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Ron, I kinda dodged that part of your question because I don't know. Certainly is possible, and I'd say if you could swap it in and out several times and repeat the symptom, you'd still have the oxygen sensor to suspect: if a good 510 expects the heated sensor to be telling the truth about which side of stoichimetric the mixture is within a half a minute, and your sensor is still dead after 10 minutes, yes you'd see a difference, I suspect.
Then there was another thought that kept me from answering. Suppose your AMM is at the far end of spec and the in-tolerance differences in the two ECUs you have are enough to cause the fuel injection to come out of closed loop when you test the 510. Both the AMM and the ECU are precision analog devices on that particular part of the feedback; the ECU uses multiple parallel precision resistors selected in final testing, and the AMM uses multiple series laser trimmed resistors in its DC offset trimming - done in final test. That's tough for a digital yes-no good-bad guy to fathom, but you could see where the addition of tolerances could make a combination of one out-of-spec device work just fine with another in or out of spec. You might be able to correct for that with the mixture pot located on the AMM.
Advice? Test your oxygen sensor (crude fashion) using your original 503 and a high impedance voltmeter on the sensor lead. See that it changes from lean to rich 5 to 10 times in 10 seconds when running warm. You may have to add a few rpm over idle. The sensor still may be a candidate for replacing, but you can at least prove it isn't stone cold dead. Meter the pink test wire. It should flip between 0 and 3.5V roughly, and you can adjust the AMM mixture screw to even the duty cycle as much as possible. Note the voltage at the mixture pot output (pin marked 12 on the AMM plug), then try with your 510. The voltage range is 0 to about 2.7V; if very close to either end, you may be looking at a problem with combined tolerances.
Symptoms of a defective ECU? Only seen open relay driver transistors myself, meaning in my own cars. I've found ECUs in the junkyard that need R56 replaced, a .47 ohm 1/2 watt resistor used to isolate the ground return current of the air mass meter. Mostly I've had AMM troubles with B23F cars. Know 'em well enough now it is the car of choice for my family. Wanna part with yours?
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Art Benstein near Baltimore
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