Fuel Gauge bouncing - Diesel Forum

kd8bao · 08-03-2008, 11:11 PM

ok so i started my truck this morning and the fuel gauge was spiked above full. the it came back down to just below full as if it were working properly. i let the truck run for 5 min and when i took off forward pulling down the driveway the gauge spiked passed full and was bounceing crazy from 3/4 to over full. then settled down, it has never done this before. i have 75 miles on this tank so i should be below 3/4, but i did top it off pretty good last fill up. dont get me wrong it moves when i gas it and stop but usualy when around 1/2 tank. from the other posts i have read most guys are either full or empty. just curious of your thoughts, thanks in advance

cdnsarguy · 08-04-2008, 11:59 PM

Could be the sender is wearing out....... You can check for the ohms.......

93 info
Here are the fuel guage test #s

22 ohms sent to the guage it reads empty "E"

145 ohm sent to the guage it reads full "F"

Here are the sender test #s

Sender at empty stop 14-18 ohms

Sender at full stop 154-162 ohms

kd8bao · 08-05-2008, 08:26 AM

Thanks i will check it out when it stops raining here

kd8bao · 08-14-2008, 02:10 PM

Where exactly do i have to check the ohms. is it on the tank itself? If you have anymore info you can send it to kd8bao@yahoo.com

Thanks

robertwoodling · 08-15-2008, 10:18 AM

I am experiencing a similar problem so please continue to post replies here.

My guage was functioning properly and then suddenly started the dance mentioned. I should have a quarter tank of fuel in the rear tank and a full tank up front. When I switch to the front tank the guage shows less than a quarter. When I switch to the rear tank the guage dances above full and 3/4 full.

rkpatt · 08-15-2008, 06:22 PM

That happened on my 1994 F250 first with the front , tank , then the ream . Both eventually quit working . The factory sending units are pricey and prone to failure . I am replacing them with either a capacitance sending unit from CENTROID PRODUCTS - Computerized Tank Display - Electronic Senders - capacitive fuel gauges (not moving parts) or a sealed tube float sensor from - Fuel Tank Senders, Gas Tank Senders, Water Tank Senders, Holding Tank Senders by WEMA USA, Inc.

Here is an example Centroid capacitace level type sending uning retrofit on a Dodge -
capacitance centroid fuel sending unit - Dodge Diesel - Diesel Truck Resource Forums

Thanks for the information on the fuel sending unit resistance values for the 1993 F250 . I presume that it is the same for my 1994 model .

kd8bao · 08-25-2008, 09:37 PM

i went to the tank and checked to ohms or at least tried to. i poked the wires with the meter and i got 800+/- one way and the meter shut off the other way. as in i couldnt tell what was positive or neg so i just poked. so i am assuming the unit is bad. the rear unit still sends a good signal to the gauge but i also am assuming the switch doesnt work because the truck will die afetr a minute or running on the rear. when i flip the switch the valve makes noise like it is switching. any thoughts

cdnsarguy · 08-25-2008, 11:42 PM

Could be if the tank plastic pickup is broken off...... truck will run out of fuel at 1/4 tank level. This is a known problem on the diesel tanks........

With the wires disconnected from the tank sender...... check ohm readings of tank sender(s) to check guage send correct ohms to guage via the wires.

danngreen · 08-27-2008, 09:33 PM

Quote:

as in i couldnt tell what was positive or neg...

here's something i actually know something about: there's no pos or neg with ohms (resistance). so it will measure the same both ways

if you are testing the gauge and want to send ohms you can use a potentiometer, get a 1k linear taper potentiometer from Radioshack or electronics store. Use the ohm meter to set your pot to the "full" value (145ohms) using the center lug and either outer lug of the pot. Then connect the pot to the gauge. Repeat for the 'empty' value.