I just picked up a 'chipped p28' after my last one blew a capacitor. I installed my chip into the new ecu and plugged it in. When i put my key in the on position the fuel pump turns out and does not go off. I confirmed i have the chip in correctly, and also tried a couple of other chips, with the same result. I put a stock LS ecu in and everything worked normally (pump turned off after a quick prime). What could be causing this ecu i just bought to behave like this?

 

Where did you buy the "chipped P28"? I'd contact the seller.

 

craigslist. i will shortly; just wanted to know what could cause this...bad transistor, etc? And if it could be repaired

 

Fuel pump controller is "shorted". You purchased a damaged ECU.

 

the caps for the fule pump probably went bad and the previous owner just grounded out pin A7 internally in the ecu. I ran one of my ecus like that for a few years. no issues at all with A7 grounded out.

 

There are no caps for the fuel pump so replacing them will not fix the problem. Grounding A7 works when the fuel pump transistor is toast and if you install another ECU on that car with A7 EXTERNALLY shorted, you'll damage the replacement.

 

Is there a way to know which transistor it is? ie. qm1, 2 or 3?

 

it's QM3, and it's a pain in the *** to replace without roasting the vias. but I would make sure the adjacent pins on the chip socket aren't just bridged before you go replacing that transistor.