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Intermitten VSS Issue -

Kevlar7R

Well-Known Member
Joined
August 18, 2007
Messages
279
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2
City, State
Phoenix, AZ
Year, Model & Trim Level
1997 Mountaineer 5.0 4x4
Hey guys,

I've searched and searched, and can't find anyone with the same issue, so I'll start a new thread.

I get the flashing O/d off light after I've been at 52mph (indicated) or higher for more than a few seconds. Had it scanned, and reads an Intermittent VSS code (Can't remember the number).

I've checked the wires, changed the VSS, pulled and cleaned the rear axle speed sensor, all to no avail.

History:
I'm on a 4406 swap, and this started after the swap. My transmission has since gone (i think unrelated) and had a new reman tranny installed (so it's a totally different transmission, same problem). My transfer case however is still the same.

Is it possible there is a tooth missing on the drive gear inside the transfer case? What other possible solutions? I'm at a bit of a loss on this one.....

Anyone experience this?
 



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Did you check the internal reluctor ring in the rear differential for cracks or missing teeth? Find out what the code number is. It's possible that the ring gear in the transfer case might be missing a tooth or cracked. Did you check the sensor on the differential besides cleaning it?
 






I didn't check the diff ring, but when I pulled it out of the diff, it was beautiful and clean, no debris, just oil.

I think this started with the tc install, which leads me to suspect it's the gear inside the tc. I guess what im really wondering is... Can that happen? That it would read fine up to 52 mph, then go intermittent?

Also, I have no issues at all (Speedo, cruise, shifting) just the flashing light.

I'm wondering if I should do the old VCR repair trick.... A little black tape over the flashing light.
 












Update:

So, I've watched the pid trace on my scanner, and can see the speed jumping up and down by 2-3 mph when driving, so I understand why the computer thinks it's intermittent. I had the sensor out, connected it to the harness, and spun it with a drill (with engine off) and the trace was rock solid at any speed up to 90mph (fastest drill went). Also shined a light in the hole and slowly spun dshaft by hand, inspecting drive gear. Looked perfect all the way around.

New theories as a result of this:
1. Nothing wrong with sensor or computer.
2. Possible bad ground on sensor lead. (vibration causing intermittent ground while driving)
3. Possible failing diode in alternator leaking AC into dc system. (causing false pulse counts while underway).
4. Possible bad output shaft bearing in case (drive gear moving away from vss while dshaft spinning).

Wish me luck on finding this!
 






Solved! I'm posting the solution incase anyone ends up finding this thread in a search.

As it turns out, there was a flat spot worn on the gear inside the transfer case. New gear, 10 bucks from ford dealer (after chasing this for a year, spending hundreds.)

I was having a secondary issue, in that I couldn't get through emissions tests, because the computer would not run the evap system monitor test. It would run all the other tests, but not the evap. It seems that any tranny codes will prevent the computer from running the evap test.

My computer is happy now, and so am I! Taking it to emissions tomorrow, then finally no more temporary plate!
 






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