Fuel Gauge Pegged Past Full

[husmann]

My 1993 Bronco has a fuel gauge that is stuck past full.

So, for years I had a dead fuel gauge that read "Empty" all the time. Last summer I put a new fuel pump in the tank and replaced the float, that of course had a leak in it. After that, it worked like a charm, it was a true beauty, I just couldn't believe I was driving a truck that had a working fuel gauge, it was like Christmas every day! Then, I went to the self-serve car wash, pressure washed the engine bay and underbody, and then the gauge pegged past full.

When I turn the ignition on, it sweeps to empty, but when the engine is started and running, it always stays past full.

I've done some reading on the Zone and know that it is likely a dead connection or a dead sender.

I checked the Ohms at the tank connection, and it reads 120, which is correct for the amount of fuel in the tank. So I don't think that it is the sender (I could be wrong, but I hope not, cause I've taken that tank off way too many times). It seems that the wire from the connector to the firewall is intact, but I haven't checked it thoroughly. So I decided to check the connections at the instrument cluster. I cleaned the contacts, but no luck, still pegged. I checked the Resistance at the instrument plug for the fuel gauge, but it read 77 Ohms. I will say that the yellow wire that coincides with the sender did not match up to the contact that goes to the fuel gauge on the instrument cluster contact sheet. This is something I have no explanation for.

Also, I did clean up the ground bolt and wire ends at the front left firewall, just to make sure.

Any thoughts? Should I check the resistance at the connector on the firewall? Is it possible that this could be a bad instrument cluster gauge?

Also, I'm pretty sure that there is not a fuse that goes to the sender, so I haven't checked any fuses. Am I right about that?

I am finally on schdule to get it painted on February 7, which will take my ride to the next level. I figure that a beautiful last gen Bronco should have a working fuel gauge.

Much thanks for any help.

 

[miesk5]

Yo Husman,
Testing in a 92-96 Bronco; "There is a yellow wire with a white tracer coming off the fuel sender to the gauge The easiest way to ck the gauge and wiring is to disconnect the y/w wire and ground the wire on the dash side of the wire. If you can slide your hand up on top of the tank and disconnect the pump and ground out the y/w wire turn the key on and watch the gauge, if the gauge goes up (FULL), suspect; open circuit (broken wire; unplugged connector; corroded terminal; burned sender) on the Y/W wire..." by me at the former FTE site owner by that idiot Ken.

"...the little resistive strip in them gets bad and causes erratic readings. Also, while you are at replacing it, check out the connector to make sure the ground is good back to the battery.
Source: by our late friend and Moderator Seabronc (Rosie, Fred W) at Ford Bronco Zone Forums

Testing in a 92-96; from 96 EVTM; "...With the sending unit float arm in the empty stop position, resistance should be 15 ohms (below E). With the sending unit float arm in the full stop position, resistance should be 160 ohms (above F). The fuel gauge should read empty at 22.5 ohms and full at 145 ohms..." by me







Testing & Connector Pin-Outs in 92-96 Bronco; Sender Range: Full = 160 Ohms; Empty = 16 Ohms; "... gauge that pegs past full indicates an open circuit (broken wire; unplugged connector; corroded terminal; burned sender) on the Y/W wire. gauge that pegs past empty indicates a short to ground (pinched to the frame, body, or dash supports) on the Y/W wire, OR a sunk float. gauge anywhere in between that doesn't move indicates an open circuit (blown fuse; corroded terminal) on the power (battery) side of the gauge OR a bad instrument cluster ground at C251 pin 9. The terminals of C251 (& C250) are known to corrode & lose contact. Polish both the connector pins AND the film circuit pads with brown paper or a pink eraser. The larger version of C441(WPT454) was used until 93. The level sender can usually be disassembled & repaired by bending the wiper arm inside the plastic housing to apply slightly more force..."

 

[husmann]

Thanks for the help miesk5. I failed to mention that I had gotten as far as I had before my post by reading yours and other posts on these tricky fuel gauge issues.

So, I grounded the Yellow/white fuel sender wire from the instrument panel side of the fuel tank quick connector, and the fuel gauge read below empty. My conclusion is that the wire and connections from that connector all the way to the fuel gauge are intact, and that the fuel gauge is working properly.

Does this mean that the most likely source is a bad fuel sender? Is there anything to the possibility that this could be related to pressure washing the undercarriage, or is it just coincidence?

Thanks again for any help.

 

[miesk5]

Yo Husmann,
Yes the spraying could be the Perpetrator.
Gauge that pegs past full indicates an open circuit (broken wire; unplugged connector; corroded terminal; burned sender) on the Y/W wire.

 

[Tiha]

I have added a ground to the tank to fix this problem. Maybe try that first.

That diagram is great but it shows the fuel pump ground and the sending unit connected and I don't think that is actually the case. Been a while but I think the sending unit grounds through the tank itself through mounting brackets and straps. They corode over time.

A quick test is just a wire or allegator clip, clean a spot on the ****** of the tank, then clamp it onto a clean spot on the frame.

 

[miesk5]

Yo Husmann,
As Tiha advised, however, I feel issue is a result of the pressure washing.
Tech Tip Guide, General; "...Many times, the Ford fuel pump hanger/sender assemblies are frequently found with extensive corrosion on the cover and on the metal tubes. Over time, the terminals can loosen and cause intermittent loss of continuity. Erratic reading of the fuel sender level is one of the other problems that could occur..." by spectrapremium.com

 

[sinker4]

I had a similar problem. I checked the ohms reading coming from the sender at the connector closest to the tank then I filled the tank and checked again, there was no change so I had to change the pump/sender unit. This can be done without dropping the tank by cutting the floor over the sender. this is much easier than dropping the tank. Here is the link by steve83

1983 Ford Bronco Bronco Fuel Pump Access Hole pictures, videos, and sounds | SuperMotors.net

37 pics, videos, and sounds

www.supermotors.net

 

[husmann]

Hey guys. Thanks again for the tips. I've taken a few days break on this issue, but I had a brainstorm that I'm gonna try before dropping that tank again. I have been wondering about the integrity of the quick connector at the fuel tank, but rather than just replacing it, I'm going to get a few of those quick connect wire splicers and bypass the connector only on the Yellow/White wire. If that fixes it, then I know I should wire in a new connector. That would also make sense with the pressure washing. I'll get back to you after I get a chance to do it.

Tiha, I'll try a temporary ground from the tank to the frame, but when I had the tank out last summer, I OCD cleaned it and the surrounding frame, so it should have a good ground.

 

[husmann]

I got it to work, but it's not fixed!!!

I tried the procedure I mentioned in my last post, but the fuel gauge was still pegged. Then I left the bypass wire in place on the Yellow/White wire, and disconnected the fuel tank 4-prong connector, and the fuel gauge read and functioned correctly. Then I cut the Yellow/White wire on either side of the 4-prong, left the bypass wire in place, and plugged in the 4-prong: it stays pegged past full just like before.

I have no idea what is going on, but here's what I do know;
1. The fuel gauge in the instrument cluster works fine.
2. The fuel sending unit SEEMS to be working just fine.
3. The integrity of the Yellow/White wire from the sender all the way to the fuel gauge is fine.
4. I am not dealing with an abnormal ground that would peg the gauge below empty.

I'm stumped, but I'm not giving up.
Could this still have something to do with the 4-prong tank connector?
Could it still be some sort of grounding problem?

I got a "D-" in "How to fix electrical stuff on automobiles" class, so any help is greatly appreciated.

 

[johnnyreb]

My 1993 Bronco has a fuel gauge that is stuck past full.

So, for years I had a dead fuel gauge that read "Empty" all the time. Last summer I put a new fuel pump in the tank and replaced the float, that of course had a leak in it. After that, it worked like a charm, it was a true beauty, I just couldn't believe I was driving a truck that had a working fuel gauge, it was like Christmas every day! Then, I went to the self-serve car wash, pressure washed the engine bay and underbody, and then the gauge pegged past full.

When I turn the ignition on, it sweeps to empty, but when the engine is started and running, it always stays past full.

I've done some reading on the Zone and know that it is likely a dead connection or a dead sender.

I checked the Ohms at the tank connection, and it reads 120, which is correct for the amount of fuel in the tank. So I don't think that it is the sender (I could be wrong, but I hope not, cause I've taken that tank off way too many times). It seems that the wire from the connector to the firewall is intact, but I haven't checked it thoroughly. So I decided to check the connections at the instrument cluster. I cleaned the contacts, but no luck, still pegged. I checked the Resistance at the instrument plug for the fuel gauge, but it read 77 Ohms. I will say that the yellow wire that coincides with the sender did not match up to the contact that goes to the fuel gauge on the instrument cluster contact sheet. This is something I have no explanation for.

Also, I did clean up the ground bolt and wire ends at the front left firewall, just to make sure.

Any thoughts? Should I check the resistance at the connector on the firewall? Is it possible that this could be a bad instrument cluster gauge?

Also, I'm pretty sure that there is not a fuse that goes to the sender, so I haven't checked any fuses. Am I right about that?

I am finally on schdule to get it painted on February 7, which will take my ride to the next level. I figure that a beautiful last gen Bronco should have a working fuel gauge.

Much thanks for any help.

Havw you thought about the NEXT time you drop the tank. MARL UNDER THE FLOOR ARE and cut it out Make a door with the cut out part(a little bigger so you can work with the wires ,sending units and gas hose). Seabron gets the credit for it. It makes it alot easier to work with. Then dropping the tank.. Good luck

 

[Bass2Mouth]

I just went through a very similar issue on my 91. Gauge was working fine for a while, then one day I noticed it pegged past full. I had been restoring the rig and only putting around 1-3 gallons of fuel into the tank at a time as I was planning to drop the tank and replace the fuel pump anyways.

I dropped the tank this past weekend and found that the float/sending unit plastic bracket had disengaged from the metal bracket that holds it in place against the metal fuel line. After reattaching, the gauge was reading without issue. Guess the entire float assembly was just literally "floating" or resting on the gas tank floor so it was reading full all the time. Or open circuit since the metal contacts for the float in the plastic bracket were not mated to metal bracket.

I'm think that running like 3 gallons in a 33 gallon tank was just letting the float bounce around violently and separate from the bracket as I drove it through the pasture to the shop.

I know this info doesnt really help as you still will need to drop the tank to check, but the behavior you are seeing was very similar to what I was seeing. I should have used some kind of sealant to keep the brackets mated, but I guess I will save that for next time haha.

 

[johnnyreb]

I just went through a very similar issue on my 91. Gauge was working fine for a while, then one day I noticed it pegged past full. I had been restoring the rig and only putting around 1-3 gallons of fuel into the tank at a time as I was planning to drop the tank and replace the fuel pump anyways.

I dropped the tank this past weekend and found that the float/sending unit plastic bracket had disengaged from the metal bracket that holds it in place against the metal fuel line. After reattaching, the gauge was reading without issue. Guess the entire float assembly was just literally "floating" or resting on the gas tank floor so it was reading full all the time. Or open circuit since the metal contacts for the float in the plastic bracket were not mated to metal bracket.

I'm think that running like 3 gallons in a 33 gallon tank was just letting the float bounce around violently and separate from the bracket as I drove it through the pasture to the shop.

I know this info doesnt really help as you still will need to drop the tank to check, but the behavior you are seeing was very similar to what I was seeing. I should have used some kind of sealant to keep the brackets mated, but I guess I will save that for next time haha.

What you saw was ETHANL GAS eating the metal bracket. ethanl gas is THE WORSE THING YOU CAN PUT IN ANY GAS TANK. Take some and put it in a clear pop bottle. Put it on a shelf and check in in a week of two. It looks like tar in the bottom. It will eat the metal float arm in the tank. I had it do the same thing in my bronco. Start using 100 % gasoline if you can. I drive 10 out of my way now to get it

 

[paul rondelli]

I just went through a very similar issue on my 91. Gauge was working fine for a while, then one day I noticed it pegged past full. I had been restoring the rig and only putting around 1-3 gallons of fuel into the tank at a time as I was planning to drop the tank and replace the fuel pump anyways.

I dropped the tank this past weekend and found that the float/sending unit plastic bracket had disengaged from the metal bracket that holds it in place against the metal fuel line. After reattaching, the gauge was reading without issue. Guess the entire float assembly was just literally "floating" or resting on the gas tank floor so it was reading full all the time. Or open circuit since the metal contacts for the float in the plastic bracket were not mated to metal bracket.

I'm think that running like 3 gallons in a 33 gallon tank was just letting the float bounce around violently and separate from the bracket as I drove it through the pasture to the shop.

I know this info doesnt really help as you still will need to drop the tank to check, but the behavior you are seeing was very similar to what I was seeing. I should have used some kind of sealant to keep the brackets mated, but I guess I will save that for next time haha.

Also remember that the fuel level is keeping the pump cool. If you only keep a few gallons in the tank it will not cover the pump and it will run hotter than when covered.

probably not that big of a deal … for a factory pump that can last 15 years … but these cheap after market pumps are not the best anyway.

 

[goodO1boydws]

When you first turn the key to ON, it sweeps to empty-which is about what it should be, with only a couple gallons in the tank.
But as soon as the engine is actually running it STAYS pegged past full.

In other words when the gauge is only getting BATTERY voltage it seems ok, but when the engine is running and the alternator is now charging the battery with a higher voltage, the gauge stays pegged.

That's what would be happening with a faulty voltage regulator, allowing too high of a voltage through to the gauge.
Fords used to have 2 voltage regulators-the main one, either attached to the alternator of mounted separately, and a secondary one, which was usually hidden under the dash.

If you have a hand held voltage meter, check the voltage across the battery with the engine running. With the main voltage regulator working properly it should never read more than about 15.5v MAX. (on newer vehicles its even lower) If the main regulator is NOT working properly it can get as high as about 18 volts as the engine revs up.

The one under the dash was very small and had only 2 terminals. One for connections in and one out. It was specifically to limit voltage for the instrument cluster LIGHTS to keep from prematurely burning out bulbs. (This is in addition to the dimmer control.)

I don't know if the instruments themselves were also being protected by that same device, or possibly by a similar one.

If you do find one of those, try taking voltage readings there when the IGNITION is ON but with the engine NOT running, and also when it is. If THAT device is working properly, the voltage reading coming out of it should be lower while the engine is running than the voltage coming in.

I think they were used up though at least the early 1990 in cars, but may have been used longer in trucks.

I don't know if the instruments themselves were also being protected by the same device or by a similar one.

Here's a link to what those look like:

Instrument Cluster Voltage Regulator for 1971-86 Ford Trucks and Cars | Dennis Carpenter Ford Restorations

Instrument Cluster Voltage Regulator 1971-86 Ford Trucks Cars 1971 1972 1973 1974 1975 1976 1977 1978 1979 1980 1981 1982 1983 1984 1985 1986 Thunderbird Econoline D1AZ10804A

www.dennis-carpenter.com

One last thing.
If it is a generalized voltage regulation problem, and if you have them (working) other electrical gauges would likely be acting off too.

 

[johnnyreb]

Yo Husmann,
Yes the spraying could be the Perpetrator.
Gauge that pegs past full indicates an open circuit (broken wire; unplugged connector; corroded terminal; burned sender) on the Y/W wire.

I remember on my old 71 Dodge pick-up. I hose inside on the cab and that night driving back to Norfolk,VA . When I put the lights on high beam--the gas gauge would go up.

 

[goodO1boydws]

I found this tread ab a 1979 Bronco with the same problem as yours, which may be of help.
In it someone states that the voltage should be about 5V to the gas gauge..

1979 F Series/Bronco Fuel Guage - Ford Truck Enthusiasts Forums

1973 - 1979 F-100 & Larger F-Series Trucks - 1979 F Series/Bronco Fuel Guage - Hi guys, My fuel gauge isn't working and I'm hoping one of you could help. So, when I bought my truck it had the sender unit disconnected with wires hanging. I have replaced the sending unit, along with the tank. I...

www.ford-trucks.com

 

[chrlsful]

didnt read the 16 posts. Once I swapped the 2 polls & got this symptom. Can U switch the 2 wires to opposite. Have U? Quick easy.
Sure the ohm sender/guage are matched? ie correct order/part for replacement (last wrk done - the guage replaced or the sender...