Bad Fuel Sending Unit?

adman02

Basic User
City
Durham
State
nc
#1
I know this has been covered many times, but I'd appreciate some electrical wisdom.

Here's my situation...

Setup:
New sending unit (less than a year old)
Gas gauge (visually inspected and windings seem to be fine; cleaned points)
Dedicated grounds run to speedo cluster and to sending unit

Situation:
I fill up and the gauge reads full. I drive ten minutes and the gauge drops to empty and stays there.
If I touch ground and signal wire at the sender, the gauge reads full.

Does this seem like a bad sending unit?
 

walkerhoundvm

Just trying to stay upright
LIFETIME
CJ-8.com Member
City
Cave Creek
State
AZ
#2
I have been going through this way too frequently over the past few months, right now as a matter of fact.

What it sounds like is your float has a hole in it. When you fill up, there's just enough air to make it float - gauge reads full. Over the next few minutes, it fills with gas and sinks to the bottom - gauge reads empty.

To rule out your gauge, there are acceptable resistance readings across the three posts you can find online. To rule out the sending unit you can check the ohms reading after you fill up. If you do it quick, it'll read ~15ohms then rise to ~75ohms (edit - if it has a hole in it, normally it'll stay at ~15 and go up slowly as your tank empties). If you do it when you get home after filling, it'll just be ~75ohms because the float has dropped already.

My most educated guess is a leaking float, and you'll have to go in and replace it. A brass float is the preferred replacement, you can find them online for $10-15, I just bought one on ebay.
 

HighSierra CJ

Scrambler Enthusiast
LIFETIME
CJ-8.com Member
City
Ducor
State
Ca
#3
I have been going through this way too frequently over the past few months, right now as a matter of fact.

What it sounds like is your float has a hole in it. When you fill up, there's just enough air to make it float - gauge reads full. Over the next few minutes, it fills with gas and sinks to the bottom - gauge reads empty.

To rule out your gauge, there are acceptable resistance readings across the three posts you can find online. To rule out the sending unit you can check the ohms reading after you fill up. If you do it quick, it'll read ~15ohms then rise to ~75ohms (edit - if it has a hole in it, normally it'll stay at ~15 and go up slowly as your tank empties). If you do it when you get home after filling, it'll just be ~75ohms because the float has dropped already.

My most educated guess is a leaking float, and you'll have to go in and replace it. A brass float is the preferred replacement, you can find them online for $10-15, I just bought one on ebay.
I replaced the floats in all three of my scramblers with brass ones. I bought them from CJ pony parts. They are a Ford mustang/bronco website.
 

walkerhoundvm

Just trying to stay upright
LIFETIME
CJ-8.com Member
City
Cave Creek
State
AZ
#4
I replaced the floats in all three of my scramblers with brass ones. I bought them from CJ pony parts. They are a Ford mustang/bronco website.
I went with the ebay in hopes it'd get here soonish; mine isn't even leaking but I figured I may as well now that I have the tank dropped, again! I hate having a full gas tank sitting on the garage floor for any longer than needed, even if all the ports are plugged.

My in-tank pump was grounding out, fried two fuel gauges 😡 I'm tired of Chinese garbage parts - I'm convinced this Walbro is a fake. Bought it from Novak.
 

HighSierra CJ

Scrambler Enthusiast
LIFETIME
CJ-8.com Member
City
Ducor
State
Ca
#5
I went with the ebay in hopes it'd get here soonish; mine isn't even leaking but I figured I may as well now that I have the tank dropped, again! I hate having a full gas tank sitting on the garage floor for any longer than needed, even if all the ports are plugged.

My in-tank pump was grounding out, fried two fuel gauges 😡 I'm tired of Chinese garbage parts - I'm convinced this Walbro is a fake. Bought it from Novak.
Amen on the Chinese parts. Absolutely horrible quality.
 

adman02

Basic User
City
Durham
State
nc
#7
I check on my purchase date - bought the sending unit in May 2020...and it's never run right. I thought it was the gauge, but I removed it from the speedo cluster and inspected the windings, cleaned the points and reinstalled. It must be the sending unit because as I noted before, I can touch the signal to the ground at the sender and the gauge goes all the way to full. Grrrr.
 

walkerhoundvm

Just trying to stay upright
LIFETIME
CJ-8.com Member
City
Cave Creek
State
AZ
#8
Use this page to verify your gauge functions: http://www.4x4wire.com/jeep/tech/electrical/gauges/

To save you a click, refer to this image and the settings below:


S is the first on the left, where your sender wire attaches. A is in the middle, for the voltage reducer that goes to the water temp. I is for ignition hot.
  • S to Ground 68-72 ohms
  • S to I 19-21 ohms
  • S to A 19-21 ohms
  • I to A Zero
  • I to Ground 49-51 ohms
  • A to Ground 49-51 ohms
If all of those readings are within specs, your fuel gauge is in good shape.

I've spent a ton of time working on the sending unit, and the gauge, and have ran into almost every conceivable problem so far (except a float with a hole, haven't had a sender long enough for it to get a hole I guess!).
 

Randyzzz

Blown Budget
LIFETIME
CJ-8.com Member
SOA Member
City
Redmond
State
OR
#9
I went with the ebay in hopes it'd get here soonish; mine isn't even leaking but I figured I may as well now that I have the tank dropped, again! I hate having a full gas tank sitting on the garage floor for any longer than needed, even if all the ports are plugged.

My in-tank pump was grounding out, fried two fuel gauges 😡 I'm tired of Chinese garbage parts - I'm convinced this Walbro is a fake. Bought it from Novak.
Novak has a reputation for good stuff-I’d let them know about the issue.

I don’t like the Chinesium junk either- but sometimes even dealer parts come from China, or overseas elsewhere, or Mexico. I just bought 3 Dorman parking brake cables- one was USA and 2 were China. Couldn’t tell the difference, to be honest. But I’ve never had good luck with Chinese electrical stuff. And, a lot of the Chinese metals are a lot softer. Crappy steel and pot metal. A Lot depends on the specifications provided by the designing company.
 

Randyzzz

Blown Budget
LIFETIME
CJ-8.com Member
SOA Member
City
Redmond
State
OR
#10
Novak has a reputation for good stuff-I’d let them know about the issue.

I don’t like the Chinesium junk either- but sometimes even dealer parts come from China, or overseas elsewhere, or Mexico. I just bought 3 Dorman parking brake cables- one was USA and 2 were China. Couldn’t tell the difference, to be honest. But I’ve never had good luck with Chinese electrical stuff. And, a lot of the Chinese metals are a lot softer. Crappy steel and pot metal. A Lot depends on the specifications provided by the designing company.
Just got this today. Genuine GM, made in China. 😡 0999F7E7-2709-414F-BB44-C7987DDB05DF.jpeg
 

mysunnshine

Legacy Registered User
City
Phoenix
State
AZ
#11
I have seen a few fuel senders lately that the resistance when checked during a float arm sweep are not linear and smooth at all. They will drop out or have dead spots. The best I can tell is the wiper arm does not make good contact thru out the sweep.
 

walkerhoundvm

Just trying to stay upright
LIFETIME
CJ-8.com Member
City
Cave Creek
State
AZ
#12
I have seen a few fuel senders lately that the resistance when checked during a float arm sweep are not linear and smooth at all. They will drop out or have dead spots. The best I can tell is the wiper arm does not make good contact thru out the sweep.
2 out of 6 of the senders passing through my hands in the past 12mos have done this. A third had the primary lead grounding out on the case surrounding the resistance winding. That really makes buying these things a crap shoot. MTS or Omix or whoever is having them produced should be tarred and feathered.
 

adman02

Basic User
City
Durham
State
nc
#14
Use this page to verify your gauge functions: http://www.4x4wire.com/jeep/tech/electrical/gauges/

To save you a click, refer to this image and the settings below:


S is the first on the left, where your sender wire attaches. A is in the middle, for the voltage reducer that goes to the water temp. I is for ignition hot.
  • S to Ground 68-72 ohms
  • S to I 19-21 ohms
  • S to A 19-21 ohms
  • I to A Zero
  • I to Ground 49-51 ohms
  • A to Ground 49-51 ohms
If all of those readings are within specs, your fuel gauge is in good shape.

I've spent a ton of time working on the sending unit, and the gauge, and have ran into almost every conceivable problem so far (except a float with a hole, haven't had a sender long enough for it to get a hole I guess!).
Well, shoot. I replaced the float (it was plastic, but only had a few drops of gas inside...but it shouldn't have any). I also adjusted the sending unit while there (empty read 83 ohms). Still no dice, so I ohm-ed the gauge and all of my resistances were waaay low...like in the single digits. I must have shorted it somehow.

Thanks for all of the help. Now to find a suitable replacement gauge...not made in China.
 

walkerhoundvm

Just trying to stay upright
LIFETIME
CJ-8.com Member
City
Cave Creek
State
AZ
#15
Well, shoot. I replaced the float (it was plastic, but only had a few drops of gas inside...but it shouldn't have any). I also adjusted the sending unit while there (empty read 83 ohms). Still no dice, so I ohm-ed the gauge and all of my resistances were waaay low...like in the single digits. I must have shorted it somehow.

Thanks for all of the help. Now to find a suitable replacement gauge...not made in China.
There is a shop here in Phoenix that can repair them - Dick's Speedo and Tach. They ship, but the gauges are delicate so ymmv. They're also really busy, maybe 1-2mo turnaround time. $150 or so.
 

ag4ever

Average Nut
LIFETIME
CJ-8.com Member
City
Richmond
State
TX
#16
If you find a source please let us know. You used to be able to find the mopar replacements for way too much $$$ on eBay, but that supply has dried up.

Next best solution is speed hut, but that is a whole different solution.
 
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