I got this p28 and it works great when it works and most of the time it doesnt work. it wont start the car. you can hear that the main relay doesnt click over twice, thus leaving the CEL on. any ideas? all the resistors are right and and it was chipped right. im stumped. nothing seems to be overheating.

 

anyone?

 

If certain address pins on the Prom are pulled (such as pulled high by circuitry), then the ecu will refuse to function appropriately. Check the socket/chip solder job for shorts, bad solder joints, or opens.

Are you using anything like a "2Timer" or something with your socket job?

 

i'm having the same exact problem with my P28 .

 

To elaborate on my statement earlier... I made a makeshift 2Timer circuit to go into my ecu.

The PROM address pin A15 was tied high with a switched pull down circuit (with current limiting resistor). Well, what happened was exactly as you described (on the low bit side) and worked great on the high bit side. The problem, the ecu has its own capacitors in circuitry that must charge/discharge at certain rates and when pulled, couldn't do so. (I need to change my pulling strategy, haven't bothered to work on it).

My point, if your address pins are intermittently pulled in various directions, the ecu will be directed to access certain binary positions within the rom. Check for solder ***** (or shorts of any kind), broken socket leads (between PCB and socket...this can easily happen if it was soldered under stress), opens (if you allow address leads to float in an electrically noisy environment), clipped leads that worked under the socket, etc.