Fuel Gauge / Sender

[NosAvrenim]

Hi forum! I've been on this site for a while; quietly reading threads and enjoying the conversation. This is my first official forum post asking for thoughts/advice/suggestions.

I recently purchased JohnnyQuest515's (and formerly Magnum's) 390 X code. :grin: Overall, she's in great shape, but needs a bit TLC.

So I spent the weekend troubleshooting the fuel gauge and installing a new dash pad and instrument bezel/panel. JohnnyQuest said that the gauge issues may be due to the voltage regulator. So while the dash was out, I went ahead and replace it (inexpensive part, so figured I go for it). While I had the dash out, I tested the gauge and wiring harness (for current flow/resistance and also with a small power source to verify the gauge would register). Everything checked out. Plugged everything back together and nothing. :frust:

So I got under the car to test out the fuel sender and found that it wasn't even connected! Tested the sender itself by just checking for current flow/resistance and it looked good.

I then tested the wiring between the dash all the way to the sender plug and everything checked out. So I plugged the wiring into the sender (after finding it tucked away above the rear wheel well. Still no go. :frust:

Anyone have any thoughts as to what the problem might be and what I should be looking for (or what I didn't test correctly)? I've checked a few threads on this and other sites, but didn't see anything that might help (other than just dropping the coin for a new sender). I'm sure some of the experts here on the forum have seen this before.

 

[CougarCJ]

Maybe the float is broken?

 

[GTCSMustang]

I'll bet the float has a hole rusted in it and will not float. It's almost always the float. It's easy to check. Just pull the sending unit out (drain the gas first) and take a look.

Let us know what you find.

Scott

 

[franklinair]

Ground the connector at the sending unit. The gage should then read 'Full'. This will verify the circuit & gage functionality. If OK, the only thing left is the sending unit.

Neil

 

[CougarCJ]

I found a Rotunda fuel gauge and sender tester at a yard sale a couple of years ago.

 

[rvrtrash]

Neil is correct. What did you read when you ohmmed the sender? If you had gas in the tank and it read 75-80 ohms or higher, the sender is bad.

Steve

 

[NosAvrenim]

Neil is correct. What did you read when you ohmmed the sender? If you had gas in the tank and it read 75-80 ohms or higher, the sender is bad.

Steve

To be honest, I can't remember. I'll need to check Friday when I get back into town. Unfortunately, I'm traveling for work this week and can't touch her until I get back.
Thanks for all the info so far. I'll post up what I find Friday.

 

[NosAvrenim]

Turns out that it was the sender. When I drained the tank, I could hear the sender float rolling around inside. Since I had the tank aleady drained, I went ahead and installed a 1970 tank (22 gallons). Took just a little bit tweaking, but works great and you can't tell from inside unless you look really close. And now I have an extra 6 gallons of range

Thanks for all the help and advice.

 

[GT/CS S Code]

Groan ...

Last year we installed a brand new fuel tank and sending unit (16 gallon stock) in our "S" code, but unfortunately I wasn't aware of the larger 22 gallon tank being a basic "bolt in" using the '70 sending unit. Groan ...
:sad:
If I'd know this I'm sure that we'd have gone this route instead. I might still "bite the bullet" and swap it out again for the larger tank just for extended cruising range on longer trips.

We're heading up to Kamloops in August for their "Hot August Nites" event and it will be a fair distance between Chevron stations driving up that long, lovely highway in a 390 with the secondaries open some of the time. (Not that I would be tempted to tromp the gas pedal anywhere along the way of course ...)
:wink:

 

[robert campbell]

Turns out that it was the sender. When I drained the tank, I could hear the sender float rolling around inside. Since I had the tank aleady drained, I went ahead and installed a 1970 tank (22 gallons). Took just a little bit tweaking, but works great and you can't tell from inside unless you look really close. And now I have an extra 6 gallons of range

Thanks for all the help and advice.

I work for systems Planning and Analysis out of Alexandria VA.

Live and work in Seattle area for them.

Rob

 

[NosAvrenim]

Last year we installed a brand new fuel tank and sending unit (16 gallon stock) in our "S" code, but unfortunately I wasn't aware of the larger 22 gallon tank being a basic "bolt in" using the '70 sending unit. Groan ...
:sad:

Yep, pretty much a bolt in mod (both the tank and sender). Only modification really needed is to cut off a small bit of the fuel filler pipe and to adjust the angle the opening on the tank -- to align with the filler pipe. Other than that went smooth as can be.

Only thing I noticed was that my local station (a BP -- I know, I know) only let me fill up to 18+/- gallons. Need to look at that next weekend.

If anyone needs/wants a 16gal tank. I'll give the spare away for cost of shipping (still have the box from the 22gal). Otherwise, it'll go to the recycler.

~Nate

 

[NosAvrenim]

I work for systems Planning and Analysis out of Alexandria VA.

Live and work in Seattle area for them.

Rob

If you're ever in town, give me a holler.

~Nate

 

[CougarCJ]

If anyone needs/wants a 16gal tank. I'll give the spare away for cost of shipping (still have the box from the 22gal). Otherwise, it'll go to the recycler.

~Nate

I do not believe that there is any shipper that will let you ship a fuel tank that has been used.

 

[gofastguy]

Only thing I noticed was that my local station (a BP -- I know, I know) only let me fill up to 18+/- gallons. Need to look at that next weekend.


~Nate

I seem to have some difficulty getting a full tank myself. If I fill until the nozzle shuts off, I end up with around 7/8 tank. If I keep going then I end up with gas on my cap and back bumper. Is there some kind of trick I should know about?

 

[NosAvrenim]

I do not believe that there is any shipper that will let you ship a fuel tank that has been used.

Good point. I'll check with the local MCA chapter to see if anyone needs one. Thanks.