Checking Fuel Senders
Thread Starter
Instructor
Joined: Mar 2019
Posts: 186
Likes: 118
From: Kansas
Checking Fuel Senders
I have both tanks and pumps out of my 2007 A6 6.0. Wanted to plug in the harnesses to make sure fuel gauge works before installing them. Will the fuel gauge work with the relay for the pumps removed? I put new pumps in last spring and have had no fuel gauge since. Was working before I changed pumps.
Regards, Jeff
Regards, Jeff
Safety Car
Joined: Dec 2006
Posts: 4,593
Likes: 1,675
From: Pearland / Houston Tx
Think the gauges work through the BCM so shouldn't matter if pumps are going or not.
That being said, highly recommend replacing with new as fuel senders are a known failure item. The rheostat sweeps lose contact either through the little fingers breaking or a film from high sulfur gas coating the contacts, causing errors.
That being said, highly recommend replacing with new as fuel senders are a known failure item. The rheostat sweeps lose contact either through the little fingers breaking or a film from high sulfur gas coating the contacts, causing errors.
Thread Starter
Instructor
Joined: Mar 2019
Posts: 186
Likes: 118
From: Kansas
That’s what sucks, new pumps came with senders. My old ones worked(138,000 mi) I just want to make sure fuel gauge will work. Don’t know if senders bad or float was caught? Just got them out last night. Going to investigate shortly.
so if I plug them in and leave the float up on drivers side and move passenger float it should read from half to full.
Then if I leave float down on passenger side and move drivers side it should read from half to empty. Do I have this right?
Thank you for the reply!!
so if I plug them in and leave the float up on drivers side and move passenger float it should read from half to full.
Then if I leave float down on passenger side and move drivers side it should read from half to empty. Do I have this right?
Thank you for the reply!!
Racer
Joined: Jun 2017
Posts: 401
Likes: 79
From: Northeast PA
Suggest that you look at a wiring diagram for the fuel system & validate the integrity of power/ground/signal at the connectors & from the units themselves, if you have the units out that should be very easy. If that checks out then you'd need to verify that the gauge is receiving its signal, at the connector & directly on the gauge. A DVOM will tell you everything for signal, ref voltage, and resistance/continuity for the senders' rheostats. Only thing that I would hate is laying under the dash... that is the worst for old guys like me!
thing knower
Joined: Mar 2017
Posts: 3,404
Likes: 943
From: wpb
ahh you should be able to check the resistance with a multmeter before pulling them.... i put a new racetronix unit just recently and the float registered fine without any effort... the float may be caught up in the plastic fuel line... was one of the things i was concerned with....
my idiot wisdom leads me to this....
when filling up with gas, the first tank (drivers) fills... which registers the first half of the gauge....
once the first tank is full, fuel spills over via the crossover tube, which starts registering on the second gauge....
you can watch the gauge jump up in steps if you have your window down and car on...
the car then monitors both gauges for level as fuel is consumed... the venturi pump keeps the fuel level the same in both tanks while the electrical pump is operating...
i can get some manual pages for ya later today if you need..
-drew
my idiot wisdom leads me to this....
when filling up with gas, the first tank (drivers) fills... which registers the first half of the gauge....
once the first tank is full, fuel spills over via the crossover tube, which starts registering on the second gauge....
you can watch the gauge jump up in steps if you have your window down and car on...
the car then monitors both gauges for level as fuel is consumed... the venturi pump keeps the fuel level the same in both tanks while the electrical pump is operating...
i can get some manual pages for ya later today if you need..
-drew
Thread Starter
Instructor
Joined: Mar 2019
Posts: 186
Likes: 118
From: Kansas
I have fuel pumps out of tanks. I was going to plug in just the pumps while they are out of the tanks to see if gauge works properly then do this:
So if I plug them in and leave the float up on drivers side and move passenger float it should read from half to full.
Then if I leave float down on passenger side and move drivers side it should read from half to empty. Do I have this right?
I was under the impression that the fuel is removed from the pass tank first then the drivers side.
Regards, Jeff
So if I plug them in and leave the float up on drivers side and move passenger float it should read from half to full.
Then if I leave float down on passenger side and move drivers side it should read from half to empty. Do I have this right?
I was under the impression that the fuel is removed from the pass tank first then the drivers side.
Regards, Jeff
Le Mans Master
Joined: Dec 2004
Posts: 5,493
Likes: 809
From: West coast CA
I have fuel pumps out of tanks. I was going to plug in just the pumps while they are out of the tanks to see if gauge works properly then do this:
So if I plug them in and leave the float up on drivers side and move passenger float it should read from half to full.
Then if I leave float down on passenger side and move drivers side it should read from half to empty. Do I have this right?
I was under the impression that the fuel is removed from the pass tank first then the drivers side.
Regards, Jeff
So if I plug them in and leave the float up on drivers side and move passenger float it should read from half to full.
Then if I leave float down on passenger side and move drivers side it should read from half to empty. Do I have this right?
I was under the impression that the fuel is removed from the pass tank first then the drivers side.
Regards, Jeff
First determine what resistance means "empty" and what resistance means "full." Early C6s (2005-2006) go from 40Ω empty to 250Ω full. The range was reversed in 2007. Later C6s (2007-2013) go from 250Ω empty to 40Ω full.
Your car is a 2007. It should be 250Ω empty to 40Ω full, but I heard somewhere that some 2007s may pre-date the transition. The best thing to do is check your old senders to make sure the resistance moves in the same direction.
With that established, assemble the fuel tanks with the new pumps and senders. With the tanks still out of the car, check the sender signals with your meter. They should read empty.
Turn the tanks upside-down and check again. They should read full.
Testing with the tanks assembled is important because it confirms that the floats aren't hung up inside.
Race Director
Joined: Dec 2002
Posts: 10,469
Likes: 1,150
From: Wayne Township WI
Cut to the chase, replace both w/ new whether old are functioning or not.
Why?
Cost of removing tanks.
New senders are dirt cheap by comparison to labor accessing 'em.
Can fiddle w/ senders at your leisure to see what they do or don't on the bench.
I don't care what service my rear end needs, if it requires removing tanks senders get replaced. YMMV
Why?
Cost of removing tanks.
New senders are dirt cheap by comparison to labor accessing 'em.
Can fiddle w/ senders at your leisure to see what they do or don't on the bench.
I don't care what service my rear end needs, if it requires removing tanks senders get replaced. YMMV
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Thread Starter
Instructor
Joined: Mar 2019
Posts: 186
Likes: 118
From: Kansas
I just plugged in the pumps and the fuel gauge registered empty. I changed the drivers side pump to my original that I took out this spring and gauge works as it should. Bad sender on new pump....GRRRRRRRRRRRR! thank you all for the replies.
Also the gauge works as I typed it in my earlier replies. Driver side float up and pass down reads 1/2 tank. Move pass side float up and gauge goes to full.
Pass side down and move drivers side up goes from empty to 1/2.
Regards, Jeff
Also the gauge works as I typed it in my earlier replies. Driver side float up and pass down reads 1/2 tank. Move pass side float up and gauge goes to full.
Pass side down and move drivers side up goes from empty to 1/2.
Regards, Jeff
Safety Car
Joined: Dec 2006
Posts: 4,593
Likes: 1,675
From: Pearland / Houston Tx
from an old write-up of mine:
FUEL SENDER OPERATION
The fuel level sender changes resistance in response to the fuel level. The engine control module (ECM) monitors the signal circuit of the primary fuel level sender and the secondary fuel level sender in order to determine the fuel level. When the fuel tank is full, the primary and the secondary fuel level sender resistance is low and the ECM senses a low signal voltage. When the fuel tank is empty, the primary and the secondary fuel level sender resistance is high and the ECM senses a high signal voltage. The ECM uses the signal circuit of the primary and secondary fuel level sender in order to calculate the percentage of remaining fuel in the tanks. The ECM sends the fuel level information via serial data circuit to the instrument panel cluster (IPC) for display in the fuel gage.
(The RH tank sender for 2007 and up should test to 247-253 Ohms from Half full to Empty and 38-41.5 Ohms at Full. 2005-06 are opposite of these readings.)
FUEL SYSTEM OPERATION
The fuel system is a returnless on-demand design. The fuel pressure regulator is a part of the fuel tank module, eliminating the need for a return pipe from the engine. A returnless fuel system reduces the internal temperature of the fuel tank by not returning hot fuel from the engine to the fuel tank. Reducing the internal temperature of the fuel tank results in lower evaporative emissions.
Two fuel tanks store the fuel supply. An electric turbine style fuel pump attaches to the fuel tank module inside the left fuel tank. The fuel pump supplies high pressure fuel through the fuel filter and the fuel feed pipe to the fuel injection system. The fuel pump provides fuel at a higher rate of flow than is needed by the fuel injection system. The fuel pump also supplies fuel to a Venturi pump located on the bottom of the left fuel tank module. The function of the Venturi pump is to fill the left fuel tank module reservoir. The primary fuel pressure regulator, a part of the left fuel tank module, maintains the correct fuel pressure to the fuel injection system. The left fuel tank module contains a reverse flow check valve. The check valve, the primary fuel pressure regulator, and the secondary fuel pressure regulator maintain fuel pressure in the fuel feed pipe and the fuel rail in order to prevent long cranking times.
The fuel pump also supplies a small amount of pressurized fuel through the auxiliary fuel feed pipe to the siphon jet pump inside the right fuel tank. The pressurized fuel creates a Venturi action inside the siphon jet pump. The Venturi action causes the fuel to be drawn out of the right fuel tank.
The fuel transfers from the right fuel tank to the left fuel tank through the auxiliary fuel return pipe. The auxiliary fuel return pipe inside the left fuel tank contains an anti-siphon hole in order to prevent fuel from siphoning from the left fuel tank into the right fuel tank. Both the auxiliary fuel feed pipe and the auxiliary fuel return pipe are located inside the convoluted stainless steel crossover hose.
The right fuel tank module contains a secondary fuel pressure regulator. The secondary fuel pressure regulator has a lower set point than the primary regulator in order to allow fuel to flow to the siphon jet pump on the right fuel tank module. When the engine is shut off, the pressure in the feed pipes immediately drops to the secondary regulator set point. This prevents the siphon jet pump from operating and in turn prevents the equalization of the left and right fuel tanks. The secondary fuel pressure regulator maintains fuel pressure in the auxiliary fuel feed pipe which reduces the time to prime the siphon jet pump. The pressurization also reduces fuel vaporization and boiling in the auxiliary fuel feed pipe.
FUEL SENDER OPERATION
The fuel level sender changes resistance in response to the fuel level. The engine control module (ECM) monitors the signal circuit of the primary fuel level sender and the secondary fuel level sender in order to determine the fuel level. When the fuel tank is full, the primary and the secondary fuel level sender resistance is low and the ECM senses a low signal voltage. When the fuel tank is empty, the primary and the secondary fuel level sender resistance is high and the ECM senses a high signal voltage. The ECM uses the signal circuit of the primary and secondary fuel level sender in order to calculate the percentage of remaining fuel in the tanks. The ECM sends the fuel level information via serial data circuit to the instrument panel cluster (IPC) for display in the fuel gage.
(The RH tank sender for 2007 and up should test to 247-253 Ohms from Half full to Empty and 38-41.5 Ohms at Full. 2005-06 are opposite of these readings.)
FUEL SYSTEM OPERATION
The fuel system is a returnless on-demand design. The fuel pressure regulator is a part of the fuel tank module, eliminating the need for a return pipe from the engine. A returnless fuel system reduces the internal temperature of the fuel tank by not returning hot fuel from the engine to the fuel tank. Reducing the internal temperature of the fuel tank results in lower evaporative emissions.
Two fuel tanks store the fuel supply. An electric turbine style fuel pump attaches to the fuel tank module inside the left fuel tank. The fuel pump supplies high pressure fuel through the fuel filter and the fuel feed pipe to the fuel injection system. The fuel pump provides fuel at a higher rate of flow than is needed by the fuel injection system. The fuel pump also supplies fuel to a Venturi pump located on the bottom of the left fuel tank module. The function of the Venturi pump is to fill the left fuel tank module reservoir. The primary fuel pressure regulator, a part of the left fuel tank module, maintains the correct fuel pressure to the fuel injection system. The left fuel tank module contains a reverse flow check valve. The check valve, the primary fuel pressure regulator, and the secondary fuel pressure regulator maintain fuel pressure in the fuel feed pipe and the fuel rail in order to prevent long cranking times.
The fuel pump also supplies a small amount of pressurized fuel through the auxiliary fuel feed pipe to the siphon jet pump inside the right fuel tank. The pressurized fuel creates a Venturi action inside the siphon jet pump. The Venturi action causes the fuel to be drawn out of the right fuel tank.
The fuel transfers from the right fuel tank to the left fuel tank through the auxiliary fuel return pipe. The auxiliary fuel return pipe inside the left fuel tank contains an anti-siphon hole in order to prevent fuel from siphoning from the left fuel tank into the right fuel tank. Both the auxiliary fuel feed pipe and the auxiliary fuel return pipe are located inside the convoluted stainless steel crossover hose.
The right fuel tank module contains a secondary fuel pressure regulator. The secondary fuel pressure regulator has a lower set point than the primary regulator in order to allow fuel to flow to the siphon jet pump on the right fuel tank module. When the engine is shut off, the pressure in the feed pipes immediately drops to the secondary regulator set point. This prevents the siphon jet pump from operating and in turn prevents the equalization of the left and right fuel tanks. The secondary fuel pressure regulator maintains fuel pressure in the auxiliary fuel feed pipe which reduces the time to prime the siphon jet pump. The pressurization also reduces fuel vaporization and boiling in the auxiliary fuel feed pipe.
Thread Starter
Instructor
Joined: Mar 2019
Posts: 186
Likes: 118
From: Kansas
Received my parts today and put everything together. I now have a functioning fuel gauge again.
I just wanted to say “Thank You” for all the help I received! I truly appreciate it!!
Wishing everyone a very Merry Christmas and a most wonderful New Year!!
Regards, Jeff
I just wanted to say “Thank You” for all the help I received! I truly appreciate it!!
Wishing everyone a very Merry Christmas and a most wonderful New Year!!
Regards, Jeff
Instructor
Joined: Jan 2019
Posts: 135
Likes: 31
From: San Diego
So what parts did you replace exactly to get your gauge working again? The drivers side fuel sender? Passenger side fuel sender? Circuit boards?
Thread Starter
Instructor
Joined: Mar 2019
Posts: 186
Likes: 118
From: Kansas
Test the level senders with a multimeter.
First determine what resistance means "empty" and what resistance means "full." Early C6s (2005-2006) go from 40Ω empty to 250Ω full. The range was reversed in 2007. Later C6s (2007-2013) go from 250Ω empty to 40Ω full.
Your car is a 2007. It should be 250Ω empty to 40Ω full, but I heard somewhere that some 2007s may pre-date the transition. The best thing to do is check your old senders to make sure the resistance moves in the same direction.
With that established, assemble the fuel tanks with the new pumps and senders. With the tanks still out of the car, check the sender signals with your meter. They should read empty.
Turn the tanks upside-down and check again. They should read full.
Testing with the tanks assembled is important because it confirms that the floats aren't hung up inside.
First determine what resistance means "empty" and what resistance means "full." Early C6s (2005-2006) go from 40Ω empty to 250Ω full. The range was reversed in 2007. Later C6s (2007-2013) go from 250Ω empty to 40Ω full.
Your car is a 2007. It should be 250Ω empty to 40Ω full, but I heard somewhere that some 2007s may pre-date the transition. The best thing to do is check your old senders to make sure the resistance moves in the same direction.
With that established, assemble the fuel tanks with the new pumps and senders. With the tanks still out of the car, check the sender signals with your meter. They should read empty.
Turn the tanks upside-down and check again. They should read full.
Testing with the tanks assembled is important because it confirms that the floats aren't hung up inside.
I had the wtong pump on the drivers side. As mentioned above mine is a 2007 and they were two pumps for the C6 and 2007 was a changeover year.
put in correct pump and fuel gauge worked.
Regards, Jeff