Transmission and speedometer problem

[baggydew]

I have a 94 B190. My speedometer bounces around wildly above 30 mph and transmission up and down shifts hard following the speedometer. I had this problem in 2016 and replaced the speed sensor on the differential with no further problems.... till now. On a trip to Florida it happened again. I had the VSS speed sensor replaced. No joy. Took it to my mechanic who told me the sensor had lost magnetism. Replaced it again. Problem still there. He said he traced the VSS signal to the PROM behind the speedometer , but it wasn't coming out. He sent the instrument cluster off to "Upfix" where it was bench tested , showing no problems. A search of the internet showed that a bad negative battery cable might cause noise in the circuit and cause the problem. I installed new ground cables and also cleaned the # 7,8,18 fuses. I'm still having problems and am at a loss in finding the problem. Has anyone out there have experience with this problem or possible solutions? My escape vehicle is unusable.

[skater]

I have a 94 B190. My speedometer bounces around wildly above 30 mph and transmission up and down shifts hard following the speedometer. I had this problem in 2016 and replaced the speed sensor on the differential with no further problems.... till now. On a trip to Florida it happened again. I had the VSS speed sensor replaced. No joy. Took it to my mechanic who told me the sensor had lost magnetism. Replaced it again. Problem still there. He said he traced the VSS signal to the PROM behind the speedometer , but it wasn't coming out. He sent the instrument cluster off to "Upfix" where it was bench tested , showing no problems. A search of the internet showed that a bad negative battery cable might cause noise in the circuit and cause the problem. I installed new ground cables and also cleaned the # 7,8,18 fuses. I'm still having problems and am at a loss in finding the problem. Has anyone out there have experience with this problem or possible solutions? My escape vehicle is unusable.

I'm wondering if you have damaged wiring somewhere between the VSS and the cluster.

You may have better luck asking a Ford vans group - like Ford Truck Enthusiasts. This kind of issue is not specific to the B190, and they may have more experience with that issue.

[baggydew]

I appreciate the link. Didn't know about that Ford group.
Perusing the topic on that link, I found most problems were solved with a new speed sensor ( located on top of the differential... drivers side). I replaced two sensors during troubleshooting but it didn't help. Researching, I found out that aftermarket sensors can be unreliable and not work as well as the old OEM parts from Ford. Unfortunately, those sensors are obsolete. Luckily, I saved the one I bought from a Ford dealer in 2016 and re-installed it after the battery negative cables had been replaced. The corrosion from the cables (inside and out) can cause noise in the circuitry and ruin the signal. My problem is fixed now.

Conclusion: Keep clean, corrosion free cables on your camper, especially the negative cables. Also, get a spare OEM VSS speed sensor. If it goes bad your camper won't shift properly and leave you stranded. (The speedometer will go wonky) Unfortunately, there are only a few of these left in the system made by Ford. The Ford name is stamped on them. They are now priced at between $350 and $450 through the dealers. I'm in search of someplace where I can get an OEM equivalent sensor built to Ford specs. One possibility is FordPartsGiant.com If anyone has bought parts from them, I'd appreciate some feedback. Thanks in advance.

[skater]

Glad you got it fixed! Unfortunately the obsolete part thing will haunt us. I haven't bought from Ford Parts Giant.