Fixing fuel guage

Disclaimer: Links on this page pointing to Amazon, eBay and other sites may include affiliate code. If you click them and make a purchase, we may earn a small commission.

TheBus

New member
Joined
Jul 10, 2011
Messages
21
Reaction score
0
My fuel gauge was having intermittent problems reading correctly, and lately has been stuck on empty. So I pulled the sender harness off the tank to check it out. Harness disconnected and key on, it will peg the gauge past full. When I reconnect the harness and key on, it goes back to empty. So apparently the gauge is functioning ok... I have three wires going into the harness. A pink positive coming from the fuel relay (to power the in tank pump?), a yellow sending (positive?) wire coming from the gauge, and a black chassis ground. If I jump the yellow and black with the key on, it should return the gauge back to empty correct? What's my next step besides dropping the tank to inspect the sender unit?

I have read that the float can develop a hole and fill with fuel causing it to sink. The tank has been replaced twice since new due to rust (in the family since 87!) I'm not sure if the sender was ever replaced though

 

Seabronc

New member
Joined
May 22, 2004
Messages
7,315
Reaction score
35
Location
North of NYC
Here is a way to check the calibration of the gauge: With the connector off and key on, a 22 ohm resistor between the two leads should give it a mid scale reading, a 73 ohm resistor should put the needle on E, and a 10 ohm resistor should put the needle on F. To check the gauge, check the resistance across the gauge, it should be between 10 and 14 ohms. Also check the voltage across the connector, it should read 5 volts. Bad connections, and grounds can also be a problem, especially the engine to body and engine to frame ground. Clean the connections for the battery to engine and frame grounds, clean the connection from the intake manifold (driver side) to the fire wall.

Good luck,

peace.gif


 
Last edited by a moderator:

Bebop Man

Member
Joined
Dec 26, 2007
Messages
257
Reaction score
1
Location
Rapid City, SD
Here is a way to check the calibration of the gauge: With the connector off and key on, a 22 ohm resistor between the two leads should give it a mid scale reading, a 73 ohm resistor should put the needle on E, and a 10 ohm resistor should put the needle on F. To check the gauge, check the resistance across the gauge, it should be between 10 and 14 ohms. Also check the voltage across the connector, it should read 5 volts. Bad connections, and grounds can also be a problem, especially the engine to body and engine to frame ground. Clean the connections for the battery to engine and frame grounds, clean the connection from the intake manifold (driver side) to the fire wall.
Does this work for all model years? The reason I ask is in my '86, I replaced the sender + in-tank pump, but the only one I could find was from an '87. My gauge now reads backwards, ie E=full, F=empty. In fact, my gauge doesn't even move off the E until I'm down to about 1/4 full.

 

Seabronc

New member
Joined
May 22, 2004
Messages
7,315
Reaction score
35
Location
North of NYC
Does this work for all model years? The reason I ask is in my '86, I replaced the sender + in-tank pump, but the only one I could find was from an '87. My gauge now reads backwards, ie E=full, F=empty. In fact, my gauge doesn't even move off the E until I'm down to about 1/4 full.
It should work on your truck, but if it reads backward, the wires are reversed. I think you can get that connector on backward.

Good luck,

peace.gif


 
OP
OP
T

TheBus

New member
Joined
Jul 10, 2011
Messages
21
Reaction score
0
Here is a way to check the calibration of the gauge: With the connector off and key on, a 22 ohm resistor between the two leads should give it a mid scale reading, a 73 ohm resistor should put the needle on E, and a 10 ohm resistor should put the needle on F. To check the gauge, check the resistance across the gauge, it should be between 10 and 14 ohms. Also check the voltage across the connector, it should read 5 volts. Bad connections, and grounds can also be a problem, especially the engine to body and engine to frame ground. Clean the connections for the battery to engine and frame grounds, clean the connection from the intake manifold (driver side) to the fire wall.

Good luck,

peace.gif
Thank you for the correct resistors to test it with. Do you know which of the three wires are ground? The harness is molded rubber and its hard to tell them apart. Two of the connectors are silver and one is golden colored. I'm getting around 8v on two of the terminals on the harness side. Resistance is 3ohms. Both with key on. I was unable to find continuity between any of the wires to the frame. I did find a bad ground strap about behind drivers side front tire running from the body to chassis. I'm sure that's not helping things either.

IMAG0057.jpg

 
OP
OP
T

TheBus

New member
Joined
Jul 10, 2011
Messages
21
Reaction score
0
I figured out the harness pins, however my resistor test was different than the values provided. 68 ohms - half tank, both 10 and 22 ohms showed empty on the guage. Reading 8.6v at the harness. So my readings where the inverse of the provided values. With the harness disconnected (open circuit) the gauge pegs well past full, with the harness connected to the sender the gauge will go back to empty.

Thats kinda funny bebop man has the issue with the gauge reading backwards. I have heard the 87 model year was kinda the ba$**** child. Most of the parts that show online for the 87 year look like the 86 and previous model years. Mine is fuel injected and I think it was the first year they converted over to EFI.

 

Bebop Man

Member
Joined
Dec 26, 2007
Messages
257
Reaction score
1
Location
Rapid City, SD
I figured out the harness pins, however my resistor test was different than the values provided. 68 ohms - half tank, both 10 and 22 ohms showed empty on the guage. Reading 8.6v at the harness. So my readings where the inverse of the provided values. With the harness disconnected (open circuit) the gauge pegs well past full, with the harness connected to the sender the gauge will go back to empty.

Thats kinda funny bebop man has the issue with the gauge reading backwards. I have heard the 87 model year was kinda the ba$**** child. Most of the parts that show online for the 87 year look like the 86 and previous model years. Mine is fuel injected and I think it was the first year they converted over to EFI.

1986 is the first year for the FI 302. In 1987, the 351 FI showed up. But I run into that a lot, so now when I track parts for an 86 302, I make sure I specify the FI version. I've gotten some funny looks in the past.

 

nelbur

New member
Joined
Oct 30, 2010
Messages
132
Reaction score
0
I have an '86 302 EFI, and I believe '86 was the first year for the fuel injection. Reading E on the fuel gauge sounds like a sunk float. A bad connection would make the gauge read high as would varnish on your sender from old gas. Dropping the tank is a pain, so when you do, replace the low pressure pump along with the sender, and paint the tank so it doesn't corrode between the skid plate and the tank. An amazing amount of dirt and salt can set up shop in there and **** your tank.

 

Seabronc

New member
Joined
May 22, 2004
Messages
7,315
Reaction score
35
Location
North of NYC
Those resistor values were from an 80-86 shop manual, for checking the gauge and circuit. Where did you get your numbers?

peace.gif


 
OP
OP
T

TheBus

New member
Joined
Jul 10, 2011
Messages
21
Reaction score
0
Which numbers do you mean? I read the voltage and resistance with a multimeter. Resistor test was done with a buddy watching the gauge, while I swapped resistors in the the harness. Any chance you have a 87+ shop manual? I have a feeling I'm going to have to drop the tank to inspect the sender. Not looking forward to it haha.

Nelbur you are right about the mud/salt building up between the tank and skidplate. Mine is on its third metal tank because of this. I found this company called MTS that manufactures polyethylene tanks. Maybe when this one finally rusts out I will replace it with one of these. http://www.mtscompany.com/bronco.htm

 
OP
OP
T

TheBus

New member
Joined
Jul 10, 2011
Messages
21
Reaction score
0
After some seaching I found some information on the gauge resistance...

75-10 Ohms (Ford Type '86 and earlier)

16-158 Ohms (Ford Type '87 and later)

So it seems the 87+ fuel gauges does indeed operate inverse of the 86-. It makes sense now that 68 ohms gave me a slightly below a half tank reading, and the 10 and 22 ohms gave me an empty reading. Going to try a higher ohm resistor just to make sure the gauge is spot on. Then I guess its on to replacing the sender/pump.

Here is the link if anyone is interested: http://www.classicinstruments.com/index.aspx?documentID=fuelgaugesandtank

 

Seabronc

New member
Joined
May 22, 2004
Messages
7,315
Reaction score
35
Location
North of NYC
After some seaching I found some information on the gauge resistance...

75-10 Ohms (Ford Type '86 and earlier)

16-158 Ohms (Ford Type '87 and later)

So it seems the 87+ fuel gauges does indeed operate inverse of the 86-. It makes sense now that 68 ohms gave me a slightly below a half tank reading, and the 10 and 22 ohms gave me an empty reading. Going to try a higher ohm resistor just to make sure the gauge is spot on. Then I guess its on to replacing the sender/pump.

Here is the link if anyone is interested: http://www.classicin...elgaugesandtank


Thanks for that link.

If you find that you may have occasions to get at the fuel sender here is how I solved the problem http://broncozone.co...t-access-panel/ .

Also you may want to invest in an EVTM, http://broncozone.co...acuum-problems/ just make sure it is fro a FSB not a BII.

Also, if you do a search in eBay like "ford bronco shop manual" you will often find a complete set of shop manuals for your year truck. This is not a complete set but good stuff. The complete set includes an Emissions Diagnosis Manual and an EVTM. http://cgi.ebay.com/ebaymotors/1987-FORD-TRUCK-SHOP-SERVICE-MANUALS-BRONCO-F-SERIES-_W0QQcmdZViewItemQQhashZitem4841084b49QQitemZ310328707913QQptZMotorsQ5fManualsQ5fLiterature

They are all well worth investing in if you do a lot of your own wrenching.

Good luck,

peace.gif


 
Last edited by a moderator:
OP
OP
T

TheBus

New member
Joined
Jul 10, 2011
Messages
21
Reaction score
0
Well operation tank drop was in full swing this evening. Everything when pretty well... Only ran into one snag. The high pressure fuel line coming from the sender needs a special tool (I think) to slip the line off the connector. Does anyone know what that's called? Or even better, what size I will need? I'm probably just going to rent on from the parts store when I pick up the sender assembly.

 

miesk5

96 Bronco 5.0
Staff member
Moderator
Joined
Oct 18, 2005
Messages
9,078
Reaction score
1,037
Location
Floating in the Pacific
Last edited by a moderator:
OP
OP
T

TheBus

New member
Joined
Jul 10, 2011
Messages
21
Reaction score
0
Yes I meant the high pressure fuel line running from the in-tank pump. It is a plastic fitting with a white clip running through it. I removed the clip but it didn't want to move. Problem is it doesn't really look like the metal quick disconnects in the video. Maybe it needs to be rotated a certain direction to remove. I'll post a pic of it shortly if I can get a decent shot of it.

 
OP
OP
T

TheBus

New member
Joined
Jul 10, 2011
Messages
21
Reaction score
0
I got the fuel line off. After you remove the white clip, I had to give mine a quarter turn to crack it loose. It was just really stuck on there. That line was actually the fuel return line. It makes sense to have the fitting on there because the return fuel would be pressured by the second high pressure pump. The supply fuel line from the in tank pump doesn't have that much pressure behind it. It was just held on by a worm gear clamp.

So the root of the problem.... A fuel float filled with gas! All that work for such a small part. I tested the sender hooked up outside the tank and the gauge was working beautifully. I went ahead and just replaced the sender/pump assembly because its such a time consuming job with one person. I haven't got the tank fully mounted yet but the gauge should be working now. Thanks for all the help and suggestions guys!

 

Members online

No members online now.

Forum statistics

Threads
22,667
Messages
136,905
Members
25,368
Latest member
digs
Top