Doesn't drop out of OD with cruise control.

[SLittle]

First tow this weekend since recently buying my 1991 F350 crew cab 7.3 IDI N/A E4OD. Towing about 8,000 lbs. Two lane black tops, 55 mph speed limits.

When I set the cruise at 55 and I come to an incline, the engine will lug, transmission never drops out of OD, and then when speed drops to 45, cruise automatically shuts off.

If I...

...Push the gas pedal all the way down when speed starts to drop, the transmission drops out of OD and maintains speed. When I lift my foot at the top of the hill, I am still on cruise and we continue on in OD at 55 mph.

...Turn off the OD at the switch when speed starts to drop, the transmission drops out of OD and maintains speed. At the crest, I turn the OD switch back on and continue at 55 on cruise in OD.

I have checked voltage at my FIPL (Grey) and I have 1.1 at idle and 3.85 at WOT.

In my opinion, the cruise is not capable of pulling the throttle completely to WOT. Is this normal? Is there any adjustment that can be made to remedy this?

 

[Thewespaul]

Looking at the throttle bracket on the side of the IP where the throttle cable connects, you will see a return spring that connects down to the bottom of the high idle solenoid bracket. This is a redundant return spring that helps the primary spring in the throttle cable. If you remove it you will see it is two intertwined springs. I would at the least remove one of the springs there or do away with it and put a lighter spring in its place from a hardware store. The older vacuum powered cruise control setups have issues overcoming the three return springs, which is likely your issue here.