professorjim

Can I read the separate fuel level sensor output voltages with an HP Tuner? If so, how?
The tanks (2) volume shows up as a total, but I need to determine individual tank levels and don't have the facilities to raise the car to get individual voltage readings directly off the sensors. Thanks for help. Jim

RonSSNova

This is what I see as logging options for the fuel tank with HPT


So it appears you might be able to see both?
I haven't tried it on my car.

Ron

professorjim

RonSSNova: Thanks, I'll see if I can find that detail. jim

professorjim

RonSSNova:
Your channel selector looks like what I should be able to access. But, my HPT doesn't show this same info.
In the VCM Editor, under Fuel System/Gauge I have the following categories:
Capacity: x gal
Primary Capacity: y gal
Sender Max A/D: 150
Sender Min A/D: 20
Gauge Output: (chart of Output PWM from 0-100 set at 0 in each box)
Primary Volumechart of gal from values 0-256 {increments of 2} from 0 at 34 to max of 9.72 at 144 to 256)
Secondary Volume: (chart of gal from values 0-256 {by 2} from 0 at 34 to max of 9.25 at 136 to 256)
No other fields available.

I deduct that the two volume charts are the RESULT of the voltage readings and are where I could modify the program to track the true volume in each tank.
But my HPT doesn't show me a way to read or record outputs.
My HPT has the latest software updates so I'm stumped as to how to get to the data shown on your outline diagram.

I also checked the Scanner program to see if there was place to find the output data and it wasn't readily apparent.

Can you advise me on what I'm doing wrong or what tool I might need to get to the base details?
Thanks,
jim

professorjim

RonSSNova: I knew there had to be a way of at least getting the data. Found using the "Add Channels" protocol worked.
I think I'm on my way to finding my tank capacity problem. Thanks for your help and the chart! jim

RonSSNova

Sweet!
Happy to help.
Ron

Mr. Black

Well you fellas may have just gave me an idea on how to further troubleshoot my C5 fuel gauge system.

It has been super wonky ever since I did my 411 PCM swap even though it is wired correctly. I also had to replace the right hand sender a couple years ago.

This could be an easy way to troubleshoot without probing wires or building resistance test boxes for the senders.

Mr. Black

So I activated fuel tank level senser and fuel tank level sensor 2 in the scanner for my logged drive today.

I assumed this system is a 0-5 volts but I don't know. The car is near full and it was showing 1.9v on the drivers side and 2.1 on the passenger tank at the start of the journey.
37 miles later it was showing 1.9 drivers and 1.65 passenger.

Not sure what that means exactly but I am going to figure out my stupid fuel gauge problems before I die.

C5MSG2004Vert

For a 2000 C5 both sensors should read 2.5 vdc when the tanks are full. They should read about .8 vdc when empty. 3/4 tank will be 2.5 vdc left tank and 1.5 vdc right tank. But half a tank should read 2.5 vdc on the left tank and about 0.8 vdc on the right tank.

Mr. Black

Thank you C5 MSG. So I just topped up to have a baseline. I'm now still 1.9v drivers tank and now 2.5v passenger side tank.

This would also explain that when the gauge does work that it shows exactly 13/16s of a tank instead of full.

Then what happens is if I drive the car for longer than a half hour it does the time out deal where the computer puts the gauge to zero and the red warning of check gauges comes on in the cluster.

It will continue to do this until below a real actual half tank and then it appears to start working again and doesn't do the time out thing.

Now I have to keep logging it until I get to a half tank and see what the voltages are doing.

I realistically think the drivers sender is just bad and no I haven't looked to see if its throwing sender codes. I was in there a couple years ago putting in my bigger fuel pump and at the time I could not find a new sender anywhere for the drivers side. It did seem to ohm out fine at that time.


Apologize for tagging on to your thread Jim. I hope it's not too much of a bother.

C5MSG2004Vert

The fault occurs because the left tank sensor voltage is less that the right side tank and that should never be. What are you empty voltages?

Mr. Black

I'll let you know soon. The weather has been crap.

I did find a new GM left hand sending unit on rock auto so I've got that coming.

Thanks for the error explanation. It totally makes sense that it would be trained to know the right should never be more than the left.

professorjim

Mr Black: I'm really glad you did tag-on as C5msg2004 answers were perfect for helping me as well and I was able to establish a baseline.
What I discovered, and have subsequently had confirmed, is that sitting overnight will tend to rebalance the voltages. The explanation I found is that the fuel pump diverts a small amount of fuel under pressure to the right tank in order to start the siphon pump process. Then over time the fuel will continue to transfer mechanically under normalized pressure between the sides.
I found this explanation on Z06Vette forum written by gmblack3 on May 25, 2004. It included an article from the winter edition of the C5 Registry compliments of Mr. Y2000 at c5dan@c5registry.com. Even my mechanic will understand how it all works now!
BTW: Hope you have better luck with the aftermarket unit than I did. Lost two in period of 6 months and I'm still struggling to get my system working correctly. But my issue is with right tank now as fuel isn't transferring correctly. Going to shop next month to have siphon pump nozzle reworked as replacements are just not available.
Good luck,
jim

Mr. Black

I was able to find a new GM unit in factory GM packaging. So I'm hopeful it will last the rest of the cars life.

Also if you need a passenger side you can still find the factory GM right hand sending unit and it will have a new jet pump attached to it.

professorjim

Great! It would be nice to get another 20 years.
I haven't found a passenger side. Any suggestions would be helpful. Would rather not try modifying one to work. My data confirms that my remaining problem is on pass side.
Mahalo, jim

Mr. Black

Looks like we may have success. Although I am disappointed to see the failure I was having may have been self induced. When taking apart the left tank fuel plate and removing the fuel tank sending unit I noticed that the very large aftermarket fuel pump wires were on the same side of the bracket as the fuel sending unit. My suspicion is that the float arm was hitting the pump wires causing the left tank to only show 1.9 volts instead of 2.5.

I put the new GM sending unit in anyways and tidied up my wiring a good bit better.

Filled it up 5 gallons at a time using gas can and watching the HP tuners scanner. Voila, 2.5 volts both sides and a FREAKING GAS GAUGE THAT SHOWS FULL!!!!!!!!!!

Thanks again guys for learning me about something as simple as being able to monitor the voltages in HP tuners scanner.