Gary Lewis

Glad you found it!

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.

In that case I think you'll have to make one from hose barbs and pipe fittings from the hardware store.

You did it this time, Bill. Looks good. But I'm with Jim - a black Sharpie and no one will know.

Looks perfect, Chris. Well done!

You are WRONG! The audience is at least TWO! That may be the coolest thing I've seen printed. WOW! How did you draw it in order to print it? I am in AWE!

I'll have to swear you to secrecy as that is a special part with a very unknown name - an "elbow". Go to Documentation/Cooling Systems/Elbows to find the skinny on them.

George - Are you talking about 18599 in this illustration?

I'll bet that works, Rob. It looks like success to me. Well done!

The speed jumps by ~6 MPH when you hit Set/Accelerate. Each and every time you hit it. And, it hunts up and down. Plus, it is aggressive. But, watch for a new thread on Speed Control Testing. I'm doing that for several reasons: Scott has shipped his Rotunda Speed Control tester to me I've created a test harness and have checked out 3 servos and learned something of how they work, or don't in the case of the one I put on Big Blue on Wednesday that didn't work I pulled one of the electronics modules out of its case and discovered a potentiometer - with no markings, but I'll see what I can figure out I'm taking the bad servo apart and will post what I find As for a smoothing cap, my theory is that the Vent valve is held closed and the Vacuum valve is left closed if you are running steady state. If you start down a hill the Vent valve is allowed to open briefly reduce vacuum to drop the throttle, and if you start up a hill the Vacuum valve is opened briefly to add vacuum to open the throttle. So if you put a large enough cap on the Vent, when the module removes the ground to allow the valve to open the cap will keep it closed a bit longer. But, as I think about it, when the output of the module goes low to close the Vent valve that will happen immediately unless there's a resistor involved. So I'd need an RC circuit. Ditto the Vacuum valve. It gets closed by the output of the module going low, so if there's an RC circuit twixt the module and the valve the square pulses will be rounded waves. I hope I don't have to resort to that, but that's one reason for taking the bad module apart - harvest its connector. That along with the male connector I already have would let me make a plug-in unit with the RC circuits in it. A little Electricity 101 and I can figure out what R's and C's I need 'cause I already know the current.

Is this it, Bill? I'm pretty sure it is, and you can see that I marked it so. I can get it out on Monday if you want it. Sorry it is so greasy. Seriously though, it'll need to be painted as it has been media-blasted.

I'm not pushing "Dynamat or any variation of it", but I'm curious why you don't want it? I really like the Noico stuff I used and it isn't nearly as expensive as Dynamat. Having said that, I can see that if you put a liquid, like Lizzard Skin, on it would help with rust prevention. Is that the reason? Just curious.

Welcome, Jim. I think we have the friendliest and best-informed community on the internet.

Jim - I have the MPCs from 1948 on trucks and 1949 on cars. So when the 1980 - 89 truck MPC gives an earlier part number but no info, I know where to go. Bill - That's interesting. I wonder about these.

You are welcome.

Bill - Did you forget the pic?

SORRY FOR THE LOOOOONG POST, but.... I've been researching the speed control issue. Fortunately there's a nice website that has both the FSM section on that awa a TSB. So let me set out what has been happening and my conclusions and y'all tell me if I'm all wet: With the original transducer, servo, and electronics module the system worked but surged, even after lubing the speedo cables. I changed out the transducer with no change whatsoever, so the transducers are good I changed out the servo and the system didn't work at all so that servo is bad I changed out the module and the surge seems less, but there's a ~6 MPH pickup when you hit Set or Accelerate that isn't acceptable. So I think that module is bad. In reading the FSM section there is this page for "Speed continually changes up and down." That seems a good place to start, and the implication of what I see there is that I may have problems in circuits 147 - 149, which are the potentiometer circuits that tell the electronics module what the servo is doing. So I'll certainly check those out. But, if all else fails, I think I see a way to smooth things. The instructions say: And they give this diagram. I've circled the Vent and Vacuum connections. From the above it looks to me like Circuit 144 has power on it and the servo pulses Vent and Vacuum to slow down or speed up. (Vent probably is grounded the majority of the time and the ground is removed to slow down, and Vacuum is only grounded to speed up.) So, I'm thinking that I could add capacitors to both Vent and Vacuum to smooth things out if everything else checks out. THOUGHTS?

Yes, good point Jim....lol! I just ordered a set of bricknose map pockets off ebay in dark gray: https://www.ebay.com/itm/87-91-Ford-Truck-Bronco-DOOR-PANEL-Map-Pockets-Dk-Gray-OEM-Pair/174406604564?hash=item289b719714:g:teQAAOSw6aRfQzhQ&autorefresh=true My interior is med gray which I will keep. I'm replacing the med gray rubber mat with Essex Dark Gray carpet and the above ordered map pockets which are also dark gray so I will have a somewhat two tone gray interior when I'm done. The current all med gray look is kinda bland actually. Think this will give it some pop! Hey Shaun, thanks for the suggestion. I liked the look and the cost much better than that which I was looking at. Thanks fellas! I think you'll like those, John. I thought about going that way on Big Blue but decided that the existing carpet pockets will do for the time being. But, I don't want larger things stored in them as I'm pretty sure the elastic will let go. Anyway, show us pics when you get them installed. I may follow your lead.

I think that grille is actually a vent. I tend to remember that they vented the door to make it easier to shut them. Or, maybe that's just what I've heard. But you wouldn't need to do anything to your door just because of that grille.

Bob - I agree it isn't good to consistently run the tank dry, although I didn't let the in-tank pump spin long at all 'cause I was watching it like a hawk and flipped the switch immediately when the bucking started. And it picked up almost instantaneously. But I don't plan to do that on a consistent basis. However, I do want to know roughly where they run dry so I don't do that. And I certainly remember what you said about your tanks. I was thinking about that yesterday as I got very different readings from my tanks. So to answer your question again after more experience, if you want the gauge to read correctly for two very different tanks then I think you'll have to have two Meter Match units, each programmed for the tank it is serving. And given what I saw yesterday, I may re-think the Arduino. It would be easy to put it ahead of the tank switch and have it select the proper table depending on which tank/sender is selected, and then drive the gauge appropriately. But, in truth I can probably live with what I have. Or just buy another Meter Match and put both ahead of the switch, powered off the switch. Jim - I think you have a good plan. But due to some variances, like in the resistance of the senders or the shape of the tanks, don't expect complete accuracy. In my case the rear tank should run out soon after the needle hits E, and the front tank went easily 30 miles after it got to E. So there must be ~3 gallons still in the front tank at E. Scott - You probably had the winds we had yesterday, which were strong out of the south. So the 10.22 MPG wasn't too surprising as most of it was directly into the wind. But it certainly would have been better if I'd been running the throttle instead of the speed control doing it. However, the 13.19 was all with the wind and I was running the throttle, and that made a huge difference. So I don't think there's much more to be had on MPG until I go with EFI. And then I do think we'll see a gain as the AFR yesterday was frequently below 14, like 12 or so. But the EFI should put it on 14 and keep it there.

Thank you, Dyn. Great post! The more I look at those, the more I think I may just pass. I found these on ebay: https://www.ebay.com/itm/Coverlay-Medium-Grey-Door-Kick-Panels-12-10K-MGR-For-80-91-Ford-F-150-Bronco/283650637011?_trkparms=aid%3D1110006%26algo%3DHOMESPLICE.SIM%26ao%3D1%26asc%3D20200520130048%26meid%3De31d1ad357d34e819296ab4131720688%26pid%3D100005%26rk%3D4%26rkt%3D12%26mehot%3Dpf%26sd%3D283650636879%26itm%3D283650637011%26pmt%3D1%26noa%3D0%26pg%3D2047675%26algv%3DSimplAMLv5PairwiseWebWithDarwoV3BBEV2b&_trksid=p2047675.c100005.m1851 Anyone shed some light on these? Of course I have the option of refurbing my OEM units, however, I think the backing is some kind of pressed board that I may have messed up a bit when I removed them last. I may pull those today and take another look. I've never seen those Coverlay map pockets, John. But the pictures don't impress me. Perhaps they would in person. Have you considered the later style pockets? I think they'll fit and can be found in the salvage.

I'm going to "read the mail" for the most part. But we have the section of the factory shop manual on ignition systems on the page at Documentation/Electrical/Ignition. And it has a decent overview of how the DS-II system works. Mike - Jim pointed out that he has his name in his signature. Would you mind doing the same? That really helps me keep names straight. Thanks!

Two things. First, stainless isn't easily formed as it work-hardens easily. So you may have problems flaring it. Second, why not just go the way the factory went and use the nylon line? That is what most manufacturers went with soon after the Bullnose era, and they work well. I bought rolls of the 3/8 and 5/16 and the connections as well as the tool to install them with and it worked nicely. I have an all-new factory system from a 90's truck under Big Blue.

Ok, here are the real part numbers. And we may be one of the few places on the net that has these. I'll put them on the Air Cleaners page.

You don’t happen to have the part # handy ? Part numbers and temp ratings are shown on the page at Documentation/Fuel Systems/Air Cleaners. And you have to click on Air Cleaners as that is an actual page. But to make it easy, here is the chart from that page but it doesn't show part numbers. Unfortunately the catalog doesn't have a listing for those parts, but just says which one goes for what vehicle. Maybe I can find that in another catalog?