Thanks for the link, Glacier. Interesting reading on the EPC adjustment issue.
And thanks to you Tim, for clarifying it some more. One of these days I'll disassemble my old EPC and see what makes it tick, and see what that adjustment screw actually 'adjusts'.
I've heard or read somewhere that Ford's answer to the 2-3 flare is to re-program the PCM to increase the line pressure slightly. I'm sure they do it through the PCM because it's quick and easy, but I think our way through valve body mods is better and I hope longer lasting.
It'll be interesting to see if the troubles come back after more miles are on the mods. I hope not. I for one am getting tired of fixing Ford's engineering mistakes for them.....
Forgive me for chiming in WAYYY late and for the ridiculous length of this post, but I work for a company that makes transmission solenoids, and I'd like to offer some unsolicited facts and semi-educated opinions on the EPC solenoids used in the 5R55E transmissions. They are made by Bosch, and are what we in the biz call "direct acting" variable force solenoids (VFSs). These have a "motor" section, which has an armature that is preloaded by a spring in the high pressure direction and pulled against the spring by magnetic force that is somewhat proportional to the current flow through the coil. Coupled to the motor they have a hydraulic section, which is a spool valve in a bore. The direct acting label means that the armature pushes directly (mechanically) against the spool. This is in contrast to other varieties of solenoids, such as "two stage" VFSs in which the spool is moved by hydraulic force and the armature only opposes the hydraulic pressure that acts on one end of the spool, but over a small area such that not much FORCE is required. Anyway, in the Bosch direct acting, the force from the armature (spring force minus magnetic force) is opposed (balanced) by the force of the output pressure acting on the other end of the spool, and this "force balance" is achieved by the spool moving to either allow oil flow from the inlet to the output (to increase output pressure) or from the output to "exhaust" (to lower output pressure). If there is no downstream leakage, then the spool moves briefly in one direction to achieve the target pressure and then returns to a point where the spool edges overlap the sleeve windows and there is no flow in either direction. In reality, however, the leakage past the downstream valve requires some level of flow through the solenoid valve to maintain the commanded pressure.
As mentioned above, direct acting solenoids rely on the spring to directly apply force through the armature to the spool valve to move it in the high pressure direction, SOOO if it takes more force to move the spool valve than the spring can deliver, the spool doesn't move and the pressure doesn't go up. AND, since there is such a tight fit between the spool and its bore, any little piece of crap or accumulations of even smaller pieces of crap that wedge in between the spool and its sleeve can bind it up to where it doesn't move smoothly or possibly at all. This, of course, can cause erratic or low pressure output which can result in poor shifts or even clutch slippage to the point destruction.
Now is a good time to mention (although it's been mentioned in other locations on this board) that the 5R55 transmission is fully adaptive, which means that the computer tries to control shift timing (feel) using feedback from the speed sensors (input and output) to determine how long the clutches are slipping during a shift. If there is too much slippage (soft shift or maybe even flare), the computer will command more pressure for the next time, and if there is too little slippage (hard shift), then the computer will command less pressure next time. These adjustments are stored in memory for the various discrete levels of engine torque so that shift feel is targeted to what the calibrator feels is appropriate for the whole range of speed and torque conditions. This means that, within limits, making adjustments to the EPC pressure output either by adjusting the screw at the back or by installing resistors, etc., will not affect long term shift feel since the computer will compensate for the changes in order to get shifts back to their "ideal" timing. AND THIS is why it would make sense that Ford's fix for the 2-3 shift flare is to flash the computer... what they are doing, most likely, is programming a different, shorter "ideal" shift timing for the 2-3 upshift at the problem torque levels. Of course, if there are other mechanical issues at fault as well, then this by itself is not likely to cure all symptoms.
Which brings us back to the design of the EPC
... as mentioned, the device is inherently weak due to the fact that the only force available to push the spool in a direction to increase the pressure comes from the armature spring, which itself must be relatively weak so that it can be overcome by magnetic force so that the output pressure can be varied over its working range (like 90psi to 0psi) as directed by the computer. And this weakness means that the part is going to be sensitive to contaminants that obstruct the smooth motion of the spool as well as any extra friction that might come from the surface of the spool bore being marred up over time. The spool itself is "anodized" which puts a very hard and wear resistant coating on the aluminum. On the other hand, two stage solenoids, such as the one used in the 4R70W (AODE) transmission, are quite robust against these issues since there is considerable hydraulic force available to move the spool through any contaminants that might build up around it, and the armature only has to act against the small force of hydraulic pressure coming through a small area (the poppet). This design comes with the compromise of higher "inlet pressure sensitivity (how much the output pressure changes as a result of supply pressure changes) and some built in leakage (usually not significant), but transmissions like the GM 4L60E and 4L80E and the Ford 4R70W/4R75 (and the CD4E) use this style and they really don't have any EPC wear issues.
Why bring all this up. Well, aside from the reason that some may find it interesting, I also happen to be working on an aftermarket EPC for the 4R/5R55 transmissions that happens to be a two stage type device... i.e., I'll probably be trying to sell these someday.
