2008 Ranger FX4 bizarre cruise control problem

[sunnyboy]

I've had my 2008 Ranger FX4 since it was brand new off the dealer's floor, and for the most part it's been flawless, until this recent cruise control problem.

About a month ago, the cruise control started to "let go" while driving at speed. That is, the cruise would show as engaged (light on the dash was on), but the speed would just starts dropping and never come back. Button pushed didn't change this, except turning it off then on again. Then it would hold speed for a while but eventually lose speed again.

I ran the static/dynamic test (pushing the buttons in sequence when power applied) and it came out with no problems. Several OBD2 readers report no codes at all. The speedometer works fine, as do the ABS brakes. There appear to be no vacuum lines to the cruise control system according to what I've read.

Update: This week now it simply won't engage at all. The dash light comes on, but nothing happens and it won't hold speed at all. Even so, the static/dynamic test comes up with no errors and there are no OBD2 codes.

It seems the only possibility I can come up with after much internet digging (the Haynes book is worthless) is that it might be the servo itself.

QUESTION: When you run the static/dynamic test, and the servo cable moves for the dynamic part, how much should the cable move? I was told "just a bit" but elsewhere I read it should go through the complete range of travel. Mine certainly does not do the full range of travel.

Is there any way to check the proper operation of the actual servo?

Any other ideas?

Thanks.

 

[sunnyboy]

Fixed!

Well, the cruise problem is now fixed. It was the servo, as suggested by Hooligan in another thread.

I had exhausted every other possibility, but new servos are $380 on Ebay and $450+ from dealers. Phoning around at wrecking yards, I found one out of the same year and model Ranger for $65. Picked it up and installed it in the parking lot as they are VERY easy to swap out. New (well, used) one worked perfectly.

I took apart the broken one. They are a very simple device - there is a fairly complex circuit board behind protective gell on the side, a servo motor with 4 connections and a magnetic clutch with two connections. My guess is it's either the circuit board or the magnetic clutch OR the plastic gears meshed by the magnetic clutch that failed.

What really annoys me about this whole process is that this servo is obviously (to me) something that could very easily be bench tested to see if it's A-OK or not. A simple plug harness (or even bare connections) could be applied and you'd quickly know if the board, servo, clutch or gears were bad (or it was all good). But in all my months of internet searching and dealer calling, there is nothing. The Haynes books are worse than useless regarding speed controllers, and the dealer always just said "bring the truck in". At $450+ for the new servo, that's not going to happen.

So - anyone out there - have you heard of a bench test setup for speed control servos like this?