should with the key on, that's what's important.

Are you sure the battery is properly connected and the engine grounds are fine? If the car itself isn't getting power, clearly the ECU wouldn't, either.

 

everything else is getting power. accessories work, starter works, im getting power to the injectors and coils with the key on.

all the grounds for the ecu are grounding as they should.

 

How do you know the ECU isn't getting power?

 

the check engine light and the red led diagnostic light is not coming on. the fuel system is not pressurizing.

 

i am getting power to the fuse pump relay. i can jump the relay to activate the fuel pump so i know thats working.

 

and the harness is completely tightened down via 10mm screw on the plug?

 

i guess so. im not using a torque wrench or anything but i tighten it til it doesnt go anymore. i dont try to over tighten it, should i?

 

no, don't overtighten... I more just wanted to make sure you were aware of the screw (if you don't tighten it, a lot of the connections clearly won't be made properly).

I can't think of any steps to take from there... if I do, I'll post back. Try TwinTurbo.NET perhaps.

 

ok thanks for your help.