While driving to day the gas gauge went to over full. It’s about 3/4 and was reading that when I left home. It shows empty when the ignition is off. The tank unit was replaced 9 years ago.. any thoughts before I start into it. With the added AC panel it’s tougher to get to the gauge…
Thanks, I started there. Tank and wire both show good grounds. I also removed the ground and jumper to frame no change. When key on.. pegged needle pst full. Listed testing results: Wire from gauge disconnected at tank sender> 126.6 ohms to ground. Wire from gauge disconnected at tank sender with key on> 13 VDC Fuel sender to ground 110.8 ohm. with 3/4 tank. Ford Manual has a gauge check with a flash light battery which would be difficult for me to do. tomorrow I am going to remove the sender (when I can vent my garage properly) mount it to a block of wood where I can set the float at different spots and see what that does. I may post this on the blocks forever page also. Some here read it but a lot over there do not visit the HAMB site..
Use the list @Tanks inc to verify the stock sending units range, but I believe it is 73-10 here's a link, which also has a troubleshooting guide for the gauges/senders https://www.tanksinc.com/index.cfm/page/ptype=results/category_id=159/mode=cat/cat159.htm
I might be wrong but my 55 goes to past full when I turn the key off and I have been told the 56 was the only 12Volt Ford that did that as well? (you would know) You said yours goes to empty with the key off so I might be wrong.
Just to add to my ignorance I went looking for the post I found when I was looking to convert my 55 to 12 Volts and it was suggested I use a 56 gauge and change the face. The 56 gauge is actually 12 volts where the 57 and later are 6 volts with a voltage regulator (AKA constant current source) but I found this post and decided that would not work. The 56 gauge (and my 55) use a weird setup according to this information, I did the conversion and used the later model voltage regulator, the gauge works but it is not accurate. Read through this post I attached, I believe it is accurate information. http://forums.y-blocksforever.com/Topic73004.aspx
Thanks for everyone’s input. I’ve thought about my few tests and feel the wire from the gauge to the sender is not grounded since it show full battery voltage. I’ll show the illustration in my Ford manual that with the key on there should be 12 volts to the sender. The full 12 volts may also not be correct because it’s reading thru the gauge heating coil but with no load disconnected it maybe fine. This morning I’m going to remove the float and sender; since it reads 100 ohm to grd already that’s a clue too. Not sure but since it’s over 70 I wound it would be under empty on the gauge and not the other way…I might search for and original also. I’ll get back for sure…
Ok, here’s what I have so far. Removed the sender and checked the level; it was down about 1” from the top. Went to supplier and the 57 up to 86 is the 10-70 ohm sender. I checked a new 56 sender he had in stock and it had a different resistance than mine its 69 to 265. From their experience in restorations he says it’s **** shoot. They try to get empty correct. Their new one was 42 to 189. I do not know what being in gasoline will do to the resistance. I decided to work with mine and the stops. I have no idea what happened yesterday but @ 7 volts with the key on it reads full, 3/4 is 8.4 …..1/2 is 9.4……1/4 is 10…..11 in on the empty dot. The key off it will go to the peg. None is with the car running yet. I’m guessing with regulated higher voltage I may see a slight change. I’m also going to try the sender aiming forward since the tank is a little thicker. I’ve also bent the stops to get these empty and full readings on the gauge. If this works I’ll have a reference to open the cover in the trunk and take voltage readings. The photo shows my set up, Extra jumper wires were for ground, feed from the gauge and the meter. The bottle is holding a cardboard gasket for the fumes…Hope it all is ok.
Ok I think I found the reason for the over full indication while out driving. It’s the voltage. With the engine running the battery indicates 14.7 and all the readings above are higher that’s neutral with the first choke step on the fast idle. In gear at 600 and turning on the lights moves it down to 14 and the AC on to 13.7 where it matches where I have it set with the stops. I guessing I didn’t have anything wrong. If I would have turned on the lights and AC I’ll bet it would come done.. Oh well learned a lot and it hasn’t been that long since I add an alternator which holds the voltage higher in the battery in general. The gauge may have been staying higher.
Finished. All back together. Most accurate with key on or acc. Voltage definitely makes a difference. Bent the rod to make it shorter. I’m pretty sure it won’t sit on the bottom anymore so I’ll always have some gasoline when it’s on E. If I put 12 gallons in it at 1/4 tank it will be fine. Learned a lot…
my 56 is a standard car,with the ignition turned off the gauge reads 3/4 full....turn the ignition on and the needle drops to the correct level.....while running gauge is pretty accurate. never really bothered me so have done nothing about it other than check all earths
Thank you for sharing everything you found, this system is unlike anything I have worked on in any newer (than 56) Ford I have owned. As I said I have a 55 and converted it to 12 volts with a 64 Falcon gauge voltage regulator, the gas and temp gauges work but both read higher than normal. At key on the temperature gauge reads about 1/3 the way up from the cold peg with the engine cold and the gas gauge reads WAY past full with the tank full but it did this when the car was still 6 volts. I am using a one wire 105 amp alternator so I suspect the higher voltage with the shunt resistor ohms value that is in the sender is causing the high gauge reading. Then again, the previous owner stated he replaced the tank and sender so who knows what he installed at that time. I have not drained the tank to see where the gas gauge drops to when empty but when it was 6 volts I ran out of gas and the gauge showed 1/4 tank. Fun stuff!
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