my 3rd thread of the day - usually not a good sign - but this is more of an annoyance problem than anything major.

since I finished my ZF swap, my fuel gauge reads dead empty whenever I select the front tank. It took 3 weeks (weekends, really) to complete the swap, so I forgot that I had just filled it beforehand. went to fill her up the other day and filled her to the brim of the filler neck - oops.

anyway - with the fuel gauge pinned dead empty (like below the E line), does that indicate an electrical connection problem? I certainly could have yanked a line loose when pulled the steering column.

seems unlikely that the gauge float would be stuck on the bottom of the tank, but I did just recently replace that tank and could have screwed up the orientation of it or something. ...it worked OK for a few months though and just started acting up now.

 

ok - just did a search with some different key words and came up with this thread:
https://www.ford-trucks.com/forums/1...l#post10074626

check me if i'm wrong, but since the selector valve apparently does the fuel tank level sender switching (not the dash switch as i'd have expected) and since the gauge reads fine on the rear tank, the issue is either in the wiring from the tank to that selector, the selector itself or the front tank sender?

time to get out the ohmmeter, I guess...

 

That sounds right to me. I would guess either a dead short or broken wire south of the selector valve. I can't remember which way it goes.

 

haven't made it through all the ground diagrams yet, but it seems like that ground runs all the way up the harness back into the engine compartment, but that the two tank grounds splice together somewhere along the frame rail. the "open" must be on that leg somewhere. ...wonder how that happened.

 

If the gauge works on the rear tank, then it isn't the ground though, correct?

If the rear tank works and the switching is done at the selector valve then the pathway from the gauge in the dash to the selector valve must be good. I would look for a problem between the selector valve and the front tank, and I would start in the frame rail since you were doing some work in there for the swap anyway. Is it possible that you may have necked crushed or pinched a harness somewhere along the way?

 

not necessarily - each sender has its own ground up to a splice point in the main frame harness "near breakout to front tank harness" - as the cryptic wording in the wiring diagrams goes. then its a common ground wire all the way back up to the connector near the engine compartment fuse box.


But yes, very good point here: it could be a break in either the signal or ground wire from the selector valve, through the sender and back to the splice into the ground wire in the harness.

the connector at the tank makes the most sense, but it seemed to be pretty snugly in place at first glance...

 

According to the way I read the schematic below, if the gauge works for the rear tank, there has to be an issue with either the wiring for the front tank sender, or the sender itself is bad. You should be able to test the sender itself by measuring the resistance of the DB/Y (presumably that's Dark Blue with a Yellow tracer) and a ground. With the tank full, the resistance should be around 145 ohms. If that is the case, then that wire (673) is good and the sender is working. From there, I would check the ground and measure from there to the frame. You should get a pretty low resistance there if the ground is good. If you get a high reading there, the issue must be between there and the junction point with the ground path for the rear tank (at S400).

If you get an open there, unfortunately all you can do is to get as close as possible to the tank and ground that wire out (which should peg the needle to the Full side). You still won't know for sure if the issue is in the sender or the last little bit of the pigtail to the tank, but it should point you in the right direction.

Hope that helps some.

 

definitely does - good plan - checking the sender first would be by far the easiest thing to do - thanks! however, does anyone have a trick for getting that connector off the sender - I recall it being a major pain to remove and not seeing any clips or anything to hold in down...

too bad its raining cats and dogs here today. guess it'll have to wait till tomorrow.

...only 50 miles on this tank so far, so I should be good for a while. ...I was kind of curious if maybe the float being pinned at dead full was over-extending the variable resistor of the sender and it would start working once I burned off some fuel. nothing yet on this hope, though.

 

IIRC, there is a short 2-3' whip on the sending unit that unplugs at the frame. I would just disconnect it there, as I recall the connector on the top of the sender being either permanently attached or a real pain to remove.

 

maybe that's my problem - i removed it when i dropped the old tank. it seemed to snap back on pretty well, but checking at that connector is a good idea.

thanks again, Nate!

 

Yuh, I don't think the wiring coming off the plate that the sender is attached to is meant to disconnect. I started prying on mine when I did the front tank on the ECLB. When it didn't come off handily, I checked pics of aftermarket senders online, and saw that wiring as integral with the replacement part. Disconnected it at the frame, and it worked fine on reinstall. So you may be in for some re-soldering....

 

well, that'd be easy enough if that's all it is. i guess i'm just too strong/stubborn :-)

 

Or maybe that's why it doesn't work anymore, lol.... Jus sayin'...

 

This same thing happened to my truck on the front tank. In the tank they used a brass float for the level sensor that was soldered together. Pulled it out and it was full of diesel making it not float anymore. However in my rear tank Ford used a different style plastic float so i suppose you could have either.
Just a suggestion. Hope this helps.

 

Same thing happened to me. I got another float from Fords it was brass.