Gary Lewis

Do you understand slang German? Jein. Yes and no. Actually, no Bullnose came with digital tank readouts. And that's not what I'm after. I'm just interfacing the later 1987+ sending unit with the Bullnose gauge. No one will ever know the Arduino is there as it'll tucked up under the dash where it can't be seen. (Unless I really do find other uses for it, as my nephew suggested.) The Bullnose gauges are really thermometers. Yes, really. There's a 12 ohm heating element in them and a bi-metal spring that moves the hand. As current flows through the heating element the spring unwinds and the hand moves up in the scale. And, since that is a slow process we can pulse the current to the resistor thousands of times a second and the gauge won't know it is getting hit with a pulsing signal. (In mathematics terms, the heat gets "integrated".) All of the pulses will be 5v in "height", but the trick is to control their width, meaning how long the pulse is. Or, in the parlance "Pulse Width Modulation" - PWM. So, that's what I'm going to do - control the width of the pulses so that the heat is exactly right to get the reading that reflects the amount of fuel in the tank. The Arduino will read the level by monitoring the voltage on the sending unit. Then it will calculate the correct duty cycle, meaning the "on" vs "off" time of the pulse, and send the pulses to the gauge's resistor. From my calculations the right duty cycle for Empty, which is different than no reading, is 14% on. And the duty cycle for Full is 55% on. But since I can plug a computer into the Arduino I can modify the equation, which is for a straight line: Y = MX + B. So, if I need to tweak either M or B I can so and see the results immediately. I'm sure that is "as clear as mud" as Dad would have said, but I'm pretty sure it will work. And, it gives us Bullnosers a way forward on the fuel systems. I'll happily share the code that I write, which will be very small, and the parts for the Arduino. Should be plug and play.

And thus, the disclaimer... [check closely for accuracy!!!] Yep. Caveat emptor.

Bill would be in good form about now. As can be seen here (Driveline/Clutch Linkage) the Bullnose part is E3TZ-7521-A. As for that part number, I'll let you find it:

Well done, David! Or resident eBay guru strikes again!

The handy dandy website I found says the windshield trim is the right stuff. And, by the way, that stuff is rare! And the bumper is right for our trucks, as shown below. But, not so for the 1973-79 as claimed. They are all D3TZ's with a couple of C4's. (I can hear Bill now. Aztek? No, it is something about cluelessness. )

Sold for $2050.00 I saw that. Even told Janey and our son about it. Surely it was worth twice that? What was wrong with it?

Not that it will educate you on electronics, but here's what I'm talking about in a drawing format. The stuff in red is what I'd be adding.

That's good MPG for those conditions. And I suspect it'll be more like 17 when you get a good reading w/o the adverse conditions. As for the front end, check out the u-joints - both in the drive shaft as well as the axle shafts. The axle shaft ones are a bear to change, but can cause noise. Try leaving it in 2Hi and locking in one hub to check for noise. Then swap to the other hub to see if anything changes. Or, go to 4Hi and leave the hubs unlocked.

Steve - Ray is a wonderful help, isn't he! Ok, now that it appears that we have the wiring sorted, sorta, I've spent some time thinking through the interface from the 1990ish FDM sending units to the Bullnose fuel gauge. And, I think I have a plan that will work. It is based on an Arduino microcontroller, and probably an Uno since it only needs a source of power to work and has a USB connector for setup via a computer. The resistance for the sending unit in the fuel delivery module will be 22.5 ohms when the tank is empty and 145 ohms full. One end of the resistor is tied to ground, so there will have to be a resistor from the 5v supply on the Arduino to the potentiometer/sending unit, meaning the circuit will go from the 5v supply through a resistor and connect there to both the analog input of the Arduino as well as to the potentiometer. My calcs say that a 220 ohm pull up resistor will give .46v at empty and 1.99v at full, with a current flow of 21 and 14 milliamps respectively. The resistance of the heating coil in the gauge is 12 ohms, and the Bullnose sending unit runs from 10 ohms at full to 73 ohms at empty. That means with the 5.4v source we would have 250 milliamps of current at Full and 60 mills at Empty. But if the digital output of the Arduino is turned on as a replacement for the sending unit it would be sinking 5.4 volts through 12 ohms, giving 460 milliamps. So we need 60/450 or 14% duty cycle to generate enough heat to register Empty, and 250/450, or 55% to give Full. But that current is too much for the outputs of an Arduino, so we need another board (shield) to sink the current. Circuitar makes one called the MOSFET Nanoshield and it is $9.90. However, the Nano board probably doesn't fit the Uno, so I'll just need to find another one. In any event, shields plug into the Arduino (stack, actually) so no wiring is needed. Just connect the wire from the gauge to the screw terminal, connect the wire from the sending unit to an input pin, provide power, program it, and go. Now we need to create an equation that gives 14% at .46v input, and 55% at 1.99vv input. Assuming a straight line then we need y=mx+b, and an online calculator gives y = .27X +.02. Plugging .464v into that equation gives 14.5%, and plugging 4.984v in gives 55.6%. Plenty close enough since none of the components we are playing with are that precise. Further, the transistor used to sink the current won't take the voltage fully to zero. But we now have an equation and can tune the "m" and "b" parts of it as this is implemented. Thoughts? Drawings/schematics to make this clearer are in the works.

Good progress. Gotta feel good after 3 years of waiting! But I would wipe the cylinders, main bearings, and lifter bores down with a lubricant to ensure they don't rust. Don't get enough on that it creeps and gets on other things, but you sure don't want rust.

Well done. And, I'm glad it cured properly. This thing sure is taking a lot of work, but will be well worth it in the end.

Same here on my 81 F100 single-tank flare side.............till I added the 2nd rear tank Dave ---- I think "single fuel" must not mean "tank" and instead means it wasn't set up for more than one fuel.

And, in case you are wondering about it, I realize the connections to the tank selection switch are quite different from the 1996 to the 1986 drawings. But since I'll be using a complete harness intended for the 6-pin switch, it will work - assuming Ford didn't change the connection order on the pumps and sending units.

And I thank you for that. Want it back? Or do you want me to keep it in case you need it? As for the 5.0L EFI harness, it is almost a slam-dunk. If you look at the wiring diagrams below you can see that I'll have to remove the power to the high-pressure pump. Beyond that I don't think there are any other changes.

Jim - Good catch. I forgot that it takes a different switch. But I've made the changes. Hope it is now right.

Bill - I'm getting myself confused, but I think you are saying that all the EFI'd 5.0's had the reservoir/switching valve and not the 6-port valve as shown in the 1985 EVTM. Is that correct? Also, wouldn't Darth's harness just be a longer version of the one that's already in Big Blue? Meaning it would be set up for the 6-port valve. Right? That's why I'm interested in a 5.0L EFI harness since it should plug right into the tanks and the tank-selection switch. What am I missing?

If you have the '86 tank wiring then I'd be very interested. But I'm not in a hurry. However, assuming it is the 5.0L EFI that I think it is, it would almost be plug & play. I think. As for the later wiring, I've been combing through Huck's and found that I have all of it, albeit in pieces. I have the tank wiring, but the rear tank connector is cut off too close to allow splicing. And that harness was cut from the underhood harness, but it would be easily spliced. Then it goes through the bulkhead connector into the dash harness, so I'd have to splice at that connector. However, it then runs, along with lots of other wires, and finally comes to the tank switch. So, with some splicing and a new tank connector I could have a the tank wiring to plug into the switch. However, if you have the '86 stuff in good shape then it should be easier and cleaner. Again, absolutely no hurry. I know it is COLD up there!

I found something in the catalog today that has me puzzled, so perhaps y'all can explain it to me. As you can see below, the catalog says that 1980 - 86 trucks with a "single fuel system" take tank selector switch D5TZ 9A050-A, which is marked D5TB 9A050-AA and has 5 terminals. I just so happen to have one of those rascals and can tell you that it takes a different connector than all of the other tank selector switches, which have a 6-pin layout. (By the way, I have a page up that shows the various switches used on these trucks: Fuel Systems/Fuel System Wiring.) I've gone to the EVTM's and am now even more confused. The 1981, 1884, and 1984 EVTM's show a 5-pin terminal that can only fit the D5TZ 9A050-A, and it isn't until the 1986 EVTM that the 6-pin layout appears. However, the catalog shows that a 6-pin format was used as early as '83. But none of the EVTM's show a switch on single-tank trucks, only show a switch for trucks with dual tanks. What am I missing? Why do trucks with only one tank need a switch? And, did they have one? Any of y'all have a single-tank truck? Does it have a switch? Or, does "single fuel system" mean that they only run on a single fuel and not, say, gasoline and LPG?

Well, I just realized that there's a big difference between the 1985 and the 1986 EVTM's on the fuel system wiring. The 1985 has a 6-port tank selector valve and the 1986 doesn't. I think I remember Bill saying something about this, but it went right over my head. The 1986 is really close to the 1996, with the obvious difference in that the '86 has a high-pressure pump and the '96 has a computer. But another subtle difference is in the pin-out on the fuel tank selector switch. So off I went to the catalog and I found that they appear to take different switches. I wrote this up on the Fuel Systems Wiring page, and I'd appreciate it if you could take a look and tell me what I'm missing. Here's the 1985 wiring for the 5.0L EFI: And here's the 1986 wiring for the 5.0L EFI with dual tanks:

Yes, I'm thinking of modifying Big Blue's wiring to go EFI. My plan is to go with the 1990ish FDM's. But I'm using the 1996 engine compartment harness, so the fuel pump relay will be in that, and I can do away with the 1985 fuel pump cut-off relay, 6-port valve, frame-mounted pump, oil pressure switch, tank selector relay, etc. I wonder if I should get an 85.5-6 5.0L EFI fuel tank harness. Or, let me see what I have from Huck......

Steve - I'm a visual person. I need to see what I am working on - especially with something as complex as this is. Ray - I'm confused as I don't see a bit of resemblance between the 1985.5-6 7.5L wiring and the 1996 7.5L wiring. Are you referring to the 1985.5-6 5.0L wiring? I've added the page from the 1985 EVTM below. And it is very similar to the 1996 wiring.

Jim - I added the verbiage, but see what you think - please.

Hard to believe they removed all of the black stuff. But it obviously has the XLS tape stripes that aren't easily faked or added later. Hmmmm. Could you special order the stripes on a standard truck, or an XLS w/o the black?

I'm not sure yet. I need to get it beside the transfer case and see how much difference there is. But I think it is going to be very close and I may not have to repaint it.

Glad you found the problem. As for your questions, I think you are looking at the as-is schematic. I'm going from that toward the 1996 version, but now I have to figure out how to integrate them. However, the oil pressure switch, the 6-port valve, etc are going the way of the Dodo bird.