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Tanks out, now what


hekdic

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I finally got the tank out and I ordered a pump and sending unit. The pump works with a few little mods but the sending unit is just backwards to my Toyota so I'm sending it back. The linear pot was backwards so it was reading opposite of what the gage said. My tank is overall, 37"x15"x13" high. Is that the 17 gal tank or the 12. There was a little over 12 in it and I thought it was nearly full but I found that the hose to the tank was rotten and was probably leaking so maybe my tank isn't as big as I thought. I'm not all that worried whether the sending unit is all that accurate as long as it will fit and be relative and not cost an arm and a leg. I'd appreciate any ideas on sources.

Dick

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Thanks for the info on the tank. Is there any chance to find a replacement fuel level sending unit for it for any reasonable price? I ordered what was said to be one that would work with a change to the connector for $35 but when it came the resistor was backwards and when I tested it before doing anything to it, it read full with the float down and empty when the float was up.

Dick

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Calibrate the gauge. Just bend the float arm a bit so that it will barely touch the bottom of the tank when it empty. OR maybe just a bit off the bottom just in case.

That way you will know how much gas is left and wont have to wonder if there is any gas left when the gauge is down to E

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  • 2 weeks later...

The variable resistor on this sensing unit, which is mechanically connected to the float shows empty when the float is all the way up. Since it's a mechanical relationship, I don't see how changing wires will make any difference. I'm sending it back for credit and am looking for one that is compatible. If I can't locate one for a reasonable price soon, I'll just cap the tank with the old unit and go back to writing down the mileage and refilling every 100 to 150 miles like I have for several years. It's no big deal but I thought I'd just fix it when the pump went.

Dick

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YOU ARE DEALING WITH D C TYPE POWER somtimes reversing polarity can make a difference FOR GOOD OR BAD.

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Yes reversing the wires at the connector is easy and should solve the problem. One wire is the high resistance end of the sensor and the other is the low resistance end. Just give the gauge what it wants for a full tank.

Between pins 1&3 you should have less than 5 ohms when "full" and 110 ohms when "empty"

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In an earlier post, I had identified that the potentiometer was reversed from what Toyota wanted. That's a mechanical problem not electrical. Just to make sure I went out and tested it with reversed leads and sure enough, it still read backwards. I'm still looking for something that is easily modifiable to work if anybody has found such.

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soory that did not help do you have a napa store near where did you get that unit or do you have car quest

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The part is a dealer only part. The dealer here wants $186 for one and he will order it. There is a place that will rebuild yours and they say that it runs about $75 to $150 depending on what they have to do. My sending unit has been out for several years and we just keep a notebook and a pen handy and write down the mileage when we refuel and then stop again when we have gone about 100 to 150 miles. It's about potty time then anyway. Since I had the tank out for the fuel pump, I was going to fix it also. For reference if anybody needs it, here is the rebuild info:

http://tristarrradiator.com/index.html

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i understand i am on retirement myself i just paid 200 dollors for a door lock dodge car sealed eltric lock unit dealer only and a lot of plastic

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I've just disassembled mine and found that the linear potentiometer is good. A little diluted muratic acid took out the rust and scum that was keeping the ground from being completed and with a little work on the wires I'll be good to go. I had planned to spend the weekend on other things but for 200 bucks, it's probably worth it.

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Just for grins and giggles, if you haven't returned the new one. Take a ohm meter and measure your old one vs the new one. See if the reading are reversed.

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They are reversed. The original goes a little higher in ohms on the one end. I didn't try to repair it at first because it didn't read anything and was so corroded that I figured it was toast. With the handling of it during this time, some of the corrosion fell off and I could see that it was just tabbed together in 3 places. Working those loose showed me the interior and when the resistor was good, I can fix the rest. The path to ground was compromised by corrosion but the acid cleared that out. I'll get a few more years out of it and I can always go back to a notepad and pencil to keep track of fuel burn.

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Thanks to everybody for their help. I'm not looking forward to putting the tank back in because the access is really bad and the fuel hose to the line to the engine will be the worst. I'm really sorry that I didn't pursue cutting in from above. Fixing the floor above and any wires that I might cut would have been a snap compared to this.

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Before I got talked into taking t;he tank out, I measured everything that I could to try to figure out what I might run into. There is about a 2 inch gap between the inside floor and the lower base of the RV. What is inside that gap is a mystery. I ran a studfinder all around the area that I was planning to cut and got very anomalous results. No clear open space right around where I would need to cut the opening. No way to determine if any structural members or wiring were there. Conquest was of absolutely no help. Once it goes out their door, tough luck. That's why I got talked into taking the tank out. Friends here said it was just a half hour job. That might be true for the average pickup but because on the RV all the fittings were right in the area of the rear axle and springs, access is a yyyy and of course since it is over 20 years old, hard to get started. I needed a cheater bar on everything.

To get to both the sender and pump would take about an 18" square hole which would interfere with the cabinetry and probably structure. Just the pump would take about 10" which might be doable. It might take more because the pump needs to be maneuvered just so to get it out and so does the sender. There is enough room between the tank and the bottom of the RV that the floor can be cut with care. A right angle die grinder with a cutoff wheel would do it easily for whatever that bottom layer is. I think it's just an aluminum sheet. At it's age and with a new fuel pump, I doubt that anybody in the future will need to get in there before it is salvaged. Right now I'm not asking for more work. I'm pretty sure it will outlast me.

For those that suggested I just switch wires, it's which direction the wiper on the variable resistor moves and that's a mechanical problem, not an electrical one. The gauge is expecting the opposite resistance. And the wiper is electrically grounded through both a ground wire and the tank structure to the frame and switching wires in the finished installation would just show a dead short and blow a fuse when you turned on the ignition.

Dick

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  • 2 months later...

Newbie here, I hope to learn from your fuel tank experience. 1987 21 ft Toyota Sun Rader with non working fuel gage. Repaired coroded wires but still not working. What would you suggest be the next step?

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For those that suggested I just switch wires, it's which direction the wiper on the variable resistor moves and that's a mechanical problem, not an electrical one. The gauge is expecting the opposite resistance. And the wiper is electrically grounded through both a ground wire and the tank structure to the frame and switching wires in the finished installation would just show a dead short and blow a fuse when you turned on the ignition.

Dick

Reversing the connections on the sending unit changes absolutely nothing and it has nothing to do with AC, DC, etc. It is a wire-wound variable resistor and the resistance in ohms is the same regardless of direction or polarity. The sending unit has two wires and they give the same result regardless of which way you hook them. If you have a 3rd wire - it's a resistor "tap" to power a "low fuel" light. Just check with a $5 ohm-meter. Full needs NO resistance - just like when you short the two wires together. An "empty": reading needs 90-100 ohms resistance. The Japanese ohm-range is different from USA stuff except Jeep comes close. It's as simple as 0-ohms is full and 100 ohms is empty. 45-50 ohms is "half tank."

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Newbie here, I hope to learn from your fuel tank experience. 1987 21 ft Toyota Sun Rader with non working fuel gage. Repaired coroded wires but still not working. What would you suggest be the next step?

The two most common problems are - a bad sender or a bad tank ground. Have you verified the tank is grounded? If you disconnect the wire harness from the tank the gauge should read empty. If you tie to the two sending unit wires together the tank should read full. If you do NOT get those results - then you got problems inside the truck cab electrics somewhere and it's not the tank, sender, or ground. That can get more complicated. Most trucks use a small voltage regulator inside the dashboard that gives low power to the fuel gauge. Usually 5-6 volts.

If you get real frustrated you can buy a complete universal gauge-sender kit and install it. Often less then $50 but the fuel gauge will no longer be in your dash.

I bought a bunch of new kits from JC Whitney a few years ago at $40 each. I've got them in several tractors and just put one in my 1978 Toyota for the aux. tank. Prices have gone up though. Here is one example. Works in any fuel tank 4" to 24" deep.

http://www.amazon.com/dp/B0000AYJO6/ref=asc_df_B0000AYJO62366626?smid=ATVPDKIKX0DER&tag=dealt784-20&linkCode=asn&creative=395093&creativeASIN=B0000AYJO6

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Here are some fuel gauge sending unit specs for autos/trucks.

0 ohms empty-30 ohms full (GM Type '64 and earlier)

0 ohms empty-90 ohms full (GM Type '66 and later)

75 ohms empty-10 ohms full (Ford and Chrysler Type '86 and earlier)
16 ohms empty-158 ohms full (Ford Type '87 and later)

90 ohms empty-0 ohms full (Toyota and Nissan)
240 ohms empty-33 ohms full (standard aftermarket like Stewart Warner)
10 ohms empty - 180 ohms full (VDO gauges)

My 1978 and 1987 Toyota pickups use a fuel level senders that works as thus: Full - 3 ohms, 1/2 full - 33 ohms, empty - 100 ohms.

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Thanks. I get my rig back from the shop tomorrow. Good information.

I just got looking at a replacement sending unit for an 87 Toyota truck. It is set up to work both ways. All depends on which wires you hook to. It has three wires and a three-prong connecting plug. The middle wire is ground. The two outside wires provide two ways to use the sender and one is opposite to the other. If you hook the truck's gauge to the two outside wires - you get the proper ohmage of 90 empty and 0 full. If instead you hook to the red/blue wire on the outside and the middle wire (ground) you get the opposite and it works with 0 ohms with empty tank and 90 ohms for a full tank. Does the sender you got have three connectors or two? Wires on the truck end of the connector should be - yellow with red stripe, yellow with blue stripe, and red with blue "collar" type bars.

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  • 6 months later...

I need your help again. I had other projects come up but now I'm back to the fuel gage, I'm looking closer at the photos you sent. I noticed your sending unit has 3 wires and my new factory unit just has 2. I don't have a Middle wire #3 from the sending unit. I do have a middle wire on the connection. I bought it from my dealer part # 83320-39466 GAGE ASSY, FUEL SN

post-6742-0-35375200-1376235042_thumb.jppost-6742-0-33295000-1376235077_thumb.jppost-6742-0-89795900-1376235108_thumb.jp

the first photo is from the new sending unit, the second is from the harness, the third is the original connector. 4th is the renewed Tank and 5th is the new sending unit. The Tank is grounded and when I tie the two wire together, the gage reads full. My Truck is 1986 my Sunrader is 1987. HELP!

post-6742-0-96338400-1376235538_thumb.jp

post-6742-0-93800200-1376235550_thumb.jp

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I need your help again. I had other projects come up but now I'm back to the fuel gage, I'm looking closer at the photos you sent. I noticed your sending unit has 3 wires and my new factory unit just has 2. I don't have a Middle wire #3 from the sending unit. I do have a middle wire on the connection. I bought it from my dealer part # 83320-39466 GAGE ASSY, FUEL SN

attachicon.gif100_3877.JPGattachicon.gif100_3889.JPGattachicon.gif100_3870.JPG

the first photo is from the new sending unit, the second is from the harness, the third is the original connector. 4th is the renewed Tank and 5th is the new sending unit. The Tank is grounded and when I tie the two wire together, the gage reads full. My Truck is 1986 my Sunrader is 1987. HELP!

If you tie two wires together and your gauge reads full, and when not together the gauge reads empty - sounds like all is fine on the gauge end. Not a 100% valid test but close. When your wires are apart that are over a billion ohms of resistance (more or less infinity ohms). Your fuel gauge is designed to read "empty" with only 90 ohms required. The sending unit is just a variable resistor when moved from one end to the other - simultates what you to when tying wires together - or pulling them apart with increments inbetween.

Put an ohm-meter on whatever sending unit you have - and find which two leads give you 90 ohms when swung to the empty end - and NO ohms when at the other (full continuity). If the sending unit is designed to also power a "low fuel light) there will be a tap in the resistor somewhere close to 80 ohms to warn you when the tank is near empty.

Whatever sending unit you have - you need to determine what the wires actually go to. Some older sending units use the tank for the "ground" connection which is also one end of the resistance loop. If the tank gets a bad ground - the gauge shoots to "full" and stays there. Very common problem in older GM vehicles. Later sending units do not rely on a problematic chassis ground and run both ends of that resistance loop through wires.

I have not seen enough Toyota-type sending units to comment on how many variations there are.

The sending unit I pulled from an 87 Toyota worked on "empty" and "full" but did not work inbetween. That because the windings in the wire-wound resistor were worn out from being rubbed too much. That is the main wear and failure part of a sending unit. A metal bar rubs against the windings at the float moves from empty to full - or bounces as you drive. That rubbing eventually ruins the wires on the resistor.

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Currently, The TWO wire BRAND NEW FACTORY sending unit is installed. Yellow /Red and White/Black wires. The tank is grounded. The gage works. I do have a low fuel indicator light. Am I correct in assuming Toyota sold me the wrong sending unit? It was an exact match to the unit I pulled out. BUT, the unit I removed was modified at the level arm and the wiring was tapped as you can see in my earlier post. They may have sold me an early 86 model when I actually have a late 86 truck.

I have a used 3 wire sending unit I bought on Ebay being shipped. I just don't have the ability to drop the tank myself. Is there a way to make the TWO wire unit work on a Three wire harness?

Maybe the next step is to just get the used 3 wire sending unit, install and test that, and if it all works, sell the TWO wire unit on Ebay.

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Ok. Put the new used 3 wire sending unit in. It worked however, not a correct reading. I always knew to reading would be off since you just can't pair a OME gage with a 26.5 gal after market tank. I estimated I would have 6 gallons left when the gage reads empty. Problem is the Fuel Light comes on at just under 1/2 tank. If I bend or extend the arm down to get a more accurate low reading, I then creat a false full reading. For now, I just won't connect the low fuel light and play it safe knowing when on E I actually have about a 1/4 tank. Any suggestions on getting the float arm to give me an accurate reading are welcome.

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A little experminting is needed. Measure the heigth inside of the tank. Lay your sender on a piece of card board and do some ploting till you get the float travel right.

You might need spmething like a z bend to adjust the full and then change the length to get the empty right

I went all this to get my gauge right.

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Ya Baby, The original installed unit had been modified like that. ANY WAY................ we also discovered the tank vent line was disconnected! That explained the fuel spills I would create at gas stations.

The story takes a twist here. The new/used ebay unit installed with the low fuel light wire now disconnected so it wouldn't come on at 1/2 tank, I tell the shop I'm taking it to the gas station to fill up. I top off the 26.5 gal tank with 14 more gallons up to the point that its in the filler neck. Yea no fuel spill!! Start up it reads 3/4. Ok................ Let's drive around the block to see if it goes to full. Gets up to about 7/8s ok I can live with this. As I start to accelerate from the stop light, the engine starts to hesitate. I hope this is just my imagination. Next light, I get tossed around like a bull rider! WHAT THE F##k!! The hesitation continues but only at certain low speed point on the accelator.

Back to the shop. Could I have over filled the tank? This Forums expert advice is needed again.

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Ok. Put the new used 3 wire sending unit in. It worked however, not a correct reading. I always knew to reading would be off since you just can't pair a OME gage with a 26.5 gal after market tank. I estimated I would have 6 gallons left when the gage reads empty. Problem is the Fuel Light comes on at just under 1/2 tank. If I bend or extend the arm down to get a more accurate low reading, I then creat a false full reading. For now, I just won't connect the low fuel light and play it safe knowing when on E I actually have about a 1/4 tank. Any suggestions on getting the float arm to give me an accurate reading are welcome.

Instead of bending - you need to increase the length of the arm that holds the float. Many aftermarket sending units come fully adjustable with a two-piece float arm.

That float needs to be onj (or near) the bottom when empty and on top when full. If your tank depth is more then OEM, then the float arm must be made longer.

I just put an aftermarket sender in the aux tank of my Chinook with a Jeep fuel tank. Worked out very nicely but the ohm-range did not match Toyota's. So I had to install a different gauge inside the cab.

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This universal sending unit is 0 to 90 ohms which matches Toyota gauges. Just need to verify this one is 0 ohms for empty and 90 ohms for full. Will fit virtually any tank depth in a car or truck. You'd probably have to make a small adapter plate to fit your tank.

http://www.classicparts.com/1931-59-Universal-Fuel-Tank-Sending-Unit-90-Ohm/productinfo/23-522B/#.Ug4deJI3uek

This kit comes with a univeral sender and gauge to match. They can be found for $50 if you shop around.

http://www.westmarine.com/webapp/wcs/stores/servlet/Product2_11151__436784_-1____ProductDisplayErrorView#.Ug4ch5I3uek

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