The EGR system remained the same from the time Ford rolled out the truck Speed Density based EFI system until they phased in Mass Airflow EFI. The picture I found already had labels on it for the model year.

DTC 327 indicates the EVP output signal is below 0.2 VDC. This could be caused by an faulty EVP sensor, open circuit or as we are trying determine a low or missing VREF signal.

Here is the theory for how the sensor works and some key measurement values: Ford Fuel Injection » EGR Valve Position sensor (EVP)

DTC 122 indicates the TPS signal output is below 0.6 VDC. Again this can be a bad sensor, open circuit or low/missing VREF signal.

Here is the theory and values of the TPS sensor: Ford Fuel Injection » Throttle Position Sensor (TPS)

DTC 334 is indicating the EVP output signal is above the closed value of 0.67VDC. This is a direct opposite of code 327. That tells me the sensor may be working, but perhaps this code, maybe the others as well, may have happened in the past? Has anyone actually cleared the codes, then rechecked after driving it for an hour or two?

DTC 998 is simply alerting us to the fact the PCM senses a hard fault. Once you resolve the 122 and 327 codes I suspect code 998 will go away, once it is cleared of course.

You really need to verify if you have the VREF signal from pin 26 of the PCM. My EVTM manual shows it is a Brown/White wire. The signal is roughly +5 VDC +/- a few millivolts.

I suspect VREF is present, but perhaps there is an open circuit somewhere along the path. If VREF was not present I would expect errors related to the MAP sensor as well, it uses the same VREF signal as the TPS and EVP sensors.

 

Latest update to My Quest for a PCM, anyone can step in anytime to help... As close as I can find I need to ship my old PCM to someone to reman my own as I have searched my local part stores and they find that mine is a one and only (Must have been a special ordered truck or something of the sort...It did come from the university of madison) factory code is F6tf-12A650-BKB, Ford Garage told me a newer updated Part # of F6PZ-12A650-EKA for the most part the stores have been able to look up under the first # but the outcome is the same. looks as if I loose my wheels for a couple of weeks. Still trying to figure out what the difference is on the truck , gvwr is 8600 3 speed auto 4 wheel with air and no DPFE senser

 

Sorry rla2005 I kinda got carried away with typing before I read yours.. Yes I have cleared codes several times. main ones coming up every time is 122 and 327 KOEO I have checked at MAP but found no voltage there either I have checked at harness to PCM all voltace going in is 13.5 but never really proded the 26th pin (I will check that in the am. BTW where do I start counting? ) I did already change TPS the only senser I have not checked in the on buried in the center of the intake

 

Start by measuring the VREF signal at the sensors, much easier than trying to probe the pins on the PCM.

For reference here is a pin-out diagram from Ryan at Ford Fuel Injection.com



Your truck is not really a special order, other than you state it is a 3 speed auto therefore it has a C6. It is a rare option, but not unheard of.

FWIW there is one for sale on E-bay right now: 1996 FORD F250 F250 351W C-6 ECU F6TF-12A650-BKB HOB1 - eBay (item 140465641252 end time Jan-11-11 19:10:25 PST)