I have tried ever way I have found to hook the gauge up, but the gauge doesn't read the fuel level. What am I missing? It's on a 1997 Blazer. Thanks.

 

Sending unit tells PCM what the fuel level is. PCM sends this and other gauge information on a single serial data line to the instrument cluster where it is interpreted and used to drive the stepper motors on the individual gauges - at least that is how it works on a 2001.

I suppose you need a sending unit designed for the aftermarket gauge, or an aftermarket gauge designed for your stock sending unit.

According to info below, your sender should read somewhere between zero and 90 ohms. If it does not, it is bad. Whatever aftermarket fuel gauge you use, it will need to work specifically with a zero-90 ohm sending unit.

Which sender should I choose?
The resistance of your fuel sender should match that of your gauge. For instance the resistance of the stock gauge in a 55 Chevy has a value of zero ohms when empty and 30 ohms when full. The following list is for stock gauges and some popular aftermarket brands:

• Ford up to 1986 - 73-10 Ohms
• Ford 1987 & up - 16-158 Ohms
• GM up to 1964 - 0-30 Ohms
• GM 1965-1997 - 0-90 Ohms
• GM 1998 & up - 40-250 Ohms
• Mopar up to 1986 - 73-10 Ohms
• AMC 1950-1977 - 73-10 Ohms
• Autometer -240-33 Ohms is the most common however other ohm ranges are made
• Classic Instruments - 240-33 Ohms (excluding vehicle specific gauge kits which use factory ohm range)
• Dolphin - 0-90 Ohms
• Dakota Digital - Programmable to work with most Ohm range senders
• VDO - 10-180 Ohms

The first number represents the empty Ohm reading and the second number is the full reading.

 

Thanks for the information, but I'm running carbed with no pcm. All gauges are mechanical except the speedo is GPS.

 

Anyone?

 

In that case Lesmyer has answered your question. When you disconnected the pcm the fuel gauge lost signal. He's also mentioned 50 years worth of sending units. Which one are you using?

 

0-90 ohms.

 

when I got the blazer the pcm was gone.

 

Your blazer has been customized so let's start with the basics and the more detail you can provide the better. Does the measured resistance of the sending unit match the level of fuel in the tank? 40-50 ohms at about half a tank. What have you tested and what were the results?

 

I haven't done a ohms test on it, but I'm pretty sure it's a stock sender. I have tried connecting the purple wire to the sender post on the gauge and the ground to the tank/filler neck ground.

 

The next step would be to test the sending unit with a meter. Not because a replacement costs $20, because the tank has to come out to change it. It's pretty common for them to wear out.