Struggling with Error Codes 52, 53, & 54 Yikes!

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I'm attempting to assist a fellow Vette owner with some trouble shooting. His 85 Vette has failed state emissions and when hooking up his scanner he finds codes 52, 53, & 54. He has just replaced the ECM and can't imagine what is driving these faults. I'm stumped....any insight would be greatly appreciated.

Thanks for your assistance in advance.

 

[Magmotor]

My information shows ('89) that if the ECM is improperly installed, a code 52 will show.....good luck...

 

[Topload]

Thanks magmotor - I think we're just about to the point where everything is suspect but I believe we've got the ECM installed properly. It's time to start checking for loose wires & the like, I guess.....it's frustrating that the car runs but won't go into closed loop.....

 

[JonM]

This is what those codes spell out.

52 Oil Temperature Circuit (Low Temperature)
Check connections at the oil temperature switch. If OK, replace switch.

53 System Charging Voltage High or Low
alternator output. Voltage with engine off should be 12 volts. Voltage with engine running should be 14-15 volts. Use digital volt meter for checks and measure at the battery terminals.

54 Fuel Pump Circuit (Low Voltage)
Using digital Ohm meter, check fuel pump circuits for shorts or opens.