Fuel Sending Unit / Fuel Gauge Issue (Updated)
 

I'm sorry to keep beating this to death, but it may help someone else in the future. Due to getting ready for the new addition to the family (wife's due with our second this thursday), I haven't been able to do the hutch/harpoon mod yet. I have everything, but the time is the issue.

Well, to be ready (in case a couple hours presented itself) I've been keeping the tank kinda low. It's because of that, I've actually started to run out of fuel twice since I had the initial problem (that I mentioned in "IDM problems"). Fortunately, I have been near enough to a gas station to spit and sputter my way to there to add only another 5 gallons or so.

Here's my question though. Both times I started to run out of fuel, I have shown 1/4 of a tank. I'm just wondering why and if there is anything I can do to possibly fix this while I'm in my fuel tank with the sending unit out. It's like it's not really calibrated correctly, because the gauge works fine when it's full reading all the way down to the 1/4 where it's run out on me a couple times. Thanks in advance for all the help you guys can give.

How much you want to bet that you're gauge is reading correctly but you're starting to suck a massive amount of air once you go below 1/4 tank which could easily be caused because of a leak on the pickup and because of clogged screens.

That is what it is sounding like to me.

If nothing else, when you have the tank out, disconnect your fuel pump, put the key in the ignition and have someone watch your fuel gauge, move the floater from the bottom to the middle and to the top and see if it changes accordingly.

Keep in mind the changes will not be instant. To make them instant you may need to cycle the key so that the PCM re-reads the float position.

And by "leak on the pickup" you mean in the vacuum side of the fuel pump (probably at one of the quick disconnects)? Thanks for your reply.

Well - I could use some more help. I finally got around to doing the hutch and harpoon mods. This was in hopes of solving a spitting and sputtering problem at lower fuel levels (gauge reading about 1/4) due to the screens/mesh being clogged. After performing the mods, I went and filled up. My needle stayed on full for about the same length (about 220) before moving. The rest of the tank seemed to last forever. Until - about 570 miles and gauge reading a little more than 1/4 tank, spitting and sputtering again (out of fuel - I can only assume). I had a couple gallons in a can, so I put it in it, and got to the gas station. I filled up (32.5 gallons + the 2 from the can = 34.5 in a 29 gallon tank - think I was out).

Ok - so is there a calibration technique or a fix for the gauge that you guys can think of? It's definitely pointing to the gauge now. It's like it's off-set about 1/4 tank actually being like right around empty. The gauge appears to work very accurately, however, while you're working your way through a tank (the issue has been very consistent). I just don't know what to do - hate using mileage as a guide as it can fluctuate so much with these trucks while towing and with mods (based on how you drive them). Thanks for any options you guys can throw out.

You could replace the sending unit or maybe bend the floating arm a bit but it sounds as if the sending unit isn't working correctly and may need to be replaced anyhow.

While you had the tank out, did you test the fuel sender as recommended earlier?

If not, see if you can get another sender unit from a wreck and plug it into your harness. You may have to drop the tank a ways to access the connector. Then have someone watch the gauge while you move the float up and down. You will have to move it and wait as mentioned earlier. What you are looking for is any difference in the gauge reading compared to the float level of the two senders. If the gauge reads the same for both senders at a given level, then the problem is likely in the gauge or the wiring.

I am guessing that the sender is bad. It changes resistance when the float moves up and down, and the gauge is really measuring the resistance. When the fuel level is high, the resistance is high. The resistance drops as the fuel level drops. It sounds like you have higher-than normal resistance in the system. If you have a VOM tester (Ohmmeter) see if the resistance of the senders is the same between the two at a given fuel level. I could not find any information of what the resistance reading should be between full and empty.

Ford says that the dash gauge is non-repairable or adjustable. You have to replace the whole instrument cluster.

Ford's troubleshooting guide lists the possible causes in order of likelihood:
Sender
Circuitry (wiring and connectors)
Fuel Tank
Instrument Cluster

Report back with what you find.

I have my sending unit out doing the Hutch/Harpoon.

12 Ohms empty (float at bottom of travel)

100 Ohms with float arm in the middle of the travel (by looking at the swing resisitor housing)

160 Ohm Full (float at top of travel)

Anything in between would be guessing, so I didn't measure it.

So what functionality would I lose if the sender is the problem. I mean, does it function differently depending on the amount of fuel that it is reading (I guess I just don't understand the function of the sender)? I can't justify replacing the unit (even for used prices) if the gauge is the only thing it will fix. Thanks, so much, for the help, guys.

I have bin having the same issue with running out at 1/4 except that it isn't consistant it shows I have 3/4 somtimes when I'm full or empty. Things like that on occation also.

I have 28 Ohms Low
180's on full

There is a screen loose in my tank that may be the problem or that I knocked off in removal.

Let me know what you figure out. Thanks

I'm in the same boat now. Last tank, I had close to 500 miles and was just under a full tank. From what I'm hearing, it's my sending unit going bad. What I don't know is if a sending unit failure affects anything other parts or if the gauge going bad is all I have to deal with? If so, I don't have the money for a new sending unit just to replace the gauge, so I'll be driving by the trip odometer until I can afford a new one and have the time to put it in. Anyone else confirm or deny what we're dealing with is simply a faulty sending unit, and any options we have? Any electronic fixes for what we're seeing? Thanks in advance.

After further testing I found that there are dead spots with infinate or extra high resistance mostly over the half full mark so I'm sure its bad.

I figure if the truck averages intermittant readings and take those high readings into count it would always say I have more than I do. At least thats my thought.

Going to get a new one now. Fingers crossed

Let me know what you find out and where you get a new one. Looking forward to the results.

So far so good. No more issues. I ran it down till the light came on. I've never bin able to do that without actually running out before. Had to get it from the dealer I couldn't find any other options. Expensive $400 and thats with my wifes employee dicount. Its way easy to do. Just a 10mm and 13mm socket, a flat head screw driver and an hour of your time. A fuel line removal tool would help a little but it was pretty easy to stick the flat head in the end and release it without any damage.

You can actually buy just the sending unit (not the whole fuel pick up assembly) is you tell the parts guy you have a gasser. The resistances are the same, and the fuel tanks are the same size, but you dont have to spend the $400. IIRC, the gasser sender is about $131. you have to drill down through the Chassis electrical category on Partsguyed.com to find it.

Is this confirmed? I am fairly sure I need a sending unit for my 2000 f250 7.3 and want to line one up before I drop the tank. $400+ for just a sender assy is a ripoff, if I can get away spending only $150, that would be great.