I hope you folks can assist me in pinpointing the problem for my 1995 powerstroke, based on the info below:

1. Symptoms / issues started about 2 months ago.
2. Speedometer quivers at 1 – 25 mph then becomes more erratic thereafter - jumping back and forth with 10 mph variances (at speeds above 45).
3. Engine idles fine upon start-up, but as soon as I put it in reverse and the truck moves an inch, then the idle starts to surge up and down (maybe 100 rpm higher than normal), and therefore I have to apply more brake pressure (possible transmission limp mode?).
4. Transmission shifts hard into 2nd & 3rd, and when driving uphill, at ½ - ¾ throttle, the transmission shutters violently until I let off the throttle – this happens while the speedometer needle fluctuates.
5. Cruise control does not lock onto a speed and rocks the trucks back and forth.
6. My ABS light has been on for at least 7 years (code 12 – loss of hydraulic brake fluid during an anti-lock stop).
7. After the truck has been sitting for about eight hours, and as I start driving it again (with the above symptoms) the speedometer will return to normal operation when I depress the odometer trip ****, and I can drive to my destination without any of the above symptoms. However, after restarting and driving the truck (now warmed up) the symptoms return, and about 20 percent of the time, after depressing the trip ****, will the truck return to normal operation and stay that way.
8. Holding the trip **** down continuously while I’m cruising keeps everything normal, but as soon as I release it the speedometer needle starts bouncing erratically again along with all the other issues. Pushing and holding the **** down again returns the truck back to normal operation.
9. Replaced the VSS (after market). The old one had a few micro metal splinters attached and black soot. After 100 miles or so I removed the new VSS for inspection, and no shavings were attached. Differential fluid is full.
10. 4 times now, after depressing the odometer trip reset button, the speedometer needle banked sharp right, then left and stayed there ( 2 times while driving, 2 times at idle) and the odometer displayed the numbers E-08-6 and 980 CAL (instead of the mileage). A year ago I had factory size tires put on – the ones they replaced were slightly larger.
11. Used a test light and all fuses in cab good.
12. 15 years ago I installed Superchips.
13. Replaced a bad MAP sensor about 3 months ago, then switched back to the old one, and the problems remained the same.

So there you have it. I’m kind of leaning towards the PSOM, but why then can I get everything back to normal operation on occasion? If something is broken does it not stay broken? If the tone ring is damaged is it possible to temporarily override the VSS signal with the press of a button? Another possibility is that I did not install a factory VSS. What are your thoughts?............Thanks ..........KLEIMANN

 

I'd lean towards the psom too. Sounds like when you get it running "normal", its after messing with it.