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I went to a holley setup on my c5. I no longer have the stock instrument cluster. I was trying to find out if an aftermarket fuel gauge would work with the stock fuel sensors that are in the tank. What type of gauge is needed? Also where would be the best place to tap into the wiring to get the signal for the new fuel gauge? I’ve read how the stock computer averages out the two tanks but I would be fine with just a signal from the tank where the fuel pump is.
This isn't exactly a straightforward project. If you look at the wiring diagram, the senders do not connect to the IP (instrument pack). Instead, they connect to the PCM and, presumably, the PCM periodically sends messages to the IP over the CAN bus, telling the IP how to drive the fuel level gauge.
Presumably the workshop manual contains the specs for the fuel level senders. If not, I expect that you could remove the fuel level sensor leads from the PCM and measure the resistance readings at various fuel levels (at least full tank(s), half full and empty). Then, you would need an aftermarket fuel gauge. This fuel gauge almost certainly will not read correctly with the C5 senders, but there may be a solution. There are a few companies that specialize in rebuilding automotive gauges and modifying clocks, for example, to add a quartz movement. It could be that given the C5 wiring diagram and your fuel level sender measurements, one of these companies could modify the gauge to be compatible with the Corvette senders.
Thank you. My first thought was to measure the resistance going into the pcm. There is so little info on this and I wasn’t sure if anyone posted anything like this before that I could use as reference. Most of the info is about common fuel sender problems that I could find. I am pretty bad at reading wiring diagrams but hopefully I can find the info as to what wires to look for. By the way the pcm is no longer in the car but I still do have all the stock wiring for now.
If you go to the "C5 General" section of this forum, look at the stickies at the top of the page. One of them is titled "Shop Manual," or something similar, The wiring diagrams are also included in this download. The fuel sender circuit is shown in the engine management diagram.
The circuit itself is simple, but since it is included in the engine management drawing, it looks "busy" and spans several pages. It will look overwhelming at first, but like I said, it's pretty simple. Just raise your hand if you have questions.
Also, jump into the C2 section of this forum. Those cars tend to have clock and instrument problems. Ask around to see who they are using to rebuild their gauges.
Just to make sure is this what you were referring to? If so which wire would I check? The )) is what exactly? Is this a fuse where it changes colors or where does this happen? I’m bad at reading these things. Thanks for your help again.
Just to make sure is this what you were referring to? If so which wire would I check? The )) is what exactly? Is this a fuse where it changes colors or where does this happen? I’m bad at reading these things. Thanks for your help again.
If you are having trouble following the wiring diagram, this is the functionality of the wires in the electrical connectors of the two fuel tanks:
LHS sender connector:
Pin A - GRY - Battery power from the fuel pump relay to the fuel pump.
Pin B - GRY - From sender to Splice S444, to PCM Pin 75 - This is the ground reference for both fuel level senders.
Pin C - PPL - Color changes to Dk BLU - to PCM Pin 10 - This is the LHS fuel level sender input to the PCM.
Pin D - BLK - To Splice S466 - to Ground G416 - This is the ground for the fuel pump and the LHS sender housing.
RHS sender connector:
Pin A - GRY/BLK - Color changes to GRY - to PCM Pin 44 - This is the 5V reference voltage feed from the PCM to the RHS fuel level sender.
Pin B - GRY - From sender to Splice S444, to PCM Pin 75 - This is the ground reference for both fuel level senders.
Pin C - BRN - Color changes to Lt BLU - to PCM Pin 12 - This is the RHS fuel level sender input to the PCM.
Pin D - BLK - To Splice S466 - to Ground G416 - This provides ground to the housing of the RHS fuel level sender.
GRY = Gray
PPL = Purple
BLK = Black
BRN = Brown
BLU = Blue
Dk = Dark
Lt = Light
If you look at the wiring diagram, the senders do not connect to the IP (instrument pack). Instead, they connect to the PCM and, presumably, the PCM periodically sends messages to the IP over the CAN bus, telling the IP how to drive the fuel level gauge.
Presumably the workshop manual contains the specs for the fuel level senders. If not, I expect that you could remove the fuel level sensor leads from the PCM and measure the resistance readings at various fuel levels (at least full tank(s), half full and empty).
Side note: The C5 uses an older bus called J1850 VPW (or just VPW for short). They didn't switch to CAN until the C6 era.
But yeah, that's basically how it works. I think you can find the tables that the PCM uses to translate from sensor voltages to fuel levels in the tune, but I'm not certain of that. But if you can get a look at those tables you can use them to get a head start on calibrating your own gauge/gauges.
Last edited by NSFW; 03-18-2024 at 07:14 PM.
Reason: I accidentally a word
There is nothing wrong with haviing multiple gauges, but they would still need to be modified in order for them to work properly with the GM fuel level senders, as there are no established standards for the resistance sweep of the senders among either the manufacturers, or their vehicle families.
But I'll admit that I've occasionally wondered how the tank levels compare over time, in which conditions, etc, and dual gauges would scratch that itch...
There is nothing wrong with haviing multiple gauges, but they would still need to be modified in order for them to work properly with the GM fuel level senders, as there are no established standards for the resistance sweep of the senders among either the manufacturers, or their vehicle families.
The aftermarket gauges are compatible with the C5 sender resistance and voltages. The big problem is that we have two senders to deal with. Since the sensors indicate fuel level in each tank you would need two gauges, one for each tank to estimate how much fuel you really have.
The aftermarket gauges are compatible with the C5 sender resistance and voltages. The big problem is that we have two senders to deal with. Since the sensors indicate fuel level in each tank you would need two gauges, one for each tank to estimate how much fuel you really have.
Do you happen to know what range the sender works in? I haven’t had a chance to start on this project yet but I have some time later this week and will try and get to work on it and figure things out.
Do you happen to know what range the sender works in? I haven’t had a chance to start on this project yet but I have some time later this week and will try and get to work on it and figure things out.
The resistance of the sender varies from 40 to 250 ohms. Many aftermarket gauges support this range. You would have to wire the gauge to the sender so it sees the variable resistance.
OEM gauge reads 0-1/2 full based on DS tank 0-5V signal. Cluster gauge reads 1/2-Full based on PS tank 0-5V reference. Anytime the car thinks the DS tank is lower level than the PS tank it will throw a CEL since the siphon pump in the PS tank should always keep the DS tank full until all furl is pumped out of the PS tank.
So the PCM sees two signals/outputs from the fuel tank senders.
03-08-2024, 07:33 PM
Aftermarket fuel gauge?
