My truck only accepts 8 gallons after showing empty

[Hectron]

Hello everyone. New to the forum and Rangers. I have recently bought a 1987 4WD Ranger with the 2.9L and 5 speed and LOVE THIS THING!! I’ve noticed that I can only put in about 8 gallons or so of fuel even though my gauge is reading empty. The gauge does go to full after fueling but is clearly not reading correctly. Has anyone else had this issue or know what the fix would be? I’ve done some searching and haven’t been able to find anyone with my same problem. Thanks in advance.

 

[Dirtman]

First thing I would do is make sure the tank doesn't have a huge dent in it...

 

[Hectron]

I’ve crawled all underneath the truck. The tank seemed to be dent free. It also seems like the previous owner has already changed the fuel filter.

 

[Dirtman]

Ok so the guage reads empty, you put only 8 gallons in and it reads full? So couple scenarios.

A. The tank is somehow only holding 8 gallons, the only way this would happen is if the tank is physically damaged.

B. The guage is reading empty when there is still plenty of fuel in the tank, this would be a problem with the sending unit or the guage itself. You can check the sending unit with a volt meter but damned if I can remeber how @RonD will know.

C. The truck is haunted. Seek an exorcist.

 

[Hectron]

A. Checked for damage-negative
B. The sending unit was my next guess but will have to figure out how to check the volts.
C. That’s just hilarious!

 

[Hectron]

I really appreciate all this help. You all are great

 

[09fx4guy]

You can check the sending unit for a problem, that would be most likely. Perhaps the float itself may be going bad. Also, I think some of those earlier Rangers had tanks that were not very large to begin with (guys more experienced in earlier Rangers could confirm).

Less likely, there is something in the tank that is taking up space of gasoline. I had heard a story about smugglers using fuel tanks to store stuff, which could be displacing space in the tank.

(I'm leaning more towards bad sending unit)

 

[Dirtman]

Though finding a stash of drugs in your fuel tank would definitely be more interesting...

 

[franklin2]

You should have a 16 gallon tank I believe. Usually tanks have about a 3 gallon reserve, so if you can get 13 to 14 gallons in it, you were basically empty.

My sending unit was giving me problems, so I decided to track the fuel by mileage manually, which I thought would be a pain with ink pens and paper and some math. But I have a trip odometer. If you have a trip odometer, it's very easy and I actually was debating about not fixing the sending unit.

I had a 86 4x4 5 speed, much like your truck. I used it on a routine drive to work, and I had checked the mileage before and was getting close to 15-20mpg. So I figured I could go 250 miles after I filled it up. So after filling to the top at the station, I reset the trip odometer and drove it till I was near 250 miles. Went to the station and filled it up again, and it only took about 12 gallons to fill. So that told me I was getting closer to 20 mpg, so I reset the trip odometer to zero again and stretched it to 275 miles. Then reset and drove again at found 300 miles was close to the limit and still have a few gallons left in the tank.

After you get your fuel usage figured out, it's very easy and becomes habit to glance down at the trip odometer to see how much fuel you have. You do have to get in the pattern of resetting the trip odometer at the fuel station. I did forget once in awhile, so I would just double the numbers and make sure I didn't go over 600 miles instead of 300 miles.

 

[09fx4guy]

You should have a 16 gallon tank I believe. Usually tanks have about a 3 gallon reserve, so if you can get 13 to 14 gallons in it, you were basically empty.

My sending unit was giving me problems, so I decided to track the fuel by mileage manually, which I thought would be a pain with ink pens and paper and some math. But I have a trip odometer. If you have a trip odometer, it's very easy and I actually was debating about not fixing the sending unit.

I had a 86 4x4 5 speed, much like your truck. I used it on a routine drive to work, and I had checked the mileage before and was getting close to 15-20mpg. So I figured I could go 250 miles after I filled it up. So after filling to the top at the station, I reset the trip odometer and drove it till I was near 250 miles. Went to the station and filled it up again, and it only took about 12 gallons to fill. So that told me I was getting closer to 20 mpg, so I reset the trip odometer to zero again and stretched it to 275 miles. Then reset and drove again at found 300 miles was close to the limit and still have a few gallons left in the tank.

After you get your fuel usage figured out, it's very easy and becomes habit to glance down at the trip odometer to see how much fuel you have. You do have to get in the pattern of resetting the trip odometer at the fuel station. I did forget once in awhile, so I would just double the numbers and make sure I didn't go over 600 miles instead of 300 miles.

I did this on my first truck, a 92 Explorer when I was in high school & college. My dad told me the trip meter trick. If I ever went over 200, I knew I had to put gas in (this was all city driving).

If you have the time and inclination to drop the tank and take a crack at it, by all means go ahead. But if it were me, I would leave it go until at least the spring / summer when it is not cold as H-E-double hockey sticks.

 

[RonD]

1987 Ranger uses the older Ford sender and gauge
73 ohms = empty
10 ohms = full

Ohms is resistance, in this case its resistance to Ground

If there was any corrosion on a sender wire then resistance goes UP
Or if sender had more resistance over time(older)

If either happens then gauge would go to empty sooner because of this higher resistance

You can pull out the cluster and test the yellow/white wire that runs to the sender in the tank, test with ohm meter
Or pull up the bed and test at the gas tank, this way you could test BOTH wires, the yellow and the black ground wire for the sender, and you can test sender itself

 

[franklin2]

If you can get to the top of the fuel tank and unplug the wires, you can also turn the key to run, engine can be off, and take the yellow/white wire and ground it. Then take if off ground and let it hang in the air. The gauge should swing full scale back and forth each time you do this. If it passes this test, the sending unit is at fault.

 

[JerrySab]

I have the exact same issue! Usually 8-10 gallons per refill. Goes from empty to full on gauge.

I've replaced in-tank and inline pump; can confirm the sending unit is functioning at proper range. Replaced vent valve and gasket. Replaced filler hose, which I thought might have been too short/filling with fume before the tank fills with gas, thus triggering shut-off.

I bought the truck with nonfunctional gas gauge. replaced with new pump, it only showed half full after refill of, yep, 8-10 gallons. thinking I damaged the float arm while installing, I replaced it with a new one. Now I have full range but still only 8-10 gallons.

I have 2 hypotheses as to why this is happening - only 1st one explains full range of gauge but limited fueling.

1. New in-tank fuel pumps have slightly different float arms and bouys.. different shape, different material. which may have different bouyancy dynamics than the resistance range in the sending unit.

2. Current pumps at gas stations have gaskets that cover the filler neck vent, so air is trapped no matter how you maneuver it. And the damn things gush gas so fast, the problem is exacerbated. Sometimes I pull back the pump gasket and find I can get another 2 gallons in after first click. But I also am not interested in soaking myself with gas by ignoring the shut off, so I give up.

 

[franklin2]

On #1. It would not surprise me if China is making the sending units wrong. Every manufacturer needs quality control and whoever orders and distributes these things do not seem to care about that.

On #2, I would carry a 5 gallon gas can with me, and do the mileage thing. It seems like you do not know if the tank is really full, or you have a filler problem. If when the gauge reads empty you can keep driving for over 150 miles, then you know the gauge is really wrong and the tank had a lot of fuel in it. if it quits on you after 50 more miles then you know the gauge is correct, and you do have another problem.

 

[Eddo Rogue]

A gas can, motorcycle loading ramp, and ice chest is always in the truck bed.