Fuel Gauge Problem?
 

My fuel gauge is acting kinda’ strange... It doesn't read the amount of fuel evenly in relation to miles traveled versus gas used.

For instance, this past weekend I drove about 280 miles round trip. 140mile there, 140 miles back, no driving in-between. On the trip there, my fuel gauge dropped from full to just over ¾'s of a tank but on the way home, it used the remaining ¾’s of the tank.
The only thing I’ve done was adding a new fuel pump, but that was about two years ago and the problem seems to have surfaced only recently.

Any Idea’s?
Thanks in advance!
Phil
Forgot to add, it's a 1989 Mustang LX, 5.0L

probally your fuel level sending unit in your tank is beat

My fuel guage is wonky too, it reads properly for the first 2/3's of a tank and then reads dead empty until I am just about out of gas and then it tells me that I have about 1/8 of a tank when I am about to run out.
I tried changing the sending unit and it didn't help so there is the possibility that iyour gauge may be screwed.

red82gt,
I've been reading that some Fords use an "Anti-Slosh-Module." I'm not sure if Mustangs do? If so, it's supposed to be mounted behing the instrument cluster.

I guess it makes the fuel guage react slowly, so as the gas sloshes around, the needle doesn't move up and down. Also, the article claims that in some applications the anti-slosh-module is calibrated to the fuel gauge and they both need to be replaced as a single unit! Again, I don't know it this is true about our Mustangs.

(if you want to read the article I mentioned go to:
http://www.smpcorp.com/download/view/TT3Q02.PDF
It's a .pdf file, look at the second page, second column)

It seems tough to get accurate information on this subject; probably becuase it's a rare problem that doesn't come up that often! Maybe I'll call the dealer today but my experience with them in the past is that they don't offer much assistance on a 14 year-old car!
Phil

i think its a common problem, i have the problem too! its either the sending unit in the tank, also, all msutang stock gauges are sh*t

GhettoPop,
red82gt said he replaced the sending unit (in the tank) and it didn't correct the problem!

I don't want to end up being a "Parts Changer!" I'm trying to figure out exactly what causes this problem so I can fix it!

All I am trying to say is that there's a ton of information when it comes to engine problems, trans problems, rear-end problems, suspension problems, etc. etc, but not much can be found about a malfuntioning fuel guage or fuel sending unit or any other componant accociated with them!

Yeah, I could drop the tank and install a new sending unit and then tear apart the dash and install a new guage...
But I'd rather figure out what's wrong and only replace the defective part(s)!
Phil

I'm at the point where I don't even want to try fixing the stocker, I'm going to put in an autometer gauge and their sending unit and then it won't be an issue.
That's what's nice about the 79-86 cars is that you can gut the instrument panel and 2 1/16" gauges fit perfectly.

welll it's time to find out what the problem is... pull the plug on the sending unit... and then use a jumper to the HOT wire and ground it... and WAIT a couple seconds for the anti slosh to work... if the gauge goes the full range then it's probably the sending unit.... You should be able to pull the harness without dropping the tank... though dropping the tank would be the easiest way...

-as

ChunkFunky,
Okay, now we're getting somewhere!

One other thing I forgot to mention..... When I fill the tank, even if I don't fill it to the brim (so to speak), the needle pegs all the way up, past the full mark.

What happens if the needle doesn't go the full range when I jumper the hot to ground? Does that indicate bad slosh module or guage?

Anyway, thanks a lot for that tip! I'm going to drop the tank either on Monday or Tuesday and do what you said. I'll report back what I find!
Phil

It's not uncommon for the sender to be toast.... I took mine to a mechanic to fix the gauge cause I just didnt feel like doing it... I assumed he'd put in a new sender and then would be it... he calls me later that day and tells me the gauge on the dash is broken...and he'll try to find a junk yard peice... after a couple days he hasnt called so I asked what's going on... he said.. they'er tough to find etc.... I tell him to forget it.. I'll just deal...

fast forward 2 months.. I go home to visit my parents.. my dad runs an auto repair shop, so I put it on the lift and I pull the harness on the sender and my dad grounds the hot wire while I sit in the car.... the gauge after a couple seconds SLOWLY moves the full range.. when he ungrounds it.. it moved back... the anti slosh mechanism keeps the needle from jumping around when you go up hiills and around corners and stuff.. it basicaly delays any sudden movements so the needle isnt all over the place...

so I dropped the tank to replace the unit and there's thier wierd piece of metal that's right inside the hole... doesnt look right.. I pulled the sender and it's missing something.... THE FLOAT.... as it turns out.. one of the baffles in teh tank.. broke loose and took out the float on the sender... no wonder it didnt work... anyway.. .I ended up getting a new tank and a new sender... I didnt the work myself... so I saved alot of money.... I just thought I'd share the story....

it's POSSIBLE it's not the sender... but you should be able to test it easy enough.... while you're dropping teh tank.. you might wanna get a higher vol fuel pump.... I wish I had.... it only makes sense since it's a pain to do... another tip... try to make sure the tank is as empty as possible.. it's alot easier.

When I fill my tank the needle goes well past full.. it stays there for about 50 miles and then starts to come down normaly.... I dunno if that's NORMAL .. but I dont find it to be a problem... cause it works the rest of the way down... give or take.. it's not like the fuel gauge on a 747, there's alittle room for error :)
-as