I have a 1996 Ford F-350 XL OBS with the 7.3 Power Stroke and E4OD automatic transmission. I'm trying to track down an intermittent drivability issue and would appreciate any ideas from those familiar with these trucks.

Symptoms:

At approximately 40-45 MPH and above, the truck will occasionally "surge."
When I say surge, I don't necessarily mean the truck lunges forward. The tachometer will suddenly jump from about 1,500 RPM to around 2,000 RPM.
The tach jump appears to happen almost instantly rather than gradually climbing.
It feels similar to the transmission trying to shift when it shouldn't.
The issue can occur while cruising at a steady speed.
Turning overdrive off does not eliminate the problem.

Things I've already done:

Replaced the fuel filter (the old one had not been changed in many years).
Replaced the neutral safety switch (MLPS) because the truck would occasionally not crank in Park, but would start in Neutral).
The no-crank-in-Park issue appears to be separate from the surge issue.

Diagnostic Information:

I received a P0344 (Camshaft Position Sensor "A" Circuit Intermittent) code one time.
The code has not returned since.
I replaced the camshaft position sensor (CPS) with a new sensor, but the truck would not start with the new sensor installed.
After reinstalling the original CPS, the truck started and ran normally.
Because of that, I'm not sure if the replacement sensor was defective, incorrect, or if I may have a wiring issue.

Additional Notes:

Fuel filter replacement did not change the symptom.
The surge still occurs with overdrive turned off.
No major loss of power.
No stalling.
No current check engine light.
Tachometer movement seems to be a key part of the issue.

Questions:

Has anyone experienced an instant tach jump like this on an OBS 7.3?
Could an intermittent CPS wiring issue cause these symptoms without repeatedly setting a code?
Would you suspect the CPS circuit, ICP sensor, APPS/TPS, or something transmission-related?
Is there a known issue with the tach signal on these trucks that can mimic transmission hunting?

Any advice or similar experiences would be appreciated. Thanks.

 

At those speeds tranny is trying to down shift and the flare you feel could be the torque converter locking on/off.

Next course of action is to read transmissions codes with a scanner capable of reading tranny codes. Then diagnostics where hopefully Mark or someone with automagic expertise can shime in.

 

Where did the new CPS come from? Only an OEM or Riffraff part is recommended. Parts store units don’t work well on these trucks.

 

Spitballing.....

Bad/maladjusted brake switch.
Bad/failing trailer brake controller.
Electrically conductive corrosion in trailer plug or associated wiring behind the rear bumper.

Any loss of ground or application of power to the brake light circuit will cause the PCM to think the brakes are being applied and the torque converter clutch will be commanded off.

Driving with this condition long enough will fry the torque converter clutch so it's best to figure out this problem quickly.