1994 F-150; 5.0 (.302 HO) stock motor; Manual M5 Tranny.

Background--A year ago replaced the computer with a rebuild and started having the no communication issues but it ran. Then a month ago it just up and died. Once the engine warmed up it would quit running. So sent off the computer once more and returned to see still unable to communicate.

I have ran all the wires to the main computer connector that activates the KOEO tests and they check out. My only issues are with Pin 30 that is seemingly tied into all the switches and sensors.
Could one switch/sensor out prevent the KOEO from starting? I dont see that possible. Numerous sites say there is not supposed to be any voltage from pin 30 and it needs a ground to start the KOEO test. Is this correct?

Just too many unanswered Issues here and Im afraid the computer is the wrong one. Im planning on taking it to the dealer for a complete look over the wiring before confronting the computer fixers.

Anything else that can be thought of would be appreciated.

 

Looking further into this I tested a few possibilities from the EEC test connector..Ignition OFF and ON
STO to Sig Return
=OFF= 15.9 ohm & 0.003VDC =ON= 2.378ohm & 0.208VDC
Sig RTN to STI
=OFF= 2.95 ohm & 0.034 VDC =ON= 2.789K & 4.78 VDC
STI to STO
=OFF= cont tested at 0.181 and Ohm just flashed open (OL) and 0.333
& 0.36 VDC
=ON= cont was open (OL) and 2.869K ohm & 4.99 VDC

The STO and SIG RTN are the two connectors on my reader that show the codes. Should there be any voltage on this pathway until the codes are flashed out?

The STO is an internal link in the EEC only wiring is to the test connector.
The SIG RTN meets up with all the sensors. Im going tot try disconnecting each sensor to see if any stop the Signal to the reader. Well thats my thoughts so far.

 

If your check engine light works, you don't even need the reader.

Just ground the STI input and turn the key to ON. The KOEO self test will begin immediately. Back in my SHO days, I carried a 12" jumper wire with an alligator clip on one end and a flat terminal on the other in my glovebox. That's all it takes if your light bulb works.


It's been a few years since I worked with EEC-IV computers, but I guess I'll have to make up a new jumper since we bought a 95 Mustang this spring.

 

That doesnt work either I thought I stated that earlier. Must have left it out.
I have tried a code reader and the paperclip method both are unable to pull codes.

 

IIRC (my old manuals are packed somewhere), the STO pin is pulled up via the CEL bulb circuit. If, for example, the bulb is burned out, you cannot pull codes with a reader unless you use a voltmeter between the battery positive terminal and the STO connector. I'd have to find my old books to look further, been a few years.

If you fix the CEL circuit, the reader will probably work.