Vehicle: '99 E350, V10

Symptoms: speedometer bouncing, O/D flashing, harsh shifts. Symptoms do not present until the van has been driven at highway speeds for about 20 miles. Then, the speedometer starts to bounce a little. Then, after another 5 - 10 miles, the O/D light starts to flash. Then, with a few more miles, the harsh shifting begins.

Parts replaced: neutral safety switch, rear ABS/speed sensor (twice), instrument cluster.

Each time after I replaced a part, when I drove the van, all was fine until it had been driven at highway speeds for about 20 - 25 miles, regardless of whether the engine was warm or cold.

Any ideas on where to go next with it?

Thanks.

 

Get the fault codes and see where they lead you, probably to an erratic VSS sensor. All you've been doing so far is guessing (wrongly).

 

projectSHO89, sorry, I left that out. Yes, the only code that it has thrown has been a faulty VSS/ABS sensor (which I have replaced twice). As I understand it, the VSS sends a signal through the neutral safety switch that then goes to the instrument cluster. I've read of several different possible failure points;
1. the toner ring is damaged, thus the VSS is sending faulty data. If that were the case, I'd expect it to happen all the time, not develop a problem only after driving 20+ miles
2. faulty VSS/ABS sensor. common issue and cheap and easy to replace. I've done it twice and it has not cured the problem.
3. defective neutral safety switch (MLPS). I'm not clear as to how this is involved, however several threads indicated that this could be the problem. So, being fairly inexpensive and easy to replace, I've done so. It did not fix the problem.
4. Bad PSOM on the back of the instrument cluster. Again, I have read here that the PSOM is a common failure. I happen to have an identical parts donor van, so I swapped the clusters out. It did not fix the problem.

I do not have a code reader that will pull the transmission codes. But, I expect that the O/D light flashing is a result of the erratic shifting rather than the cause.

So, I don't really feel that I've just been guessing here. I've been following the signal from the VSS up the chain, trying to eliminate some of the common failures. I'll bet that most here would expect that the three parts that I've replaced would cure 90%+ of cases like this.

The question remains, if not the VSS, MPLS, or the PSOM, what else might cause this?

Thanks for you input!

 

At least now I understand why you replaced the TRS (or what you called the neutral safety switch.) The vehicle speed signal does not go through any other sensor. It is wired directly to the PCM.

And you've replaced the wrong sensor, twice. The vans use the sensor on the output shaft of the transmission for vehicle speed, not the one on the rear axle.

There is no PSOM in '99. It had already been eliminated.

That's quite a jump. I'd expect that the OD light is flashing due to the problem with the vehicle speed.

 

Thanks Mark. I was hoping you'd weigh in on this one. And dang it, I knew that there was a separate VSS on the tranny, but had forgotten. In this case, because it is a Quigley 4x4 conversion, that sensor wire had to be lengthened to reach the sensor that is actually on the transfer case. So, there's a strong likelihood of an issue where the wire is spliced. I'll check that first, and then swap out the sensor with one from my parts donor van and see where we are. Guess I'll put the original instrument cluster back in too, since that swap added about 100k miles to the van.

Thanks Mark!