Speed Control Testing

[Gary Lewis]

Some of you know that I'm having trouble with the speed control, aka cruise control, on Big Blue.  There is some discussion about the problems in that thread, but I want to bring the discussion here so more people can see it.

Basically the problem is that the various combinations of speed control parts I've put on the truck have one thing in common - the speed varies up and down, even when on a level road.  And, the system is too aggressive, causing the throttle to be opened or closed too much at the slightest provocation.

I started testing components today using information available on our page at Documentation/Electrical/Speed Control.  But in the midst of that I got a text from Scott/kramttocs and he shipped me his Rotunda Speed Control tester.    (If you want to read about how he acquired it, go here.)

I'm thrilled to have the use of that device as it appears to test several of the components as well as serve as a test replacement for the electronics module.  So I finished the testing I was doing and will await arrival of Scott's tester.  However, I want to document what I found today as it may well be useful to some of you as well as to me later.

If you aren't aware of how the speed control works, there is a writeup in the FSM instructions on the page referred to above.  But that doesn't really explain it very well IMO so let me tell it the way I think it works.

The schematic below is from that FSM page.  And there are two things I want to point out on it - the valves marked Vent and Vac that are circled, and the potentiometer to the left of them.  From my reading and testing it appears that battery voltage is applied to Circuit 144, which is the O/Y hash wire, when you press the On button on the horn pad.  Then when you press Set/Accelerate the electronics module saves the pulse rate coming in from the Speed Cable Sensor on the left and applies a ground to the Vent valve, which causes it to close.  That causes vacuum via the Servo Motor to pull the actuator and open the throttle.  And if that causes the vehicle to speed up that is sensed by the pulses coming from the Speed Cable Sensor and the module applies a ground to the Vacuum valve, causing it to open and drop the vacuum.  I'm guessing, but I believe that the speed is maintained by the module pulsing the two valves at varying rates using pulse-width modulation.

But what I don't know yet is exactly how the potentiometer's output is used.  It is part of a feed-back loop, and it is possible the system will work w/o that feedback as the FSM's troubleshooting guide indicates that if the speed hunts up/down that one thing to check is that the outputs from the potentiometer are getting back to the electronics module.  And it is possible that one of the three wires on Big Blue has a bad connection and the feedback loop isn't working, which might account for the speed variations.



Now for some results of my testing.  First, I found that if you put 12v to the orange-yellow hash lead (wire 144) and ground the white-pink hash lead (wire 146) that closes the Vent valve and you can pump up vacuum in the servo to prove that it is working.  (The servo contains a reservoir so it takes a LOT of pumping with a Mityvac to see it on the vacuum gauge.)  And you can see that the reservoir is tight by timing how long it takes to bleed vacuum off.  In my case it took between 30 seconds and one minute for the three servos I tested to go from 25" to 20" of vacuum.

Also, while my potentiometers measured roughly 50k ohms across them, when measuring from the P/LB wire (Circuit 147) to the Y/R hash wire (Circuit 148) I got ~24K with no vacuum, meaning the throttle cable wasn't being pulled, and 36K with full vacuum meaning the throttle was opened as far as the servo could open it.

And, in doing my testing I learned why the servo that I put on Big Blue didn't work - the Vacuum solenoid valve doesn't work.  So I decided to take that servo apart.

It has the best throttle cable of all of my servos, so I removee the two nuts that hold the cable system to the servo.  You can see from this shot how it comes off.  There's a ball on the end of the cable and it goes into the clevis you see in the middle of the servo.  Also visible are the two solenoid valves and the connector.




And here's what the electronics module looks like.  As you can see, there's a trim pot in the lower right corner of it.  But there are no markings that tell what the pot does.  So at some point I'll take Big Blue out with that module exposed so I can adjust the pot and see if it happens to adjust either the set speed or how aggressive the speed control is.  

[85lebaront2]

I still have the 2 extra speed control modules, one of which I believe has a 1993 or newer date on it. I believe one of them has "sensitivity" by the hole for the pot. One has F4DF-9D843-AA, the other has no sticker but E7AF PN on the circuit board. I know the 94 one came from a Taurus (mine when I was having a problem). Problem was a bad connection in the harness. It always would set about 1 - 1 1/2 mph high, and upon resume might climb some more. Since I no longer have anything Ford with a vacuum speed control, I will send them your way. Darth has the electronic one and both Flexes are drive by wire so like Blue Jeans, use the throttle actuator for everything.

[Gary Lewis]

Thanks!  I'm going to crack this yet with the help of my friends!

So, you think the pot is sensitivity?  That would be sweet.  I really don't like an aggressive speed control as they kill the MPG, especially on an engine with lots of power, so do want to desensitize this thing.

[kramttocs]

Subscribed. Very interested to see how all this works and pans out. As always - appreciate the detail to documentation.

[Dorsai]

Do all those electronic components have their own Ford engineering numbers on them??

[ArdWrknTrk]

Subscribed as well!
Since a little kid I love taking things apart to figure out how they work.

You're living my dream, Gary!  

I'd also be interested in how Matthew is getting on with the transmission controller in his nephews truck's diesel transplant.

[Gary Lewis]

Matthew - I didn't find any Ford numbers on the circuit board, although I'll look again this afternoon.

However that chip has an ID number on it of D9AF-14A607-A1B and a Motorola # of QQ8429B.  I haven't found any hits on either, although some sites say they have, but I didn't look in the cross reference to see if I can find the ID# and cross it to a part #.  I just did - no dice.

Jim - I'm glad you are enjoying it.  I am as well.  I've often wondered how the speed control works, and now I'm finding out.  

[85lebaront2]

Gary my two units have the following numbers on the circuit boards:
Old unit - E7AF-14A608-AA
New unit - F1VF-14A608-CD
On the old one it is on the circuit side of the board, new one on the component side. Both have the same chip number - D9AF-14A607-A3B which is probably the actual "brain". The old one looks like your pictures internally, new one is completely different in the layout.

If you would like a Rotunda Speed Control Tester, I bought one on eBay when the Taurus was driving me nuts with the speed control not working. It told me I had a speed sensor fault, which I knew was partially wrong as I had no EEC-IV code for it and the transaxle was shifting and engaging the lockup converter as it should.

[Gary Lewis]

Bill - Let's make a DEAL!    (I was reminded of Don Rickles/Crapgame in Kelly's Heroes when I typed that.)  I sure wouldn't mind having a tester of my own as well as the other modules.

But does that Rotunda tester look like Scott's?  Does it do these units or the later ones?  Here's Scott's:

[85lebaront2]

Yes, looks like the same one. The molded plastic hinges on the case broke when Matt was using it on his 1986 F150. I haven't seen a tester for the electronic speed controls.

[Gary Lewis]

Then I'm interested.

But it might be a reason to stay with the vacuum system if that tester doesn't work with the new electronic ones.  Plus, I might figure out how to make the vacuum systems do what I want easier than doing the same with the electronic one since I have access to the signals between the servo and the brains on the vacuum system.  And, there's that tantalizing potentiometer that may take the sensitivity out.

[Gary Lewis]

Bill - It looks like there is an ID # on this speed control board: E3AF-14A608-DA.

[Gary Lewis]

Bill - Looks like I'd like that tester sooner rather than later.  See below.

Scott - As said in the text, I can't get your tester to work properly.  According to the instructions, which I've now put on this page (Documentation/Electrical/Speed Tester) the display should come on when you fire it up.  But the display doesn't come on at all.  

Having said that, it sorta works.  I can put it in the "harness test" mode and when I test the circuits going to the servo I hear a beep on each one.  But I think that just tells me that the tester "saw" that I'd made a connection and then the display is supposed to say if it is correct or not.

So I turned to the DVM and tested the servo, which passed.  Then I tested the harness and on the first pass I found that the two outside legs of the potentiometer, meaning the P/LB and B/LG wires, connected to an O/LG wire in the Pin 7 position, which is supposed to be Servo Signal ( + ), which is either the P/LB wire or the B/LG wire.

But, after testing everything else, which tested correctly, I went back to those two and couldn't repeat what I'd found.  IOW, they tested perfectly.  And I pulled, twisted, etc all of the wires.

So I'm at a loss.  I'm stuck.   

Any suggestions?

[kramttocs]

Sorry Gary - bad deal on that tester  
Good thing Bill has a known working one.

Thanks for adding the doc though!

[85lebaront2]

Now I have to find it, I probably put it up on my "storage floor" over the office, bathroom and wood shop. Once I track it down I will pack it and the spare modules and send it West.

[Gary Lewis]

Thanks, Bill!  In the interim I'll re-test the pot's wiring, and if I don't find a problem I'm going to start positioning the air cleaner and PDB.  Then when I get your tester I'll compare to Scott's and see if I can figure out what is going on with it.

[Gsmblue]

Gary, Keep in mind I have a tester arriving around 1/2 that I would be happy to send on for you to borrow too.

Once it arrives with me I will let you know how it goes. I am sure I will have questions about it anyhow.

[Gary Lewis]

Thanks!  It isn't urgent as I have plenty to do on other things, so let's see how this plays out.

[Gary Lewis]

Well, the FSM section on Speed control says "Speed control system tests should be performed using the Rotunda Tester Model 007-00013 or equivalent. If the Model 007-00013 Tester is not available, use the Following procedures."  And then it has you testing for voltage here, resistance there, ect.

So, I tested components as best I could and assembled a system out of the best of the pieces.  And then I followed the instructions for testing, and found nothing.  NADA.  Everything checked out.

But, knowing that there's a potentiometer buried in the electronic "amplifier" I drilled a hole in the housing to allow access, as you can see in the pic.  And, I marked the case where the current setting is.  But when it came time to "install" the amplifier I realized that the access to the hole wouldn't be easy, so I held it in place w/a zip tie in a position where I could tweak it when stopped.



Then we took the truck for a drive.  You'll remember that the last time I had it out there were two problems - a 6 MPH surge when you hit Set, and an aggressiveness to holding the speed that caused it to overcompensate on throttle settings.

Well, when I hit Set the set point was spot-on with the speed we were going.  Yippee!  But, it was still too aggressive.  So I pulled over and turned the pot counterclockwise a bit.  And after that set point was a little lower.  Then I turned it clockwise quite a bit and when you hit Set the speed jumped 3 MPH up.  Last, I turned it all the way counterclockwise and the set point was 3 MPH low.

But, there didn't seem to be any change in how aggressive the speed control is.  So apparently that pot only controls where the set point is and not the sensitivity.

I'll put it back to the marks and expect the set point to be just right.  However, I'm not happy with how aggressive it is and will be thinking about how to change that to smooth things out.  

[85lebaront2]

Gary, will this help you? Also I will throw the control modules in.