1996 Ford F250XL Nightmare

Hello,
I just joined and am up against a wall. I have a 1996 Ford F250 5.8, e4od transmission with 254,000 miles. California emissions, over 8500 lbs. Pickup with Reading style toolbox utility body.
It had p0175, p0172 and p0713. Data reading on transmission fluid temperature sensor reads -40⁰F.
Until purge valve is unplugged, then it reads ambient temperature correctly. All pcm powers and grounds verified good, All vehicle grounds clean and intact. Transmission electrical harness removed and bench tested, wiggle tested under a load. Also tested all circuits concerning transmission solenoids and range swich. Started unplugging all sensors sharing grey/red circuit no change. Happened to unplug purge solenoid while monitoring tft data and boom it started reading ambient temp. Rebuilt Bluestreak Computer, new Ford shift solenoid pack with Integrated tft sensor, and New pigtail for transmission 12 pin plug. This is killing me now!
Any ideas or help would be a God send!
Thank you,
Steve S.

Hello,
I just joined and am up against a wall. I have a 1996 Ford F250 5.8, e4od transmission with 254,000 miles. California emissions, over 8500 lbs. Pickup with Reading style toolbox utility body.
It had p0175, p0172 and p0713. Data reading on transmission fluid temperature sensor reads -40⁰F.
Until purge valve is unplugged, then it reads ambient temperature correctly. All pcm powers and grounds verified good, All vehicle grounds clean and intact. Transmission electrical harness removed and bench tested, wiggle tested under a load. Also tested all circuits concerning transmission solenoids and range swich. Started unplugging all sensors sharing grey/red signal return circuit no change. Happened to unplug purge solenoid while monitoring tft data and boom it started reading ambient temp. Rebuilt Bluestreak Computer, new Ford shift solenoid pack with Integrated tft sensor, and New pigtail for transmission 12 pin plug. This is killing me now!
Any ideas or help would be a God send!
Thank you,
Steve Seniuk

Seems like no one is interested in getting involved with this one, so I called Diagnostic Hotline, since time pressure is a reality here. Pretty disappointed with this forum actually.

Sorry Steve,
Please understand that we all have full time jobs. I personally have been quite engaged multiple problem vehicles. Your issue is intriguing, I would love to hear the resolution.

Can you put a noid light in place of the purge valve?

I usually try to respond in middle of the week and help. I had one just like this one last year. You have a short in the harness. The wirES ARE shorted to completely unrelated circuits. The purge valve is on a completely different circuit than everything that shares the low reference/signal return wire GREY/RED.

Get a simple voltmeter and switch it to continuity. Tap into Grey/red wire. And the other side to the Grey/Yellow wire. There should be no continuity between two. If there is. Start unplugging sensors on the Grey/Red circuit until it goes away. If not there is a short in the wires usually close to Egr harness

Hope that helps

Also. The purge valve has battery voltage at all times shared with a bunch of other items like the injectors


If the purge valve is stuck open. Sometimes so is the contact that in turns will direct voltage thru the coil of thr purge valve straight thru and flowing to the Grey/Yellow wire and If that wire is shorted anywhere to the Grey/Red wire. That will send your temp reading completely out of range

Hello All,
So after many hours, phone calls to fellow electrical guru's, and 2 calls to Diagnostic Hotline, I finally found my issue.
RF upstream oxygen sensor harness side hidden inside loom, wires bare and a few melted together! 12 volt circuit for heater was bleeding into 5 volt reference and signal return circuits. Very difficult to track down due to in accurate schematic information and /or lack of information. Thank you for your help and I hope this helps someone else from this type of nightmare. I've been into this level of repair work for many years and this one was one of the worst!
Steve S.

Thank you for posting the resolution to this problem, even though you didn't get the responses you wanted. I'm sure this will help someone in the future!

(Good call RPD, you nailed it)