Tim,
Check all the sensors for vRef. That's the place to start rather than replacing parts haphazardly. This does sound very familiar to what happened to my 91 last summer. Did you do anything at all under the hood after the last time you had it running? If you did, chances are the problem is close to the area you were working.
Check the vRef at the TPS.
Key off > disconnect TP sensor > Key on, engine off > measure voltage between vRef circuit and Sig Rtn circuit as seen in pic above.
The voltage should be between 4.0 & 6.0 volts. If it is, check your spark to make sure that it's present and consistent.
If it's not then:
Key off.
Disconnect 60 pin connector. Inspect for damaged or pushed out pins, corrosion, loose wires, etc. Service as necessary.
Install breakout box and connect processor to breakout box.
Key on, engine off.
Measure voltage between Test Pin 37 at the breakout box (if you have one...if not you can still test this) and SIG RTN circuit in the Self-Test connector. Note voltage.
Measure voltage across battery terminals. Note voltage.
Are both voltages greater than 10.5 volts, and are both voltages within 1.0 volt of each other?
If yes:
lKey on, engine off.
Breakout box installed (need one for this test), processor connected.
Measure voltage between Test Pin 26 and Test Pin 46 at the breakout box.
What is the voltage?
Greater than 6.0 volts
Less than 4.0 volts
Between 4.0 volts and 6.0 volts
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Aggg.......these tests are very helpful but they go on and on and on with many variables. Do you have the 92 PCED Tim?
If not I'll get you mine, just PM me your address and I'll have it out in the morning mail. It really is of most value and very easy to use. I didn't understand a darn thing about electrical stuff before last summer. Now I know more than I want to know.