Fuel sender putting out 40 M ohms - Second Generation Pontiac Firebird (1970 - 1981) - Firebird Nation

Jump to content


FirebirdNation.com is the premier Pontiac Firebird forum on the internet. Supporting Members do not see the above ads.
Photo
- - - - -

Fuel sender putting out 40 M ohms


  • Please log in to reply
3 replies to this topic

#1 msammy93

msammy93

    Firebird Oil Changer

  • Full Member
  • PipPipPip
  • 188 posts
  • Gender:Male
  • First Name:Michael
  • City:Hamilton
  • State or Province:NJ
  • Country:USA
  • Year: 1981
  • Make: Pontiac
  • Model: Trans Am
  • Engine: Chevy 400
  • Transmission: TH400 MVB

Posted 4 days ago

So the fuel sender is putting out 40 M ohms. I am assuming this means mega ohms.

Does this mean the sender is bad? Or just stuck?

Fuel tank was empty and leaning up sideways for a week while I was changing the lead springs and rear axle.

I did change the fuel gauge out thinking it was bad and it's still pegged past full but the the sender is not reading open loop like it would with a broken wire.

#2 ZumpTA

ZumpTA

    Firebird Master Tech.

  • Administrator
  • 2041 posts
  • Gender:Male
  • First Name:Tony
  • City:Holiday
  • State or Province:FL
  • Country:USA
  • Year: 1993
  • Make: Pontiac
  • Model: Trans Am
  • Engine: LT1
  • Transmission: 6-Spd

Posted 4 days ago

With a full tank the sender should should have an equal resistance to the gauge.  If the guage has 100ohm resistance, and you're seeing 40Mohms from the sender, the the guage thinks the tank is 400,000 times fuller than full.  Seeing as it's not infinite resistance, you're correct, not a broken wire.  Sounds like it was working before it sat, so I would guess the resistor board on the sender needs cleaning.  It could have corroded or oxidized or something when exposed to air.


"There are two major products that come out of Berkeley: LSD and UNIX.
We don't believe this to be a coincidence."
-- Jeremy S. Anderson

"Man is the best computer we can put aboard a spacecraft...
and the only one that can be mass produced with unskilled labor."
-- Wernher von Braun


#3 msammy93

msammy93

    Firebird Oil Changer

  • Full Member
  • PipPipPip
  • 188 posts
  • Gender:Male
  • First Name:Michael
  • City:Hamilton
  • State or Province:NJ
  • Country:USA
  • Year: 1981
  • Make: Pontiac
  • Model: Trans Am
  • Engine: Chevy 400
  • Transmission: TH400 MVB

Posted 4 days ago

With a full tank the sender should should have an equal resistance to the gauge.  If the guage has 100ohm resistance, and you're seeing 40Mohms from the sender, the the guage thinks the tank is 400,000 times fuller than full.  Seeing as it's not infinite resistance, you're correct, not a broken wire.  Sounds like it was working before it sat, so I would guess the resistor board on the sender needs cleaning.  It could have corroded or oxidized or something when exposed to air.


The resistance at the gauge is the same as the resistance at the sender. It was working prior to me removing the tank. Seems like I need to pull the sender out and clean it like you said.

#4 fireforeffect

fireforeffect

    Firebird Newbie

  • Full Member
  • Pip
  • 27 posts
  • Gender:Male
  • First Name:Jason
  • City:Sykesville
  • State or Province:MD
  • Country:USA
  • Year: 1978
  • Make: Pontiac
  • Model: Trans Am WS6
  • Engine: 400
  • Transmission: Auto

Posted A day ago

The resistance at the gauge is the same as the resistance at the sender. It was working prior to me removing the tank. Seems like I need to pull the sender out and clean it like you said.

Went thru this exact same issue a few weeks ago and my gauge would bounce back and forth as soon as the fuel dipped below full. Narrowed down the problem to the sender, the resistor wasn't working correctly and drove the needle all the way to the right past full despite the continuity showing it was doing what it should be doing. Replaced w/ a quality part (sock on my original pickup was falling apart too) and gauge reads as it should and stops at Full when filled. I had several folks tell me my gauge was bad, it needed to be replaced... including a respected Pontiac only parts guy in Frederick, MD. But replacing the gauge is the most intensive fix and in this case the symptoms are telling you it isn't the gauge... 


Edited by fireforeffect, A day ago.





0 user(s) are reading this topic

0 members, 0 guests, 0 anonymous users