Bad computer or vacuum sensor?

Thanks. This is federal emissions. I have seen 2 degrees after for this car also, Under hood sticker says 7 BTDC, so I tried it both places, but seems to run best at 7 BTDC. Still blistering my plugs. Checked for air or vacuum leaks-none. Vacuum gauge held steady at 17 inches hg. At idle, and my altitude is about 2500 ft. Above sea level, if that matters.
My new O2 sensor has a 3 wire connector. I have not tried to test it since installed, about a month ago.
I was checking vacuum sensor operation per Chilton: voltmeter on terminal 9 to ecu should show 4 volts with no vacuum applied. I had near battery voltage-didn't write it down, just noted "batt voltage?". So did not proceed to applying 25 in, vacuum and checking for 0.5 volts. Took a coffee break, had a few smokes. Do I have a bad vacuum sensor? I checked voltage into the firewall mounted sensor (it has 3 wires: ground, signal from, and signal to computer. Well, that only middle wire had voltage and that was near battery voltage, like 12.0 volts, if I recall. Would the ecu send battery voltage to this sensor? When it is supposed to measure about 4 volts ranging down to about 0.5 volts as a signal to the ecu? So I'm at a loss, bad sensor or bad ecu?
Last question, if I check sensor again and note voltage with no vacuum applied, and then apply vacuum to sensor and note a voltage drop of about 3.5 volts, can I assume that sensor is working right, and that I have a bad ecu? Kinda hoping so, cause a remanufactured control unit is about $200, but their vacuum sensor is $420. And I only paid $300 for this 71,000 original miles Sentra, not running. Are map sensors critically calibrated, or can an old gm map sensor work just like my "vacuum sensor"?

Okay, thanks, KHLow. Good to know about the sensor. Yes, I was checking the red/yellow wire and had near battery voltage, so looks like I need a new sensor. I have a wrecking yard putting out a nationwide locator for one. Any suggestions where else I might look for one? Guess I will try a few sites online.
I took a one month subscription to Mitchell 1 yesterday. Now I see the green/white wire does send battery voltage from the ECC relay. Chilton had me all confused, with only partial diagrams. I just hope I didn't ruin my control unit with my haphazard tests run to date. I didn't understand the import of disconnecting battery before taking connectors off control unit. In fact, battery off, connectors off, remove pin retainers from connectors for back probing, reconnect control unit, then battery, then key on-to run any voltage checks on the computer. I was going at it cowboy style, just pulling and checking. With Mitchell's help, now I can run a full and thorough testing to see where I'm at. Do you suspect it is a lean running condition blistering my spark plugs? I just want to see if I can get it running right before replacing the timing belt- it is probably the original one with only 71,000 miles, and been on there since 1987!
Thanks for your help. It is great to hear from experts, you guys have a great site with invaluable help. I will donate soon when I can.

Test test test cannot post, test

Tried a fourth time to post long response, didn't work again-will try tomorrow.

And now, even another time-I may have a connectivity problem today or some time-out voodoo.

The valve clearance check is as of now a top priority.
Do not believe it is running too hot.
Timing does advance by computer, the peak on my timing light was between 20-30 BTDC.

Exhaust was checked, if it leaks between exhaust and converter where once disconnected, would that cause engine management problem? Will be checking that seal tomorrow or soon. Previous owner had done that and said it made no difference in the engine running condition-(he had a dead spark plug, his converter was getting red hot, running rich, the oil sump had lots of gas in it).
The carb is adjusted right is all I can say about it. PO had it rebuilt by a shop in Kalispell, Montana. He said he had receipts to prove it. I just took his word on that. Fuel bowl level is on the dot, looks good, runs good, idles good, resistance check on mixture ratio solenoid good.
I will be getting into tests and diagnostics since I finally found the red and green LED lights on the control unit. Will let you know when I find anything. I'm slow in the head and slow on my feet.

No, it wasn't blowby. Previous owner had put new spark plugs in, but one was defective-dead. Found that when I did a compression test (for very weak power-I didn't even realize the engine was missing when I got it started. Noticed a strange burble in the exhaust - I thought that was normal Nissan exhaust sound. Tried a different plug from old Datsun truck, and suddenly instant power, incredible power, and no more "burble".) Compression was 155-165. I assumed the gas from number one cylinder had washed down the cylinder walls into the crankcase-looked like it may have had about a quart or 2 of gas with the oil. The engine and exhaust really smoked the first time I got it started. But then it all straightened out and settled down, but that is when my spark plugs started blistering white.
About all I have put on it is a new air filter and a new set of plugs, besides changing the oil and filter, well two oil changes now. The plugs that were in it were a cold range plug, and I put standard plugs in. Funny thing: when I pulled the plugs for a compression test, number one, the dead plug, was black and soot covered, but number 2, 3, and 4 plugs were normal-not white, not soot covered or black, but normal looking with a light brown color.

OK, I put new plugs in and changed the oil when I did the compression test. I have not been running the car except for tests or any little thing, after finding my blistered plugs.
Well, my vacuum sensor must be ok, took it off car and with battery voltage applied, the signal said 3.6 volts, then with about 20 in. Vacuum, it said 0.9 volts. So put it back on and checked at ecu-when I said I had battery voltage, I must have been seeing 1.1 or 1.2 volts like I saw today-Dumb! So ran the systems check per Mitchell- and the red LED was off, and green on steady at step 5-meaning system is good, no problems.

Next checked coil and power transistor. I need help with this: the coil primary spec is 0.82 - 1.02. Mine said 1.1 ohms. My secondary check was good, 9600 ohms-within the spec.
Then the power transistor which (?) Amplifies signal from ignition module, Is that so? Says to check with coil, the transistor can't be tested by itself. And says to use ohmmeter to run 4 checks. I did. The two checks where I was supposed to show no continuity, both were very close to same, at approximately 5 mega ohms. The two checks where I was supposed to show continuity- I did have continuity, bot both were at approximately 1 mega ohms. I checked several times, not like my bunk vacuum sensor testing originally. Do I have a bad power transistor and/or coil? Could THIS be why my spark plugs are blistering?
Need Help!

Okay, thank you. I will. Rrrrroadhouse, lol.