I have a 1997 F350 7.5L gas incomplete chassis (it has a service body) CA Emissions OBDII. Just swapped engines to a reman engine identical to the original.

Symptoms:

Transmission will intermittently enter ‘limp mode’ and throw a P0500 code and the Overdrive selector light that says “OFF” will flash. When this happens, the transmission will not engage the converter and rpm’s increase with zero power and zero speed increases but you can hear what I think is the converter whirling. In ‘limp mode’ it has really hard and delayed shifts.

If I baby the truck I can drive around softly, these symptoms never arise and it has smooth, on-time shifts thru all gears and overdrive. Even at freeway speeds. But as soon as I get on it, like the entrance to a freeway, ‘limp mode’.

New parts:
7.5L CA Emissions Engine, VSS, EGR Valve, water pump, air filter, all fluids, harmonic balancer, transmission oil filter, engine oil filter, fuel filter, fuel pressure regulator, PCV valve, radiator cap, fuel tank cap, spark plugs, fuel injector o-rings, distributor cap and rotor, oil pump and filler tube, vacuum canister ball, idle air control valve and thermostat.

Tests ran per Ford Powertrain Manual:

Vacuum pressure (idle; from intake manifold tree): flickers between 13 and 14 in hg (low? I’m at 4,500’ above sea level)

Transmission line pressure test (idle): Pass
Park/N: 62psi
R: 100psi
D/2: 63psi
1: 100psi

Transmission shift control cable adjustment: Completed

Shift indicator cable adjustment: Completed

Transmission fluid cooler flow test: Pass

Procedures done:

Flushed transmission lines, external cooler and cooler that’s inside the radiator with solvent

 

If we start with the code you received, there seems to be a problem involving the vehicle speed sensor. That does not definitely mean the sensor is defective. Suggest you check and insure all electrical connections to the trans are clean and good.
There is always the possibility in the process of switching engines , something was overlooked, especially if the problem was not present before the switch was done.
Carefully check all plugs for any pins that might have been pushed out..

 

Thanks for the response!
I thought this might be a good step but was mentally setting it aside because it does not sound easy to do. I'm going to my garage and will start scouring the wiring/connectors now. I will update later today...hopefully soon as that means i find something right away but we both know the universe will make me search for at least several hours first.