Ifitaintbroke Posted March 28 Share Posted March 28 This has been the most troublesome system on this truck. I've been trying to fix it for 4 years now with no success. I'll start with where I am now. I am running an Autometer fuel gauge. It uses a 12v signal. I did forsee any problems with that, but now am second guessing. First, the front tank: The front tank has worked fine ever since I put in a new sending unit 4 years ago. That is until about 2 months ago it started acting up. It would read sporadically and the reading was incorrect. Now it does not read at all. I pulled the bed today (for the 4th time) and removed both sending units. The front unit is covered in white corrosion. The sending unit itself has a butn mark right in the center of the resistor bank. It's shows no continuity at any position, except when the float is pulled up as far as it will go. It then shows 16 ohms, which isn't even correct. It should be about 10 ohms. Here's what it looks like: The rear tank: The rear tank has given me trouble since day one. Long story short, it has never worked, except for once when I installed the current sending unit. It only worked for a matter of days, then the reading started to get lower until it didn't read at all. Recently however, it has started reading again. I pulled the unit today, and it is working flawlessly. 10 to 74.5, no problem. The tank is roughly 3/4 full, but the gauge reads 1/4. Obviously it is in the wiring. Some corrosion has developed somewhere. BTW, the rear unit has its own ground, about 12 inches long with a self-tapping screw in the frame. Another problem: I fear my selector valve setup is not working correctly. Yep, the system that I talked so much about and spent so much time on! Here's the issue: the front tank is nearly empty, and the back tank is 3/4 full. Why that's a problem: I just put 5 gallons in the front tank, which was already 1/2 full. Thats roughly 15 gallons. Now, the truck has been driven about 2.1 miles since then, and it has idled in the yard quite a bit, but 15 gallons? Unfortunately, I don't know how much was in the rear tank, because the gauge hasn't been working. I fear the return valve is not working and the rear tank has been filling from the front tank. I'm very close to putting in manual valves. Link to comment Share on other sites More sharing options...
Ifitaintbroke Posted March 28 Author Share Posted March 28 Forgot to mention: I fear the 12v signal from the Autometer fuel gauge may have fried the front unit. Remember, the factory gauges were regulated down to 5v. I did not think this would be an issue, as the gauge reads by resistance, not voltage(to my thinking). But the gauge cannot directly sense the resistance of the sending unit, so the only way for it to know the level would be by a drop in voltage, right? Link to comment Share on other sites More sharing options...
mat in tn Posted March 28 Share Posted March 28 Forgot to mention: I fear the 12v signal from the Autometer fuel gauge may have fried the front unit. Remember, the factory gauges were regulated down to 5v. I did not think this would be an issue, as the gauge reads by resistance, not voltage(to my thinking). But the gauge cannot directly sense the resistance of the sending unit, so the only way for it to know the level would be by a drop in voltage, right? I'm assuming this is the 86 f250. the voltage is "regulated" to somewhat of 6-7 volts. if your gauge is being fed 12v therefore sending 12v by way of the sending units to ground then there may be an issue. Link to comment Share on other sites More sharing options...
Gary Lewis Posted March 28 Share Posted March 28 Forgot to mention: I fear the 12v signal from the Autometer fuel gauge may have fried the front unit. Remember, the factory gauges were regulated down to 5v. I did not think this would be an issue, as the gauge reads by resistance, not voltage(to my thinking). But the gauge cannot directly sense the resistance of the sending unit, so the only way for it to know the level would be by a drop in voltage, right? I think you've nailed it - placing 12v directly on the sending unit has burned it. Is the original gauge bad? I'd go back to the original gauge because you need the instrument cluster voltage regulator for the coolant temp and oil pressure gauges, so why not use it for the fuel gauge as well? But, while you are in there I'd recommend replacing the ICVR with a true voltage regulator instead of the factory's chopper. Link to comment Share on other sites More sharing options...
Ifitaintbroke Posted March 29 Author Share Posted March 29 I think you've nailed it - placing 12v directly on the sending unit has burned it. Is the original gauge bad? I'd go back to the original gauge because you need the instrument cluster voltage regulator for the coolant temp and oil pressure gauges, so why not use it for the fuel gauge as well? But, while you are in there I'd recommend replacing the ICVR with a true voltage regulator instead of the factory's chopper. Good insight but it's too late for that solution now. My entire instrument cluster is aftermarket, and all 12v. I may have to make custom senders. Link to comment Share on other sites More sharing options...
Ifitaintbroke Posted March 29 Author Share Posted March 29 I think you've nailed it - placing 12v directly on the sending unit has burned it. Is the original gauge bad? I'd go back to the original gauge because you need the instrument cluster voltage regulator for the coolant temp and oil pressure gauges, so why not use it for the fuel gauge as well? But, while you are in there I'd recommend replacing the ICVR with a true voltage regulator instead of the factory's chopper. Here's what I might fo with: https://www.tanksinc.com/index.cfm/page/ptype=product/product_id=926/category_id=184/mode=prod/prd926.htm It would require new holes in the tank but that's no big deal. Link to comment Share on other sites More sharing options...
viven44 Posted March 29 Share Posted March 29 Here's what I might fo with: https://www.tanksinc.com/index.cfm/page/ptype=product/product_id=926/category_id=184/mode=prod/prd926.htm It would require new holes in the tank but that's no big deal. Supposedly the 1973 Bronco came with a 6 port manual valve. Those are unicorns. If I ever come across one.. man that would be cool. Probably looked like this https://www.amazon.com/dp/B00YMZ3YZM/?coliid=I2K7E4NJF0IPS6&colid=3IGQF00LDI4AO&psc=1&ref_=cm_sw_r_cp_ud_lstpd_41T6E65369DQB9Q9W4Y2 Else this would be what I would use next time https://shop.broncograveyard.com/1966-1977-Ford-Bronco-Mechanical-Tank-Switching-Valve/productinfo/10260/ Jim talks highly about the Pollak valve. I will also definitely consider that.. but something about manual makes it sound dead reliable. Which it is. Since I went manual on big blue 2wd, it has been peace of mind. Link to comment Share on other sites More sharing options...
Ifitaintbroke Posted March 29 Author Share Posted March 29 Supposedly the 1973 Bronco came with a 6 port manual valve. Those are unicorns. If I ever come across one.. man that would be cool. Probably looked like this https://www.amazon.com/dp/B00YMZ3YZM/?coliid=I2K7E4NJF0IPS6&colid=3IGQF00LDI4AO&psc=1&ref_=cm_sw_r_cp_ud_lstpd_41T6E65369DQB9Q9W4Y2 Else this would be what I would use next time https://shop.broncograveyard.com/1966-1977-Ford-Bronco-Mechanical-Tank-Switching-Valve/productinfo/10260/ Jim talks highly about the Pollak valve. I will also definitely consider that.. but something about manual makes it sound dead reliable. Which it is. Since I went manual on big blue 2wd, it has been peace of mind. Yeah I'm tired of band-aiding this system. As they say, "you can't fix stupid", and this is the dumbest system I've ever seen in my life. That manual valve looks tempting... Link to comment Share on other sites More sharing options...
viven44 Posted March 29 Share Posted March 29 Yeah I'm tired of band-aiding this system. As they say, "you can't fix stupid", and this is the dumbest system I've ever seen in my life. That manual valve looks tempting... Took them only 25 years to get rid of the ridiculous dual tank approach and using 1 monster tank. With that 38 gallon rear tank of yours, I would be mighty happy just having it. Even with the 460, thats over 300 miles range. Respectable. Link to comment Share on other sites More sharing options...
ArdWrknTrk Posted March 29 Share Posted March 29 Took them only 25 years to get rid of the ridiculous dual tank approach and using 1 monster tank. With that 38 gallon rear tank of yours, I would be mighty happy just having it. Even with the 460, thats over 300 miles range. Respectable. I'm not sure where you expected Ford to put a single tank and a spare tire, but I like the fact that I have a completely separate 'reserve' tank if the other gets a hole (or pump goes bad) if you have electric in-tank pumps. They boxed the frame by then. And all those frames rot in half like some damned Taco. I've done away with the plastic 'nose cone' on my midship tank. It only traps salt and muck, causing rot. I'm sure 12v is causing arcing of the resistor board of the sender. Have you considered 6v (ICVR) to the senders and using one of those, to make your cluster read correctly? 💡 My instrument won't read at all with the Meter Match, so I'm ready to eliminate it and go back to my needle moving up to 5/8 as empty. Maybe we can make a deal? Link to comment Share on other sites More sharing options...
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