"New" ECU does not work

[02BLUR]

I bought an ECU from a guy online and just got it today, but it does nothing, I checked for spark and it has none. So I put in my old one and it least the car barely runs(thats why I got a "new" one). Am I missing something? Its the EXACT same computer for a 1990 Talon TSI AWD. I don't have to flip some switch do I? Help!

 

[Kevin90GSX]

The 90 and the 91 ECU's are different. If he sent you a TRUE 90 ECU you shouldnt be having any issues unless its beat.

Otherwise Im thinking you may have a 91 ECU now. Check out http://www.vfaq.com and it will tell you which pin you need to switch in order for it to work correctly.

PS Sweet rims!!!

 

[Diceman19]

even though still, if the years are different, you will still have problems with the tech since there are other differences between 90 and 91-94 than just that one wire.

 

[02BLUR]

But the numbers are exactly the same. And the guy said it was off a 90 Turbo
5903
MD145903
E2T34478A

He said he took the ECU out and did not touch it and wrapped it up. Unless my car's wiring is TOTALLY screwed and somehow the other ECU lets it run? That makes no sense. I'M GOIN NUTZ BABY!!

 

[steve]

Open the cover and check a few things. First that the four digits on the edge connector match the last four digits in E2T34478A (It should say 4478A). Second look at the area around the capacitors for any discoloration or crusty stuff, the signs of capacitor leakage. It's possible that it has leakage but still worked but bouncing around in shipping loosened up the crud that was conducting the signals and now you have a few open circuits. (giving the guy the benefit of doubt).

Steve

 

[02BLUR]

Yes, the one big cap is leaking and there is some brown residue around it. I guess thats the problem. I don't think I should touch it. Last time I messed it up and now it runs like this: www.zero2blur.com/leak.mpg

 

[steve]

It's pretty unusual once the capacitors have leaked for there not to be other damage to the circuit board. People don't actually notice the problem until the leakage takes out something critical or the caps get so bad that the ECU reboots all the time from power problems.

Half the challenge to fixing them is finding all the places where the electrolyte has eaten through the circuit traces. I get lots of use out of my 10x Loupe inspecting trace to pad/via damage. They can ohm out fine but be reduced to a thread conducting and open in normal use. The plated through holes connecting one side to the other vanish quickly in the presence of electrolyte.

The good news is that, short of boards where the caps have exploded, they can be repaired. The bad new is it's sometimes cheaper to buy another used ECU but your just as likely to wind up with another set of problems, like you did in this case.

Steve