1G 1991 NT FWD TCU

[brassc2007]

Alright here goes. I have a 1991 fwd, my TCU has blown the capacitor. The TCU# is MD750525. I couldn't find much info on it. What TCU's are compatible or if it has to be the same # TCU? Any info would be greatly appreciated.

 

[sniver]

Alright here goes. I have a 1991 fwd, my TCU has blown the capacitor. The TCU# is MD750525. I couldn't find much info on it. What TCU's are compatible or if it has to be the same # TCU? Any info would be greatly appreciated.

Any 91-early 92 (has 6-bolt) cars n/t TCU will work. I think the turbo ones will work to, but I haven't dealt with it in a while.

 

[91 TSi GP]

I have a Auto N/T TCU. Car had a 6 bolt and drove fine. $25 shipped if your interested. Message me or text me 330-728-3979

 

[brassc2007]

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I believe the tcu is unsavable

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[sniver]

Problem with tcu's are that when the caps go bad it dumps 12v into 5v circuits and ruins parts not worth fixing.

 

[steve]

To avoid any problems you really want another MD750525.
That one is likely dead.

 

[brassc2007]

i got the exact same one so all should be well when it arrives

 

[steve]

Make sure the caps are or get replaced before you use it.

 

[brassc2007]

ok well i replaced the tcu with know good one and double checked the caps before i put it in and they looked great replaced the trans with a good one and it is still stuck in limp mode i tried searching again but what can all cause the trans to go into limp mode

 

[steve]

Read the codes from the TCU.

BTW you can't visually inspect the caps except to note that they are original or not and replace them if they are. All the 47uf original caps by the voltage regulator will leak given time and when they do it's likely they will destroy the TCU.

 

[brassc2007]

id pull the codes but i dont have a volt or ohms meter is there anyway to bypass the tcu without a standalone trans controller?

If the tcu is still the culprit i dont want want to waste money on another faulty tcu

So would i replace the 47uf cap with just another 47uf cap from radioshack?

 

[steve]

Go to radioshack and buy a 273-059 Piezo Buzzer and connect the red lead to pin 11 on the DLM and the black to pin 12. Read the code just like the ECU and look up the result.

It will cost you less than lunch.

So would i replace the 47uf cap with just another 47uf cap from radioshack?

The 47uf 35v electrolytic (272-1027) they have should work. I don't know how big in diameter it is. I use 105C rated ones like I use in the ECUs.

 

[brassc2007]

wouldnt a piezo buzzer work the same as a test light, just sound instead of light flashes?

 

[steve]

The buzzer only draws 10ma of current, most test lights draw 10x that and might damage the driver.

 

[brassc2007]

sorry for so many questions but since there is no visible leakage could i assume that the tcu is working properly and the problem lies elsewhere with the trans system

 

[steve]

No. The TCU will give you a heartbeat or a transmission fault code out of the diagnostic pins if it's CPU powers up, then you can assume it works until proven otherwise.

 

[brassc2007]

ok well the tcu does not give me constant short pulses or a code so this one is fried since its constant voltage and makes me not want to buy any more iteams off of dsmtuners as i obviously got scunked so anyone have any leads on a tcu

 

[brassc2007]

ok i need the input of a wiseman i replaced the capacitor with a 272-1072 from radio shack but instead of pulses all i get is constant voltage at the test port but the mpi prong about it gives me pulses so im curious as to what the next step i can do is or if this is a sign that i need another tcu

 

[steve]

Did this one work before you changed the cap? It's not clear if you're working on the same or another TCU.

Try measuring the output voltage from the regulator. If it's not about 5v it's not working, above ~7v and other chips can get damaged.