4R70W -- lost and confused

[SoHK_alumni]

My '96 Explorer 5.0/4R70W powered 02 Ranger has suddenly developed a bunch of separate seeming transmission issues:

From the initial install a couple months ago, it's always behaved well when cold. Sometimes the 1/2 or 2/3 shifts have been a bit baulkey/harsh but nothing significant. Have suspected the accumulators, had been planning on a set of pistons and springs for them.

Today, ran fine going to work, but getting off the interstate, things went nuts. Really poor 2/3 shift, o/d light starts flashing, seemed to drop in and out of neutral a couple times, started hunting gears between 3rd and 4th.

Ran an errand an hour later and at first, symptoms were not bad but got progressively worse. Finally tossed a P0720 error code, speed sensor.

So too going home this afternoon. Cold, seemed acceptable at first but quickly escalated to fairly poor. Along with the prior symptoms, the transmission almost seemed to cause the engine to buck a couple times.

Stopped off at a transmission shop on the way home. The proprietor tossed in a trusted speed sensor with no effect but was clearly uncomfortable with working on the Expo drivetrain the Ranger.

Fluid is quite new, about 2K miles, at the proper level and still clean and unburnt. Internally the transmission was spotlessly clean when I changed the fluid and filter prior to the install in the Ranger.

I'm at a loss. Symptoms almost appear electrical, but I can't see the one CEL if the electrics are going nuts along with the fair behavior when cold.

Any ideas anyone?

 

[JK080]

The first thing I would do is to watch the VSS (vehicle speed sensor) - (code p0720) with a scan tool, if it drops out and you start experiencing problems I would look for wiring and connection problems with that sensor, both of which can be affected by temp.

With the same scan tool you can also watch things like the MLPS switch, speed sensors, temp readings, etc. Any of these types of data the computer needs to know how to operate the tranny.

 

[SoHK_alumni]

Getting a bit more information.

Nearly exactly the same symptoms this morning, and the worst of the problems appeared at exactly the same point in the morning commute.

This time, it's tossed a P0750 to go with the P0720 -- Shift solenoid A along with the speed sensor.

Def starting to look electrical in nature, going to have to inspect the wiring harness end to end (Oh joy!)

JK080, thanks for the input: my ODB scanner only shows the VSS as a monitorable PID. Is the early EEC-V odb more capable than my code scanner or is the PCM only capable of offering such limited data on the transmission?

 

[SoHK_alumni]

Got under the Ranger today, found a couple nicked wires up above the transmission at the firewall/floorpan pinch weld.

Did a bit of reshaping of the pinch weld, slipped some heat shrink tubing over the nicked wires and added some heat to the tubing.

Time for a test drive!

Since my Actron CP9180 won't really tell me that much about the transmission, going to try an ELM327 adapter and FORScan. Might give me the same results, or might tell me a lot more than that.

 

[SoHK_alumni]

And resolved!

Ran a 50 mile test on the transmission, everything from stop and go to interstate.

Impeccable performance, no shifting/lockup issues at all.

Going to call it a success.